Hydrologic Cycle and its Role in Arctic and Global Environmental Change: A Rationale and Strategy for Synthesis Study

The Hydrologic Cycle and its Role in Arctic and Global Environmental Change: A Rationale and Strategy for Synthesis Study A Report from the Scientific Community to the National Science Foundation Arctic System Science Program NSF-ARCSS Hydrology Workshop Steering Committee Charles Vörösmarty (University of New Hampshire) Larry Hinzman (University of Alaska Fairbanks) Bruce Peterson (Marine Biological Laboratory) David Bromwich (Ohio State University) Lawrence Hamilton (University of New Hampshire) James Morison (University of Washington) Vladimir Romanovsky (University of Alaska Fairbanks) Matthew Sturm (CRREL, Fort Wainwright, Alaska) Robert Webb (NOAA, Boulder, Colorado) With contributions from scientists at the NSF-ARCSS Hydrology Workshop, Santa Barbara, CA, September 2000 2 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change This report may be cited as: Vörösmarty, C. J., L. D. Hinzman, B. J. Peterson, D. H. Bromwich, L. C. Hamilton, J. Morison, V. E. Romanovsky, M. Sturm, and R. S. Webb. 2001. The Hydrologic Cycle and its Role in Arctic and Global Environmental Change: A Rationale and Strategy for Synthesis Study. Fairbanks, Alaska: Arctic Research Consortium of the U.S., 84 pp. Cover photo: Aerial view of Accomplishment Creek and the Sagavanirktok River in the Brooks Range of Alaska. Photo by D. L. Kane. The workshop and this report were funded by the National Science Foundation under Grant OPP-9910264 and Cooperative Agreement #0101279. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the National Science Foundation. 3 Acknowledgements ................................................................................. 4 Executive Summary with Key Findings and Recommendations ............ 5 Current State of the Art ........................................................................... 5 Key Scientific Challenges and Recommendations ................................ 5 Major New Synthesis Initiative Required .............................................. 6 Implementation of Arctic-CHAMP ........................................................ 6 Policy Implications ................................................................................. 7 Summary .................................................................................................. 8 1. Introduction ........................................................................................ 9 Rationale for Pan-Arctic Hydrologic Synthesis ..................................... 9 Report Framework ................................................................................. 13 2. A Strategy for Detecting and Understanding Arctic Hydrological Change: Arctic-CHAMP ............................................ 15 Arctic-CHAMP Basic Long-Term Monitoring ...................................... 15 Arctic-CHAMP Field-Based Process Studies ........................................ 18 Arctic-CHAMP Synthesis Modeling ..................................................... 19 Execution of Arctic-CHAMP ................................................................. 23 3. Role and Importance of Water in the Arctic System..................... 29 The Integrated Water Cycle of the Pan-Arctic ...................................... 29 Land ....................................................................................................... 29 Atmosphere............................................................................................ 31 Ocean ..................................................................................................... 32 Importance of Arctic Hydrology to the Arctic System ........................ 32 Importance of the Arctic to the Earth System ..................................... 33 4. Unprecedented Change to Arctic Hydrological Systems ............. 35 Changes to the Land-Based Hydrologic Cycle .................................... 35 Changes to the Atmosphere ................................................................. 36 The Changing Arctic Ocean and its Regional Seas.............................. 40 5. Impacts and Feedbacks Associated with Arctic Hydrological Change ...................................................................... 43 Direct Impacts on Ecosystems .............................................................. 43 Arctic Water Cycle Change and Humans............................................. 47 Land-Atmosphere-Ocean Feedbacks .................................................... 48 Land-Atmosphere-Ocean-Human Feedbacks ..................................... 49 6. Implementation of Arctic-CHAMP................................................... 53 References ............................................................................................ 61 Appendix 1. NSF-ARCSS Arctic Hydrology Workshop Participants ..... 71 Appendix 2. Current Gaps in Understanding the Pan-Arctic Hydrological Cycle ........................................................ 75 Appendix 3. Integration of Arctic-CHAMP with NSF and Other Federal Agency Initiatives ............................................ 79 Appendix 4. International Collaborations .......................................... 83 Contents 4 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Acknowledgements The Hydrology Workshop Steering Committee wishes to express its appreciation to those reviewers from the broader community and to the thirty-three scientists who met in a workshop at the National Center for Ecological Analysis and Synthesis (NCEAS) in Santa Barbara, California, to discuss the gaps in our current understanding of arctic hydrology and to formulate a plan for future synthesis studies. Many scientists reviewed a draft of this document and provided written comments, which greatly improved the final publication. The Arctic Research Consortium of the United States (ARCUS), through Sue Mitchell, project manager, and Wendy Warnick, executive director, provided publication support, including layout design and development, preparation of graphics, technical editing, and coordination of the publication process. Darlene Dube, administrative assistant at the University of New Hampshire (UNH), and Tamara Platt, administrative assistant at the University of Alaska Fairbanks (UAF), provided much-needed and much-appreciated help throughout development of this document. We are indebted to Jim Reichman and Marilyn Snowball and the staff of NCEAS for providing a stimulating meeting place and essential workshop support. We are also grateful to the National Science Foundation Arctic System Science Program for supporting the workshop and the publication of this document. —Charles Vörösmarty and Larry Hinzman, co-chairs NSF-ARCSS Hydrology Workshop Steering Committee 5 Executive Summary with Key Findings and Recommendations The arctic system constitutes a unique and important environment with a central role in the dynamics and evolution of the earth system. The Arctic is inherently a highly dynamic system. Yet there is mounting evidence that it is now experiencing an unprecedented degree of environmental change. Many of these changes are linked to the arctic hydrologic cycle and are quite possibly the result of both the direct and indirect impacts of human activities. Despite the importance of this issue, the current state of the art cannot adequately establish these potential linkages to global change. Understanding the full dimension of arctic change is a fundamental challenge to the science community over the coming decades and will require a major new effort at interdisciplinary synthesis. It also requires an unprecedented degree of international cooperation. Current State of the Art The water cycle is an inseparable element of the climate, biology, and biogeochemistry of the arctic region. The sensitivity of arctic hydrology to environmental change has been demonstrated through dozens of disciplinary studies focused on individual elements of the water cycle such as precipitation, evaporation, or runoff. We know much less about waterrelated teleconnections to regional and global climate. The absence of cross-disciplinary synthesis studies contributes to our inability to formulate a clear and quantitative picture of the integrated arctic system. In the face of global environmental change, the arctic science community has made predictions of system-wide impacts, but with little confidence. These key, unresolved issues can be cast as a set of scientific questions, fundamentally cross-disciplinary and synthetic in nature: • What are the major features (i.e., stocks and fluxes) of the panarctic water balance and how do they vary over time and space? • How will the arctic hydrologic cycle respond to natural variability and global change? • What are the direct impacts of arctic hydrology changes on nutrient biogeochemistry and ecosystem structure and function? • What are the hydrologic cycle feedbacks to the oceans and atmosphere in the face of natural variability and global change? How will these feedbacks influence human systems? Key Scientific Challenges and Recommendations How well are we poised to answer such questions? A survey of the arctic science community—represented by an interdisciplinary workshop convened by ARCSS in September 2000 and summarized in the remainder of this volume— revealed several notable gaps in our current level of understanding of arctic hydrological systems. At the same time, rapidly emerging data sets, technologies, and modeling resources provide us with an unprecedented opportunity to move substantially forward. Three major research and synthesis challenges with accompanying recommendations for strategic investments in arctic system science are given below. Understanding, simulating, and predicting contemporary and future hydrological dynamics is greatly limited by: 1.A sparse observational network for routine monitoring together with the absence of integrated data sets of spatial and temporally harmonized biogeophysical information over the pan-arctic domain. The situation is far from optimal and deteriorating rapidly over much of the pan-arctic, especially in Russia and Canada. Executive Summary 6 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Recommendations: A substantial commitment should be made to rescue, maintain, and expand current meteorological and hydrological data collection efforts. Establishing high-resolution gridded maps of climatic, hydrologic, topographic, vegetation, and soil property attributes for the Arctic Ocean watershed is strongly advised. Additional resources must be invested in scaling techniques, including the expanded use of remote sensing. Support for free and open access to arctic environmental data sets is essential to future progress. Coordination with existing U.S. and international monitoring programs is critical. 2.Numerous gaps in our current understanding of basic scientific principles and processes regarding the water cycle over the entire pan-arctic domain. Recommendations: Interdisciplinary synthesis studies linking hydrologic processes with other dependent biogeochemical and biogeophysical processes should be fostered to assemble a more complete understanding of the arctic system and its role in the broader earth system. Investments in longterm, process-based hydrological field studies are required. 3.The lack of cross-disciplinary synthesis research and modeling to decipher feedbacks arising from arctic hydrological change on the earth system and on society. Recommendations: Support should be given to integrative research that identifies the unique role of arctic hydrosystems in the broader earth system. An assessment of the feedback mechanisms through which progressive hydrological change influences both natural and human systems is urgently needed. New research devoted to establishing quantitative linkages between the biogeophysical and socioeconomic research communities is strongly advised. Major New Synthesis Initiative Required The gaps identified above demonstrate an urgent need to reformulate the manner in which arctic hydrological research is funded and executed. Implementation of the recommended actions will require a dedicated research program to support arctic hydrological synthesis studies. Such a program does not now exist, yet has been called for as a component of the U.S. Global Change Research Program’s initiative on the water cycle. To support this new science, the committee’s central recommendation is that: • NSF-ARCSS invest in the development of a pan-Arctic Community-wide Hydrological Analysis and Monitoring Program (ArcticCHAMP) to provide a framework for integration studies of the pan-arctic water cycle and to articulate the role of freshwater in terrestrial ecosystem, biogeochemical, biogeophysical, ocean, climate, and human dynamics. The primary aim of Arctic-CHAMP is to catalyze and coordinate interdisciplinary research with the goal of constructing a holistic understanding of arctic hydrology through integration of routine observations, process-based field studies, and modeling. Four goals should guide this effort: Goal 1: Assess and better understand the stocks and fluxes which constitute the arctic hydrologic cycle. Goal 2: Document changes to the arctic water cycle, contributing a hydrological component to the multiagency SEARCH Program. Goal 3: Understand the causes of arctic water cycle change and assess their direct impacts on biological and biogeochemical systems. Goal 4: Develop predictive simulations of the response of the earth system and human society to feedbacks arising from progressive changes to arctic hydrological systems. Implementation of Arctic-CHAMP To execute this initiative, the committee strongly recommends: • creating an Arctic-CHAMP Scientific Steering Committee (AC-SSC) to formulate a detailed interdisciplinary implementation plan and then supervise execution of the initiative • supporting a multidisciplinary set of process-based catchment studies • initiating a major effort to improve our current monitoring of water cycle variables, coordinating with U.S. and international agency partners as required • establishing the Arctic-CHAMP Synthesis and Education Center 7 (CSEC) to serve as the physical location for several of the scientific activities of the program. The center should lead the coordination of modeling, field research, and monitoring efforts within CHAMP. • selecting a core group of ArcticCHAMP researchers, chosen through peer review, to execute process studies, monitoring, and modeling efforts. The research team would include principal investigators and their post-doctoral fellows and graduate students, in residence at CSEC. The team would have representatives from the biogeophysical and socioeconomic realms and include both observationalists and modelers. • convening an Arctic-CHAMP Workshop Series and Open Science Meetings to promote a continuing involvement of the arctic and earth systems science communities • fostering collaboration with the many relevant U.S. arctic research initiatives. This will help to ensure maximum synergy across programs and avoid duplication of effort. The hydrologic cycle studies of ArcticCHAMP could serve as the NSFARCSS contribution to the multiagency SEARCH Program. They also will support NSF Biocomplexity and Information Technology programs as well as public outreach and education efforts. • creating and sustaining a vigorous set of international science and monitoring partnerships. Most of the pan-arctic land mass resides in Russia and Canada. No single National Science Foundation program, or even the U.S. arctic research community as a whole, could achieve the degree of synthesis required. The NSF must forge strategic international partnerships to be successful in this endeavor. Policy Implications Scientists have yet to observe and understand the full dimension of pan-arctic variability and progressive change, but at the same time, they are under increasing pressure to advise the policy-making community as it struggles with how best to manage the full dimension of contemporary and future global change. The impact of arctic system change is likely to extend far beyond the Arctic per se and thus become of critical concern to society at large. An investment in knowledge is of clear and immediate necessity. The contributions of an Arctic-CHAMP toward articulating the diverse physical, biological, and human vulnerabilities to this change provide an important impetus for international cooperation in wisely managing this critical part of the earth system. Executive Summary 8 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Key Unresolved Scientific Questions • What are the major features (i.e., stocks and fluxes) of the pan-arctic water balance and how do they vary over time and space? • How will the arctic hydrologic cycle respond to natural variability and global change? • What are the direct impacts of arctic hydrology changes on nutrient biogeochemistry and ecosystem structure and function? • What are the hydrologic cycle feedbacks to the oceans and atmosphere in the face of natural variability and global change? How will these feedbacks influence human systems? Recommendations • A substantial commitment should be made to rescue, maintain, and expand data collection efforts. Establishing high-resolution gridded maps of climatic, hydrologic, topographic, vegetation, and soil property attributes for the Arctic Ocean watershed is strongly advised. Additional resources must be invested in scaling techniques, including the expanded use of remote sensing. •Interdisciplinary synthesis studies linking hydrologic processes with other dependent biogeochemical and biogeophysical processes should be fostered. Investments in long-term, process-based hydrological field studies are required. • Support integrative research that identifies the unique role of arctic hydrosystems in the broader earth system. • Develop a pan-Arctic Community-wide Hydrological Analysis and Monitoring Program (Arctic-CHAMP). Arctic-CHAMP Implementation • Create an Arctic-CHAMP Scientific Steering Committee (AC-SSC) to formulate a detailed interdisciplinary implementation plan and then supervise execution of the initiative. • Support a multidisciplinary set of process-based catchment studies. • Initiate a major effort to improve our current monitoring of water cycle variables, coordinating with U.S. and international agency partners as required. • Establish the Arctic-CHAMP Synthesis and Education Center (CSEC) to serve as the physical location for several of the scientific activities of the program. The center should lead the coordination of modeling, field research, and monitoring efforts within CHAMP. • Convene an Arctic-CHAMP Workshop Series and Open Science Meetings to promote a continuing involvement of the arctic and earth systems science communities. •Foster collaboration with the many relevant U.S. arctic research initiatives. The hydrologic cycle studies of Arctic-CHAMP could serve as the NSF-ARCSS contribution to the multiagency SEARCH Program. They also will support NSF Biocomplexity and Information Technology programs and public outreach and education efforts. • Create and sustain a vigorous set of international science and monitoring partnerships. The NSF must forge strategic international collaborations to achieve the degree of synthesis required. 9 derstand the rapidly changing state of the Arctic and predict its future condition, we need to synthesize existing hydrologic knowledge and to identify gaps in that knowledge. It is critical to organize our current understanding into a framework that captures the essential workings and complexities of the arctic water cycle, taken as a whole. In this way we can more effectively articulate the Arctic’s unique place within the larger earth system and its role in global change, as called for in the recent U.S. Global Change Research Program water cycle initiative (USGCRP Water Cycle Study Group 2001). An understanding of the contemporary and potential future states of the arctic hydrological system is a precursor to assessments of the associated impact on natural ecosystems and human society. Such assessments must rely on high quality, quantitative information and are thus critical to sound policies for environmental protection. The Arctic Water Cycle as an Integrating Framework The hydrologic cycle provides an ideal framework for arctic system synthesis. First, the arctic hydrologic system spans three realms: land, ocean, and atmosphere. Second, the water cycle is more than just a set of physical processes: it includes living things—plant, animal, and human—and they all Introduction • Assess the state of the art in arctic systems hydrology and identify research priorities for achieving predictive understanding of the role of the arctic water cycle in global change. The meeting had broad representation from within the arctic research community, with more than 30 members having expertise in land surface hydrology, terrestrial and freshwater ecology, atmospheric dynamics, ocean processes, simulation modeling and geo-spatial analysis (Appendix 1). A steering committee attempted to capture consensus views articulated during the meeting and represented by this current document. Major thrusts of the workshop were to articulate the need for interdisciplinary arctic hydrologic studies and to formulate a strategy for new synthesis research. Rationale for Pan-Arctic Hydrologic Synthesis The pan-arctic hydrological system is complex and currently undergoing a period of rapid change that will influence all aspects of life in the Arctic. The changes will also interact in important ways with the global system. In the following chapters, we document these changes and show the complex linkages within the arctic hydrologic system and between the arctic and global systems. If we are to unThe water cycle of the Arctic plays a central role in regulating both the planetary heat balance and circulation of the global oceans. Recent and unprecedented environmental changes, such as declines in the total area of winter snow cover on land and declining sea ice cover throughout the Arctic Ocean, are now well documented. Unfortunately, the causes of these changes and their impact on the global ocean and atmosphere are still poorly understood. The cycle of freshwater in the arctic landatmosphere-ocean system is central to these observed changes (Figure 1-1). Yet, knowledge of the hydrology of the arctic region remains incomplete due to the complexities of permafrost terrain, difficulties in acquiring data in harsh environments, decline in routine monitoring, and a lack of interdisciplinary research. Progress in predicting global change can only be achieved through development of a new more synthetic and systematic understanding of the water cycle of the Arctic. In September of 2000, a workshop supported by the National Science Foundation Arctic System Science (ARCSS) Program was convened at the National Center for Ecological Analysis and Synthesis in Santa Barbara, California. The workshop’s central goal was to: 1 1. Introduction 17 Box 2-1. The Deterioration of Arctic Hydrographic Monitoring Networks Despite sensitivity of the pan-arctic region to global change and mounting evidence of its response expressed through the arctic water cycle, we see an increasing number of obstacles to the timely and broad distribution of in situ monitoring data. Precipitation data are threatened for several reasons. In spite of the universal importance and high value of accurate measurements of rain and snowfall, the number of measurement stations continues to decrease. The data that does exist is not always usable due to gauge undercatch that occurs (particularly for snow) in windy areas (Benson 1982, Goodison et al. 1998, Yang et al. 2000). The situation has been particularly troublesome with respect to discharge data, which are viewed as a strategic information resource subject to formal and informal data policy restrictions and commercialized for cost-recovery (National Research Council 1999, IAHS Ad Hoc Committee on Global Data Sets 2001). Time series of available pan-arctic discharge monitoring station data sets is shown below (Lammers et al. 2001), and the problem is obvious. In the Russian Arctic, we have seen a 30% decline in operational capacity since 1990. Delays in data reduction and release, in many countries amounting to several years, greatly exacerbate the problem. Large quantities of otherwise reliable data exist in difficult-to-use paper formats, warehoused for 0 500 1000 1500 2000 2500 3000 3500 1935 1945 1955 1965 1975 1985 1995 Years Number of stations Arctic-Net 2.0 Whole Pan-Arctic Russian Arctic North America 0 10 20 30 40 50 60 Jun-99 Jun-00 Jun-01 Number of stations Arctic-RIMS years and in grave risk of damage. Canada has seen a 20% reduction in the number of discharge stations since 1990, many in the Arctic (B. Goodison, Environment Canada, Downsview ONT, personal communication, 2000). In Canada there has been a push to establish instrumented monitoring stations that are untended during the winter. Much data such as snow depths are now not collected and other data are compromised by instrument failure during winter. The U.S. also has lost river station time series, including the vital lowermost station on the Yukon River, which fortunately has just been reopened. Accurate water chemistry data over the pan-arctic are even more fragmentary (Holmes et al. 2000). The situation is in stark contrast to the realtime availability of meteorological and oceanological data for weather forecasting. The mismatch between river discharge and meteorological data availability interferes with the timely identification and interpretation of a changing hydrology of the pan-arctic. A good example is the most recent estimate of present-day freshwater inflow to the Arctic Ocean, based on six-yearold observations (I. Shiklomanov et al. 2000). A temporally harmonized data set for pan-arctic hydrology and meteorology will be essential to the future monitoring of global change in the region. Time series of station holdings from a panarctic hydrographic archive (R-ArcticNet) (Lammers et al. 2001) and an operational data bank (Arctic-RIMS). Both net declines in operating stations (lines) and multiyear delays in data access (unshaded area) are apparent in the panel on the left. Arctic-RIMS represents a concerted effort to obtain timely hydrographic records for a set of key stations (from Shiklomanov et al. in review). 2. A Strategy for Detecting and Understanding Arctic Hydrological Change 18 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Arctic-CHAMP Field-Based Process Studies We recommend that a commitment be made toward establishing a core set of pan-arctic watershed study sites where a tightly integrated set of process-based measurements and monitoring can be systematically carried out over a long time frame. An interdisciplinary perspective is central to the success of these field studies. There is a conspicuous lack of fully coordinated studies of hydrological processes in the Arctic. Decades-long watershed studies like Coweeta, Hubbard Brook, and H. J. Andrews have made major contributions toward our processbased understanding of temperate ecosystems and provide essential calibration and validation data to a wide spectrum of hydrological and hydrological-biogeochemical models. From these sites has emerged critical information on water cycle dynamics, for instance, how precipitation and evapotranspiration interact to regulate runoff throughout the year. Comparable facilities dedicated to integrated analyses of arctic hydrological processes must be established. To fill current gaps in our processbased knowledge and to improve our capacity to simulate and predict arctic hydrologic and ecosystem change, research at these sites would comprise: •experiments to uncover hydrologic mechanisms through the conjunction of fieldwork and modeling; •measurements allowing comparative analyses with other watersheds; and Box 2-2. Open Data Policy The success of CHAMP will depend heavily on a policy of free and unrestricted data exchange. In light of the continued loss of hydrometeorological monitoring capacity (Box 2-1) this continues to be of critical importance. The arctic scientific community has only recently compiled an adequate historical archive of data sets that can be combined to detect systematic changes to the arctic system. When this has been done for the issue of change detection (Serreze et al. 2000), it has provided compelling evidence of major warming trends, atmospheric circulation changes, and a host of associated impacts. The NSF Arctic System Science Program has already invested heavily in community-wide databases by supporting the National Snow and Ice Data Center in Boulder, Colorado. An Arctic-CHAMP Hydrometeorological Data Archive (HDA), representing an integrated community data resource, should be created as part of the overall CHAMP effort. HDA should serve as a repository not only for station-based measurements (such as meteorological and hydrological data) but also for second-generation data (gridded interpolations of point measurements and thematic interpretations of spatially distributed data sets) and model input and output files (such as associated with GCMs or regional climatic models). Each of these data sets should be organized in standard formatting, distributed through the Internet, and accompanied by appropriate metadata to explain the methodology used to create each data product. Contributions of data to the archive should be an obligation of every scientist who receives funding under NSF ARCSS programs, and in particular Arctic-CHAMP. Charging a fee to use data or limiting access to that data places obstacles in the path of rapid scientific advancement (IAHS Ad Hoc Group on Global Water Data Sets 2001, Kanciruk 1997). Data should be freely distributed to anyone upon request. However, in keeping with the long-standing tradition in the NSF-funded geosciences, an exclusive right to data providers to first complete their analyses and publish those data as appropriate should be granted before release to the general community. •research to improve the transferability of site-specific process studies and measurements to unmonitored sites, larger drainage basins, and the entire panarctic. The coordinated set of activities would constitute hydrological as well as biogeochemical and biological measurements, including seldom-made winter observations (Table 2-1). Since permafrost is the single most dominant control on arctic terrestrial hydrological pro- 19 cesses, it is important that the sites span a latitudinal gradient extending southward from the Arctic Ocean into the region of discontinuous permafrost. The sites must also encompass both tundra and boreal forest biomes because there is evidence that these ecosystems are changing rapidly and that the change is intimately linked to hydrology. As shrub invades tundra, or spruce follows shrubs, a variety of hydrologic consequences and feedbacks are operating, all of which impact humans and potentially the global system. We recommend that a joint NSF working group consisting of researchers from LAII, OAII, HARC, PARCS, SIMS, and LTER be convened to study the costs and benefits of establishing and maintaining an integrated set of wellinstrumented small arctic catchments. The group should advise on an optimal set of measurements that would support process understanding, process modeling, and pan-Arctic extrapolation, as well as on-site location to encompass the full range of landscapes typical of the pan-arctic land mass. The group should include observationalists, modelers, and researchers from Canada, Scandinavia, and Russia and international scientific programs so that the choice of sites augments existing networks and is of greatest value to modeling. Arctic-CHAMP Synthesis Modeling We recommend that an ArcticCHAMP Integrated System Model (ARC-ISM) be developed. One way to promote synthesis in arctic hydrology is to integrate existing models and develop a simulation system that can provide a formal mechanism for mass and energy balance accounting, process-level testing, hypothesis generation, and pan-arctic application. ARC-ISM is intended to provide such a mechanism. It also provides a framework for integrating the long-term monitoring and process-based experimental elements of Arctic-CHAMP. ARC-ISM (Figure 2-3) is an earth system model focused on the Arctic. It should treat in an integrated fashion the Arctic’s climate, land surface hydrology, ocean, vegetation, biogeochemical, and human systems. Equally as important, it must be able to quantitatively articulate the pan-arctic’s connection to the larger earth system, which will be critical for analyzing feedbacks in response to global change. Retrospective, contemporary, and future time frames need to be analyzed, with ARC-ISM cast as a diagnostic as well as prognostic modeling tool. ARC-ISM should be considered to be a numerical modeling framework serving as a flux coupler to which various component models (land, ocean, Table 2-1. Examples of the coordinated set of measurements that might be made at an Arctic-CHAMP study site. Efforts should be made to expand the number of sites and the number of variables routinely observed. Hydrological and Other Geophysical Measurements •Precipitation Amount (Year Round) •Evapotranspiration and Sublimation •Solar Flux and Surface Energy Measurements •Snow Pack •Snow Redistribution •Snow Melt •Soil Thermal Properties and Their Variation - Temperature Profiles - Active Layer Depth - Permafrost Temperature - Thermal Conductivity •Infiltration on Frozen and Unfrozen Soils •Soil Moisture •Runoff Flow Paths •Stream and Large River Discharge •High-Resolution and Accurate Digital Elevation Models Biological and Biogeochemical Measurements •Precipitation Chemistry •Vegetation Surveys •Soil Mapping •Monitoring of Vegetation, Soil, and Groundwater Chemistry •Stream and River Constituent Concentration •Aquatic Ecosystem Surveys •Isotope and Other Tracers for Discharge Entering Arctic Ocean 2. A Strategy for Detecting and Understanding Arctic Hydrological Change 20 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Figure 2-3. Major features of the Arctic-CHAMP Integrated System Model (ARC-ISM) showing (top) the overall conceptual domains of the model and (bottom) the land surface hydrological component in more detail. The land includes vegetation, soils, river corridors, wetlands, and aquatic ecosystems. Carbon, nutrient, and other constituent fluxes will be modeled in tandem with the simulated water cycle dynamics. diagnostic prognostic prognostic diagnostic diagnostic prognostic diagnostic prognostic diagnostic prognostic Conduction Int e rfl ow Int e rfl ow A c tiv e La y e r P e rm a fr ost Free t P e rm a fr ost 21 atmosphere) could be attached. This would allow for the necessary flexibility to make the overall modeling scheme accessible to the broadest user community. Success will require strict adherence to rules governing module coupling and documentation. ARC-ISM in diagnostic mode should be used to analyze retrospective and near-real time water cycle dynamics, drawing on experience and techniques developed through state-of-the-art atmospheric modeling. These models include the current generation of General Circulation Models (GCMs) and Regional Climate Models (RCMs). “Reanalysis” efforts by the National Centers for Environmental Prediction (NCEP) and the European Centre for Medium-Range Weather Forecasts (ECMWF) constitute a promising method for obtaining relevant fields for the pan-Arctic. Atmospheric transports of water vapor provide the fastest and most direct link between the pan-arctic and global climates and are therefore of great value in articulating the coupling of the Arctic to the earth system. Such models provide us with the necessary tools for analyzing this linkage and for quantitatively assessing changes to the panarctic water budget. An emphasis on improving the accuracy of such models is clearly warranted (e.g., Gutowski et al. 1997). Data assimilation for all key variables of the hydrologic cycle should also be fostered explicitly. The diagnostic ARC-ISM can also offer an important resource in the design of optimal monitoring networks for hydrological variables. Precipitation, for example, remains one of the most crucial but difficult-to-estimate hydrologic measurements. Precipitation fields can be obtained through spatial interpolation techniques that produce high-resolution gridded data sets (e.g., Willmott and Rawlins 1999, Willmott and Matsuura 1995, Hutchinson 1998) based on station data, topography and/or existing climate information. The techniques are sensitive to station density, which is in decline over much of the Arctic. The diagnostic version of ARC-ISM could be used in numerical experiments to identify critical stations requiring formal protection and to formulate an optimal deployment strategy for new sites. Identification of the appropriate level of spatial and temporal detail necessary to capture the salient features of hydrological processes—working from the intensive field site models up to the domain of the pan-arctic— would be a major activity of the ARC-ISM modeling group. An important opportunity presents itself to the arctic research community through a rapidly emerging suite of remote sensing data resources provided by U.S. and international space agencies. Given its pan-Arctic perspective, ARC-ISM could provide an important testbed for satellite sensors specifically targeted at the hydrology of highlatitude landscapes. Its initial use could be in testing data sets in existing remote sensing repositories (Alaska SAR Facility [http:// www.asf.alaska edu], National Snow and Ice Data Center [http:// nsidc.org]), which have not yet been adequately exploited for hydrological studies (Walsh et al. 2001). One particularly important data set for high-latitude runoff simulation would be an accurate and high-resolution digital elevation model (DEM), which has yet to be collected for the pan-Arctic despite major investments to obtain this information for other parts of the world (i.e., recent NASA Shuttle Radar Topography Mission). Space-borne sensors that show promise in delineating critical seasonal transitions in the arctic hydrologic cycle (McDonald et al. 1999, Running et al. 1999, Frolking et al. 1999, Kimball et al. 2001) could be investigated and rigorously tested in the context of ARC-ISM. It could also be used to create specific new sensor science requirements that could be acted upon in the design phase of these sensors (Cline et al. 1999). ARC-ISM should also be configured to run in prognostic mode over the pan-Arctic. Current arctic regional climate models incorporate several interacting components of the hydrologic system, including atmosphere, ocean, land surface, and biosphere (e.g., Lynch et al. 2001, Wei et al. in review). These regional climate models operate at much higher spatial resolutions than global climate models, but their boundaries are provided by the coarse-scale GCMs into which they are nested. Such models may eventually provide detailed spatial descriptions of climate change scenarios. The models could thus be used to gauge the impacts of greenhouse warming on plant community structure or altered runoff generation and river discharge to the Arctic Ocean. Some specific applications of the ARC-ISM integrated modeling 2. A Strategy for Detecting and Understanding Arctic Hydrological Change 22 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Box 2-3. Arctic-CHAMP Framework Application: Atmosphere/Land Surface Hydrology Reanalysis As the sophistication of atmospheric modeling has increased, it is now possible to begin quantifying a wide array of hydrologically relevant components of the overall climate system—for example, the troposphere, land surface, ocean, and stratosphere. New techniques for assimilating meteorological observations directly into Numerical Weather Prediction (NWP) models fosters the improvement of operational products as well as the reanalysis of long time series of historical archive data. These are important data sets because they provide us with the raw material for analyzing quasi-periodic phenomena such as ENSO, AO, and NAO. Working with U.S. (NCEP) and European (ECMWF) meteorological services, ARC-ISM researchers would be well positioned to develop an optimal land surface model for Arctic NWP. Improved representations of specific processes would include runoff generation at the surface and at depth, storage in Q a Q b PE ∂ Wa ∂ t X g ∂ Ws ∂ t RO g ∂ Wg ∂ t G a G b ∂ Wr ∂ t D a X s D b the soil in liquid and solid forms, surface sublimation or evapotranspiration, surface storage in the form of snow, river routing, etc. When combined with atmospheric and oceanic models that contain an optimal representation of arctic physical processes (e.g., sea ice, arctic stratus, arctic haze, etc.), a reanalysis designed specifically for arctic hydrology could be realized. Hydrologic predictions constrained by all available observations would be obtained with high time resolution for a period of many years using an appropriate data assimilation scheme. Such a project would have to be a combined effort of the arctic hydrology community and experts in NWP. Improved reanalysis parameterizations have a major additional benefit: the enhancement of near-real-time, operational weather forecasts for the pan-arctic using versions of the same NWP models. An application of the equations shown here can be found in Box 2-4. Wa = precipitable water (vertically integrated) Xs = excess water to river/surface pools ∇Q = horizontal water vapor flux divergence Wg = groundwater storage E = evaporation + transpiration ∇G = horizontal groundwater flux divergence P = precipitation ROg = runoff from groundwater Ws = snowpack/soil water storage Wr = river water storage Xg = excess water to groundwater pool ∇D = horizontal discharge divergence t = time Atmosphere Observations Processes Water Vapor Cloud Micro Physics Aerosol Profiles Boundary Layer Processes Wind Profiles Moisture Convergence Temperature Profiles Modulation/Influence Cloud Cover by AO, NAO, ENSO, PNA Precipitation Evaporation Land Observations Processes Precipitation Infiltration Evaporation Snow Melt Snow Cover Freeze Soil Moisture Thaw Permafrost Thermokarsting Discharge Runoff (Xs + ROg) ∂Wa = –∇Q + E – P ∂t ∂Ws = P – E – Xg – Xs ∂t ∂Wg = –∇G + X – ROg ∂t ∂Wr = –∇D + ROg + Xs ∂t Ground Water River Snowpack & Soil Atmosphere → → → → → → 23 framework are given in Boxes 2-3 through 2-8. Execution of Arctic-CHAMP While each element of ArcticCHAMP is important in its own right, we believe their integration will be the key to significant and rapid progress. To that end, ArcticCHAMP has been structured to provide facilities and synthesis support activities linking the three components of the initiative— monitoring, process studies, and synthesis modeling. To afford panarctic integration, a multiscale approach will be fundamental, incorporating under a single framework broad-scale monitoring network data sets, site-specific hydrologic research, and simulation. Successful synthesis will not be automatic, and the otherwise independent monitoring, field experimentation, and simulation components of Arctic-CHAMP will require a continual and concerted effort at integration. The management of the program will thus be a key to its success. The overall program goals can be achieved by incorporating guidance from a steering committee, providing support to targeted science and technology projects, entraining promising young investigators, funding expanded monitoring, coordinating with existing arctic research programs, and making a strategic investment in science infrastructure. These programmatic elements are detailed in Chapter 6. Box 2-4. Arctic-CHAMP Framework Application: Diagnosing the Performance of Model Outputs Computed evapotranspiration from the combination of aerological budgets from NWP reanalysis and an independent precipitation data set (Willmott and Matsuura 2000). Note the negative values, incongruent with our current understanding of system dynamics. The framework for combining such data sets is at the heart of the ARC-ISM algorithm and Arctic-CHAMP more generally. In its diagnostic mode, Arctic-CHAMP should be designed to maximize our ability to judge the consistency among individual data sets, both against themselves and observational archives. Thus, Arctic-CHAMP would be a test bed for intercomparison studies using equations of the form shown in Box 2-3. An example would be testing for disparities among several existing precipitation data sets and the translation of these discrepancies into runoff uncertainty. In another example, preliminary assessment by M. Serreze (University of Colorado, Boulder, unpublished data) demonstrates that when NCEP atmospheric divergence fields and station-based, interpolated precipitation fields are blended to generate estimates of spatially varying evapotranspiration, these estimates give wholly unrealistic, large negative evapotranspiration values (see Figure). Ongoing work demonstrates that fields can be somewhat improved by accounting for gauge undercatch of solid precipitation (Serreze et al. in review). Such sensitivity tests allow the community to judge the degree to which observations of individual water cycle elements contribute uncertainty to the overall water budget closure across the pan-Arctic. Identification of such “weak links” is a necessary step in identifying fertile areas for future research. 2. A Strategy for Detecting and Understanding Arctic Hydrological Change 24 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Box 2-5. Arctic-CHAMP Framework Application: Design of Optimal Monitoring Networks Potential bias in river basin precipitation as inferred from closure experiments on global water budgets. For much of the arctic drainage basin there are strong negative biases (blue color), which are likely associated with underestimates of regional precipitation (from Fekete et al. 1999). River discharge is one of the more accurate observations associated with the global hydrological cycle. However, real-time river discharge data has been underutilized within the ocean-atmosphere modeling community due to typical threeto-five-year delays in data posting (GRDC 1996), network closure, and data policy restrictions. Recent work (Fekete et al. 1999) has demonstrated the capacity to identify possible sources of error in particular elements of the water cycle when judged objectively against the instrumental record. The figure above shows the spatial distribution of potential biases in precipitation when compared against observed discharge and a physically consistent water budget model. It is noteworthy that the Arctic, when analyzed from the standpoint of river discharge records over large river basins, shows sizable underestimation. This corroborates, from an independent perspective, the well-known problems with gauge catch and interpolation bias in both liquid and solid precipitation measurements in such harsh environments (Groisman 1991, Groisman et al. 2001, Willmott and Matsuura 1995). The experiment shown in the figure indicates that by combining otherwise decoupled data sets and models, we can assess the degree of uncertainty and potential bias (see also Box 2-4). In addition, it lends hope that the synergy embodied in these data sets can yield a mutually consistent picture of water and energy budget closure. ARC-ISM should be used to optimize such an integration of data and model results and could beneficially be applied in the design of future monitoring systems for the pan-arctic system. These should be optimized to retrieve information of direct value to the scientific objectives of Arctic-CHAMP. However, of particular note would be the additional use of ARC-ISM derived products to help improve operational forecast and reanalysis products from weather prediction services. A coherent pan-arctic observational program in support of Arctic-CHAMP thus would provide an important framework for improving our capacity to monitor change over the Arctic and to interpret its impact. WBM Runoff Correction Coefficients 30-minute spatial resolution 25 Box 2-6. Remote Sensing Support for Pan-Arctic Synthesis Daily Maximum Air Temperature Interpolated from Met Stations 31 March 12 April 20 April 26 April 1997 1997 1997 1997 Comparison of maximum air temperature, interpolated from measurements acquired from 72 meteorological stations in Alaska with freeze/ thaw index maps derived from two-day NASA Scatterometer (NSCAT) satellite sensor composite mosaics. NSCAT was extremely sensitive to the presence of unfrozen water on the surface of the snow or ground and is therefore a promising platform for determining hydrologic conditions over wide areas. The bottom four graphs show temporal series of NSCAT backscatter at four locations along a north-south transect extending (1) from Toolik Lake on the north slope of the Brooks Range, (2) to the Dietrich Valley, surrounding Coldfoot, Alaska, near the northern limit of the boreal forest, (3) through the Bonanza Creek Experimental Forest in the central interior, and (4) to Denali National Park in the Alaska Range. Each point on the four graphs represents mean NSCAT backscatter computed over a 50 km region centered at the respective ground location. The broken vertical lines mark the times initiating the two-day NSCAT composite mosaics. Remote sensing will provide critical observational support to Arctic-CHAMP synthesis studies. From the unique vantage point of space, satellite-based sensors constitute an important monitoring asset for constructing comprehensive views of the changing biogeophysical character of the entire pan-arctic domain (see Walsh et al. 2001). Use of such remote sensing data sets will be critical to observational support for panarctic synthesis studies as part of Arctic-CHAMP and to afford pan-arctic coverage. Figure from Running et al. 1999. NSCAT-Based Freeze/Thaw State 2. A Strategy for Detecting and Understanding Arctic Hydrological Change 26 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Box 2-7. Arctic-CHAMP Framework Application: Prognostic Simulation The Arctic-CHAMP model can be used in a prognostic mode to produce high-resolution sets of scenarios on the potential future state of the pan-arctic system. The ARC-ISM model could easily be envisioned to represent a regional simulation nested within a larger earth system model, but with higher detail in its physical representation of land surface hydrology, ecosystem and vegetation state, coastal and Arctic Ocean, sea ice, and the dynamic atmosphere. The coupling has several advantages. It permits the fullsystem behavior to be assessed, as well as any subcomponents that would be the targets of more focused studies, thereby enabling feedbacks to be better elucidated. In addition, through scenario analysis it could be used to test for system sensitivities. And, using results derived from the error analysis developed under the diagnostic mode, ARC-ISM could be used to predict the impact of uncertainties in our understanding of possible future trajectories of environmental change. Changes in annual mean surface air temperature (top), precipitation (center), and surface solar radiation (bottom) over the 100 years from 1961– 1990 to 2061–2090, according to a greenhouse simulation by the GFDL coupled global climate model. Units are degrees C, mm per day, and Watts per square meter, respectively. Yellow and red denote increases; green and blue denote decreases, and gray denotes little or no change (IPCC Data Distribution Center, http://www.dkrz.de/ipcc/ddc/html/ dkrzmain.html). 33 arctic hydrological regimes in order to compute water budgets remains both an open area of research and a significant monitoring challenge. The delivery of freshwater from the continental land mass is of special importance to the Arctic Ocean since it contains only 1% of the world’s ocean water, yet receives 11% of world river runoff (Shiklomanov et al. 2000). The Arctic Ocean is the most river-influenced and landlocked of all oceans and is the only ocean with a contributing land area greater than its surface area (Ivanov 1976; Vörösmarty et al. 2000). Annual freshwater inflow contributes as much as 10% of the freshwater in the upper 100 meters of the water column for the entire Arctic Ocean (Barry and Serreze 2000). Approximately three-quarters of Arctic Ocean riverine freshwater input derives from the Eurasian portion of the Arctic Ocean watershed, and three rivers (Yenisei, Lena, Ob) are responsible for approximately 70% of this contribution (Carmack 1990, Gordeev et al. 1996). This water exerts a tremendous influence on the Arctic Ocean and especially on the Eurasian shelf seas (the Barents, Kara, Laptev, and East Siberian). Salinity distribution and sea ice formation are affected by continental runoff. As mentioned before, the cumulative impact of changes in freshwater flux to the Arctic Ocean may exert significant control over global ocean circulation by affecting the volume of North Atlantic Deep Water formation (Aagaard and Carmack 1989, WMO/World Climate Research Program 1994, Broecker 1997). River inputs of water and constituents influence delta, estuarine, and near-shore ecosystems that have historically provided the basis for subsistence of northern Eurasian human populations. Climate change during the transition from the Pleistocene to the Holocene was accompanied by major shifts from utilization of terrestrial foods to use of riverine and coastal marine resources including fishes and mammals (Makeyev et al. 1993). Importance of the Arctic to the Earth System From a large body of GCM experiments, the Arctic is thought to be particularly sensitive to global climate change (Manabe et al. 1991, Manabe and Stouffer 1995, Houghton et al. 1996, 2001; Watson et al. 1998). Manabe et al. (1991) show that under a representative global warming scenario, temperature increases will be amplified in the Arctic, and the upper Arctic Ocean salinity will decrease due to enhanced precipitation at high latitudes. Analysis of a broad suite of archived hydrometeorological data sets further supports this view and suggests the presence of a global warming signal across the region (Serreze et al. 2000). Preliminary assessments for some regions of the Arctic show that recent changes in winter temperature and mean annual precipitation have affected local runoff conditions and river discharge to the Arctic Ocean (Lammers et al. 2001, A. Shiklomanov 1994, I. Shiklomanov 1997, Georgievsky et al. 1996). At the same time teleconnections have been established between El Niño Southern Oscillation (ENSO) events and climate anomalies in parts of the arctic drainage system (Brown and Goodison 1996, Shabbar et al. 1997). Key indicators of global change thus involve major components of the high-latitude water cycle, and the reciprocal response of the Arctic—beyond its land-based hydrology—must be considered. For 3. Role and Importance of Water in the Arctic System Figure 3-4. Arctic wetlands depend on the presence of permafrost (photo by L. Hinzman). 34 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change example, the Arctic Ocean’s stratification and ice cover provide a control on the surface heat and mass budgets of the north polar region, and thereby on the global heat sink (e.g., Manabe et al. 1991). If the distribution of sea ice—a significant stock of arctic freshwater—were substantially different from that of the present, then the altered surface fluxes would affect both the atmosphere and the ocean and would likely have significant consequences for regional and global climate. Also, the export of low-salinity waters, whether liquid or in the form of desalinated sea ice, has the potential to influence the overturning cell of the global ocean through control of convection in the subpolar gyres, which in turn feed the North Atlantic (Aagaard and Carmack 1989). Recent suggestions that North Atlantic and Eurasian climate variability may be predictable on decadal time scales (Griffies and Bryan 1997) rest in part on the variability of such upstream forcing in the Greenland Sea (Delworth et al. 1997). Central Question: What Are the Major Features and Natural Variability of the Pan-Arctic Water Balance? Key Gaps in Current Understanding and Needed Studies: •Fluxes throughout the water cycle (atmospheric vapor transport precipitation, evaporation, soil water, runoff) •Arctic atmospheric teleconnections to the larger climate system •Role of seasonal snowpack and permafrost water storages •Runoff generation and pathways •Continental discharge and connections to sea ice and deep ocean convection On the atmospheric side, results of Thompson and Wallace (1998) and others show that the atmospheric circulation of the Northern Hemisphere changes as part of a pole-centered pattern, termed the Arctic Oscillation (AO). Recent modeling studies suggest the AO is a fundamental mode of atmospheric change and that the positive trend seen in recent decades may be symptomatic of the greenhouse effect (Fyfe et al. 1999, Shindell et al. 1999). Consideration of the coupled set of atmosphere-ocean interactions is thus absolutely essential to our understanding of the ultimate impact that arctic environmental changes have on the earth system. The hydrological cycle will figure prominently in any such analysis. 35 Unprecedented Change to Arctic Hydrological Systems et al. 1997, Overpeck 1996, SEARCH SSC 2001, Serreze et al. 2000). The multiagency SEARCH Science Plan (SEARCH SSC, 2001) provides an in-depth analysis of the spatial and temporal extent of recent changes to the arctic system. Many significant changes are observable from what is admittedly an incomplete and in many cases fragmentary record. The review given below focuses on the arctic system as well, but highlights those changes related specifically to the arctic water cycle. Changes to the Land-Based Hydrologic Cycle A wide range of changes in terrestrial arctic hydrology has been detected, and many of these changes started, or accelerated, in the mid1970s. The arctic hydrologic system is particularly sensitive to changes in the magnitude and timing of rain and snowfall, freeze-up and thaw, and the intensity and seasonality of storm activity that reflect changes in large-scale atmospheric circulation rather than simple responses to temperature increases. Although historical changes in these fields are poorly known and characterized by enormous spatial and temporal variability, observations suggest that the arctic hydrologic system may be entering a state that is unprecedented, at least over a historical timeframe (Serreze et al. 2000, Lammers et al. 2001). Integrated measures of hydrological status, such as glacier mass balance studies that record both summer and winter precipitation, indicate that over the last 30 years, smaller glaciers in the Arctic have experienced decidedly negative mass balances (Dyurgerov and Change is an inherent property of the Arctic, with the paleoclimatic record providing ample evidence of the enormous changes experienced by the region since the last glacial maximum (Mayewski et al. 1994, Alverson, Oldfield, and Bradley 2000). The system has alternately experienced extensive and thick ice sheets, the blockage of northward flowing rivers, exposed coastal shelf regions, giant catastrophic floods, and most recently the complex signature of human-induced climate change. High-resolution paleo-records indicate that arctic climate can move rapidly from one regime to another, resulting in the anomalous persistence of warm temperatures, shifts in seasonality, extreme events, and changes in ocean circulation (e.g., Bond et al. 1999, Douglas et al. 1994). These and many other paleoclimate studies provide an understanding of arctic hydrologic variability and are needed to place the recent observations of Arctic system change into appropriate context (Stein 1998). Although changes to many environmental variables have occurred previously throughout geologic time, the rate of changes observed within the last few decades to century are quite likely unprecedented and indeed have evoked a sense of urgency within the community (Overpeck Figure 4-1. The McCall Glacier in the Romanzof Mountains of Arctic Alaska has been losing mass since measurements began in 1957, with accelerated losses over the last two decades (Rabus et al. 1995). -25 -20 -15 -10 -5 0 5 55 60 65 70 75 80 85 90 95 Year Elevation relative to 1969 (m) McCall Glacier Mean Surface Elevation o f Transverse Profile vs. Time –1.0 m/yr –0.3 m/yr 4 4. Unprecedented Change to Arctic Hydrological Systems 36 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Meier, 1997). The 1957 to 1995 record for McCall Glacier in arctic Alaska (Figure 4-1) shows that the mass balance has not only been negative, but the rate of downwasting has increased dramatically since 1976 (Rabus et al. 1995). The Greenland Ice Sheet has also increased in melt area throughout the 1980s (Abdalati and Steffen 1997), and the associated reduction in volume is about equal to those of all the smaller glacier systems in the Arctic (Dyurgerov and Meier 1997). Observed responses of arctic river systems to changes in temperature and precipitation reflect a complex set of spatial patterns, including a mean delay of nine days for freezeup and a ten-day earlier ice breakup date for lakes and rivers, comparing conditions 150 years ago to today (Figure 4-2; Magnuson et al. 2000). Trend analysis of river outflow has been inconclusive. Shiklomanov et al. (2000) suggest very little change in mean annual discharge for large rivers over the last several decades, whereas Semiletov et al. (2000) document increases for several Eurasian rivers. Changes in the seasonal pattern of discharge in many Arctic rivers have occurred (Savelieva et al. 2000), but these changes are challenging to detect because of large natural variations. Changes in the base flow, such as the increases in the Yenisei River between 1936 and 1995 (Figure 43) (Yang et al. in review), are more distinct and thought to reflect increased groundwater infiltration coupled to reductions in permafrost and an increase in active layer thickness due to warmer temperatures (Figure 4-4). A recent analysis of discharge records from several hundred stations distributed across the pan-Arctic (Lammers et al. 2001) indicates there has been an increase in winter flow in several Siberian river basins during the 1980s. Such hydrologic changes can impact stream habitat, increase icing, and elevate the export of sediment and solutes to the ocean. Changes to the Atmosphere Within the atmosphere, evidence of unprecedented change is documented in the instrumental record of precipitation and temperature as well as in changes in synoptic scale circulation and variability. The paleo perspective extends the relatively short instrumental Figure 4-2. With increasing temperature, there have been noticeable changes in the dates of freeze up and ice breakup in many lakes and rivers of the Arctic. The average change over the 150-year period was nearly nine days later for freeze up dates and almost 10 days earlier for ice breakup dates of rivers and lakes in the Northern Hemisphere (Magnuson et al. 2000). YEAR Freeze Sites MacKenzie Red River Mendota Grand Traverse Bay Kallavesi Angara Baikal Suwa 1845 19951860 1875 1890 1905 1920 1935 1950 1965 1980 Smoothed Freeze and Breakup Dates Freeze Dates Break Up Dates May 1 Apr 1 Mar 1 Feb 1 Dec 1 Nov 1 Jan 1 Red River Mendota Grand Traverse Bay Kallavessi Tornionjoki Angara Baikal Breakup Sites 37 period and thus provides a more complete context for interpreting recent hydrologic variability and change. Overpeck et al. (1997) used a multiproxy regional synthesis to determine that arctic summer air temperatures of the 20th century have been the highest in the last 400 years, despite showing both positive and negative shorter term temperature trends. One warm period began in the 1920s and extended to the late 1940s; a second, still underway, started in the 1970s (Figure 4-5). The instrumental record of change in the Arctic indicates that high northern latitudes have increased in mean annual temperature by ~1˚C, with the largest increase in winter temperatures (~2˚C), whereas summer temperatures increased by ~0.5˚C (Lugina 1999, Lugina et al. 2001). Serreze et al. (2000) confirm that temperature changes are spatially complex, with warming in northern Eurasia and western North America but cooling in eastern Canada and southern Greenland (Figure 4-6). Instrumental precipitation records document a significant increase over northern Eurasia (Groisman 1991) over the last 50 years across northern North America (Groisman and Easterling 1994), whereas in eastern Russia over the same period there has been a decrease in summer precipitation (Sun and Groisman 2000). This decrease in eastern Russia over the last 50 years has been accompanied by a replacement of stratiform clouds with convective clouds. Overall, across much of Russia there has been an increase in convective cloudiness associated with an increase in the number of days Figure 4-3. The base flow (non-surface runoff) of the Yenisei River increased markedly over the period from 1936 to 1995. For each month the plot shows the average conditions for each sequential year. This change is postulated to arise from increased groundwater infiltration coupled with permafrost degradation, which itself is a response to climate warming (Yang et al., in review). The construction of large artificial impoundments may also contribute to these changes. Yenisei River at Igarka, 1936–1995 0 20,000 40,000 60,000 80,000 100,000 120,000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Monthly discharge (m3/s) Figure 4-4. Springs represent an important connection between groundwater and surface water, often forming at the permafrost boundary. Presence of welldeveloped minerotrophic vegetation indicates the spring has existed for many years. As permafrost degrades, the connections between groundwater and surface water increase, allowing springs to form or in some cases ponds to shrink (photo by L. Hinzman). 4. Unprecedented Change to Arctic Hydrological Systems 38 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change with heavy precipitation (Sun et al. 2001). The primary modes and variability of the North Atlantic Oscillation (NAO), and the closely related Arctic Oscillation (AO), determine interannual precipitation variations over Eurasia and eastern North America whereas western North America responds to variability in the North Pacific Ocean. Consistent with intensification of the NAO/AO over the last two decades, winter precipitation amounts and surface air temperatures have been increasing in northern Eurasia, decreasing in southern Eurasia, and decreasing in northeastern Canada in response to enhanced storm activity in northern latitudes (Serreze et al. 2000). Over the same period that winter precipitation has increased, there has been a dramatic decline in northern hemisphere snow cover (Robinson 1999) (Figure 4-7). Eurasian snow cover extent has decreased over the past 20 years (primarily in the spring and summer; Groisman et al. 1994). The same is true for Alaska where during the past 50 years a general retreat of spring snow cover was reported (Groisman et al. 2001). Most of this retreat has occurred during the past two decades, resulting in an earlier onset of spring by approximately two weeks. These climate trends are consistent with greenhouse warming, however, uncertainty remains whether these phenomena reflect natural climate variability, anthropogenic forced (i.e., “global warming”) or a combination. Changes in rainfall, snowfall, and the recycling of water back to the atmosphere through evaporation and sublimation are difficult to assess from the instrumental record because the network of stations is sparse and data collection difficult (Black 1954; Woo et al. 1983; Yang et al. 1999, 2001). Summer precipitation trends, determined by computing precipitation (P) minus evaporation (E) from numerical weather prediction model reanalysis (Walsh et al. 1994, Serreze et al. 1995, Cullather et al. 2000), reveal little systematic change over the past 30 years. Site-specific studies often yield less ambiguous results. In locations where direct landFigure 4-5. Time series of temperature anomalies for the 20th century for the Northern Hemisphere from 55o to 85o N (based on update to Eischeid et al. 1995). DJF MAM JJA SON Annual Temperature Anomaly (˚C) Year 39 Figure 4-6. The geography of recent circumarctic temperature change. Updated from Chapman and Walsh (1993). based measurements have been available (Oechel et al. 2000), an observed trend toward increasing summer precipitation (1960 to 1998) has been offset by increasing air temperature and evapotranspiration, resulting in a net gain of water vapor to the atmosphere and drying of the soil (Figure 4-8). Although pan-arctic data sets of critical hydroclimatic variables can be assembled at relatively high resolutions using state-of-the-art interpolation and gridding techniques (Price et al. 2000, Willmott and Rawlins 1999), accuracy is limited by a deteriorating network of ground-based monitoring stations. Intercomparison tests (Rawlins 2000) suggest that not only are new techniques still 4. Unprecedented Change to Arctic Hydrological Systems Figure 4-7. Understanding the processes controlling the variability of snowpack properties and snow cover distribution are critically important to understanding the current hydrologic regime and in predicting potential responses to climate change (photo by L. Hinzman). 40 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Figure 4-9. Impact of interpolation technique on the resulting bias in pan-arctic temperature climatologies. Latitudinally averaged (over 30’ latitude bands) mean surface temperature for winter is shown for traditional spherical interpolation versus Digital topography-Aided Interpolation (DAI) (Rawlins 2000). This graphic highlights the need to address systematic errors in our monitoring of hydrologically relevant variables across the panArctic. Figure 4-8. Changes in precipitation (P), potential evapotranspiration (PET), and their difference, a measure of net water available for soil water recharge and runoff. These data represent measurements made at four sites in northern Alaska. A net change in CO2 flux is also tabulated as terrestrial primary productivity and ecosystem respiration are linked closely to moisture availability at these sites during the growing season (Oechel et al. 2000). -800 -600 -400 Total summer P-PET (mm) 1960 1965 1970 1975 1980 1985 1990 1995 Years 0 50 100 150 Total summer precipitation (mm) D C 10 11 12 Average summer temperaure (°C) B -100 0 100 200 300 400 Net CO 2 flux (gC m -2 season -1 ) Source Sink A necessary to narrow the substantial gaps in our detection of climate warming but a substantial upgrading of station holdings remains critical (Figure 4-9). The Changing Arctic Ocean and its Regional Seas Recent hydrologically related changes within the Arctic Ocean system include increased salinity in the central region, shrinking of the cold halocline layer, and decreased surface salinity off of western North America (SEARCH SSC, 2001). Specific hydrological observations include changes in ice drift pattern, decreased sea ice extent, and decreased sea ice thickness. Arctic sea ice extent decreased by 2.9 +/- 0.4% per decade over the last 30 years (Cavalieri et al. 1997) and analyses of passive microwave time series from satellites indicate that ice reductions have been accompanied by an increased length of ice melt season (Smith 1998). Arctic sea ice thickness measured by U.S. Navy submarines over the last 20 years record an average 43% reduction in thickness for the central Arctic Ocean (Rothrock et al. 1999). The yearly average pressure maps indicate a shift in the 41 Box 4-1. The Arctic Oscillation and Hypothesized Connections to the Water Cycle Based on extensive oceanographic observation, critical changes in the Arctic Ocean and changes to the land-based hydrologic cycle are hypothesized to relate closely to the onset of the Arctic Oscillation (AO) (Thompson and Wallace 1998). The working hypothesis is that as the AO index rises, the strength of the polar vortex increases, and the surface pressure in the Arctic Basin decreases, weakening the Beaufort high (Walsh et al. 1996). This applies positive vorticity to the sea ice and ocean circulation (Proshutinsky and Johnson 1997), resulting in reduced convergence in the Beaufort Gyre. This in turn results in more open water, greater radiative heat input, increased summer melt, and decreased Beaufort Sea surface salinity (McPhee et al. 1998). The change in circulation may also account for the decreased ice cover on the Siberian shelves (Maslanik et al. 1996). Increasing surface air temperatures are also thought to influence land-based freeze-thaw with potential acceleration of the terrestrial water cycle. Steele and Boyd (1998) argue that the change in circulation reroutes Siberian river runoff to the east rather than allowing it to mix with Atlantic water, cool, and move cross-shelf to form cold halocline water. It is thereby responsible for thinning the cold halocline layer. The shift of Siberian runoff to the east may also be in part responsible for the freshening of the upper layers of the Beaufort Sea (McPhee et al. 1998, Macdonald et al. 1999). The increased cyclonic vorticity added to the Arctic Ocean may also act to draw surface water from the lower salinity, western region of the basin and increase the amount of fresh surface water flowing out through Fram Strait. This could increase stratification in the Greenland Sea and contribute to the weakened deep convection observed there in recent years (Aagaard et al. 1991, Schlosser et al. 1991). An intriguing possibility is that reduced thermohaline circulation imposes a negative feedback on this system by causing less northward ocean heat flux into the Nordic seas and thereby cooling northern Europe and Russia, with important consequences for terrestrial ecosystems and human society. These complex interconnections argue strongly for synthesis studies of the entire coupled arctic system. Integrated monitoring and simulation—at the heart of the overall Arctic-CHAMP initiative—will be essential to future progress in understanding these geophysical processes. 4. Unprecedented Change to Arctic Hydrological Systems 42 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change position of the Beaufort high, usually centered over 180˚ longitude before 1988–1989, to a more western position and weakening thereafter. These pressure anomalies are linked to changes in ocean circulation patterns and therefore the distribution of sea ice, terrestrially derived runoff, and salinity. Collectively these changes represent some of the most compelling lines of evidence for arctic environmental change and suggest a substantial reorganization of the Arctic Ocean system, with important implications for ice cover, the ice-albedo feedback, and the terrestrial water cycle. These changes also highlight the integrative nature of the hydrologic cycle, linking land, atmosphere, and ocean. Box 4-1 describes some of the hypothesized links between the Arctic Ocean and freshwater dynamics. The full impact of the unfolding changes to the Arctic Ocean hydrologic system remains unknown, but the dramatic changes evident in numerous paleoclimate records underscore the importance of understanding both the magnitude and consequences of contemporary hydrological changes across this climatically sensitive region (Stein 2000). Central Question: Are the Observed Changes in Arctic Hydrology Part of the Natural Variability or Are They Related Uniquely to Human-forced Global Warming? Key Gaps in Current Understanding and Needed Studies: •Design and implementation of long-term, coherent observational programs for water-related variables over land, atmosphere, ocean, and cryosphere •Historical and paleo studies to establish benchmarks by which contemporary change can be measured •Quantify the underlying processes controlling the natural variability and the observed unprecedented changes •Studies that identify the causal agents of observed changes to arctic hydrosystems •Trend analysis for early detection of global climate change 49 Arctic land-atmosphere-ocean feedbacks extend far beyond coastal seas and influence the Arctic Ocean as well as other oceans of the world. Recent analysis of periodic atmospheric phenomena such as the AO and NAO suggest interconnections among the major land, ocean, and atmospheric components of the larger arctic system (Hilmer and Jung 2000, Morison et al. 2000). Salinity anomalies originating with freshwater pulses from the Arctic have had oceanographic, climatic, and economic consequences around the northern Atlantic (Malmberg et al. 1999). Such observations give hints about how the system is woven together and its potential sensitivities to global change (Box 4-1). Land-Atmosphere-OceanHuman Feedbacks The commercial fisheries of the North Atlantic, important economically to more than a dozen nations and as food sources to many more (Figure 5-8), are immediately “downstream” from the Arctic Ocean. Often, they have been directly affected by the arctic hydrologic cycle (see Box 5-4). It is possible to trace causal links from arctic winds and precipitation, to arctic and Atlantic oceanographic changes, to primary biological production and key fisheries resources. The health of these resources in turn affects the well-being of people, enterprises, communities, and even nations. The cold-ocean ecosystems of the northern Atlantic support some of the most fisheries-dependent societies on Earth. Marine resources are critical as well to many arctic and sub-arctic indigenous commuBox 5-2. Large-Scale Circulation/ Snow Cover Linkages Interactions between the arctic land mass and overlying atmosphere have been found to have an important impact on the development and sustainability of snow cover and on arctic weather patterns. Several studies have shown how the atmosphere affects Eurasian snow cover (e.g., Clark et al. 1999). Other investigations have emphasized the atmospheric response to snow such as the relationship between anomalous Eurasian snow cover extent and the strength of the Asian monsoon (e.g., Douville and Royer 1996). Cohen and Entekhabi (1999) showed a statistically significant impact of autumn Eurasian snow cover patterns on the strength and spatial coverage of the Siberian high and how that can affect the position of the Icelandic low, resulting in shifts in the North Atlantic-Arctic atmospheric circulation. Large negative (positive) snow extent anomalies that exist in autumn can act as a heating (cooling) mechanism through albedo conditions and have an effect on the following wintertime atmospheric conditions (Watanabe and Nitta 1999). Figure is from Arsenault (2000). AO Index (1972–1997) Eurasian Snow Covered Area ( 10 6 km 2 ) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 –0.5 –1.0 –1.5 21 22 23 24 25 26 27 nities, for whom subsistence hunting and fishing provide cultural continuity and significant sources of food. Water fluxes also regulate the spread and bioaccumulation of contaminants, originating both from northern and more distant sources, in arctic wildlife (AMAP 1999). Such contaminants are understandably of great concern to arctic residents (Figure 5-8). Airborne transport of pollutants and deposition through precipitation constitute a major transboundary environmental issue (Figure 5-9). Other important land–atmosphere–ocean–human connections linked through the water cycle affect arctic industrial activities and 5. Impacts and Feedbacks Associated with Arctic Hydrological Change 50 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Box 5-3. Feedbacks Among Sea Ice, Precipitation, River Runoff, and Coastal Oceans Recent studies indicate the presence of decadalscale variability in the extent and thickness of arctic sea ice. Recent trends show decreasing sea ice, especially in coastal and marginal seas. The box diagram shows some potential land-oceanice-atmosphere feedbacks and interactions that might occur in such a changing environment. We start with an assumption of decreasing sea ice cover near the coast in response to climate warming, which would encourage cloud formation and increased precipitation. More open water fosters a potential biotically mediated positive feedback on clouds through production of dimethyl sulfide (DMS) by marine phytoplankton. DMS then serves as a source of cloud condensation nuclei. We also note the potential for additional water vapor advected to the coastal region from the central Arctic Ocean and/or lower latitude areas. In summer, increased precipitation would create more runoff and thus more discharge of fresh waters to the coastal ocean. A potential negative feedback might then result, since all other effects being constant, freshwater tends to stratify the coastal ocean and Increased Evaporation Climate Change Climate Change Radiative Feedbacks? Radiative Feedbacks? Increased Precipitation Decreased Ice/ Increased Open Water Increased Discharge Increased Snow & Warmer Permafrost positive feedbacks negative feedbacks Increased Clouds Heat and Moisture From Lower Latitudes Increased Evaporation Increased Biologic Activity positive/negative?? encourage sea ice growth. (In fact, the annual volume of river discharge to the Arctic Ocean approximately equals the volume of sea ice exported southward through Fram Strait.) However, positive feedbacks could also occur as the stratified ocean warms (Macdonald 2000). The above scenario assumes that the land surface is fixed. In reality, increased precipitation might encourage a warming of the land surface, for example, as the insulating effects of snow cover act to warm permafrost. This might lead to plant community changes, increased evaporation and thus more clouds, more precipitation, and so on. We also note the potential for radiative feedbacks in this scenario, yet predicting cloud properties and their specific response to perturbation will constitute a major challenge. An important caveat is the presence of lateral advection, which would certainly produce a threedimensional structure that is not captured by this two-dimensional schematic. The unknowns and uncertainties are many, and the hydrological cycle figures prominently in each. 51 Box 5-4. Freshwater Fluxes, Ocean Salinity, and Fisheries The graph above shows total catches in Icelandic waters of herring and capelin, 1905 to 1997. Dashed vertical lines show approximate arrivals of cold, low-salinity arctic water anomalies (GSA ’70s and GSA ’80s) off North Iceland. These anomalies have strong linkages to the water cycle and affect biological production of importance to humans. The “Great Salinity Anomaly” (GSA ’70s), a low-salinity surface water mass that circulated around the North Atlantic ca. 1968–82, is thought to have originated with a freshwater/sea ice pulse from the Arctic via Fram Strait. A second North Atlantic salinity anomaly (GSA ’80s) that circulated ca. 1982–89 had different origins, forming in the Labrador Sea/Baffin Bay due to severe winters and possibly arctic freshwater outflow through the Canadian Archipelago (Belkin et al. 1998). Arctic hydrological factors, including precipitation and runoff in northern Canada, and the sea-ice extent in the western Arctic Ocean, are thus linked (Power and Mysak 1992, cited in Belkin et al. 1998) to a phenomenon that has been described as “one of the most persistent and extreme variations in global ocean climate yet observed in this century” (Dickson et al. 1988). As they moved for years through the North Atlantic, both GSAs had effects on marine life, commercial fisheries, and human societies. The seas north of Iceland are characterized by relatively large variations in temperature and salinity in comparison with seas to the south. These variations affect phytoplankton production: a cold, fresh surface layer inhibits vertical mixing, reducing the nutrients available to maintain the spring phytoplankton blooms (Gudmundsson 1998). Phytoplankton production controls the biomass of zooplankton, which in turn provides food for larval cod, capelin, and herring (Astthorsson and Gislason 1995). The cold, relatively fresh water of GSA ’70s was first observed northeast of Iceland in 1965–71, coinciding with the collapse of Iceland-waters herring catches seen in the graph above (Hamilton and Allanson 2001). Herring stocks never fully recovered from this collapse. In subsequent years another forage species, capelin, played a larger commercial role. GSA ’80s circulated through North Icelandic waters in 1982, and again in 1989–90. Both these events were followed by steep falls in capelin catches. Onshore in Iceland, fluctuating fisheries catches translated into economic hardship for individuals and businesses who count heavily on these resources. Some employers were forced to shut down and some communities lost inhabitants as well as jobs. Herring: 1000s of tons Capelin: 1000s of tons Herring Capelin 1910 1930 1950 1970 1990 0 100 200 300 400 500 600 700 0 200 400 600 800 1000 1200 A capelin catch in southeast Iceland (photo by Larry Hamilton). 5. Impacts and Feedbacks Associated with Arctic Hydrological Change 52 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Figure 5-9. Sulfur dioxide and other pollutants from this smelter in the Murmansk region of Russia have killed forests in an area more than 40 kilometers across and caused measurable damage well into Norway and Finland (photo by L. Hamilton). Figure 5-8. Fish are an important part of the subsistence diet and the commercial economy for many arctic people. This Native family is harvesting salmon on the Arctic Red River in the Northwest Territories, Canada (photo by L. Hinzman). settlements. Development and maintenance of infrastructure in arctic regions is thoroughly intertwined with permafrost-dominated hydrological processes. Facilities built over permafrost remain stable only so long as the permafrost remains frozen. A weak understanding of hydrologic science and a warming climate combine to make construction and maintenance of infrastructure tenuous. Construction of roads or bridges requires knowledge of the biogeophysical characteristics of the drainages that must be traversed. These include the frequency of floods, average high and low flows, potential for icing, rainfall distributions, snow loads and dominant drift directions, soil properties, and vegetation. For most regions of the Arctic, such information is essentially nonexistent. This often leads to costly mistakes and extensive re-engineering. Construction or removal of roadways also threatens to damage fragile ecosystems that will require decades or centuries to recover. Roads create impoundments of water, which if not properly drained can result in extensive thermokarsting (Figure 5-7). All of these issues become especially problematical under rapid environmental change and highlight the role of humans in the interacting arctic biogeophysical system. Central Questions: What are the impacts of arctic hydrological changes on ecosystems and humans? How does the hydrologic cycle feed back to the oceans and atmosphere? Key Gaps in Current Understanding and Needed Studies: • Synthesis studies coupling atmosphere-land-ocean dynamics • Permafrost impacts on vegetation, biogeochemistry, and trace gas exchanges • Documentation of changes in the distribution and dynamics of arctic vegetation • Documentation of changes to arctic animal populations, many of importance to humans • Altered weather and human response • Sensitivity of human infrastructure to permafrost warming and associated hydrological change • Synthesis studies embedding human dimension issues into coupled atmosphere-land-ocean system studies 53 ocean studies, terrestrial and aquatic ecology, and socioeconomics. In addition, membership should include scientists active in executing large-scale synthesis studies, specifically, those developing earth and arctic systems models. A balance between process-level field researchers, operational monitoring agency representatives, and simulation modelers should be sought. The charge of AC-SSC will be to set the science agenda of the overall initiative, to coordinate its research activities, and to ensure that results are disseminated to a broad user community. The AC-SSC should critically assess the initiative’s progress and scientific relevancy, as well as provide guidance to NSFARCSS on future funding requirements. To ensure continuity across NSF arctic research programs, the AC-SSC should be represented on the ARCSS Committee. •The committee recommends that an Arctic-CHAMP science agenda should be more fully developed through an interdisciplinary implementation plan. A detailed science plan should go beyond this current document, presenting guidance on the institutional structure for Arctic-CHAMP, its governance, a set of specific scientific investigations and observational campaigns, and coordination with other NSF, national, and international agency efforts. The implementation plan would be augmented through annual reports summarizing progress on ArcticCHAMP and providing revised plans for future work. Additional documentation of progress would be provided through, first and foremost, peer-reviewed publications by participating researchers. A newsletter, workshop reports, and a frequently updated web page would also help to promote a broad following. •The committee strongly recommends that NSF support a set of multidisciplinary, processbased catchment studies. Through the normal peer review process, NSF should identify and fund experiments at a core group of field sites aimed at developing a mechanistic view of the hydrology of the Arctic. Integration of hydrology, land-atmosphere interaction, biology, and biogeochemical processes should be a fundamental feature of this research. An emphasis on up-scaling to ensure the relevancy of these studies to the full pan-arctic domain is encouraged. •The committee recommends an immediate and major effort to improve our current monitoring of water cycle variables across the pan-Arctic. Detecting and interpreting progressive changes to the arctic hydrologic cycle will be impossible without a coherent observational Arctic-CHAMP must be inclusive and structured to enlist a continuing input of new ideas from the scientific community at large. The initiative also requires a “corporate identity” through which scientists can propose and participate in the monitoring, modeling, and process study components of the initiative. The committee envisions this identity-building to be aided by an Arctic-CHAMP steering committee, an institutional home for the program, research plans, and a workshop series. A successful ArcticCHAMP should complement, contribute to, and draw from other important NSF, federal agency, and international arctic initiatives. These issues are articulated as a set of specific recommendations to NSF, mapped to the scientific and technical requirements of ArcticCHAMP identified throughout earlier portions of this report (Box 6-1). •This committee recommends that an Arctic-CHAMP Scientific Steering Committee (AC-SSC) be formed to catalyze conceptual development of ArcticCHAMP and to provide ongoing supervision of its execution. The AC-SSC should constitute an interdisciplinary advisory board, with representatives from the fields of land surface hydrology, atmospheric dynamics, sea ice and Implementation of Arctic-CHAMP 6 6. Implementation of Arctic-CHAMP 54 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change strategy. This requires immediate attention as well as long-term vigilance. NSF should invest in an expanded, hydrologically oriented monitoring program across the pan-Arctic, coordinating, as required, with U.S. and international agency partners. Enhancing our current capacity will involve data rescue, expansion of current observational networks, and development of new technologies for harsh weather instrumentation. It should also foster development of new interpolation and remote sensing techniques to achieve panarctic coverage at high spatial and temporal resolutions. •This committee recommends creation of an Arctic-CHAMP Synthesis and Education Center (CSEC) to serve as the institutional focal point for the initiative, open to the entire community of arctic researchers. We recommend NSF create a central facility to catalyze ongoing synthesis studies of pan-arctic hydrology. Arctic-CHAMP synthesis models would be developed at CSEC. The center should lead the coordination of modeling, field research, and monitoring efforts within Arctic-CHAMP. Each developmental version of the ArcticCHAMP models would reside at CSEC, but when sufficiently mature, distributed to the broader research community. In coordination with the National Snow and Ice Data Center (Boulder, Colorado), CSEC would produce a continually evolving Arctic-CHAMP Hydrometeorological Data Archive (HDA) for station-based monitoring data and value-added project outputs emerging from the synthesis work. Arctic-CHAMP science Box 6-1. Arctic-CHAMP Scientific and Technical Needs Several specific research needs aimed at improving our current understanding of the arctic water cycle and its sensitivity to change were identified throughout the text, setting the scientific stage for Arctic-CHAMP. In response to the integrative nature of the arctic water cycle, these issues will need to be addressed in a systematic and comprehensive fashion. A synthetic view of the entire pan-arctic hydrologic system, based on focused process, feedback, and sensitivity studies, will be critical to ensure the necessary transfer of knowledge between fine and large scale studies and between campaigns dedicated to observation and process understanding. Specific activities that are required to develop such an integrated view of the entire pan-arctic system include: •maintenance of existing and establishment of new, long-term, and coherent monitoring programs for key hydrological and biogeochemical variables, including both water itself and the constituents it supports; •enhancement of the current generation of field programs to support process-based understanding of arctic hydrology; •development of methods to bridge the gap between process-level studies, point-scale monitoring, and the hydrodynamics of the pan-Arctic through combined field-based measurements, remote sensing, and modeling; •design of a strategy to achieve synthesis and water budget closure over the full water cycle, encompassing interactions across atmospheric, land surface, and oceanic components with links to the larger earth system; •determination of the links between water-related changes, ecosystem dynamics, biogeochemical cycling, and trace gas emission which feed back to the hydrologic cycle and climate system; •assessment of the vulnerability of humans to arctic water cycle changes; •full-system feedback and sensitivity studies, including human systems, in response to global change; and •implementation of a viable administrative structure and mechanism to promote full pan-arctic system integration. A more exhaustive listing of recommended actions representing the views of a broad cross-section of the arctic science community is presented in a collection of position papers (Hinzman and Vörösmarty 2001). Appendix 2 offers a summary listing of these issues. 55 activities will serve as an important application of state-of-the-art technologies and should be coordinated with relevant activities of the NSF Information Technology Research Program. Researchers and their students and post-docs would be chosen through a competitive fellowship program attracting the most highly qualified applicants. CSEC would bring together observationalists, processlevel scientists, and modelers in a collaborative physical setting to share insight and to cross-fertilize ideas. Research would be performed by graduate students and post-doctoral fellows on site, but supervised by contributing researchers from several parent institutions. A useful model for CSEC is that of the NCEAS (National Center for Ecological Analysis and Synthesis in Santa Barbara, California). To inform the public of the need to study the otherwise distant Arctic and its role in environmental change, direct links to the NSF Interagency Education Research Initiative are advised. A vigorous K-12 effort could be mounted through the CSEC. •This committee recommends that funding be committed to an Arctic-CHAMP Workshop Series and Open Science Meetings to provide ongoing intellectual support for the overall initiative. Arctic-CHAMP would serve as an excellent focal point for working groups seeking to execute field programs, create and implement community-based models, and interpret specific observational data sets. A major initial effort should be directed toward understanding the changing contemporary condition of the pan-arctic water cycle. Other workshops in the series could focus on historical/paleo and future settings. Biogeophysical and human dimension issues should be jointly addressed. Periodic Open Science Meetings should also be convened to solicit input from the broader research community. •The success of Arctic-CHAMP will depend on a purposeful integration across other programmatic elements of the National Science Foundation and allied federal agencies, and the committee strongly advises that steps be implemented to foster this collaboration. A primary goal of the current NSFARCSS Program (Box 6-2) is to promote an understanding of the impacts of global change on the physical, biological, and human resources of the Arctic (ARCUS 1998). The issue of feedbacks across the pan-Arctic is an important emphasis of the future ARCSS Program and thus integrates well with the concept of an ArcticCHAMP. This interdisciplinary perspective is driven not only by scientific curiosity but as well by the needs of the policy community, which seeks response strategies to impending climate change that transcend the domains of traditional disciplines (e.g., U.S. National Assessment 2000). By their very nature, multiagency efforts such as the U.S. National Assessment and SEARCH would serve as important sources of information and would be served, in turn, by the unique set of hydrologically oriented results emerging from Arctic-CHAMP. As a good example, remote sensing for freezethaw dynamics, envisioned as a NASA post-2002 mission (Cline et al. 1999), would provide an enormously important data set for hydrological studies across the entire pan-Arctic. Coordination with Arctic-CHAMP field studies could provide critical ground-truth, while Arctic-CHAMP simulation studies would constitute an immediate hydrological application for this satellite system. Arctic-CHAMP studies on biological and biogeochemical feedbacks in response to global change would directly support the central scientific concerns of the NSF Biocomplexity Program. A coordination is clearly needed to avoid duplication of effort and to optimize the use of federal research dollars. Appendix 3 lists several specific opportunities for collaboration within the U.S. Arctic research community. •There are several ideal opportunities for international collaboration in arctic hydrological research. The committee urges an active linkage of these ongoing programs with ArcticCHAMP. Arctic-CHAMP’s treatment of coupled water dynamics across the entire pan-Arctic will enlist the interest and involvement of the international research community. There are several well-established experimental, monitoring, and analysis programs in place to which Arctic-CHAMP should be linked, with the aim of providing synergistic benefits not otherwise achievable through each individual effort. These involve significant ongoing as well as new initiatives organized around scientific and 6. Implementation of Arctic-CHAMP 56 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change monitoring activities. Box 6-3 summarizes several noteworthy efforts. Among these are major arctic field campaigns over a variety of spatial scales, routine environmental monitoring, intercomparison modeling studies, remote sensing, numerical weather prediction and reanalysis, data archiving activities, and policy-relevant assessments. Bilateral agreements involving the U.S. and other arctic scientific partners should be fostered, in particular with Russia to help sustain its scientific infrastructure and human resources. •The Arctic, as a harbinger of global climate change, will continue to be an important focal point for ongoing research and international policy formulation. It is recommended that a policy arm of Arctic-CHAMP be established to disseminate scientific findings to the environmental management community. It is noteworthy that ongoing IPCC assessments include a polar regional analysis, due to the many years of research indicating a high sensitivity of the Arctic to greenhouse warming. Integrative, panarctic understanding of hydrologic interactions and feedbacks in Box 6-2. NSF ARCSS Program Elements As a consequence of its ambitious mandate, ARCSS has been organized into a series of more manageable programmatic components: •Land-Atmosphere-Ice Interactions (LAII); •Ocean-Atmosphere-Ice Interactions (OAII); •Paleoenvironmental Studies (Greenland Ice Sheet Project Two [GISP2], Paleoclimates from Arctic Lakes and Estuaries [PALE]), both part of Paleoenvironmental Arctic Sciences (PARCS); •Human Dimensions of the Arctic System (HARC); and •Russian-American Initiative on Shelf-Land Environments (RAISE). The LAII Flux Study in Alaska, North American Tundra Experiment (NATEX), Arctic Transitions in the Land-Atmosphere System (ATLAS) program, and U.S. contributions to the International Tundra Experiment (ITEX) provide important observational components to the overall ARCSS effort. These studies have supported a broad array of observational programs, process-based studies, modeling efforts, and environmental assessments. Several have been high profile and highly successful (e.g., Greenland Ice Sheet Project, SHEBA), both scientifically and in raising public awareness of the importance of the Arctic in global change. While these programs provide important new science, synthesis across these efforts has yet to be achieved. Integration and synthesis is emphasized as part of the new ARCSS research agenda. response to global change—of the type envisioned for ArcticCHAMP—provides critical scientific support to U.N. Framework Convention activities. The international diplomacy issues associated with arctic system change are enormous. The contributions of ArcticCHAMP toward articulating the diverse physical, biological, and human vulnerabilities to this change provide an important impetus for international cooperation in wisely managing this critical part of the arctic and earth systems. 57 Box 6-3. International Programs Sharing the Scientific, Observational, and Policy-Oriented Objectives of Arctic-CHAMP Several opportunities are apparent for mutually beneficial collaboration, taking advantage of existing infrastructure and ongoing investment in these programs. The listing below shows some major representative programs and is not meant to be exhaustive. INTERNATIONAL PROGRAM PRIMARY GOALS/ACTIVITIES Major International Science Initiatives 1. World Meteorological Organization’s World Climate Research Program (WMO/WCRP) (a) Global Water and Energy Experiment Coupling studies of land-atmosphere for regional and (GEWEX) global modeling; Continental-Scale Experiments (CSE’s) include Baltic Sea (BALTEX), Mackenzie GEWEX Study (MAGS), GEWEX Asian Monsoon Experiment (GAME) for Lena River; organizing major Coordinated Enhanced Observation Period (CEOP) for 2001–02. (b) Climate Variability and Predictability Understanding climate variability on a months-toStudy (CLIVAR) decades time frame. (c) Climate and Cryosphere (CliC) Broad set of cryosphere/atmosphere interactions (snow, ice, land, sea ice, oceans); Arctic as harbinger of global change; strong monitoring component including WMO meteorology and hydrology networks; follow-on to existing Arctic Climate System Study (ACSYS). 2. International Geosphere-Biosphere Program and Subsidiary Program (IGBP) Elements (a) Past Global Changes (PAGES) Response of earth system to change over numerous time domains including rapid climatic shifts; analysis of sea ice, salinity, thermohaline circulation under current versus glacial maximum conditions, paleoclimatic reconstructions along Pole-Equator-Pole (PEP) transects; paleoclimate modeling including dynamic vegetation; human dimension issues during the Holocene. (b) Task Force of Global Analysis, Development of linked models of the complete Interpretation, and Modeling (GAIM) earth system, integrating dynamic atmosphere, ocean, biosphere, and biogeochemical models; feedback studies and system sensitivity to global change. (c) Biospheric Aspects of the Hydrological Enhancements of land surface-atmosphere transfer Cycle (BAHC) schemes; design and execution of large-scale field experiments; monitoring of carbon, water and energy fluxes at instrumented sites; constituent transport across drainage basins; dynamic vegetation and its role in regulating climate. (d) International Global Atmospheric Biosphere-atmosphere exchanges of trace gases, Chemistry (IGAC) including arctic wetlands; development of new gas emission instrumentation. 6. Implementation of Arctic-CHAMP 58 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Intercomparison Studies (a) GEWEX/ACSYS Project for InterImprove arctic land surface transfer schemes through comparison of Land Surface multiyear, spatial comparisons of participating model Parameterization Schemes (PILPS-2e) results; explore alternative treatments of snowpack, soil, permafrost, frozen lake, wetland dynamics. (b) International Association of Hydrological Improve understanding of snow/hydrology process-level Sciences Snow Model Intercomparison linkages. Project (SNOWMIP) (c) WMO Commission for Instruments and Correction of well-known biases in precipitation Methods of Observation: Solid measurements. Precipitation Measurement Intercomparison (d) IGBP Paleo-Model Intercomparison Assess relative performance of models contrasting glacial Project (PMIP) maximum (20K years before present) to Holocene altithermal (6K bp). (e) European Ice Sheet Modeling Initiative Test, compare, improve upon numerical ice-sheet, ice- (EISMINT) shelf, and glacier models. (f) ACSYS Sea Ice Model Intercomparison Improve understanding of freshwater dynamics Project (SIMIP) associated with growth, transport, and decay of Arctic Ocean sea ice. (g) Arctic Ocean Model Intercomparison Understand processes influencing Arctic Ocean climate Project (AOMIP) of ACSYS-CliC and how to best represent and forecast these in numerical models. Existing Field/Process Study Sites (a) U.S. and International Long-Term Two LTER sites with integrated research, intensive Ecological Research Network monitoring, and experimentation. Two other sites (LTER/ILTER) beginning to develop long-term and integrated research. (b) International Tundra Experiment (ITEX) MAB-NSN initiative (Man-And-the-Biosphere, Northern Sciences Network); provides systematic meteorological station data, monitoring of permafrost in collaboration with IPA, snow cover and lake ice data, and analysis of permanent plot studies. (c) Northern Hemisphere Climate-Processes Long-term catchment studies, soil-plant-atmosphere Land-Surface Experiment (NOPEX) monitoring, regional climate surveys, use of remote sensing for data inputs to models, development of coldweather measurement techniques. (d) BOREAS Major U.S.-Canadian initiative to develop improvements in understanding of land surface-atmosphere exchanges of energy, water, carbon, and other biogeochemical fluxes, including trace gases; bulk of field effort ended in mid-1990s, analysis continues. Remote Sensing (a) Glacier Inventory of the Commission on Based on Landsat-7 data, provides benchmarks for Glaciation, International Union for future change in freshwater stocks trapped on land Quaternary Research (INQUA) as “permanent” ice. INTERNATIONAL PROGRAM PRIMARY GOALS/ACTIVITIES 65 Jorgenson, M. T., C. H. Racine, J. C. Walters, and T. E. Osterkamp. 2001. Permafrost degradation and ecological changes associated with a warming climate in central Alaska. 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Geophys. Res. 98:5,017–5,023. References 71 Appendix 1 NSF-ARCSS Arctic Hydrology Workshop Participants National Center for Ecological Analysis and Synthesis, Santa Barbara, California, 18–20 September 2000 John Christensen Bigelow Laboratory for Ocean Sciences 180 McKown Point West Boothbay, ME 04575 Tel.: (207) 633-9601 Fax: (207) 633-9641 [email protected] Andrew Fountain Portland State University Depts. Geology and Geography 17 Cramer Hall, 1721 SW Broadway Portland, OR 97201 Tel.: (503) 725-3386 Fax: (503) 726-3025 [email protected] Steve Frolking University of New Hampshire Complex Systems Research Center 39 College Road, Morse Hall Durham, NH 03824-3525 Tel.: (603) 862-0244 Fax: (603) 862-0188 steve[email protected] Barry Goodison Environment Canada AES-Climate Research Branch 4905 Dufferin Street Downsview, ON M3H 5T4 Canada Tel.: (416) 739-4345 Fax: (416) 739-5700 Barry[email protected] Pavel Groisman University of Massachusetts at Amherst Dept. of Geosciences Morrill Science Cntr, Box 35820 Amherst, MA 01003 Tel.: (413) 545-9573 Fax: (413) 545-1200 [email protected]v William Gutowski Iowa State University Dept. of Geological and Atmospheric Sciences 3021 Agronomy Ames, IA 50011-1010 Tel.: (515) 294-5632 Fax: (515) 294-2619/3163 [email protected] Lawrence Hamilton University of New Hampshire Dept. of Sociology 20 College Road Durham, NH 03824-3509 Tel.: (603) 862-1859 Fax: (630) 862-3558 lawrence[email protected] Larry Hinzman University of Alaska Fairbanks Water and Environmental Research Center PO Box 755860 Fairbanks, AK 99775-5860 Tel.: (907) 474-7331 Fax: (907) 474-7979 [email protected] Carl Bøggild Geological Survey of Denmark and Greenland Dept. of Hydrology and Glaciology Thoravej 8 Copenhagen NV DK-2400 Denmark Tel.: 45 38 14 27 94 Fax: 45 38 14 20 50 [email protected] David Bromwich The Ohio State University Polar Meteorology Group Byrd Polar Research Center 1090 Carmack Road Columbus, OH 43210 Tel.: (614) 292-6692 Fax: (614) 292-4697 [email protected] David Brooks Texas A&M University Oceanography/College of Geosciences College Station, TX 77843-3148 Tel.: (409) 845-3651 Fax: (409) 845-0056 [email protected] F. Stuart Chapin III University of Alaska Fairbanks Institute of Arctic Biology PO Box 757000 Fairbanks, AK 99775-7000 Tel.: (907) 474-7922 Fax: (907) 474-6967 [email protected] Appendix 1. Workshop Participants 72 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change Doug Kane University of Alaska Fairbanks Water and Environmental Research Center PO Box 755900 Fairbanks, AK 99775-5860 Tel.: (907) 474-7808 Fax: (907) 474-7979 [email protected] Yuji Kodama Institute of Low Temperature Science Hokkaido University Sapporo 060-0819 Japan Tel./Fax: 81-11-706-5509 [email protected] Richard Lammers University of New Hampshire Institute for the Study of Earth, Oceans, and Space Water Systems Analysis Group 39 College Road, Morse Hall Durham, NH 03824-3525 Tel.: (603) 862-4699 Fax: (603) 862-0587 [email protected] Dennis Lettenmaier University of Washington Civil and Environmental Engineering 164 Wilcox Hall, Box 352700 Seattle, WA 98195-5270 Tel.: (206) 685-1024 Fax: (206) 685-3036 [email protected] Glen Liston Colorado State University Dept. of Atmospheric Science Fort Collins, CO 80523-1371 Tel.: (970) 491-8220 Fax: (970) 491-8293 [email protected].edu Wieslaw Maslowski Naval Postgraduate School Dept. of Oceanography—Code OC/Ma 833 Dyer Road, Room 331 Monterey, CA 93943-5122 Tel.: (831) 656-3162 Fax: (831) 656-2712 [email protected] James McNamara Boise State University Geoscience Dept. Mail Stop 1535 Boise, ID 83725 Tel.: (208) 426-1354 Fax: (208) 426-4061 [email protected] James Morison University of Washington Polar Science Center - Applied Physics Laboratory 1013 NE 40th Street Seattle, WA 98105-6698 Tel.: (206) 543-1394 Fax: (206) 616-3142 [email protected] Frederick Nelson University of Delaware Department of Geography 216 Pearson Hall Newark, DE 19716 Tel.: (302) 831-0852 Fax: (302) 831-6654 [email protected] Bruce Peterson Marine Biological Laboratory The Ecosystems Center 7 MBL Street Woods Hole, MA 02543 Tel.: (508) 289-7484 Fax: (508) 457-1548 [email protected] Terry Prowse Environment Canada National Water Research Institute 11 Innovation Boulevard Saskatoon, SK S7N 3H5 Canada Tel.: (306) 975-5737 Fax: (306) 975-5143 terry.prow[email protected] Alan Robock Rutgers University Dept. of Environmental Sciences 14 College Farm Road New Brunswick, NJ 08901-8551 Tel.: (732) 932-9478 Fax: (732) 932-8644 [email protected].edu Vladimir Romanovsky University of Alaska Fairbanks Geophysical Institute PO Box 750109 Fairbanks, AK 99755-0109 Tel.: (907) 474-7459 Fax: (907) 474-7290 ffv[email protected] Mark Serreze University of Colorado at Boulder Coop. Inst. for Research in Env. Sci. Div. of Cryospheric and Polar Processes Campus Box 216 Boulder, CO 80309-0216 Tel.: (303) 492-2963 Fax: (303) 492-1149 [email protected] Michael Steele Polar Science Center Applied Physics Laboratory 1013 NE 40th Street Seattle, WA 98105 Tel.: (206) 543-6586 Fax: (206) 616-3142 [email protected]ashington.edu Marc Stieglitz Columbia University Lamont-Doherty Earth Observatory Route 9W Palisades, NY 10964 Tel.: (914) 365-8342 Fax: (914) 365-8156 [email protected] Matthew Sturm Cold Regions Research and Engineering Laboratory PO Box 35170 Ft. Wainwright, AK 99703-0170 Tel.: (907) 353-5183 Fax: (907) 353-5142 [email protected].army.mil James Syvitski University of Colorado Institute of Arctic and Alpine Research Campus Box 450 Boulder, CO 80309-0450 Tel.: (303) 492-7909 Fax: (303) 492-6388 james[email protected] 73 Charles Vörösmarty University of New Hampshire Water Systems Analysis Group 39 College Road, Morse Hall Durham, NH 03824-3525 Tel.: (603) 862-0850 Fax: (603) 862-0587 charles.v[email protected] Robert Webb NOAA/OAR/CDC 325 Broadway Boulder, CO 80303 Tel.: (303) 497-6967 Fax: (303) 497-7013 rw[email protected]v Cort Willmott University of Delaware Geography Department 216 Pearson Hall Newark, DE 19716 Tel.: (302) 831-2292 Fax: (302) 831-6654 [email protected] Appendix 1. Workshop Participants 75 Appendix 2 Current Gaps in Understanding the Pan-Arctic Hydrological Cycle •What determines the regional and temporal distribution of snow trends? Is it tied to the AO? •How important is lateral transfer of heat during snowmelt? •What are the mechanisms of vegetation-snow feedback? •What is the role of vegetation in water budgets and how does it vary in space and time? •What is the affect of boreal forests on pan-arctic hydrologic processes? •Is there widespread drying of soil and ponds across the pan-Arctic in response to regional warming trends, and if so what is its impact on resident ecosystems? •What is the distribution and importance of rock glaciers and rock fields as a source of late summer arctic discharge? •What controls basin morphology in watersheds underlain by permafrost and how will it change with a warming climate? •How does the fact that sediment is immobile (frozen) at the time of maximum stream power affect the sediment load in arctic rivers? •What are the pathways of sediment discharged into the continental shelves by the arctic rivers and is the variability of this sediment delivery large enough to be represented in paleorecords? •What is the timing and magnitude of sediment, carbon, and nutrient loads from hillslopes to large rivers and what is the effective constituent discharge of iceaffected rivers? •How will sediment and other constituent discharges change as permafrost distribution responds to climate warming? •What are the controls on the transfer of nutrients and organic matter from soils to streams across the pan-Arctic? Technical Needs and Uncertainties •Study energy, water, and carbon cycles as a linked system. •Develop methods to quantify historic levels of soil moisture. •Quantify the cumulative impacts of industrial and civil development on hydrologic systems. •Improve understanding of water storage and subsurface flow processes in discontinuous permafrost and mountainous regions. • Improve understanding of the surface heat and mass transfer processes in mountain regions. •Better define the role of geometric patterns of permafrost degradation and its ecological and hydrological consequences. •Develop better understanding of hydraulic routing through The listing below was drawn from the set of key, unresolved scientific and technical issues that were solicited from participants of the NSF-ARCSS Arctic Hydrology Workshop, held at the National Center for Ecological Analysis and Synthesis, Santa Barbara, California, in September 2000. This listing is organized by the major domains over which the water cycle plays an integrative role: land, oceans, atmosphere, society (see Figures 1-1, 1-3, 2-1, 2-2). A subset of these issues has been identified and further articulated in the main body of this report. Land Systems Scientific Questions •What would be the river response to extreme Holocene climatic events? •How is spring meltwater partitioned into infiltration and runoff? •What is the relative role of soil moisture dynamics in relation to other hydrological processes? •What is the role of wind-pumping convection in arctic depth hoar and what is the importance of hard slab and snow dune formation processes? Appendix 2. Current Gaps in Understanding the Pan-Arctic Hydrological Cycle 76 The Hydrologic Cycle and its Role in Arctic and Global Environmental Change glaciers; models of glacier runoff need better depiction of water dynamics at the base of the glaciers. •Improve understanding of groundwater fluxes, including dynamics during winter. •Sublimation needs better quantification. •Methods need to be developed for improved mid-winter discharge measurements in highlatitude rivers. •Wind-blown flux of snow and its redistribution is a critical unknown. •Winter wind speed and direction often unreliable due to riming/ icing of sensors; improved technology is required. •Reliable methods to provide electrical power to remote weather stations need to be developed. •Stratigraphy is hard to measure widely but determines critical bulk thermal and physical properties of arctic soils. •Accurate and widespread measurement of winter precipitation not yet achieved. •Improve upon the quality and documentation of observing techniques for making precipitation measurements. •Link NSF arctic hydrological initiatives more closely to GEWEX/ Mags, Crysys/ACSYS/CLiC. Data Needs •Quantify paleoclimatic forcing fields. •Requirement for long-term observations of soil moisture at stations with climate data. •Need for time series of discharge along the Arctic Coast that is ocean model-ready (including gauged and ungauged, chemistry, pollutants, sediments and heat). •Accurate digital elevation models and vegetation maps necessary for hydrological studies. •Thermal and hydraulic properties of frozen soils need to be sampled more systematically. •Critical need for permafrost temperatures and distribution, including active zone dynamics. •Measure the spatial and temporal variation of P-E around the Arctic. •Develop and apply standard methods of precipitation measurement and correction. •Fully quantify and map current glacier-covered areas to provide baseline for change. •Need more arctic glacier mass balance measurements. •Data rescue of hydrology observations from former USSR. •Assessment of hydrometeorological data across national and other administrative borders is necessary due to wide array of sampling equipment. •Need streamflow from a wide range of watershed scales. •Snow cover depth maps derived from remote sensing or meteorological inputs need to be harmonized and cross-validated. •Conventional networks are under severe cost pressures and automation leads to loss of key data and data degradation. •Develop baseline data set of chemical (nutrient, sediment, contaminant, tracer) flux from all rivers in the Arctic Basin. Scaling-Related Issues •Do processes in the headwater basins really matter when modeling large basins and regions? •New methods are necessary to scale hydrologic fluxes across basin sizes, from smallest headwaters to scale of the pan-Arctic. •Improved techniques are needed to rescale hydrologic processes from points to GCM domains. •Creation of gridded data sets by interpolation of sparse data across space and time requires additional attention. Modeling and Related Analysis •Need extensive soil moisture modeling over cold regions. •Need improved methods for remotely sensing soil moisture over large areas. •Snow sub-grid distribution variations by modeling or remote sensing remains a need. •Spatial variation of snow cover insulation and density (snow water equivalent) is currently poorly articulated. •Validation of model outputs of snow cover, snow water equivalent, snow depth, and precipitation is required. •Develop and verify models of mass transport from ungauged watersheds for water, nutrients, and sediment. •Compare regional water balances across Siberian, North American, and Northern European domains. •Improve representation of permafrost in regional and global climate and hydrological models. •Improve compatibility of in situ measurements, remotely sensed, and modeled data. •Need for model intercomparison from local to pan-arctic scale.