Flash drought response to precipitation and atmospheric evaporative demand in Sspain

a mosphe e A icle Flash D ough Response o P ecipi a ion and A mosphe ic E apo a i e Demand in Spain I án Nogue a 1, Fe nando Domínguez-Cas o 2,3 and Se gio M. Vicen e-Se ano 1,*   Ci a ion: Nogue a, I.; Domínguez-Cas o, F.; Vicen e-Se ano, S.M. Flash D ough Response o P ecipi a ion and A mosphe ic E apo a i e Demand in Spain. A mosphe e 2021,12, 165. h ps://doi.o g/10.3390/ a mos12020165 Academic Edi o : Sonia Raquel Gámiz-Fo is Recei ed: 5 Janua y 2021 Accep ed: 24 Janua y 2021 Published: 27 Janua y 2021 Publishe ’s No e: MDPI s ays neu al wi h ega d o ju isdic ional claims in published maps and ins i u ional a il- ia ions. Copy igh : © 2021 by he au ho s. Licensee MDPI, Basel, Swi ze land. This a icle is an open access a icle dis ibu ed unde he e ms and condi ions o he C ea i e Commons A ibu ion (CC BY) license (h ps:// c ea i ecommons.o g/licenses/by/ 4.0/). 1Ins i u o Pi enaico de Ecología, Consejo Supe io de In es igaciones Cien í icas (IPE–CSIC), E-50059 Za agoza, Spain; [email p o ec ed] 2Depa men o Geog aphy, Uni e si y o Za agoza, 50009 Za agoza, Spain; dominguez@uniza .es 3ARAID Founda ion, 50018 Za agoza, Spain *Co espondence: [email p o ec ed] Abs ac : Flash d ough is he esul o s ong p ecipi a ion de ici s and/o anomalous inc eases in a mosphe ic e apo a i e demand (AED), which igge s a apid decline in soil mois u e and s esses ege a ion o e sho pe iods o ime. Howe e , li le is known abou he ole o p ecipi a ion and AED in he de elopmen o lash d ough s. Fo his pape , we compa ed he s anda dized p ecipi a ion index (SPI) based on p ecipi a ion, he e apo a i e demand d ough index (EDDI) based on AED, and he s anda dized e apo a ion p ecipi a ion index (SPEI) based on he di e ences be ween p ecipi a ion and AED as lash d ough indica o s o mainland Spain and he Balea ic Islands o 1961–2018. The esul s show la ge di e ences in he spa ial and empo al pa e ns o lash d ough s be ween indices. In gene al, he e was a high deg ee o consis ency be ween he lash d ough pa e ns iden i ied by he SPI and SPEI, wi h he excep ion o sou he n Spain in he summe . The EDDI showed no able spa ial and empo al di e ences om he SPI in win e and summe , while i exhibi ed g ea cohe ence wi h he SPEI in summe . We also examined he sensi i i y o he SPEI o AED in each mon h o he yea o explain i s con ibu ion o he possible de elopmen o lash d ough s. Ou indings showed ha p ecipi a ion is he main d i e o lash d ough s in Spain, al hough AED can play a key ole in he de elopmen o hese du ing pe iods o low p ecipi a ion, especially in he d ies a eas and in summe . Keywo ds: lash d ough ; sensi i i y; a mosphe ic e apo a i e demand; p ecipi a ion; s anda dized d ough indices; SPEI; Spain 1. In oduc ion D ough is one o he mos complex na u al haza ds a ec ing na u al and human sys ems [ 1 – 3 ]. Typically, d ough is conside ed o be a me eo ological phenomenon ha is slow o de elop, aking many mon hs o e en yea s o each maximum in ensi y [ 4 , 5 ]. Howe e , ecen s udies ha e p o ed ha d ough may also de elop in he sho - e m as a esul o la ge p ecipi a ion de ici s and/o anomalous inc eases in a mosphe ic e apo a i e demand (AED) [ 6 ]. The e m “ lash d ough ” has become popula in he scien i ic li e a u e o desc ibe hese d ough episodes cha ac e ized by apid onse and in ensi ica ion. Flash d ough s usually begin as a me eo ological d ough ha becomes an ag icul u al d ough wi hin a sho ime, due o a decline in soil mois u e and an inc ease in ege a ion s ess [ 7 ], wi h a s ong po en ial impac on ag icul u e and he en i onmen [8]. P ecipi a ion is he mos impo an ac o in he de elopmen o d ough s [ 9 ]. How- e e , he occu ence o lash d ough s has been commonly ela ed o d as ic inc eases in AED and he associa ed land–a mosphe e eedbacks (e.g., inc eased land e apo an- spi a ion) ha can igge o ein o ce d ough condi ions [ 10 ]. Nume ous s udies ha e e idenced ha AED can play a key ole in he de elopmen and in ensi ica ion o ce ain d ough episodes [ 11 – 13 ]. The e o e, he AED can be a c ucial a iable in explaining he apid deple ion o soil mois u e and ege a ion s ess caused by lash d ough s [ 12 , 14 – 16 ]. A mosphe e 2021,12, 165. h ps://doi.o g/10.3390/a mos12020165 h ps://www.mdpi.com/jou nal/a mosphe e A mosphe e 2021,12, 165 2 o 22 Howe e , gi en complex land–a mosphe e eedbacks in ol ing d ough [ 10 ], he ole o AED in he de elopmen o lash d ough s could be e y complex and a iable in ime and space [17]. E o s o de elop objec i e me hodologies and ea ly wa ning sys ems o iden i y lash d ough s ha e inc eased in ecen yea s [ 7 , 14 – 16 , 18 – 26 ], bu none is widely accep able [ 6 ]. Mos me hods p oposed o iden i ying lash d ough s mainly ocus on apid changes in e e ence e apo anspi a ion (ET o ) o soil mois u e [ 7 , 19 , 23 , 24 ], wi hou including p e- cipi a ion as an inpu a iable. O he au ho s, such as Mo and Le enmaie [ 16 , 22 ] o Zhang e al. [ 27 ] sugges ed di e en ia ing wo ypes o lash d ough s: “hea wa e lash d ough s” linked o high empe a u es and “p ecipi a ion de ici lash d ough s” linked o anomalously low ain all. In his wo k, we s udied he ole o p ecipi a ion de ici and a mosphe ic e apo a i e demand inc ease on lash d ough s in Spain, whe e lash d ough s a e a equen phe- nomenon wi h app oxima ely ou in e e y 10 d ough e en s (i.e., a e u n pe iod o 1 in 10 yea s) esul ing in a lash d ough [ 18 ]. Se e al s udies showed he high occu ence o se e e d ough s episodes in Spain h ough his o ical [ 28 – 30 ] and ins umen al eco ds [ 31 ]. Spain has s ong clima ic con as s wi h ma ked spa ial and seasonal di e ences in p e- cipi a ion [ 32 – 35 ] and AED [ 36 – 39 ]. No he n Spain is cha ac e ized by i s humid oceanic clima e wi h abundan p ecipi a ion o e he yea , while no heas e n and sou heas e n egions a e mainly cha ac e ized by semia id condi ions wi h annual p ecipi a ion gen- e ally below 300 mm [ 40 ]. On he o he hand, he complex opog aphy gi en by he p esence o nume ous moun ain chains esul s in a s ong con inen al ea u es in cen al Spain. This clima ic complexi y is also e lec ed in he spa ial and empo al a ia ion o d ough s [ 41 , 42 ] and he a ie y o a mosphe ic mechanisms igge ing hem [ 43 – 45 ], which enable an e alua ion o he ole o p ecipi a ion de ici s and AED in he de elopmen o lash d ough s o e a wide ange o clima e condi ions. Fo his pu pose, we compa ed h ee s anda dized d ough indices based on di e en clima e a iables o lash d ough analysis. The objec i es o his s udy we e wo old: (i) o compa e he spa ial and empo al pa e ns o lash d ough s iden i ied by h ee obus s anda dized d ough indices based on di e en clima ic a iables: he s anda dized p ecipi a ion index (SPI), e apo a i e demand d ough index (EDDI), and s anda dized e apo a ion p ecipi a ion index (SPEI); and (ii) o analyze he ole o p ecipi a ion de ici s and AED excess in lash d ough s in Spain o e he pe iod 1961–2018. 2. Me hods 2.1. Da a This esea ch used a high spa ial esolu ion (1.21 km 2 ) g idded clima e da ase wi h co e age o mainland Spain and he Balea ic Islands om 1961 o 2018 a weekly e- quency. The clima e da ase included da a on p ecipi a ion, maximum and minimum ai empe a u e, ela i e humidi y, sunshine du a ion, and wind speed. The g idded da ase was c ea ed based on all daily obse a ional in o ma ion om he Na ional Spanish Me eo- ological Se ice (AEMET) by means o an in e pola ion scheme o uni e sal k iging using as inpu he me eo ological da a measu ed in he di e en me eo ological s a ions and he e ain ele a ion. The clima e se ies we e subjec ed o a homogeniza ion p ocess and a ca e ul quali y con ol (see de ails in Tomas-Bu gue a e al. [ 46 ]). Addi ional in o ma ion abou he da ase de elopmen , in e pola ion me hodology, and alida ion a e a ailable in Vicen e-Se ano e al. [ 47 ]. The e e ence e apo anspi a ion (ET o ), as a me ic o he AED, was calcula ed om he maximum and minimum empe a u e, ela i e humidi y, wind speed, and sunshine du a ion, using he FAO-56 Penman–Mon ei h equa ion [48]. 2.2. Compu ing he D ough Indices: SPI, EDDI, and SPEI S anda dized d ough indices a e commonly used in d ough analysis and moni o ing ac oss he wo ld. Among hese, some o he mos widely used o d ough analysis a e he s anda dized p ecipi a ion index (SPI; see Mckee e al. [ 49 ]) based on p ecipi a ion and he A mosphe e 2021,12, 165 3 o 22 s anda dized e apo a ion p ecipi a ion index (SPEI; see Vicen e-Se ano e al. [ 50 ]) based on he di e ence be ween p ecipi a ion and AED. In pa icula , he SPI and SPEI also p o ed o be obus me ics o iden i ying lash d ough s [ 51 ]. Recen ly, o he s anda dized d ough indices, such as he e apo a i e demand d ough index (EDDI; see Hobbins e al. [ 52 ]) based exclusi ely on AED, was de eloped and ecommended o lash d ough analysis [ 19 ]. The EDDI quan i y d ough se e i y as AED inc eases unde wa e -limi ed condi ions, which is e y use ul du ing pe iods o low p ecipi a ion o soil mois u e and impo an land–a mosphe e coupling [17]. The SPI and SPEI we e calcula ed using pa ame ic app oaches, i ing he da a o Gamma and Log-logis ic dis ibu ions, espec i ely. Mo eo e , he EDDI was calcula ed by a pa ame ic app oach based on Log-logis ic dis ibu ion [ 53 ]. The SPI, EDDI, and SPEI a e compa able in ime and space and can be calcula ed on di e en ime scales o adap he esponse o hyd ological, ag icul u al, and en i onmen al sys ems o he clima e a iabili y [ 54 ]. Howe e , he sho e scales be e cap u e he apid a ia ions in p ecipi a ion and/o a mosphe ic e apo a i e demand ha can igge a lash d ough , since he anomalies accumula ed o e pas clima e condi ions do no a ec he index alues. The e o e, we calcula ed he SPI, EDDI, and SPEI a a sho ime scale (1-mon h) and a weekly equency o each g id poin o he clima e da ase om 1961 o 2018 (see de ails in Nogue a e al. [18]). 2.3. Iden i ying Flash D ough s Based on S anda dized D ough Indices: SPI, EDDI, and SPEI Flashd ough e en swe eiden i ied ollowing heme hodologyp oposedbyNogue ae al.[ 18 ]. The o iginal app oach was based on he SPEI a a sho ime scale (1-mon h) and high- equency da a (weekly) o iden i y he onse o lash d ough episodes. This me hod ocuses on he apid de elopmen cha ac e is ic o lash d ough s, which esul s in a sudden, e y sha p d op in he index alues. Thus, lash d ough is de ined as: (i) a minimum leng h o ou weeks in he de elopmen phase; (ii) an ∆ SPEI (in 4 weeks) equal o o less han − 2 z-uni s; and (iii) a inal SPEI alue equal o o less han − 1.28 z-uni s (i.e., a 10-yea e u n pe iod). This me hod was used he e o iden i y lash d ough s based on he h ee s anda dized d ough indices: SPI, EDDI, and SPEI. 2.4. Compa ison o he SPI, EDDI, and SPEI We analyzed he spa ial and empo al a iabili y o he SPI, EDDI, and SPEI by compa ing he spa ial and empo al beha io o he alues o each index in each mon h o he yea . Pea son’s co ela ion coe icien (95% con idence le el) was used o examine he ela ionship be ween SPI, EDDI, and SPEI se ies o e ime and space. Gi en ha each weekly da a is calcula ed based on he p ecipi a ion, AED, o clima e balance (D=P − AED) da a accumula ed o e ou weeks (co esponding o a 1-mon h ime scale), we used he weekly da a o he las week o each mon h o calcula e he co ela ion be ween he indices in o de o e lec he a iabili y o e he whole mon h. The ela ionship be ween he equency o annual and seasonal lash d ough se ies eco ded by he SPI, EDDI, and SPEI o each g id poin om 1961 o 2018 was also examined by means o Pea son’s co ela ion coe icien (95% con idence le el). In addi ion, we analyzed he ela ionship be ween he o al equency o lash d ough s iden i ied by each index and he associa ed signi icance. The signi icance o Pea son’s coe icien s was es ima ed using a Mon e Ca lo app oach, in which he o al numbe o lash d ough s eco ded by SPI, EDDI, and SPEI was co ela ed in 1000 andom samples o 30 poin s om he en i e da ase a annual and seasonal scales. We also examined he end o annual and seasonal lash d ough se ies eco ded by he non-pa ame ic Mann–Kendall s a is ic. Au oco ela ion was included in he end analysis by he modi ied Mann–Kendall end es , which e u ned co ec ed p- alues a e accoun ing o empo al pseudo eplica ion [ 55 , 56 ]. To assess he magni ude o change in he equencies o lash d ough s, we used a linea eg ession analysis be ween he se ies o ime (independen a iable) and he seasonal and annual se ies o d ough equencies (dependen a iable). The slope o he eg ession indica ed he amoun o A mosphe e 2021,12, 165 4 o 22 change in he numbe o e en s pe yea , wi h highe slope alues indica ing g ea e a ia ion. In o de o iden i y changes be ween he equencies o lash d ough s eco ded o each index, we also calcula ed he di e ences (e en s/ o each g id poin ) be ween he lash d ough se ies ob ained h ough he SPI, EDDI, and SPEI annually and seasonally and also examined hei ends using he non-pa ame ic Mann–Kendall s a is ic. 2.5. E alua ion o Sensi i i y o Flash D ough s o AED To analyze he ole o p ecipi a ion de ici s and a mosphe ic e apo a i e demand (AED) posi i e anomalies in he de elopmen o lash d ough e en s in Spain, we cal- cula ed he sensi i i y o SPEI o he AED a a sho ime scale (1-mon h) and compa ed i wi h he o al equency o lash d ough e en s eco ded in each mon h o he yea in he pe iod om 1961 o 2018. The sensi i i y o SPEI o AED di e s be ween clima e condi ions [ 9 , 17 ]. The SPEI is based on s anda diza ion o he clima e balance (D) esul ing om di e ences be ween p ecipi a ion and AED (D=P − AED), making i possible o quan i y he con ibu ion o p ecipi a ion and AED o he a iabili y o SPEI alues, ollow- ing he me hodology p oposed by Tomas-Bu gue a e al. [ 9 ]. Thus, using he p ecipi a ion and AED se ies employed o compu e SPEI, we calcula ed he pa ial de i a i es o he clima e balance (D) o de e mina e he ela i e con ibu ion o bo h a iables in each mon h o e he pe iod 1961–2018. The se ies o p ecipi a ion and AED we e de ended p io o making he analysis o a oid he possible e ec s o ends on he esul s (see mo e de ails in Tomas-Bu gue a e al. [9]). 3. Resul s 3.1. Spa ial and Tempo al Va iabili y o he SPI, EDDI, and SPEI In gene al, he indices p esen high in e annual a iabili y in all mon hs (Figu e 1). The SPI and EDDI show non-signi ican co ela ion om No embe o Janua y. On he con a y, he e is a signi ican co ela ion be ween he SPI and EDDI om Ma ch o June and Sep embe –Oc obe (Pea son’s > 0.7). Feb ua y, July, and Augus e u ned lowe co ela ion alues, al hough he e was a signi ican co ela ion. Co ela ion be ween he EDDI and SPEI was also low om No embe o Feb ua y, al hough wi h sligh ly highe co ela ion alues han hose ound be ween he SPI and EDDI. F om Ma ch o Oc obe , he e was a high co ela ion be ween EDDI and SPEI, eaching a maximum in May, June, and July (Pea son’s ≥ 0.9). Co ela ion be ween he SPI and SPEI was e y high and signi ican in all mon hs o he yea , al hough i was sligh ly lowe in July and Augus . The spa ial pa e n o he co ela ion and associa ed signi icance be ween mon hly se ies o he SPI, EDDI, and SPEI o e he pe iod 1961–2018 also show some ele an di e ences (Figu e 2). In gene al, he e is a low, non-signi ican co ela ion be ween he SPI and EDDI in no hwes e n egions om No embe o Janua y, while i is high and signi ican in he Medi e anean coas land and sou he n Spain. F om Feb ua y o June, also in Sep embe and Oc obe , he e is a high, signi ican co ela ion be ween SPI and EDDI. In con as , co ela ion be ween he SPI and EDDI was low and non-signi ican in July and Augus in la ge a eas o sou he n Spain. Co ela ion be ween he EDDI and SPEI was also low and non-signi ican in no hwes e n egions, bu i was high and signi ican in sou he n and eas e n Spain om No embe o Janua y. F om Feb ua y o Oc obe , he e was a signi ican co ela ion be ween he EDDI and SPEI o e mos o he s udy a ea, eaching a maximum om May o July. As expec ed, he e was e y high and signi ican co ela ion be ween he SPI and SPEI in e e y mon h o e almos all o he s udy a ea, wi h only some a eas in sou he n Spain, whe e p ecipi a ion is e y low in summe , e u ning low alues in July and Augus . A mosphe e 2021,12, 165 5 o 22 A mosphe e 2021, 17, x FOR PEER REVIEW 5 o 24 Field Code Changed Field Code Changed and signi ican co ela ion be ween he SPI and SPEI in e e y mon h o e almos all o he s udy a ea, wi h only some a eas in sou he n Spain, whe e p ecipi a ion is e y low in summe , e u ning low alues in July and Augus . Figu e 1. Tempo al e olu ion o mon hly se ies o he s anda dized p ecipi a ion index (SPI), e apo a i e demand d ough index (EDDI), and s anda dized e apo a ion p ecipi a ion index (SPEI) based on a e age da a on mainland Spain and he Balea ic Islands o e he pe iod 1961–2018 a a sho ime scale (1-mon h). The mon hly se ies includes he weekly da a o he las week o each mon h in each yea . Figu e 2. Spa ial pa e n o he co ela ion (Pea son’s ) and associa ed signi icance be ween mon hly se ies o he SPI, EDDI, and SPEI o e he pe iod 1961–2018. The mon hly se ies include he weekly da a o he las week o each mon h in each yea . 3.2. Spa ial Dis ibu ion and T ends in Flash D ough Figu e 3 shows he spa ial dis ibu ion and equency o lash d ough s (e en s/ o each g id poin ) iden i ied by he SPI, EDDI, and SPEI om 1961 o 2018 a annual and seasonal scales. The e we e no able di e ences in he spa ial dis ibu ion o lash d ough s iden i ied by he SPI, EDDI, and SPEI (Figu e 3a), as well as in he a e age e- quency o e en s eco ded o each index (Figu e 3b). The a e age equency o lash d ough s ob ained by he SPI (≈70 e en s/ o each g id poin ) was conside ably highe han o he EDDI and SPEI (≈40 e en s/ o each g id poin ) a an annual scale. In gen- e al, he SPI iden i ied a high occu ence o lash d ough s in mos o he s udy a ea a Figu e 1. Tempo al e olu ion o mon hly se ies o he s anda dized p ecipi a ion index (SPI), e apo a i e demand d ough index (EDDI), and s anda dized e apo a ion p ecipi a ion index (SPEI) based on a e age da a on mainland Spain and he Balea ic Islands o e he pe iod 1961–2018 a a sho ime scale (1-mon h). The mon hly se ies includes he weekly da a o he las week o each mon h in each yea . A mosphe e2021,17,xFORPEERREVIEW5o 24  andsigni ican co ela ionbe ween heSPIandSPEIine e ymon ho e almos allo  hes udya ea,wi honlysomea easinsou he nSpain,whe ep ecipi a ionis e ylow insumme , e u ninglow aluesinJulyandAugus .  Figu e1.Tempo ale olu iono mon hlyse ieso  hes anda dizedp ecipi a ionindex(SPI),e apo a i edemand d ough index(EDDI),ands anda dizede apo a ionp ecipi a ionindex(SPEI)basedona e ageda aonmainland Spainand heBalea icIslandso e  hepe iod1961–2018a asho  imescale(1‐mon h).Themon hlyse iesincludes he weeklyda a o  helas weeko eachmon hineachyea .  Figu e 2. Spa ial pa e n o he co ela ion (Pea son’s ) and associa ed signi icance be ween mon hly se ies o he SPI, EDDI, and SPEI o e he pe iod 1961–2018. The mon hly se ies include he weekly da a o he las week o each mon h in each yea . A mosphe e 2021,12, 165 6 o 22 3.2. Spa ial Dis ibu ion and T ends in Flash D ough Figu e 3shows he spa ial dis ibu ion and equency o lash d ough s (e en s/ o each g id poin ) iden i ied by he SPI, EDDI, and SPEI om 1961 o 2018 a annual and seasonal scales. The e we e no able di e ences in he spa ial dis ibu ion o lash d ough s iden i ied by he SPI, EDDI, and SPEI (Figu e 3a), as well as in he a e age equency o e en s eco ded o each index (Figu e 3b). The a e age equency o lash d ough s ob ained by he SPI ( ≈ 70 e en s/ o each g id poin ) was conside ably highe han o he EDDI and SPEI ( ≈ 40 e en s/ o each g id poin ) a an annual scale. In gene al, he SPI iden i ied a high occu ence o lash d ough s in mos o he s udy a ea a an annual scale, which was also no ed in some a eas o cen al and no heas e n Spain, while he Medi e - anean coas land eco ded he lowes numbe o e en s. The EDDI and SPEI eco ded he highes numbe o lash d ough e en s in no he n and no hwes e n Spain, al hough he EDDI also eco ded a g ea many in some a eas o he Medi e anean coas land. A a seasonal scale, he e we e also spa ial di e ences be ween pa e ns o he a e age equency o lash d ough s eco ded by he SPI, EDDI, and SPEI. In win e , simila spa ial pa e ns we e ound o SPI and SPEI, wi h he highes occu ence ound in he no he n and eas e n egions o he Ibe ian Peninsula and in he Balea ic Islands. Howe e , he a e age equency o lash d ough s iden i ied by he SPI ( ≈ 16 e en s/ o each g id poin ) was subs an ially highe han by he SPEI, which eco ded he lowes a e age equency in his season ( ≈ 9 e en s/ o each g id poin ). On he o he hand, he EDDI eco ded a g ea many lash d ough s in la ge a eas o cen al Spain in win e , eaching i s maximum a e age equency o he season, wi h app oxima ely 13 e en s/ o each g id poin . In sp ing, he spa ial dis ibu ion and a e age equency o lash d ough s eco ded by he SPI showed g ea dispa i ies wi h he EDDI and SPEI. The a e age equency o he lash d ough s eco ded by he SPI ( ≈ 17 e en s/ o each g id poin ) was conside ably highe han by he EDDI and SPEI ( ≈ 10 e en s/ o each g id poin ). The SPI eco ded a high incidence o lash d ough s in sp ing in mos o cen al and wes e n Spain, and also in some a eas o he Py enees. In con as , he EDDI eco ded a low numbe o lash d ough s in hose egions, and mo e e en s we e ound in ce ain a eas o he Medi e anean coas land and no he n and no hwes e n Spain. Simila ly, he SPEI iden i ied a high occu ence o lash d ough e en s in no he n and no hwes e n egions bu also in la ge a eas o sou he n Spain. In summe , he SPI and EDDI eco ded hei lowes a e age equency, while he SPEI eached i s maximum a e age equency ( ≈ 12 e en s/ o each g id poin ). The e is no clea spa ial pa e n o lash d ough iden i ied by he SPI in summe , wi h a high numbe o lash d ough s occu ing in cen al, no hwes e n, and no heas e n Spain. The EDDI iden i ied he highes numbe o lash d ough s in no he n and wes e n egions, while cen al and eas e n Spain had ew e en s. In gene al, he SPEI eco ded a high equency o lash d ough e en s in summe , wi h wide a eas o he sou h and no hwes exceeding 15 e en s/ o each g id poin . In au umn, he pa e n o spa ial dis ibu ion o lash d ough s iden i ied by he SPI and SPEI was simila in no he n Spain, and bo h eco ded a low numbe o e en s in he Medi e anean coas land. Howe e , he SPI also iden i ied a high numbe o e en s in la ge a eas o cen al Spain, eaching i s maximum a e age equency in his season wi h app oxima ely 19 e en s/ o each g id poin . Unlike he SPI and SPEI, he EDDI eco ded he highes incidence o lash d ough s in he Medi e anean coas land in au umn, bu i only eco ded a ew in wes e n Spain. In gene al, he e was non-signi ican spa ial co ela ion be ween he o al numbe o e en s iden i ied o each index and he sha ed a iance was no high, due o no able spa ial di e ences annually and seasonally (Figu e 4). A an annual scale, he e was a nega i e and non-signi ican co ela ion be ween he spa ial dis ibu ion o he o al numbe o lash d ough s eco ded by he SPI and EDDI. The highes co ela ion was ound be ween he EDDI and SPEI a annual scale, al hough i was non-signi ican . The SPI and SPEI also e u ned a posi i e, bu non-signi ican , co ela ion annually. A mosphe e 2021,12, 165 7 o 22 A mosphe e2021,17,xFORPEERREVIEW7o 24   Figu e3.Annualandseasonal(a)spa ialdis ibu ion o  he equencyo  lashd ough s(e en s/ o eachg idpoin ) iden i iedby heSPI,EDDI,andSPEIo e  hepe iod1961–2018,(b)boxplo ssumma izing heannualandseasonal Figu e 3. Annual and seasonal ( a ) spa ial dis ibu ion o he equency o lash d ough s (e en s/ o each g id poin ) iden i ied by he SPI, EDDI, and SPEI o e he pe iod 1961–2018, ( b ) box plo s summa izing he annual and seasonal equencies ob ained wi h he di e en indices. In he box plo , he le axis ep esen s he annual da a and he igh axis ep esen s he seasonal da a. A mosphe e 2021,12, 165 8 o 22 A mosphe e2021,17,xFORPEERREVIEW9o 24   Figu e4.Sca e plo sshowing heannualandseasonal ela ionshipbe ween he o alnumbe o  lashd ough e en s eco dedby heSPI,EDDI,andSPEI.Thecolo s ep esen  hedensi yo  poin s,wi h eddeno ing hehighes densi y. Figu e 4. Sca e plo s showing he annual and seasonal ela ionship be ween he o al numbe o lash d ough e en s eco ded by he SPI, EDDI, and SPEI. The colo s ep esen he densi y o poin s, wi h ed deno ing he highes densi y. A mosphe e 2021,12, 165 9 o 22 A a seasonal scale, he e was a nega i e and non-signi ican co ela ion be ween he spa ial dis ibu ion o he o al numbe o lash d ough s eco ded by he SPI and he EDDI in all seasons, excep in win e . Co ela ion be ween he EDDI and SPEI in win e was nega i e and non-signi ican , while i was posi i e and non-signi ican in sp ing, summe , and au umn. The highes co ela ion be ween he EDDI and SPEI was ound in summe (Pea son’s = 0.33). The spa ial dis ibu ion o he o al numbe o lash d ough s eco ded by he SPI and SPEI showed a posi i e co ela ion in all seasons, eaching he maximum alues in win e (Pea son’s = 0.58) and au umn (Pea son’s = 0.41), al hough i was only signi ican in win e . Figu e 5depic s he spa ial dis ibu ion o he magni ude o change and signi icance o ends in annual and seasonal equency o lash d ough s eco ded by he SPI, EDDI, and SPEI o e he pe iod 1961–2018. A an annual scale, he e was a signi ican decline in he numbe o lash d ough s iden i ied by he SPI ac oss wide a eas o cen al Spain, and only small a eas o he Medi e anean coas and no he n Spain showed signi ican inc eases in lash d ough s. The EDDI also eco ded a dec ease in lash d ough s in some a eas o cen al Spain, bu his decline was gene ally non-signi ican . In con as , he e was a signi ican inc ease in he equency o lash d ough e en s iden i ied by he EDDI in some a eas o sou he n and no hwes e n Spain. The SPEI also iden i ied signi ican inc eases in lash d ough s in sou he n Spain annually, as well as in some a eas o he Medi e anean coas land. Simila o he SPI and EDDI, he SPEI also eco ded a gene al dec ease in lash d ough s in cen al and no he n Spain, al hough his was only s a is ically signi ican in a ew a eas. A a seasonal scale, mos o he s udy a ea showed non-signi ican ends in he occu ence o lash d ough s eco ded by he SPI, EDDI, and SPEI o e he pe iod 1961– 2018. The h ee indices iden i ied a gene al decline in lash d ough e en s in cen al Spain in win e , al hough only he SPI and EDDI ound s a is ically signi ican dec eases in some o hese a eas. In sp ing, simila ends we e ound by he SPI, EDDI, and SPEI, wi h nega i e and non-signi ican ends in mos o he s udy a ea. Fu he mo e, he h ee indices eco ded inc eases in he equency o lash d ough s in he Medi e anean coas land and Balea ic Islands in his season, bu only he SPEI and he SPI showed posi i e and s a is ically signi ican ends. In summe , he e we e no able di e ences in lash d ough ends eco ded by he SPI, EDDI, and SPEI. The SPI iden i ied nega i e, non- signi ican ends in mos o he s udy a ea, while he EDDI and SPEI showed a gene al inc ease in lash d ough s. The SPEI iden i ied some signi ican inc eases in lash d ough s in sou he n egions in summe , while he EDDI eco ded s a is ically signi ican inc eases in a ew small a eas o wes e n Spain. In au umn, he SPI e u ned a gene al dec ease in lash d ough s in mos o he s udy a ea, al hough his was only signi ican in no heas e n Spain. On he con a y, he EDDI and SPEI iden i ied posi i e, non-signi ican ends in he occu ence o lash d ough in mos o he s udy a ea, wi h he excep ion o no he n egions, whe e nega i e, non-signi ican ends we e no ed. The empo al e olu ion o he a e age equency o lash d ough e en s iden i ied by he SPI, EDDI, and SPEI on mainland Spain and he Balea ic Islands o e he pe iod 1961– 2018 showed a high a iabili y a annual and seasonal scales (Figu e 6). The annual se ies o lash d ough s eco ded by he SPI, EDDI, and SPEI exhibi ed s a is ically signi ican co ela ions among hem, al hough he a e age equency o lash d ough s iden i ied by he SPI was subs an ially highe un il he yea 2000. The e was a signi ican decline in lash d ough s eco ded by he SPI annually, while he annual se ies ob ained by he SPEI and EDDI showed non-signi ican ends. A mosphe e 2021,12, 165 16 o 22 A mosphe e2021,17,xFORPEERREVIEW18o 24   Figu e9.Mon hly equencyo  lashd ough e en s/ o eachg idpoin ob ained om heSPEI andi ssensi i i y(%) oAEDonmainlandSpainand heBalea icIslandsineachmon ho e  he pe iod1961–2018a asho  imescale(1‐mon h).F equencieso  lashd ough e en swi ha e‐ sidualnumbe o casesa eno  ep esen ed. 4.Discussion In hiss udy,weiden i ied lashd ough sbasedondi e en d ough indicesin‐ cluding heSPI, heEDDI,and heSPEI.Thisenabled he oleo p ecipi a ionandAED in hede elopmen o  lashd ough s obees ablished,inaddi ion ohow his olede‐ e mines hespa ialand empo alpa e nso  lashd ough sinSpain.Themainad‐ an ageo  heses anda dizedindexesincompa ison oo he me icsis ha  heya e Figu e 9. Mon hly equency o lash d ough e en s/ o each g id poin ob ained om he SPEI and i s sensi i i y (%) o AED on mainland Spain and he Balea ic Islands in each mon h o e he pe iod 1961–2018 a a sho ime scale (1-mon h). F equencies o lash d ough e en s wi h a esidual numbe o cases a e no ep esen ed. 4. Discussion In his s udy, we iden i ied lash d ough s based on di e en d ough indices including he SPI, he EDDI, and he SPEI. This enabled he ole o p ecipi a ion and AED in he de elopmen o lash d ough s o be es ablished, in addi ion o how his ole de e mines he spa ial and empo al pa e ns o lash d ough s in Spain. The main ad an age o hese s anda dized indexes in compa ison o o he me ics is ha hey a e compa able A mosphe e 2021,12, 165 17 o 22 in ime and space, making i possible o apply he same me hodology and o ob ain compa able esul s based on indices om di e en a iables. Fu he mo e, hese indices also enable lash d ough analyses in he long- e m, since hey a e based on widely a ailable clima e in o ma ion. Nume ous s udies p o ed he use ulness o widely used, s anda dized d ough in- dices such as he SPI o SPEI in iden i ying di e en ypes o impac s [ 57 – 60 ]. P e ious s udies also p o ed he obus ness o s anda dized d ough indices, such as he SPI, EDDI, and SPEI in iden i ying and cha ac e izing lash d ough s o e di e en egions o he wo ld [18,19,51,61]. Al hough i is no easy o de e mine which me ic is mo e sui able o he analysis o lash d ough s, we hink ha he implemen a ion o di e en indices o lash d ough analysis can be use ul o a mo e comp ehensi e unde s anding. The spa ial and empo al beha io o lash d ough s in Spain is highly complex and a iable [ 18 ]. The esul s ob ained in his esea ch sugges ed ha lash d ough s in Spain can de elop om bo h p ecipi a ion de ici s and anomalous inc eases in AED, al hough he e is a di e en ia ed seasonal and spa ial beha io . This is e lec ed in he no able di e ences ound be ween he spa ial and empo al pa e ns o lash d ough s iden i ied by he SPI, EDDI, and SPEI. Thus, e en when he d ough indices showed high spa ial and empo al co ela ion in mos mon hs o he yea , he spa ial and empo al equency o lash d ough e en s was dependen on he index used, since al hough he e is consis ency among he h ee indices, he e a e la ge seasonal di e ences. Fo example, in win e , in which AED is low and d ough condi ions a e closely ela ed o p ecipi a ion de ici s, co ela ion be ween he EDDI and SPI is low. The e o e, i is no ecommended o use he EDDI o assess d ough se e i y and, pa icula ly, o iden i y lash d ough s du ing win e . In au umn and sp ing, when he AED is sligh ly highe bu p ecipi a ion is also he main d i e con olling a ia ions in index alues, co ela ion o he EDDI wi h he SPI and SPEI was gene ally high, especially wi h he SPEI. This sugges s an inc ease in he in luence o he AED on d ough se e i y. In summe , he e is highe consis ency be ween he EDDI and SPEI, wi h co ela ions simila o hose ound be ween he SPI and SPEI. This means ha changes in AED can be as ele an o e en mo e so han p ecipi a ion de ici s in he esponse o indices du ing he summe , pa icula ly in he d ies a eas. This indica es ha in summe , he use o indices based exclusi ely on p ecipi a ion is no sui able o assess d ough se e i y, and hey a e pa icula ly unsui able o iden i y lash d ough s. The SPI showed a high spa ial and empo al cohe ence wi h he SPEI in almos e e y mon h o he yea , e lec ing he ac ha he SPEI esponds mainly o a ia ions in p ecipi a ion, excep in he d y summe pe iod. These indings p o e he sensi i i y o he SPEI o changes in AED du ing d y pe iods, and hey a e e y consis en wi h he pa e ns in he esponse o he SPEI o AED shown by Tomas-Bu gue a e al. [9] a a global scale. In gene al, he e a e no iceable spa ial di e ences in he occu ence o lash d ough s iden i ied o each index. The spa ial pa e ns eco ded by he SPI and SPEI we e s ongly cohe en in win e , pa icula ly in no he n Spain. This sugges s ha du ing we pe iods, in which he ole o p ecipi a ion de ici s in d ough de elopmen is no in doub [ 17 ], p ecipi a ion is he main d i e o lash d ough s. Howe e , he ole o he a mosphe ic e apo a i e demand (AED) on d ough s is mo e complex and exhibi s la ge spa ial and seasonal di e ences [ 17 , 62 ], making i di icul o de e mine i s ole in he de elopmen o lash d ough s [ 63 ]. Se e al s udies showed ha lash d ough s can be d i en by anomalous inc eases in AED associa ed wi h hea wa es and land–a mosphe e eedbacks ha cause o ein o ce he apid deple ion o soil mois u e [ 12 , 14 – 16 ]. Thus, he occu ence o lash d ough is usually associa ed wi h s ong anomalies o AED [ 6 , 19 ]. He e, we ha e shown ha AED can play an impo an ole in he wa m season. In summe , when p ecipi a ion is gene ally e y low in Spain [ 40 , 64 ], he e we e no able di e ences in he spa ial pa e ns o lash d ough s ound by he SPI and SPEI. Compa ed o he SPI, he SPEI showed a g ea e spa ial consis ency wi h he EDDI, indica ing ha du ing he wa m season, he AED is a key a iable in explaining he occu ence o lash d ough s. The physical p ocesses explaining he impo ance o his a iable can be di e se. Some s udies showed ha in pe iods o A mosphe e 2021,12, 165 18 o 22 e y low soil mois u e and s ong land–a mosphe e coupling, AED would be d i en by he limi ed la en hea luxes om a d y soil, which could a o some sel -in ensi ica ion o d ough condi ions [ 10 , 62 ]. Howe e , in Spain, i is mo e p obably due o he dominan ole o wa m, d y ai ad ec ions o igina ing in he Saha a, which a e e y equen in summe [65]. In sp ing and au umn, opposi e spa ial pa e ns we e ound o he lash d ough s iden- i ied by he SPI and EDDI. This could be ela ed o a a iable con ibu ion o p ecipi a ion and AED in he de elopmen o he lash d ough s, which seems easonable conside ing he wide spa ial and empo al a iabili y o p ecipi a ion [ 32 – 35 ] and AED [36–38] du ing hese seasons. Thus, i is possible ha AED plays an impo an ole in he occu ence o lash d ough s in he Medi e anean coas land and no heas e n Spain whe e he EDDI eco ded a high incidence in sp ing and, o a lesse ex en , in au umn. Howe e , i would be seconda y o p ecipi a ion in mos o Spain. This is also e lec ed in he spa ial pa e ns o he numbe o lash d ough s iden i ied by he SPEI, since he e is spa ial consis ency wi h he SPI in mos o he s udy a ea in sp ing and especially in au umn, bu he SPEI also epo ed a high equency o lash d ough s in he Medi e anean coas land in sp ing, which is a pa e n also ound in he EDDI. Al hough in some cases, he di e en indices showed simila spa ial pa e ns a an annual and seasonal scale, he sha ed a iance was no gene ally high. This seems o con i m ha he lash d ough s in Spain can be igge ed by di e en d i e s, as well as he ole o p ecipi a ion and AED being seasonally and spa ially a iable. Only he SPI epo ed a nega i e and signi ican end in he equency o lash d ough s, whe eas he EDDI and SPEI eco ded a non-signi ican end o hese e en s om 1961 o 2018. Howe e , he EDDI and SPEI epo ed signi ican inc eases in he equency o lash d ough s in some a eas o sou he n and sou heas e n Spain. Since he SPI epo ed non-signi ican ends in summe o e mos o he s udy a ea, hese inc eases mus necessa ily be ela ed o an inc ease in he con ibu ion o he AED o he de elopmen o lash d ough s in hese a eas. This hypo hesis seems cohe en wi h a ious s udies ha eco ded inc eased AED in Spain du ing he summe [ 36 , 38 ]. Some a eas o he Medi e anean coas land also showed inc eases in lash d ough s in sp ing, bu conside ing ha only he SPI and SPEI epo ed a s a is ically signi ican end, hese inc eases could ela e o a ia ions in p ecipi a ion. In addi ion o he ma kedly seasonal cha ac e indica ing he ole o AED in he de elopmen o lash d ough s, we also ound a s ong spa ial componen de e mining he ole o AED in hese e en s in Spain. The AED shows s ong spa ial di e ences in Spain, wi h a clea no h–sou h g adien be ween he humid egions o he no h and he d ie egions o sou he n and cen al Spain [ 36 , 39 ]. Se e al s udies sugges ed ha he con ibu ion o AED is much highe in d y egions han in humid ones, since i s ole is only impo an du ing pe iods o low p ecipi a ion o limi ed soil mois u e [ 9 , 17 ]. This could explain he con as s ound be ween he d ie egions o cen al and sou he n Spain and he humid ones in no he n Spain, which, e en in summe , exhibi ed e y low sensi i i y o AED. Thus, du ing summe , when he AED in Spain is high and p ecipi a ion is gene ally e y low [ 40 ], s ong AED anomalies play a key ole in he de elopmen o lash d ough s, especially in d y a eas such as he Eb o Dep ession and sou he n Spain. Al hough he inc eased in AED was p obably he main d i e o changes in lash d ough equency in summe , we mus s ess ha we ha e demons a ed ha p ecipi a ion is s ill he main d i e in he empo al a iabili y o d ough s in Spain, and i is also he main con ibu ing ac o in igge ing lash d ough s. P ecipi a ion de ici s a e he majo clima ic a iable igge ing d ough condi ions [ 66 , 67 ], and i seems easonable o expec ha p ecipi a ion also has an essen ial ole in he de elopmen o lash d ough s. We ha e demons a ed his pa e n in win e as well as in sp ing and au umn. Howe e , i is possible ha he AED has a ele an ole in he de elopmen o ce ain lash d ough e en s in he la e sp ing. The esul s o his esea ch canno be easily ex apola ed. Spain is cha ac e ized by high spa ial and seasonal a iabili y in p ecipi a ion and AED, so i was expec ed ha A mosphe e 2021,12, 165 19 o 22 hei ole in he de elopmen o lash d ough s would be s ongly a iable. Howe e , he ole o p ecipi a ion and AED anomalies may exhibi signi ican changes in o he egions o he wo ld, and lash d ough s could de elop unde di e se condi ions. Fo example, Hobbins e al. [ 52 ] and Pende g ass e al. [ 19 ] poin ed ou ha he occu ence o lash d ough s is ypically ela ed o a change om ene gy-limi ed o wa e -limi ed condi ions. This can be ue in some cases, bu i canno be conside ed as a si ua ion cha ac e is ic o mos lash d ough e en s wo ldwide. A a global scale, p e ious s udies ound simila pa e ns in he con ibu ion o AED du ing pe iods cha ac e ized by low le els o p ecipi a ion in sub-humid egions [ 9 ]. Speci ically, ce ain s udies also indica ed ha p ecipi a ion is he main a iable explaining he occu ence o lash d ough s in he Uni ed S a es [ 63 ]. Howe e , conside ing he complexi y o he ole played by AED in d ough de elopmen , and i s spa ial and seasonal a iabili y [ 17 ], u he esea ch in o hese issues is needed. 5. Conclusions This s udy ocused on he analysis o he ole o p ecipi a ion and a mosphe ic e apo- a i e demand (AED) in he occu ence o lash d ough s in Spain. Fo his pu pose, we analyzed he spa ial and empo al pa e ns o lash d ough iden i ied h ough di e en d ough indices based on p ecipi a ion (SPI), AED (EDDI), and bo h (SPEI). We also exam- ined he sensi i i y o he SPEI o AED o cla i y he possible con ibu ion o p ecipi a ion de ici s and anomalous inc eases in AED o he de elopmen o lash d ough s. The main conclusions om his s udy a e as ollows: • S anda dized d ough indices such as SPI, EDDI, and SPEI a e obus me ics o he iden i ica ion o lash d ough s. Howe e , he use o indices based exclusi ely on p ecipi a ion o AED may ha e some limi a ions unde ce ain ci cums ances. • The spa ial and empo al pa e ns o lash d ough s can be highly a iable, depending on he me ics used in analysis. • Flash d ough s in Spain can be igge ed by bo h p ecipi a ion de ici s and inc eases in AED, bu hei con ibu ion o he de elopmen o lash d ough s is highly a iable spa ially and seasonally. • P ecipi a ion is he main a iable d i ing lash d ough s in Spain, al hough AED anomalies can play a c ucial ole in he de elopmen o some lash d ough e en s, especially in a id a eas du ing he wa m season. • The sensi i i y o he SPEI o AED du ing d y pe iods enables he d ough condi ions igge ed by anomalous dec eases o p ecipi a ion and/o inc eases o he AED o be cap u ed, making i possible o iden i y and cha ac e ize lash d ough s o e e y di e en clima ic condi ions seasonally and spa ially. Supplemen a y Ma e ials: The ollowing a e a ailable online a h ps://www.mdpi.com/2073-443 3/12/2/165/s1, Figu e S1: Tempo al e olu ion o he annual and seasonal di e ences (e en s/ o each g id poin ) be ween he lash d ough se ies eco ded by he SPI, EDDI and SPEI on mainland Spain and he Balea ic Islands o e he pe iod 1961–2018, Figu e S2: Mon hly equency o he sensi i i y (%) o he SPEI o AED on mainland Spain and he Balea ic Islands o e he pe iod 1961–2018 a a sho ime scale (1-mon h). The mon hly se ies include he weekly da a o he las week o each mon h in each yea . Au ho Con ibu ions: Da a cu a ion, I.N., F.D.-C. and S.M.V.-S; Fo mal analysis, I.N., F.D.-C. and S.M.V.-S.; Funding acquisi ion, S.M.V.-S.; So wa e, I.N.; Supe ision, I.N., F.D.-C. and S.M.V.-S.; W i ing—o iginal d a , I.N., F.D.-C. and S.M.V.-S; W i ing— e iew & edi ing, I.N., F.D.-C. and S.M.V.-S. All au ho s ha e ead and ag eed o he published e sion o he manusc ip . Funding: Resea ch p ojec s CGL2017-82216-R, PCI2019-103631, and PID2019-108589RA-I00 inanced by he Spanish Commission o Science and Technology and FEDER; CROSSDRO p ojec inanced by he AXIS (Assessmen o C oss(X)—sec o al clima e Impac s and pa hways o Sus ainable ans o ma ion), JPI-Clima e co- unded call o he Eu opean Commission and INDECIS which is pa A mosphe e 2021,12, 165 20 o 22 o ERA4CS, an ERA-NET ini ia ed by JPI Clima e, and unded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) wi h co- unding by he Eu opean Union (G an 690462). Ins i u ional Re iew Boa d S a emen : No applicable. In o med Consen S a emen : No applicable. Da a A ailabili y S a emen : Da a used in his s udy is a ailable unde eques . Acknowledgmen s: The i s au ho would like o hank he p edoc o al ellowship “Sub enciones des inadas a la con a ación de pe sonal in es igado p edoc o al en o mación (2017)” awa ded by he Gobie no de A agón (Go e nmen o A agón, Spain). 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