Risk%assessment%of%flash%floods%in%central%Pyrenees%(Spain)%through%land%use%change%analysis!! Roberto%SERRANO@NOTIVOLI1*,%Daniel%MORA1,2,%Alfredo%OLLERO1,%Miguel%SÁNCHEZ@FABRE1,%Paloma%SANZ1,%Miguel%Ángel%SAZ1% 1!Department!of!Geography!and!Regional!Planning,!University!of!Zaragoza,!Zaragoza,!Spain.!1Environmental!Sciencie!InsAtute!of!the!University!of!Zaragoza!(IUCA),!Spain.!2!MASTERGEO!
*
[email protected]% ! !
DATA%AND%METHODS:%
RESULTS:% FLASH%FLOODS%OCCURRENCE%:%
LAND%USE%CHANGE:%
Area%occupied%by%10%years%return%period%
LEGEND%
! The! urbanizaAon! in! tourisAc! areas! in! Pyrenees! has! increased! enormously! in! last! 25! years,!and!the!most!of!urban!development!have!been!made!on!land!occupied!by!the! stream! channel.! Flash! floods! cause! more! damage! now! because! of! the! increasing! of! urban!development.!We!present!two!different!case!studies!in!central!Pyrenees:!one! in!Aragón!river!and!one!in!Ésera!river.!These!two!rivers!were!affected!by!flash!floods! in!2012!(Aragón!river)!and!2013!(Esera)!causing!damage!by!to!the!amount!of!96!and! 28.5!millions!of!euros!respecAvely.!
Aragón%river% Villanúa%
CasZello%de%Jaca%
Water!
Crops!
Riparian!woods!
Sediment!bars!
Shrub!and!bush! Sediment!bars!
ImproducAve!(human!intervenAon)!
Urban!areas!
Percentage%of%change%
Land%use%change%%
!
100 90 80 70
We!made!a!land!use!analysis!using!aerial!photographs!in!1956,!1984!and!2012!in!the! headwaters!of!these!two!rivers!by!delimiAng!the!channel!in!different!moments.!Also! we! extracted! the! historical! data! and! set! the! 10\years! return! period! computed! by! Gumbel!distribuAon.!This!study!area!is!characterized!by!convecAve!precipitaAons!that! usually!produces!big!discharges!to!headwaters!of!rivers!in!high\sloped!areas!and!with! high!sediment\carry!capacity.!!
60 50 40 30 20 10
Ésera%river% Eriste%
Castejón%de%Sos%
Aragón%river%
INTRODUCTION:%
dendroteam.unizar.es.
0 1956
1984
2012
Complete!colonizaAon!of!the!channel!by!urbanizaAon.! Shape!of!the!river!changed!by!land!uses.! 100 90 80 70 60 50 40 30 20 10 0 1956
1984
2012
1984
2012
New!urban!zones!are!within!the!old!course!of!the!river.! Old!sediment!bars!have!been!colonizated!by!riparian! woods.!Old!crops!by!shrub!areas.! 100 90 80
Frequency%of%10%years%return%period%flows%
STUDY%AREA%
70 60 50
Aragón%river%
40 30
450
20 Aragón in Jaca Threshold return period 10
350
0 1956
250 200 150 100 50 0 1954 1957 1960 1964 1967 1970 1974 1977 1980 1984 1987 1990 1994 1997 2000 2004 2007 2010
Monthly Q (m3/s)
!
ACKNOWLEDGEMENTS:% This!study!was!supported!by!the!government!of!Aragon!througout!the!‘Program!of!research!groups’!(group!Clima,!Cambio!Global!y!Sistemas!Naturales,! BOA!147!of!18\12\2002)!and!FEDER!funds!!
90 80 70
40 30 20 10
800
0 1956
600
1984
2012
The!river!has!less!area!to!circulate!freely.!VegetaAon!at! south!has!been!replaced!by!urbanizaAon.!
400 200
ACÍN!NAVERAC,!V.,!BALLARÍN!FERRER,!D.,!BRUFAO!CURIEL,!P,!DOMENECH!ZUECO,!S,!ESPEJO!GIL,!F,!GONZÁLEZ!HIDALGO,!J.C.,!GRANADO!GARCÍA,!D,! GONZÁLEZ! DE! MATAUCO,! A.I.,! MARCÉN! ALBERO,! C.,! MORA! MUR,! D.,! NADAL! ROMERO,! E.,! OLLERO! OJEDA,! A.,! SÁNCHEZ! FABRE,! M.,! SAZ! SÁNCHEZ,! M.A.,!SERRANO\!NOTIVOLI,!R.!(2012):!“Sobre!las!precipitaciones!de!octubre!de!2012!en!el!Pirineo!Aragonés.!Su!respuesta!hidrológica!y!la!gesAón!de! riesgos”.!Geographicalia,!61,!pp.!101\128.!% SERRANO\NOTIVOLI,! R.,! MORA! MUR,! D.,! OLLERO! OJEDA,! A.,! SÁNCHEZ! FABRE,! M.,! SAZ! SÁNCHEZ,! M.! (2014):! “Respuesta! hidrológica! al! evento! de! precipitación!de!junio!de!2013!en!el!Pirineo!central”.!Inves7gaciones.Geográficas,!62,!pp.!5\21.!DOI:!10.14198/INGEO2014.62.01.! ROSSO,!R.,!RULLI,!M.C.!(2002):!“An!integrated!simulaAon!method!for!flash\flood!risk!assesment:! !2.!Effects!of!changes!in!land\use!under!a!historical! perspecAve”.!Hydrology.and.Earth.System.Sciences.6(3),!285\294.!
100
50
Ésera in Graus Threshold return period 10
1000
Riparian!vegetaAon!has!been!removed!first!by!crops!and! now!by!urban!zones.!At!present!there!is!no!sediment!bars.!
60
Ésera%river% 1200
REFERENCES:%
10
300
Ésera%river%
• 5! gaugin! staAons! to! get! historical! flows! of! the! rivers! in! different! locaAons! • 25!precipitaAon!observatories!in!both!watersheds! • 3! moments! of! aerial! photograph:! 1956! (“american! flight”);! 1984! and! 2012!(spanish!minister!flights)!
Monthly Q (m3/s)
400
0 1954 1957 1960 1964 1967 1970 1974 1977 1980 1984 1987 1990 1994 1997 2000 2004 2007 2010
Source.of.data.and.cartography:.Spanish.Environment.Minister.
CONCLUSIONS:% • 10!years!return!period!will!cause!damages!in!all!analysed!towns.!Even!though!the!area!occupied! by!these!events!is!not!so!high,!actual!urban!areas!are!too!near!to!the!main!channel! • Frequency! of! 10\years\return\period! flash\floods! is! relaAvely! common! by! analysing! historical! data.!
• All!locaAons!incremented!urban!areas!near!or!within!the!main!channel! • Natural!areas!have!been!reduced!in!all!cases.!Rivers!have!less!area!to!move!in! flood!events.!