Integrated planning for reducing flash flood risk through blue-green infrastructure

Integrated planning for reducing flash flood risk through blue-green infrastructure A guideline using the city of Amman in Jordan as an example Daniel Schumann-Hindenberg, Ahmad Awad, Katja Brinkmann, Linnea Fölster, Martina Winker Integrated planning for reducing flash flood risk through blue-green infrastructure 2 Acknowledgments We would like to thank our Jordanian research partners for their valuable contributions to, and excellent cooperation in, our research. The Federal Ministry of Research, Technology and Space (BMFTR) funded the project CapTain Rain as part of the funding measure “CLIENT II – International Partnerships for Sustainable Innovation” in the context of the framework program “Research for Sustainable Development” (FONA) under the funding code 01LZ2006A-F. The responsibility for the content of this publication lies with the authors. Imprint Publisher Institute for Social-Ecological Research (ISOE) Hamburger Allee 45 60486 Frankfurt am Main, Germany www.isoe.de The PDF version is freely available at www.isoe.de/en/research-and-teaching/publications (Open Access) CC BY-SA 4.0 international Suggested Citation: Schumann-Hindenberg, Daniel, Ahmad Awad, Katja Brinkmann, Linnea Fölster, Martina Winker (2025): Integrated planning for reducing flash flood risk through blue-green infrastructure. A guideline using the city of Amman in Jordan as an example. DOI: 10.5281/zenodo.17351802 Funding reference: Federal Ministry of Research, Technology and Space (BMFTR), 01LZ2006A-F. October 2025, Frankfurt am Main Project partners 3 Table of contents List of figures ..........................................................................................................................................4 List of tables ...........................................................................................................................................4 1 Introduction.......................................................................................................................................5 1.1 Overview of the stepwise planning process ................................................................................5 2 Data collection and analysis ...........................................................................................................7 2.1 Identification of planning areas and data collection ....................................................................7 2.2 Categorization of land use types .............................................................................................. 10 2.3 Assessment of area potential ................................................................................................... 11 3 Planning and localization ............................................................................................................. 12 3.1 Stakeholder engagement ......................................................................................................... 12 3.2 Identification of planning goals ................................................................................................. 12 3.3 Identification of measures for flash flood protection................................................................. 15 3.4 Determination of entry points and focus areas ........................................................................ 16 3.5 Selection and localization of measures .................................................................................... 19 4 Development and Strategy ........................................................................................................... 20 4.1 Scenario Development ............................................................................................................. 20 4.2 Impact assessment and readjustment ..................................................................................... 21 4.2.1 Scenario results for the focus area Marj Al Hamam ...................................................... 21 4.2.2 Scenario results for the focus area Al Abdali ................................................................. 25 4.3 Integration into planning concepts ........................................................................................... 26 4.4 Development of detailed plans ................................................................................................. 29 5 Recommendations for Jordan ..................................................................................................... 30 6 References ..................................................................................................................................... 31 7 Appendix ........................................................................................................................................ 32 Integrated planning for reducing flash flood risk through blue-green infrastructure 4 List of figures Figure 1: Overview of the stepwise planning process comprising data collection & analysis, planning & localization, and development & strategy ........................................................... 6 Figure 2: Topographic conditions and flowpaths of the catchment area encompassing downtown Amman................................................................................................................. 8 Figure 3: Overview of the public areas in relation to the utilisation categories for the planning area. ...................................................................................................................................... 9 Figure 4: Workflow of the categorization of the land use for the Amman catchment area ................ 10 Figure 5: Overview of the public areas in relation to the utilisation categories for the “downtown” Amman catchment area .................................................................................. 11 Figure 6: Overview about different measures and their benefits regarding different planning goals .................................................................................................................................... 16 Figure 7: Location of the focus area and catchment of downtown Amman ....................................... 17 Figure 8: Overlay of flood hazard with potential availability of public spaces .................................... 18 Figure 9: Online whiteboardshowing the results of an online workshop within the CapTain Rain projects for the selection and localisation of measures ...................................................... 19 Figure 10: Percentage distribution of space requirements for measures in the “Public space” scenario ............................................................................................................................... 21 Figure 11: Percentage distribution of space requirements for measures in the “Public and private space” scenario ....................................................................................................... 22 Figure 12: Overview of the allocation of the measures in the focus area Marj Al Hamam for the “private and public space scenario” .................................................................................... 23 Figure 13: Map of the focus area Marj Al Hamam showing flood risk zones, max water depth and the location of the concept ........................................................................................... 26 Figure 14: Concept design for blue green infrastructure for Royal Village .......................................... 27 Figure 15: Map of the focus area Marj Al Hamam showing flood risk zones, max water depth and the location of the concept example 2 comprising public and privat lands. ................. 28 Figure 16: Conceptual design of measures in public areas ................................................................. 28 List of tables Table 1: Planning goals for each focus area and a pre-selection of measures. Results from the CapTain Rain stakeholder workshop in January 2023 ....................................................... 18 Table 2: Developed possible future rainfall scenarios (baseline, moderate, intense, catastrophic) ........................................................................................................................ 20 Table 3: Description of the selected measures scenarios, which were simulated using hydraulic models ................................................................................................................. 20 Table 4: Distribution of the potential area requirement and possible volume retained in public and in private space ............................................................................................................ 25 5 1 Introduction Jordan is one of the world’s most water-scarce countries and has increasingly faced flash floods caused by heavy rainfall, often resulting in severe damage. The CapTain Rain research project (“Capture and Retain Heavy Rainfalls in Jordan” – www.captain-rain.de) aimed to address this challenge by enhancing rainwater retention and minimising flood-related risks. This guideline summarises the key outcomes of the participatory development of adaptation measures for climate change and flash flood protection, undertaken as part of the interdisciplinary CapTain Rain initiative. The adaptation of urban areas to the risk of flash floods encompasses a range of measures, including technical solutions and other instruments such as behavioural prevention and communication. While large-scale technical measures, such as the construction of additional culverts, may offer a partial solution, they are constrained by limitations in construction methods, costs and the availability of space. Consequently, a comprehensive approach that encompasses a diverse array of measures on public and private land is necessary. A variety of measures for the retention, safe discharge, storage and use of heavy rainfall have been documented and their individual characteristics understood. These measures can be applied to various types of urban infrastructure, including roads, parks, residential areas and drainage systems, and they can be implemented at different scales, ranging from neighbourhoods to catchment areas. Using multifunctional land use and blue-green infrastructure (BGI) to mitigate the impact of heavy rainfall is a promising additional approach, particularly in urban areas where land is under high pressure. Such measures utilise natural features, such as wetlands, green/blue roofs and rain gardens, to manage rainwater through absorption, filtration and storage. However, planning authorities often neglect the multifunctional aspects of BGI and its positive side effects, mainly due to a lack of knowledge. When identifying suitable measures, the various needs and perspectives of society must be considered and integrated by designing and evaluating promising adaptation measures in collaboration with local stakeholders and officials, who have different areas of responsibility. Priority areas must be identified and appropriate measures integrated in an iterative process that takes into account baseline data on site conditions and incorporates information and knowledge from scientists, practitioners and stakeholders. It is very important to obtain robust initial ideas by involving stakeholders from relevant institutions as well as citizens. This guideline supports the identification and planning of measures to reduce the risk of flash flood damage. Outlining a step-by-step planning approach, it serves as a practical reference for urban and infrastructure planners – especially those in the city of Amman (e.g. the Greater Amman Municipality, GAM) – as well as other stakeholders involved in fields ranging from road construction to urban master planning. An initial site analysis, incorporating available data and spatial maps, is a crucial first step in understanding local conditions. In parallel, defining clear planning goals will help determine the scope of potential measures and facilitate informed decision-making. In this context, geospatial data as well as hydrological and hydraulic assessments play a central role in evaluating both needs and potential impacts. In areas with limited data availability, planning goals and content must be adapted accordingly. Emphasising available data, collaborating with local stakeholders, and exploring alternative sources – such as OpenStreetMap or freely accessible satellite imagery – can help address data gaps. This adaptive planning approach enables progress and resilience even in data-constrained settings. 1.1 Overview of the stepwise planning process The structured approach to integrating new projects into existing landscapes or urban environments takes into account various factors, including infrastructure analysis, stakeholder engagement, scenario planning and impact assessment. Although it is primarily intended for urban planners and environmental managers, it can also help other stakeholders gain a better understanding of the planning process and their respective roles and responsibilities. The process is divided into three main steps: Data collection and analysis, planning and localisation, and development and strategy (Figure 1). Integrated planning for reducing flash flood risk through blue-green infrastructure 6 1. Data collection and analysis  Definition of planning areas and data collection: Definition of the (catchment-) area for the planning process and procurement and processing of geographical data for the area.  Categorisation of land use types: Categorization of the identified planning areas based on their land use types.  Assessment of area potential: Assessment of the potential of these areas for integration into BGI. 2. Planning and Localisation  Stakeholder engagement: Engaging stakeholders and prioritizing actions based on their input.  Planning goals: Identification and prioritization of collective planning goals among stakeholders.  Measures for flash flood protection: Identification of suitable measures that have the potential to decrease flash flood damages as well as the other identified goals.  Determination of entry points and focus areas: Integrating additional geospatial-data (infrastructure, geology, and land cover) and results from hydraulic and hydrological analysis (e.g. flood prone areas) to evaluate potential hazards and determine the focus areas for detailed planning.  Selection and localisation of measures: Selecting and localizing spaces within focus areas for the implementation of measures, taking into account specific planning goals. 3. Development and Strategy  Scenario Development: Developing different scenarios for potential implementation of measures.  Impact assessment and readjustment: Evaluating the different scenarios and strategic importance of the selected areas.  Integration into Planning Concepts: Transferring the selected focus areas of interest and scenarios into concrete spatial planning concepts.  Development of Detailed Plans: Creating detailed plans for the implementation of the selected areas Figure 1: Overview of the stepwise planning process comprising data collection & analysis, planning & localization, and development & strategy. 1. Data Collection & Analysis •Identification of planning area and data collection •Categorization of land use types •Assessment of area potential 2. Planning & Localization •Stakeholder engagement •Identification of planning goals and measures •Determination of entry points and focus areas •Selection and localization of measures 3. Development & Strategy •Scenario development •Impact assessment and readjustment •Integration into planning concepts •Development of detailed Plans 7 2 Data collection and analysis 2.1 Identification of planning areas and data collection The first step is to determine the planning area, which may be a catchment or sub-catchment area, or a specific urban area. The relevant geographical data for the subsequent analysis of this area is then collected and processed using a geographic information system (GIS). For our case study in Amman, the capital of Jordan, the planning area is the central catchment area, which extends to the area known as “Downtown Amman” (approximately 150 km² in size) and is characterised by high levels of urbanisation. The following datasets and maps were used: Catchment areas: The total catchment area of Downtown Amman has been divided into eight subcatchments, derived from hydrological analysis and topographic information. Hydrological modelling provides additional information for each sub-catchment, such as average slope, time of concentration and curve number as well as soil type. The sub-catchment polygons are also used in further processing the land use data and assessing the area’s potential. Topography: Amman is situated on the East Bank Plateau, which is characterised by three major wadis running through it. The topography is distinct and rough, with elevations ranging from 471 to 1,101 metres above sea level (a.s.l.). On average, elevations increase from east to west and from north to south. The topographical roughness of the city, with varying elevations over short distances, gives rise to its distinctive hill-wadi systems. For example, downtown Amman is located in the Ras Al-Ain wadi, surrounded by seven hills. Integrated planning for reducing flash flood risk through blue-green infrastructure 8 Figure 2: Topographic conditions (left) and flowpaths (right) of the catchment area encompassing downtown Amman. 9 Figure 3: Overview of the public areas in relation to the utilisation categories for the planning area. Integrated planning for reducing flash flood risk through blue-green infrastructure 16 Figure 6: Overview about different measures and their benefits regarding different planning goals. Base for the development of this overview was Winker et al. (2019) 3.4 Determination of entry points and focus areas The process of identifying entry points for flood mitigation measures typically involves focusing on specific sub-units within the planning area. These sub-units are referred to as “focus areas” here. These can be sub-catchment areas, neighbourhoods, streets or other defined spaces. These entry points may form part of existing urban planning processes, such as road or sewage construction, or other urban or infrastructure developments (e.g. the Royal Village Project Area). Another approach to identifying entry points is driven by the need to reduce damage caused by regular heavy rainfall, as determined by the following criteria:  Areas with high potential for implementing measures (e.g., due to the availability of open spaces)  Areas with high flood risk or vulnerability  Areas with good data availability or suitability for modeling For our case study we used the latter approach and selected three focus areas (Figure 6), each with different characteristics, to develop various solutions. These are examples of how different characteristics and needs can guide the identification of entry points: Icons Measures Reduction of flash flood damage Water supply (provision) Groundwater recharge Erosion reduction Urban climate Quality of stay Water protection Biodiversity Health promotion Environmental education Production of food and renewables Urban gardening and agriculture Water harvesting: Terracing nnnnnnnnnnnn Roof top harvesting (Enjasa) nnn n n n nn n nnn Blue-green infrastructure: Rain gardens nnn n n n nnnnn n x Green roofs nnnnn n nnnnn n Blue roof nnnn n nnn n nnn Bioswale nnn n n nnnnnnn Infiltration trench nnnn n n nnn n n n Detention basin nnnnn n nnnnnn Multifunctional Area nnnnn n n nnnnn Rainwater harvesting nnn n n nnnn n nn Urban Forest nn n n n n nnnnnn Object protection: Mobile flood protection elements nn n nn n n n n n n n Controlled flooding nnnnnnnnnnnn Structural measures: Check Dams nnnnn n nnnnn n Dike/Flood barriers nnnnn n nn n nn n Diversion channel / culvert nn n n n n nnnnnn Expansion of canalisation nn n n n n n nnnnn n = no impact n = low impact n = high impact 17 1. Eastern part of Marj Al Hamam: This sub-catchment was chosen for hydraulic reasons and features a variety of land uses. Upon closer inspection, the Royal Village Project and a preschool were identified as specific neighbourhoods requiring detailed planning. 2a. Sports City and later b. Jordan University: This public area has many green spaces, offering significant potential for BGI. Initially focusing on the sports area, the project later changed towards and inclusion of the area of Jordan University. 3. Al Abdali: This area includes critical infrastructure, such as hospitals, making it a priority for flood mitigation measures to protect these essential services. Figure 7: Location of the focus area and catchment of downtown Amman The graph below illustrates the process of identifying entry points according to the criteria of potential public open space and high flood risk. Integrated planning for reducing flash flood risk through blue-green infrastructure 18 Figure 8: Overlay of flood hazard with potential availability of public spaces. During a large stakeholder workshop held as part of the CapTain Rain project in January 2022, planning goals were jointly determined for each of the focus areas, along with possible measures to contribute to these goals (see Table 1). This process generated a shared vision of what flash flood-oriented planning for the selected areas could entail, as well as identifying additional objectives to consider. The workshop also included a quality check of the three focus areas, the results of which were discussed with the stakeholders. Table 1: Planning goals for each focus area and a pre-selection of measures. Results from the CapTain Rain stakeholder workshop in January 2023. Focus Area/Group Eastern part of Marj Al-Hamam Sports City Al Abdali Selected planning goals  Groundwater recharge  Quality of stay  Health promotion  Protection of food & renewable raw materials  Urban climate  Biodiversity  Quality of stay  Health promotion  Reduction of flash flood damage  Health promotion  Erosion control  Urban gardening (general greening) Possible measures  Rooftop harvesting (Enjasa)  Rain gardens  Bioswales  Infiltration trenches  Diversion channel/culvert  Rain gardens  Green roofs  Bioswales  Green roofs  Bioswales  Rain gardens  Porous roads (new)  Higher curb stones and small walls (new) 19 3.5 Selection and localization of measures The selection and localisation of measures is an iterative and participatory process. To this end, several workshops were held with the key stakeholders identified. During the first stakeholder workshop, a brainstorming session was held to share knowledge, with the following aims:  Share information held by each stakeholder about existing plans, approaches or other knowledge relating to the focus area.  Prioritise planning goals.  Sharing the workshop results within the institution to identify synergies and/or conflicts. The identified focus areas were visualised on a map or touch table. During the workshop, participants gathered around the map to discuss the analysis results regarding flooding and explore possible options. It is important to document the following:  existing knowledge of flash flood events and damage in the area;  already existing or planned infrastructure;  possible spaces for measures, as described in Chapter 2.3 The following example shows the allocation of measures with comments from participants from an online workshop, which can be an alternative if a face-to-face meeting is not possible. Figure 9: Online whiteboard (https://conceptboard.com/) showing the results of an online workshop within the CapTain Rain projects for the selection and localisation of measures. After the workshop, the host or respective expert team evaluates the results. These results are then passed on for further planning and assessment by professional urban planners and engineers. In the CapTain Rain project, the results were presented, explained and jointly discussed with the stakeholders in a second workshop. Depending on the specific process, further revisions and adjustments may be possible. In other processes, the integration stage ends here. Integrated planning for reducing flash flood risk through blue-green infrastructure 20 4 Development and Strategy 4.1 Scenario Development If sufficient capacity is available, the planning process can be supplemented by simulating and analysing different scenarios in order to assess the impact of various measures. Hydrological and hydraulic models can provide valuable insights into the potential outcomes of measures aimed at mitigating the effects of heavy rainfall and flash flooding. This allows a broader range of options to be considered. As part of the CapTain Rain project, a comprehensive scenario analysis was conducted, integrating the results of various research activities. In collaboration with Jordanian stakeholders, several possible future scenarios were selected to simulate the effects of changes in heavy rainfall, as well as measures to reduce flash flood damage, using hydraulic and hydrological models. Further details on this scientific approach, along with the hydraulic and hydrological results, can be found in the CapTain Rain Wiki (https://gitlab.pik-potsdam.de/peterh/captainrain/-/wikis/Home/) and the final CapTain Rain project report (Brinkmann at al. 2025). Altogether four possible future rainfall scenarios were developed for Amman based on the results of a retrospective and prospective analysis on heavy rainfall events. Table 2: Developed possible future rainfall scenarios (baseline, moderate, intense, catastrophic). Scenario Description Rainfall amount and duration Baseline Most intense period of a well-known past heavy rainfall event (Amman: Feb. 2019 / Wadi Musa: Dec. 2022) 19–64 mm in 5.5 h Moderate Baseline + 20 % climate change effect 23–77 mm in 5.5 h Intense Max. station and total length of baseline event (Amman: Airport station / Wadi Musa: PDTRA station 180) 136 mm in 27 h Catastrophic ~ Annual rainfall amount in one event 300 mm in 27 h The measures scenarios were developed in a participatory manner during two stakeholder workshops and then refined by experts (Table 3). The measures were attributed to the scenarios according to their location (public space versus private space). Table 3: Description of the selected measures scenarios, which were simulated using hydraulic models Scenario Description Selected measures Public space scenario Public areas such as streets, plazas, public and municipal plots of land, undeveloped municipal areas, public green spaces. Measures in such areas are more easy to implement: only a limited number of stakeholders need to be involved (the city administration), planning and implementation from a single source, direct start and implementation in the near future possible. retention basin, infiltration trenches, bioswales Public and private space scenario Public areas as well as private land (developed and undeveloped). Measures are more complicated to implement: various professional and private stakeholders have to be involved, the municipality is more in the role of steering and guiding the process than implementing measures; process requires through preparation and a participatory element, also when starting directly, implementation will require time. retention basin, infiltration trenches, bioswales, multifunctional areas, pipe infiltration trenches 21 4.2 Impact assessment and readjustment Due to the large number of scenarios, it is not possible to show the combination of all possible rainfall and measure scenarios. As an example, the results of the combination of the baseline rainfall scenario with the two different measure scenarios are presented in the following section. It should be noted that the baseline scenario is currently the heaviest precipitation event observed in the area. 4.2.1 Scenario results for the focus area Marj Al Hamam The focus area of Marj Al Hamam was selected for the scenario analysis as it is located on the outskirts of Amman, where urban, densely built structures begin to blend with rural elements, displaying a clear peri-urban character. Generally, some blocks are densely built, while agriculture is practised next to them or they remain undeveloped. This area was also chosen because it is a complete sub-catchment. It was interesting to see how the catchment itself could be improved in terms of flash flood mitigation, particularly in view of the planned further developments, and to assess its potential contribution to the situation downstream. A thorough allocation of measures was carried out in this focus area, and hydrological modelling of water flows and their changing patterns was undertaken. This also enables us to obtain quantitative results regarding the impact of the measures. Public space scenario In this scenario, only public spaces were considered for the implementation of measures. The total potential usable space amounts to 0.43 km², corresponding to 4 % of the total focus area. A total of 11 measures were identified and allocated in public spaces, including one retention basin, eight infiltration trenches and two bioswales. The measures require an area of 49,048 m², corresponding to 11 % of the potential usable space. Infiltration trenches situated along streets, especially main roads, occupy nearly half of this area. Most of the measures are located in the lower part of Marj Al Hamam, in an area that still has a very high percentage of open land (mainly rangelands and croplands). Only one infiltration trench is located in the upper part of Al Quds Street. This means that the main impact of the measures is on the downstream areas of Haman, rather than on the focus area itself. Nevertheless, this example illustrates how easy it is to mitigate the effects of further development and sealing of the area by allocating just 1 % of the focus area to measures. Figure 10: Percentage distribution of space requirements for measures in the “Public space” scenario. Rooftop harvesting, rain gardens and diversion/culverts were not considered in the subsequent planning process, since the scenario definition was confined to public land. In the case of the diversion channel/ culvert, this was because the focus was on small-scale projects and BGI. The detention pond was later added by professional planners because its effectiveness in reducing peak flows in the downstream 41% 48% 11% Retention basin Multifunctional area Infiltration trench Bioswale Integrated planning for reducing flash flood risk through blue-green infrastructure 22 area depends heavily on its location. Data analysis in this case shows an overlay of high flow concentration and public open space availability. In total, the measures can retain 16,376 m³ of water. Hydraulic simulation results for different rainfall scenarios show a reduction in peak runoff of 34 % for the base scenario, 21 % for the intense scenario, and 6 % for the catastrophic scenario (Brinkmann et al. 2025). As most of the measures are located in the lower part of the focus area, their major impact in terms of reducing runoff volumes and flash flood damages is seen further downstream. Nevertheless, they also have some impact on critical areas in the focus area itself like the huge inundation potential at the intersection of Dead Sea Road and Airport Road. With regard to the selected planning goals (Figure 6) flash flood reduction is certainly achieved as already discussed. As all measures retain and infiltrate water into the ground, they positively affect groundwater recharge. However, it is not possible to quantify the overall benefit. It cannot be expected that these measures will promote health. Perhaps the infiltration trenches and other measures along main roads with heavy traffic can contribute to cleaning and rinsing the water, as well as holding back heavy metals, microplastics, etc. Food production is not achieved, but the production of renewable raw materials may be possible with a good selection of plants, such as reeds, for greening the measures. These can then be used for composting or in processes relating to renewable energies. Private and public space scenario This scenario focuses on private areas and public land. The potential usable area is 20 % of the total catchment area. The potential usable space is 2 km², which corresponds to 20 % of the focus area. Within this scenario, 23 measures have been identified: 11 in public spaces and 12 on private land, which are in addition to the measures in in the public space scenario. The measures include five retention basins, seven multifunctional areas, eight infiltration trenches, two bioswales and one pipe infiltration trench. All measures require an area of 0.18 km², 0.13 km² of which is located on private land. The measures “multifunctional area” and “retention basin” are particularly noteworthy as they represent four new locations and require most of the area (82 %). Overall, the measures require an area of 0.18 km², corresponding to 10 % of the potential usable space and 2 % of the focus area. Most of the measures are situated in the upper part of Marj Al Hamam, in an area which can be classified as urban and characterised by high levels of sealing (Figure 12). Figure 11: Percentage distribution of space requirements for measures in the “Public and private space” scenario. 59% 24% 13% 3% 1% Retention basin Multifunctional area Infiltration trench Bioswale Pipe infiltration trench 23 Figure 12: Overview of the allocation of the measures in the focus area Marj Al Hamam for the “private and public space scenario”. Integrated planning for reducing flash flood risk through blue-green infrastructure 24 Model results show that Marj Al Hamam itself will benefit most from the measures. Two significant areas are subject to regular inundation: one in close proximity to the Prince Hussein Interchange, and the other in the vicinity of the intersection between Prince Hia Bent Hamza Street and Prince Nails’ Bent Asem Street. The planned retention basins at the interchange and the two multifunctional areas at the intersection might help here. However, the retention basin and multifunctional area on Princes Najla’ Bint Asem Street are located directly within a major runoff pathway. Additionally, the multifunctional areas are located directly behind an existing hotspot. This indicates that they will contribute directly to reducing the existing flash flood damage in their immediate vicinity. The large retention basin in the Royal Village (see also Chapter 4.2) is necessary to prevent damage to the neighbourhood downstream, as well as to the Royal Village itself. This large open and unsealed area would have a significant impact if it were to be transformed into housing areas without such measures in place. It should be noted that there are two retention basins with a combined surface area of 52,156 m² in the lower area. While it is unlikely that these will be a priority for implementation, they will become relevant in the event of heavy rainfall, providing additional backup volume. Therefore, it is strongly recommended that these reservoirs are designed for multifunctional use (e.g. in combination with urban forests). Furthermore, this scenario did not consider the measures of rooftop harvesting, rain gardens on private land, and diversion channels/culverts. During the ongoing planning process and discussions with stakeholders, it became clear that the selected measures would have a significant impact on reducing flash flooding. Therefore, additional measures were no longer required. We cut down on measures that demand high resource intensity in terms of planning and implementation. Rooftop harvesting and rain gardens are resource-intensive because a large number of landowners need to be addressed, while diversion channels/culverts are costly and ultimately only guide water without retaining it. This scenario has two focal points. Firstly, it aims to reduce the risk and damage of flash floods in the downstream areas and central Amman. Secondly, it considers potential improvements to the focus area itself based on how water flows during flash floods. As previously discussed, the selected planning goals will certainly achieve flash flood reduction. As all measures infiltrate water into the ground as well as holding it back, they have a positive effect on groundwater recharge. This effect is even greater than in the public space scenario because the additional measures cover an area of 0.13 km², three times the size of the public space scenario, and also contribute to health promotion. However, the overall benefit cannot be quantified. The retention basin is located next to a very dense neighbourhood and could be designed as a green space for recreation. However, it would require a good access for pedestrians as they have to cross Marj-Al-Hamam-Street. Also the multifunctional area, maybe even in combination with the pipe infiltration trench, can create benefit. They are located close to Rosary Kindergarden and Rosary School. Both facilities seems to be completely sealed. A multifunctional area for kids to play and for further leisure or even school activities might be beneficial. In addition, the multifunctional areas in the highly dense area at the crossing of Prince Hia bent Hamza Street and Prince Nails’ bent Asem Street can improve the quality of stay as well. Production of food is not achieved as a primary goal. But maybe some urban gardening elements could also be integrated in the multifunctional areas. Renewable raw materials can be produced by choosing the right plants for greening and using them for composting or renewable energy, such as reeds. The multifunctional areas deliver manifold opportunities and their design depends on local needs, space requirements and capacities. It depends very much on their individual and detailed design. Overall, the selected measures are able to hold back a volume of 36,209 m³. The hydraulic simulation results of the different rainfall scenarios showed a peak run off reduction of 75 % for the baseline scenario, of 46 % for the intense scenario, and of 13 % for the catastrophic event (Brinkmann et al. 2025). The comparison between area requirements and retained volume between public and private land highlights the benefits of additional measures on private lands. However, measures on public space have a lower area consumption (27 %) compared to measures on private land (73 %) with nearly similar volume retained (Table 4). 25 Table 4: Distribution of the potential area requirement and possible volume retained in public and in private space. Public space Private space Total potential area requirement [m²] 49,048 27 % 130,476 73 % Volume retained [m³] 16,376 45 % 19,833 55 % 4.2.2 Scenario results for the focus area Al Abdali The Al Abdali area was selected as it exhibits the typical structure of inner-city neighbourhoods, which are often built on hillsides with steep slopes. These areas are generally densely built up, with open spaces consisting of car parks and small green areas. This focus area was selected to examine the scale of a neighbourhood. As several hospitals are located in the area, the effects on this critical infrastructure and how object protection can be implemented were a major focus. In this focus area only a first sketch of potential flood protection measures were developed, no calculation was undertaken so far regarding the required area and the volume of water holt back. Public space scenario The public space scenario focused on multifunctional areas, bioretention, the use of open spaces for detention and flood barriers in form of higher curb stones. The first sketch considered the area around the Abdali Hospital, which is located to the south of the focus area. It was found that three bioretention areas could be established in this southern area, and that five spots could be designated as multifunctional areas. Two open spaces with greenery and scrubs could be used for detention, and flood barriers could be installed by adjusting the curbs to keep the water mainly on King Hussein Street and direct it into Umyyah Ben Abd Shams Street. According to expert knowledge, it is not possible to hold or infiltrate the water in the area, even during periods of heavy rainfall, due to its topographic conditions and limited unsealed space. Therefore, the main focus is on protecting the four hospitals surrounding the focus area. This kind of object protection means keeping the hospitals functioning and free of water, as well as ensuring that their access routes remain free of water and accessible. The suggested measure could also offer some additional benefits: It could improve the quality of the available open spaces (“quality of stay”), as well as the cooling effect they provide. This is an important consideration in such a densely populated area, which has many hospitals and a correspondingly high number of visitors, as well as people who come to the area to work. Furthermore, large undeveloped areas are currently used solely for parking, which is an inefficient use of land in such densely populated areas of the capital. These parking spaces could be converted into multifunctional areas. In addition to reducing flash floods, the planning goals health promotion, erosion control and urban gardening were also selected for this focus area. Once multifunctional areas have been implemented and existing open spaces upgraded, elements enabling urban gardening could also be integrated if this remains a high priority. Private and public areas In this scenario, additional measures are added, such as blue roofs in combination with retention systems (bioretention or rain gardens) and rainwater harvesting and terraces. Given the lack of information regarding the structural characteristics of the buildings in question, it is difficult to ascertain the number of blue roofs that could be installed. In general, however, all roofs are flat, indicating basic potential for blue roof installation. This approach should therefore be pursued. Some hospitals may also have the potential for blue roofs and this should be considered further. Typically, around 20 % of rooftops are suitable. This measure can be combined with retention systems and rainwater harvesting regardless of roof suitability. While these measures will not eliminate the effects of flooding altogether, they will Integrated planning for reducing flash flood risk through blue-green infrastructure 32 7 Appendix Appendix A: Assignment of a utilisation factor for each of the 47 land use categories within the Amman catchment. ID Utilisation factor Land use categories of GAM (Greater Amman Municipality) for the City of Amman Kat_01_ 0 Alley roads_impervious surfaces Kat_02_ 0,2 Alley roads_potential open spaces Kat_03_ 0,2 Commercial_Building Kat_04_ 0,1 Commercial_Developed parcel Kat_05_ 0,2 Commercial_Undeveloped parcel Kat_06_ 0 Cultural heritage_Building Kat_07_ 0,1 Cultural heritage_Developed parcel Kat_08_ 0,2 Cultural heritage_Undeveloped parcel Kat_09_ 0 Entrance roads_impervious surfaces Kat_10_ 0,4 Entrance roads_potential open spaces Kat_11_ 0 Follower_impervious surfaces Kat_12_ 0,4 Follower_potential open spaces Kat_13_ 0,2 Low-income public housing_Building Kat_14_ 0,1 Low-income public housing_Developed parcel Kat_15_ 0,2 Low-income public housing_Undeveloped parcel Kat_16_ 0,3 Others_Building Kat_17_ 0,1 Others_Developed parcel Kat_18_ 0,2 Others_Undeveloped parcel Kat_19_ 0 Primary roads_impervious surfaces Kat_20_ 0,4 Primary roads_potential open spaces Kat_21_ 0,4 Public_Building Kat_22_ 0,2 Public_Developed parcel Kat_23_ 0,4 Public_Undeveloped parcel Kat_24_ 0 Railway_impervious surfaces Kat_25_ 0 Railway_potential open spaces Kat_26_ 0 Religious_Building Kat_27_ 0,2 Religious_Developed parcel Kat_28_ 0,4 Religious_Undeveloped parcel Kat_29_ 0,3 Residential C/D_Building Kat_30_ 0,1 Residential C/D_Developed parcel Kat_31_ 0,2 Residential C/D_Undeveloped parcel Kat_32_ 0,5 Residential villas/A/B_Building Kat_33_ 0,2 Residential villas/A/B_Developed parcel Kat_34_ 0,4 Residential villas/A/B_Undeveloped parcel Kat_35_ 0 Secondary roads_impervious surfaces Kat_36_ 0,2 Secondary roads_potential open spaces Kat_37_ 0 Side roads_impervious surfaces 33 ID Utilisation factor Land use categories of GAM (Greater Amman Municipality) for the City of Amman Kat_38_ 0 Side roads_potential open spaces Kat_39_ 0 Square_impervious surfaces Kat_40_ 0,4 Square_potential open spaces Kat_41_ 0 Stairs_impervious surfaces Kat_42_ 0 Stairs_potential open spaces Kat_43_ 0,3 Traffic zones_Building Kat_44_ 0,15 Traffic zones_Developed parcel Kat_45_ 0,3 Traffic zones_Undeveloped parcel Kat_46_ 0 Unclassified roads_impervious surfaces Kat_47_ 0 Unclassified roads_potential open spaces Integrated planning for reducing flash flood risk through blue-green infrastructure 34 Appendix B: Infocards of seven measures recommended for future implementation in the city of Amman 35 Integrated planning for reducing flash flood risk through blue-green infrastructure 36 37 Integrated planning for reducing flash flood risk through blue-green infrastructure 38