Potential impact of climate change on groundwater resources in the Central Huai Luang Basin, Northeast Thailand

2018·8.7 MB·English

by  Kewaree Pholkern

ScienceoftheTotalEnvironment633(2018)1518–1535
ContentslistsavailableatScienceDirect
Science of the Total Environment
journal homepage: www.elsevier.com/locate/scitotenv
Potential impact of climate change on groundwater resources in the
Central Huai Luang Basin, Northeast Thailand
KewareePholkerna,b,PhayomSaraphiroma,c,⁎,KriengsakSrisuka
aGroundwaterResourcesResearchInstitute,KhonKaenUniversity,Thailand
bDepartmentofEnvironmentalEngineering,FacultyofEngineering,KhonKaenUniversity,Thailand
cDepartmentofAgriculturalEngineering,FacultyofEngineering,KhonKaenUniversity,Thailand
H I G H L I G H T S G R A P H I C A L A B S T R A C T
• ThecentralHuaiLuangbasinisunder-
lainbyrocksaltsresultinginspreading
ofgroundwaterandsoilsalinity.
• Climatechangemayimpactonground-
waterrecharge,waterloggingandsoil
salinitydistributioninthisbasin.
• Groundwaterlevel,waterloggingand
salinitydistributionareasareprojected
tobeincreased,inthefutureprecipita-
tion.
• Thesoilsalinityistheconsequenceef-
fectthatmayexacerbatefutureliveli-
hoodconditionsinthisarea.
a r t i c l e i n f o a b s t r a c t
Articlehistory: TheCentralHuaiLuangBasinisoneoftheimportantriceproducingareasofUdonThaniProvinceinNortheastern
Received31October2017 Thailand.ThebasinisunderlainbytherocksaltlayersoftheMahaSarakhamFormationandisthesourceofsaline
Receivedinrevisedform24March2018 groundwaterandsoilsalinity.Theregionalandlocalgroundwaterflowsystemsarethemajormechanismsresponsible
Accepted24March2018
forspreadingsalinegroundwaterandsalinesoilsinthisbasin.Climatechangemayhaveanimpactongroundwater
Availableonline4April2018
recharge,onwatertabledepthandtheconsequencesofwaterlogging,andonthedistributionofsoilsalinityinthis
basin.SixfutureclimateconditionsfromtheSEACAMandCanESM2modelsweredownscaledtoinvestigatethepoten-
Keywords:
tialimpactoffutureclimateconditionsongroundwaterquantityandqualityinthisbasin.Thepotentialimpactwasin-
Climatechange
Groundwaterresources vestigatedbyusingasetofnumericalmodels,namelyHELP3andSEAWAT,toestimatethegroundwaterrechargeand
Salinity flowandthesalttransportofgroundwatersimulation,respectively.Theresultsrevealedthatwithinnext30years
HELP3 (2045),thefutureaverageannualtemperatureisprojectedtoincreaseby3.1°Cand2.2°CunderSEACAMand
SEAWAT CanESM2models,respectively,whilethefutureprecipitationisprojectedtodecreaseby20.85%underSEACAMand
HuaiLuangBasin increaseby18.35%undertheCanESM2.GroundwaterrechargeisprojectedtoincreaseundertheCanESM2model
andtoslightlydecreaseundertheSEACAMmodel.Moreover,forallfutureclimateconditions,thedepthsofthe
groundwaterwatertableareprojectedtocontinuouslyincrease.Theresultsshowedtheimpactofclimatechange
onsalinitydistributionforboththedeepandshallowgroundwatersystems.Thesalinitydistributionareasare
projectedtoincreasebyabout8.08%and56.92%inthedeepandshallowgroundwatersystems,respectively.The
waterloggingareasarealsoprojectedtoexpandbyabout63.65%fromthebaselineperiod.
©2018ElsevierB.V.Allrightsreserved.
⁎ Correspondingauthorat:DepartmentofAgriculturalEngineering,FacultyofEngineering,KhonKaenUniversity,Thailand.
E-mailaddress:[email protected].(P.Saraphirom).
https://doi.org/10.1016/j.scitotenv.2018.03.300
0048-9697/©2018ElsevierB.V.Allrightsreserved.
K.Pholkernetal./ScienceoftheTotalEnvironment633(2018)1518–1535 1519
1.Introduction ThesestudieswerebasedontheSpecialReportonEmissionScenarios
(SRES)publishedbytheIntergovernmentalPanelonClimateChange
GroundwaterplaysanimportantroleinThailandbecauseitisa (IPCC)FourthAssessmentReport(AR4)(IPCC,2007).Byutilizingthe
sourceoffreshwaterforhumanconsumption,agriculture,andindus- dynamicdownscaledmodel,PRECIS(ProvidingRegionalClimatesfor
tries,especiallyduringperiodsofdrought.Servingasthewatersupply Impacts Studies) of the Hadley Centre Climate Model version 3
forapproximately35millionpeopleinruralandurbanareas,ground- (HadCM3)boundarydata(asubsetofCMIP3),theSoutheastAsiaCli-
waterresourcesplayamajorrole.InNortheasternThailand,atleast mateAnalyses&Modeling(SEACAM)regionalclimatemodelingexper-
80%ofthegroundwaterwellshavebeendrilledanddevelopedinthe imenthasbeenusedtoassessthecapacityforsimulatingthemajor
consolidatedaquifers(SrisukandNettasana,2017),whichareunderlain featuresoftheSoutheastAsianclimateandforcapturingthebroadest
withtherocksaltoftheMahaSarakhamFormationatdepthsofabout rangeoffutureprojectionsfortemperature,monsooncharacteristics,
50–1000mfromthegroundsurface.Thisrocksaltisthesourceofsaline andforprecipitation.Theresultsindicatedthattherewillbeanincreas-
groundwaterandsalinesoilsinthisareaatN40%and35%,respectively ingtrendintheaverageannualrainfallandtemperatureintheperiod
(DGR,2000;Arunin,1996).TheCentralHuaiLuangBasin(CHLB)isspa- from2016to2056(Chinvanno,2014).AccordingtotheIPCCFifthAs-
tiallyaffectedbythesalinegroundwaterandsalinesoilsalongtheHuai sessment(AR5)(IPCC,2013),thetemperatureispredictedtoincrease
LuangFloodplain.TheCHLBisanimportantareaintermsofthefollow- by1.8°Coverthenext4decades(2055),andtheprecipitationforthe
ing:(1)thesocio-economicstatusofthesecondbiggestprovincein wholecountryispredictedtoincreasebyapproximately5%within
Northeastern Thailand, and (2) the Gross Provincial Product, GPP 40yearsundertheRepresentativeConcentrationPathways(RCP)8.5
(NSO,2016)duetothesefacts:(a)theCHLBiscoveredbycommercial scenario(HAII,2016).Theexpectedchangesintheamountsandpat-
areas,andb)it is themostimportantriceproducing area of Udon ternsofrainfallandtemperaturewillleadtoanalterationofgroundwa-
Thani Province. Groundwater and soil salinity problems have ter resources (Zektser and Loaiciga, 1993) which can change the
interruptedactivitiesandhaverequiredasupplyofwaterinthisarea, rechargerates,caninfluencethequalityofthegroundwater,andcan
suchaswaterforirrigationandagriculturalpurposes,etc. altergroundwaterflowpatterns.Inaddition,theexpectedchanges
Themajorprocessesresponsibleforspreadingsalinegroundwater, mayaffectwaterlogging(thedepthofwatertablecanupwardmove-
soil water and saline soils and sub-surface water are groundwater menttosoilsurfaceandcausetheaccumulationofsalt),aswellasthe
flowandevaporationofsoilwater(Srisuk,1994).Inaddition,naturally spreading of saline water. This is especially true in Northeastern
occurringsaltaffectedareasarecausedbysubsurfaceflowwhichisa Thailandinwhichthereareexistingproblemswithgroundwaterand
primarysourceofsalinity(Allan,1994).Asearlyasthe1980s,itwasrec- soilsalinity.
ognizedthatvarioushumanactivitiesareresponsibleforthespreading From1990to2010,therewereapproximately198peer-reviewed
ofsalinizationorsecondarysourcesofsalinity(Arunin,1984;Beresford publicationsthatfocuseddirectlyonclimatechangeandgroundwater,
etal.,2001).Thesehumanactivitiesincludedeforestation,theconstruc- but the potential impact of climate change on groundwater
tionofreservoirsinareasinwhichthereisanoccurrenceofshallowsa- (Pratoomchaietal.,2014)andthefutureofgroundwaterinthecontext
line groundwater, salt production, and irrigation (Arunin, 1989; ofglobalandregionalclimatechangesremainlargelyunknown(Toews
Yuvaniyama,2004).Theseactivitiesarebeginningtodramaticallyaffect andAllen,2009;Greenetal.,2011;KurylykandMacQuarrie,2013).In
thenaturalenvironmentandtoreducetheviabilityoftheagricultural NortheasternThailand,changesinclimaticvariablescansignificantly
sector(Arunin,1984;Beresfordetal.,2001). alterthehydrologiccycleandgroundwaterrecharge,bothofwhich
Globalclimatechangeisdefinedasaclimatesituationinanyareathat controlthedistributionofsalinitywithintheshallowaquifersystems
haschangedordifferedoverthepast30years(HAII,2016)andasaconse- andthus,affecttheavailabilityoflandforagriculture(Saraphirom
quence,hashadanimpactonvarioussectors,includingwaterresourcesin etal.,2013a).Ghassemietal.(1995)reportedthatthisphenomenon
alltheregionsaroundtheworld.Likeotherregionsandcountriesinthe has created an expansion of land salinity as shown by Casas and
world,Thailandisalsofacingclimatechangeandisexperiencingtheeffects Pitaluga (1990) who investigated climatic changes expressed in
associatedwithit.Thailandisparticularlyvulnerabletodroughtandto PampaArenosa,Argentina,after1971,duetosignificantlyincreasesin
floodingasevidencedbyseveralextremeclimaticeventsintherecent theaverageannualrainfallofapproximately200mmperyear.
past(CHRR,2005).Astheresultofheavyrainfall,Thailandfacedabig Numericalmodelingisaquickandusefulapproachtoassessthepast
floodforseveralmonthsduring2011(WorldBank,2011).Afewyears and future groundwater resources in response to climate change
later,Thailandexperiencedoneoftheworstdroughtsindecades(ONEP, (Pratoomchaietal.,2014)specificallythetemperatureandprecipita-
2016).Eventhoughscenariosforfutureeventsofclimatechangearestill tion changes to groundwater recharge (Moeck et al., 2016).
beingdebated,itislikelythatThailandwillbeaffectedincomplexways Saraphirometal.(2013b)studiedtheimpactofclimatechangeonthe
bytheconsequencesofclimatechange(Naruchaikusol,2016).According salinizationprocessesintheHuaiKhamrianSub-watershedinNorth-
tothemeteorologicaldatarecordsfrom1955to2014,thetrendintheav- eastern Thailand by using a variable density groundwater model
erageannualtemperatureinThailandwasanadditionalincreaseinthe namedSEAWAT,whichwassupportedwithrechargeestimatesfrom
number of warm days and nights (Chatdarong, 2009; TRF, 2011; theHydrologicEvaluationofLandfillPerformance(HELP)model.The
Limsakuletal.,2010).Yet,thetotalamountofrainfalldidnotchangesignif- resultsoftherechargeratesattheendofthe21thcenturywerepre-
icantly.TherehavebeenregionaldivergingtrendsinrainfallvolumeinCen- dicted,anditwasfoundthatshallowsalinegroundwaterareaswillin-
traland Eastern Thailand wheredecreases in totalrainfall havebeen creasebyapproximately14%.However,therearenostudiesthatshow
observed.However,therehavebeenincreasingamountsofrainfallinthe theimpactofclimatechangeongroundwaterresourcesintheCHLB
Northeastern and Gulf regions, as well as in Metropolitan Bangkok whichisofsocio-economicimportancetoUdonThaniProvince,espe-
(LimsakulandSinghruck,2016).Therehavebeensignificantincreasesin ciallyunderSRESandRCPscenarios.
rainfallinthedryseasonanddecreasesinthewetseason,whichincludes Theobjectivesofthisstudyareasfollows:1)tocharacterizethehy-
adecreaseinthenumberofrainydaysandincreaseinthenumberof drologicandhydrogeologicframeworksoftheCHLB,2)tosimulatethe
dayswithintenseprecipitation(LimsakulandSinghruck,2016).Theentire processesofgroundwaterflowandsalinitydistribution,and3)topre-
changingtrendofrainfallhasledtochangesinrainfallpatternsduringthe dicttheimpactoffutureclimateongroundwaterflowandsalinitydis-
wetseason(May–October),withlongerdryspellsinthemiddleofthe tributionbyapplyingnumericalmodels.Thisstudyinvolvedthefield
rainyseasonandmoreintenseprecipitation(Jarupongsakul,2011). characterizationofsoils,thehydrologicandhydrogeologicconditions,
Severalearlierstudiesdevelopedandappliedfutureclimatechange andtheapplicationofthehydrologicalmodel.Theseprocesseswere
in Thailand for different purposes (Chinvanno et al., 2009; carriedoutinordertoestimatethegroundwaterrecharge.Usingvari-
Manomaiphiboon et al., 2009; Santisirisomboon, 2009; TRF,2011). abledensityofgroundwater,thegroundwaterflowmodelwasusedto
1520 K.Pholkernetal./ScienceoftheTotalEnvironment633(2018)1518–1535
calculatethewatertables,flowpatterns,andgroundwatersalinity.The TheareaofstudyhasatropicalgrasslandclimateorSavanna-Awin
resultsandfindingswillbeusefultoassistdecision-makersandstake- whichtheaveragedailytemperatureis27.0°C.Januaryisthecoolest
holdersinformulatingtheappropriatepoliciesforwaterresourceman- monthwithadailytemperatureofabout22.4°Candapproximately
agementintheCHLB. 29.8°CinAprilwhichisthehottestmonth(TMD,2015).Anaverage
evaporation from the Class A Pan measurement is 1683 mm/year
(TMD, 2015). The average annual rainfall was calculated from the
2.Theareaofstudy UdonThanimeteorologicalstationusing11raingaugestations(TMD,
2015;RID,2015)between1984and2015.Almost90%ofrainfalloccurs
TheCHLBislocatedinthecentralpartoftheHuaiLuangBasinin intherainyseasonfromMaythroughOctober.Theaverageannualrain-
UdonThaniProvinceinNortheasternThailand.Itcoversanareaof fallvariesfrom1100to1500mm(Average=1268.6mm).
1529 km2andis locatedin threedistrictsofUdonThani Province: Thehydrologicalandhydrogeologicalstudyoftheareaweresys-
MuangUdonThani,KutChap,andNongWuaSo,asshowninFig.1. tematicallycharacterizedandpresentedashydrogeologicmapsand
Thetopographicelevationsvaryfrom160to564maboveMeanSea cross-sections.Theproceduresofdrillingpumpingtestwells,installing
Level(mAMSL).Themountainousandhillyterrainsaboundinthe piezometers(33wells),monitoringthewaterlevels,checkingthequal-
Western,Southern,andNorthernregionswhichrepresentthesurface ityofthegroundwaterandsurfacewater,analyzingthesoilmoisture,
waterandgroundwaterdividesofthebasin.Apopulationofabout andtestingforsoilsalinitywereallconductedduringtheperiodfrom
448,000personsorabout29%ofUdonThaniProvince'spopulationare September2014toDecember2015.TheHuaiLuangreservoirinlocated
livinginthebasin(DPA,2014).TheCentralHuaiLuangBasinisoneof intheSouthwestandtheHuaiLuangRiverisamajorwatersourceof
theimportantagriculturalandfoodproductionareasinUdonThani waterandthesupplyforirrigation.TheHuaiLuangRiverflowsfrom
Province.ThisareaisunderlainwithrocksaltfromtheMahaSarakham the west to the east with a length, width, and a depth of 50 km,
formation,andthiscausesthespreadofsaltsintothegroundwater,the 50–90m,and5–7m,respectively.AlongtheHuaiLuangRiver,two
surfacewater,andthesoil. streamgaugingstationsarelocatedatKh.53andKh.103(RID,2015).
Fig.1.LocationmapoftheCHLBandsoilsalinitydistribution.
(ModifiedfromLDD,2006)
K.Pholkernetal./ScienceoftheTotalEnvironment633(2018)1518–1535 1521
ThetotalannualrunofffortheCHLBisaround262.4MCM/year(Mm3/ andpresenttheregionalandlocalgroundwaterflowpatterns.Gener-
year).Thesurfacewatersalinitywasmonitoredbymeasuringtheelec- ally,intherechargeareas,groundwaterrechargestoaquifersarelo-
tricalconductivity(EC)acrossthebasin.Duringthedryseason,the cated in the West, South, and the local high areas in the North. In
waterqualityoftheHuaiLuangRiveranditstributaryaremildlybrack- contrast,thedischargeareasarenormallylocatedalongcentralpartof
ishwithelectricalconductivitiesofN1500μS/cmorTotalDissolved studied area and the Huai Luang River floodplain. Throughout the
Solids(TDS)ofN1000mg/l,whereasduringtherainyseason,thesurface basin,theTotalDissolvedSolids(TDS)ofthegroundwatervariesfrom
waterbecomesslightlybrackishtofresh. b1000mg/l(fresh)tob10,000mg/l(brackish)andtoN10,000mg/l(sa-
Basedonthesaturatedhydraulicconductivityvalues,soilareclassi- line).ThehighTDSorsalinityvarieswiththedepthofthewaterandis
fiedintothreegroups:slow,moderate,andrapid(FarrandHenderson, foundinthelowlandareasatthecentralpartofstudiedareaalongHuai
1986).Theslowsoilshaveveryslowinfiltrationrates(b5×10−7m/s) LuangRiver.Groundwatertypesvaryfromrechargeareastodischarge
andconsistchieflyofclaysoils.InthelowlandsalongtheHuaiLuang areas and include Ca-HCO , Ca-Na-HCO and Na-Cl, Na-Cl types
3 3
River,siltyclaysoiloccursoveranearlyimperviousmaterial.Themod- (Deutsch,1997).
eratesoilshaveinfiltrationrates(5×10−7to5×10−6m/s)andconsist Thereareabout650waterwellsbeingusedfordomestic,agricul-
ofmoderatelywell-drainedsoilsasfinetomoderatelyfinetextures, tural,andindustrialpurposes.Mostofthedomesticwellswerepro-
suchasloamandsandyclayloam.Thesesoilsaremostlylocatedinup- vided by the Department of Groundwater Resources. Water wells
landareas.Therapidsoilshavehighinfiltrationrates(N5×10−6m/s) were drilled at depths ranging from about 20 to 122 m below the
andconsistofexcessivelywell-drainedmaterials,suchasloamysand groundsurface.Accordingtothefieldsurveyandthecensusofwater
andsand.Mostoftheareaiscoveredwithmoderatelyinfiltratedsoils usein2015,itwasfoundthatgroundwaterresourcewasbeingused
andcoversabout52%ofthelandarea.Thesoilsalinityintheareatypi- fordomestic,agricultural,andindustrialpurposesatratioof75%,20%,
callycommenceswithdeforestationintherechargearea,saltmaking, and5%,respectively.Thetotalannualgroundwaterusagewithinthe
andthereplacementofthetreeswithshallowrootcropsinthelow- basinhasbeenestimatedatabout6,758,606m3,whichisarelatively
landsorlocaldischargeareas.Thesepracticeshavesignificantlyledto smallvolumewhencomparedtotheactivitiesandthepopulationin
ariseinthewatertable,toariseintherechargeratesinthelocalre- thestudiedarea.Thiswasduetothefactthatsomecommunitiesarelo-
chargeareas,andtotheescalationofsalinityproblems(Arunin,1984; catedinareaswithsalinegroundwater.Asaresult,itwasnecessaryfor
Srisuk,1994).Thesoilsalinitywasclassifiedbasedonsaltcrustoccur- alternativesourcesofwatersupplytobeallocatedbytheProvincialWa-
ring on ground surface and giving rise to saline soil. As shown in terworksAuthority(PWA).
Fig.1,thesoilswereaffectedbysaltatabout35%.Highlysalt-affected
soilcoveredabout0.1%ofthestudiedlowlandarea,andthesaturation
extract(ECe)hadanelectricalconductivityofN8dS/m.Moderatelysa- 3.Methodology
linesoilcoveredthelowlandofthecentralandeasternpartsofthestud-
iedareawithECeabout4–8dS/m.Slightlysalinesoilwasfoundupland Thisworkisunderpinnedbytheneedtothoroughlyunderstandthe
inthewesternandsouthernpartsofthestudiedareawithECeabout hydrogeologicsystemsandthesalinizationprocesses.Thestructuraldi-
2–4dS/m.Inhighlysalt-affectedareas,cropscannotbegrown.Most agramofthemethodologyandtherequireddataareillustratedinFig.3.
oftheareahadbeenabandonedandinvadedbysalttolerantweeds. Thesalinewatertransport,waterbudgets,andwaterloggingweresim-
Incontrast,farmersintheslightlyandmoderatelysalt-affectedareas ulatedbyusingthevariabledensitygroundwatermodel(SEAWATver-
cangrowrice,buttheplantgrowthisnotuniform(Wichaidit,1997). sion4groundwaterflow):salinewatertransport,waterbudgets,and
Aroughapproximationofdecreaseinthericeyield,causedbysalinity waterlogging(Langevinetal.,2008).Rechargerateswereestimated
ofmoderatelysalinesoil,isN50%insusceptiblecultivars,whilethere- basedontheHELP3Model(Schroederetal.,1994)andclimatevariables
duction of rice production in the slightly saline soil is only about suchastemperatureandprecipitation.Aftercertaincalibrationshad
10–50%(DobermannandFairhurst,2000).Thelandusagetypesare beencompletedforboththeSEAWATandHELP3models,simulations
mainlypaddyfields,fieldcrops(sugarcaneandcassava),urbanareas, ofgroundwaterflowandsalttransportwereconductedunderthefu-
bodiesofwater,andforests.Thepaddyfields,whicharelocatedalong tureclimatevariablesfrom2sets.Inthefirstset,theGCMs(GeneralCir-
HuaiLuangRiverfloodplainandintheeasternparts,occupiedabout culation Models) were retrieved from the CMIP3 (Coupled Model
40%oftheland.Thereisonlyonecropofricethatgrowseachyear IntercomparisonProject3)dataportalunder4scenariosofSEACAM.
fromMaytoNovemberintherain-fedagriculturalarea,whereasinirri- Inthesecondset,theGCMswereretrievedfromtheCMIP5dataportal
gatedareas,cropscanbegrowntwiceperyear.Fieldcropsaregrownin undertwoscenariosofCanESM2asdiscussedinSection3.2.Thesesim-
thenorthwesterntosouthwesternregionsandcoverabout23%ofthe ulationswereaccomplishedinordertoexaminetheimpactofclimate
totallandarea,whileforestedareas,urbanareas,andwaterbodies changeongroundwaterresourceswithrespecttobothquantityand
cover19%,13%,and5%,respectively(LDD,2013). quality.Theprojectedclimatescenarioswereusedastheinputdata
Thecomprehensivehydrogeologicmapandsomecross-sections forthenetrechargeestimations.Groundwaterlevels,flows,salinitydis-
acrossthestudiedareawerereconstructedbyusingthefieldinvestiga- tributionpatterns,andwatertabledepthsintheuppermostlayerofthe
tionsandtheexistingdatathathadbeencompiledfromtheprevious modelwereallusedtoassessthedegreesofshallowgroundwatersali-
works (DMR, 2009; Suwanich, 1986; Cotanont, 2014) as shown in nization and distribution. The impact of future climate change on
Fig.2.ThefloodplainoftheHuaiLuangRiveriscoveredwithsand, waterlogging and salinity distribution was evaluated by using the
clay,andgravelofAlluvium(Al).Inaddition,Terrace(Te)Depositsare means of the areal distribution of the water table depths and by
foundinthehillyareasinthesouthernregion.Theseunconsolidated expanding the boundaries of the saline groundwater, which were
units,havinganaveragethicknessof30m,areunderlainbysiltstone taken from simulation results projected over the coming 30 years
andsandstoneaquifersoftheUpperPhuThok(Upt)unit.TheLower (2016to2045)foreachclimatescenario.
PhuTok(Lpt)unitconsistsofshaleandmudstonewithathicknessof
50to200mwhichisunderlainbytherocksaltlayersoftheMaha
Sarakham(Ms)unit.TheKhokKruat(Kk)unitisfoundatthetoeof 3.1.Numericalmodel
themountainandconsistsofsiltstoneandsandstonewithathickness
of430to700m.TheLowerKhoratGroup(Lkg)Unitliesunderneath In this study, the physically-based hydrologic models, USGS
theKkunitandconsistsofsandstone,siltstone,claystone,andconglom- SEAWAT Version 4 (Langevin et al., 2008) and HELP version 3.07
erate.Accordingtowaterlevelmeasurementsfrom2014to2015,the (HELP)(Schroederetal.,1994),wereusedtoestimatechangesinthe
groundwaterflownetshavebeenconceptuallyconstructedinFig.2 rechargerate,waterbalance,andsalinitydistributionintheCHLB.
1522 K.Pholkernetal./ScienceoftheTotalEnvironment633(2018)1518–1535
W1 E1
5710F030 5710D024 E38H1uaRi iLveurang NW1E-S4E713 N1-S1 A117 Huai Makkang RiverKN020-1S2Huai Mung RiverE496 E925 K085
Hydrogeological Units
N1 S1
Huai Luang W1-E1 NW1-SE1 5410H010
River E032 C13C06
K006 E693
Fig.2.Hydrogeologicmapsandcross-sectionsoftheCHLB.
K.Pholkernetal./ScienceoftheTotalEnvironment633(2018)1518–1535 1523
3.1.1.Groundwaterflowandsalttransport inbold.):
TheSEAWATprogramisacoupledversionofMODFLOW(Harbaugh (cid:4) (cid:1) (cid:3)(cid:5)
e1t99a9l.),2fo0r0a0d)vefocrtivgero-duinspdewrsaitveertflraonwspaonrtd.TMogTe3tDhMerS,S(EZAhWenAgTaisnddeWsigannegd, ∇(cid:1) ρμμ0K0 ∇h0þρ−ρρ0∇z ¼ρSs;0∂∂ht0þθ∂∂Cρ∂∂Ct−ρsq0s ð1Þ
0
tosimulatethree-dimensionalvariabledensitysaturatedgroundwater
flows.Flexibleequationswereaddedtotheprogramtoallowthefluid ρ isthefluiddensity[ML−3]atthereferenceconcentrationandref-
0
densitytobecalculatedasafunctionofoneormoreMT3DMSspecies. erencetemperature;μisthedynamicviscosity[ML−1T−1];K isthehy-
0
Fluiddensitymayalsobecalculatedasafunctionoffluidpressure. draulicconductivitytensorofmaterialsaturatedwiththereference
Theeffectsofthefluidviscosityvariationsongroundwaterflowwere fluid[LT−1];andh isthehydraulichead[L]whichismeasuredin
0
includedasanoption.Fluidviscositycanbecalculatedasafunctionof termsofthereferencefluidataspecifiedconcentrationandtempera-
oneormoreMT3DMSspecies,andtheprogramincludesadditional ture(asthereferencefluidiscommonlyfreshwater).Furthermore,S
s,0
functionsthatrepresentthedependenceupontemperature.Having isthespecificstorage[L−1],whichisdefinedasthevolumeofwater
theabilitytocombineflexibleequationsforfluiddensityandviscosity thatisreleasedfromstorageperunitvolumeperunitdeclineofh ;t
0
with multi-species transport, the SEAWAT Version 4 allows for istime[T];θisporosity[−];Cissaltconcentration[ML−3];q' isa
s
variable-densitygroundwaterflowcoupledwithmulti-speciessolute sourceorsink[T−1]offluidwithdensityρ;andzistheelevation
s
andheattransport(Langevinetal.,2008).TheVariable-DensityFlow head[L].
(VDF)ProcessinSEAWATsolvesthefollowingformofthevariable- ThelimitationsofSEAWATVersion4donotexplicitlyallowforthe
densityground-waterflowequation(tensorsandvectorsareshown dissolutionandprecipitationofmineralsthatmaylikelyresultfrom
Future climate scenarios Recharge Estimation Model
(HELP3)
Downscaling of GCM under
4 scenarios of 2 scenarios of
SEACAM model CanESM2 model
-HadCM3Q3 -RCP 4.5
-HadCM3Q13 -RCP 8.5
-HadCM3Q10
-HadCM3Q11
Projected duration 2016-2046 for:
-Precipitation
-Temperature
Soil properties
-Total porosity (Ø)
-Field capacity (FC)
-Wilting point (WP)
Recharge rate -Saturated hydraulic
conductivity (KS)
Groundwater Model (SEAWAT)
Recharge rate
YES
Prediction using Groundwater level and TDS calibration NO
future climate data and validation
YES
Waterloggingand saline groundwater Waterloggingand saline groundwater
area under future climate change impact area at baseline period
Fig.3.Structuraldiagramofthemodelingapproachandrequireddata.
(ModifiedfromSaraphirometal.,2013b)
1524 K.Pholkernetal./ScienceoftheTotalEnvironment633(2018)1518–1535
Zone 5
40F-(2-10)
Zone 2
Zone 3 Zone 8 40A1-(0-2) Lpt Lpt Upt
40A2-(0-2)
Urban
Zone 4 Upt Al
Zone 9 40A2-(2-10)
Water body
Zone 7 A A’
61F-(>10) Zone 6
61A1-(0-2) Kk Te
Zone 1 Lpt
17A1-(0-2) Lkg Kk
(1) (a)
Lkg
280 A A’
240
200 Al Te
160 Lkg Upt Al Lpt
120 Kk
80 Lpt
Rs
40
0222500 232000 240000 248000 256000 264000 272000 282500
(c)
(2) (b)
Fig.4.Rechargezones(a),RiverboundaryandObservationwells(b),andGriddesignanddistributionoftheHydraulicparameters(c)ofCHLBmodel.
largetemperaturechangesandtheheatwhichislostorgainedfrom hydraulicconductivity,weremeasuredduringthefieldinvestigations
thosereactions.Theformulationisrepresentedforwaterintheliquid andexperiments.
phaseonlyanddoesnotrepresentthetransitionstoiceortovapor. Themodelwasdesignedasafinitedifferencegridwithaspatialres-
SEAWATmodelwasselectedtosimulategroundwaterflowandsalt olutionof500m×500m.Themodelwasseparatedinto8layersrang-
transport.Thegroundwatermodeldomainhasbeenidentifiedbythe ing from 10 to 40 m in thickness, between the altitudes of the
physical boundaries of the CHLB (Fig. 4). Seven hydrostratigraphic topographytothelowestlayerofmeansealevel(AMSL).Theupper
units(aquifersandaquitards)havebeenassignedtothemodelasfol- layers(Layer1-Layer3)wereassignedwithathicknessof10m.The
lows:(a)thesand,clay,andgraveloftheAlandtheTeunitswitha rangesoftheinputparameterswerevaluesofthefollowing:vertical
thicknessof10–30m,(b)thesiltstoneandthesandstoneaquifersof andhorizontalhydraulicconductivity;specificyieldandstorage;total
theUptunitwiththicknessesof30–200m,(c)thesiltstoneandsand- andeffectiveporosity;anddispersivity.Themodelwascalibratedand
stoneaquifersoftheKkunitandLkgunitwithathicknessof430to validatedusingsomepreviousgroundwaterlevelsandsalinitymonitor-
700m,and(d)theclaystoneoftheLptunitwhichisunderlainbythe ingfromCotanont(2014)andinformationfromthecurrentstudy,such
rocksaltlayersoftheMsunit.ThisMsunitwastreatedasanoflow aspumpingtests,dispersivitytests,groundwaterlevels,andsalinity
boundary. The lateral boundaries and the bottom boundary of the monitoring.Thepumpingtestanddispersivitytestresultsforeach
flowdomainweretreatedasnoflow.ThevolumeofGeneralHead hydrogeologicunitareshowninTable1.Theinitialconditionsofthehy-
boundaries(GHB),assignedforHuaiLuangRiverwherethestudied draulicheadsandgroundwatersalinitywereassignedfrommeasure-
areawascutofffromthewholebasin,werecollectedfromhydrological ments taken in September of 2014 on the 152 observed wells. A
stationKh.103.ThegroundwaterrechargewascalculatedusingHELP3 constantconcentrationof100,000mg/lofsalinewaterwasassigned
modelasdiscussedinSection3.1.2.Thedrainagesystemandriver torepresenttherocksaltlayer.Theseasonalgroundwaterabstraction
inputparametersincludingtheriverstageandwidth,andthevertical fromeachaquiferlayerwasobtainedfromtheinvestigationduring
Table1
FlowandmasstransportparametersusedinSEAWATmodel.
Hydrogeologic Horizontalhydraulic Verticalhydraulic Specificstorage,Ss Specificyield, Effective Total Longitudinal
units conductivity,Kh(m/s) conductivity,Kv(m/s) (m−1)* Sy(−) porosity(−) porosity(−) DI(m)
Alluvium(Al) 1.10×10−7to1.10×10−5 1.10×10−7to1.10×10−5 1.00×10−2 0.30 0.35 0.40 500
TerraceDeposit(Te) 1.00×10−5to5.00×10−2 5.00×10−6to5.00×10−3 8.00×10−3 0.25 0.30 0.40 600
Upperphutok(Upt) 3.70×10−7to1.80×10−6 3.70×10−8to4.80×10−7 3.00×10−3 0.15 0.25 0.30 150
Lowerphutok(Lpt) 1.09×10−7to2.70×10−4 1.09×10−8to2.70×10−5 1.70×10−3 0.17 0.22 0.31 70
Rocksalt(RS) 2.00×10−14 2.00×10−14 1.00×10−5 0.01 0.02 0.10 50
KhokKruat(Kk) 7.49×10−8to5.76×10−5 7.49×10−9to5.76×10−6 5.00×10−3 0.20 0.25 0.30 70
LowerKhoratGroup(Lkg) 5.00×10−9to5.00×10−7 5.00×10−10to5.00×10−8 2.00×10−3 0.20 0.25 0.30 150
K.Pholkernetal./ScienceoftheTotalEnvironment633(2018)1518–1535 1525
theyearsof2014to2015.Accordingtothegroundwaterusageinvesti- processes,suchasinterception,infiltration,evaporation,andsurface
gationintheCHLB,thereisabout1880m3ofwaterabstracteddailyand run-off.Inthisstudy,theHydrologicEvaluationofLandfillPerformance
itisabstractedfromvariousaquifersatabout30%,25%,15%,15%,10%, (HELP)computerprogram(Schroederetal.,1994)wasselectedtobe
and5%fromtheUpt,Lpt,Kk,Te,Al,andLkgunits,respectively. usedtoestimatethegroundwaterrechargerates.Ithasalsobeenused
toestimatetheimpactofclimatechangeonthespatialvaryingground-
3.1.2.Groundwaterrechargeestimation waterrechargeratesinNewJersey(Jyrkamaetal.,2002),oftheGrand
Groundwaterrechargeratesdependupontherainfallintensity,tem- RiverWatershed(JyrkamaandSykes,2007),intheGrandForksArea
peratures,otherweatherconditions,slopes,soils,andgroundsurface (ScibekandAllen,2006;Scibeketal.,2007)andintheHuaiKhamrian
covers.Incontrast,therechargerateissubjectedtovarioushydrological subwatershed(Saraphirometal.,2013a).Foradetaileddescriptionof
Fig.5.Rechargezonesestimatedbyanintegrationoflanduse,soiltypes,andtopographicslopes.
1526 K.Pholkernetal./ScienceoftheTotalEnvironment633(2018)1518–1535
theHELPmodel,seeSchroederetal.(1994).TheHELP3modelisa theprojectedimpactofclimatechangeonthegroundwaterquantity
quasi-two-dimensional,deterministicwaterroutingmodelforcomput- andqualityintheCHLBduetothefactthatitwasdevelopedforSEAre-
ingwaterbalances.Itsimulatesthedailymovementofwaterintothe gion,whichisparticularlyvulnerabletoweatherandclimateextremes
groundandaccountsforprecipitationinanyform:surfacestorage;run- andisaffectedbyextremeweatherevents,particularlytropicalcy-
off;evapotranspiration;vegetativeinterceptionandgrowth;unsatu- clones, drought, and floods (Weiss, 2009). Large areas of SEA are
ratedflow;andtemperatureeffects(Saraphirometal.,2013a).The pronetoflooding,andmuchoftheregionisheavilyinfluencedbymon-
waterbalancemethodisusedtobecalculatedthenetpotentialre- soonsystemswhichoftenbringextremeweather(YusufandFrancisco,
chargeasaresidualofalloftheotherwaterbalancecomponents.Itis 2009).TheSEACAMclimatemodelwasusedtostudytheimpactofcli-
expressedinthefollowingformula: matechangeontheSEAmembercountries,duetothefactthatithas
beendevelopedbyclimatechangespecialistsandscientistsintheir
R¼P−D−ETa–ΔW ð2Þ owncountriesandthatitreliablyrepresentsfutureclimate.Inorder
toevaluateanappropriateclimatemodelthatisabletorepresentthe
inwhichRisthepotentialnetrecharge(LT−1),Pistheprecipitation futureclimateoftheCHLB,visualcomparisonsandstatisticalmeasure-
(LT−1),Disthenetrun-off(LT−1),ETaistheactualamountofevapo- mentsoftheobservedtemperatureandtheprecipitationdataofCHLB
transpiration(LT−1),andΔWisthechangeinthesoilwaterstorage and SEACAM climate model were analyzed for the baseline period
(LT−1). (2006–2015).TheresultsshowedthatthehistoricaldataofSEACAM
Variousdatawererequired,suchastheclimateandthesoiltypes, andtheobserveddataofthebaselineperiodhadcorrelatedwell.As
whichwereusedtoestimatethewaterflowthroughasoilcolumn can be seen from the results of the statistical measurements in
andwhichrepresentstherechargeratesofeachzone.HELP3wascho- Table3,thefindingshadbeenreasonablyreliableinrepresentingthefu-
sentocooperatewithSEAWATbecauseitcansimulatealloftheimpor- tureclimateoftheCHLB.
tant processes in the hydrologic cycle in each recharge zone. The TheSEACAMclimatemodelisavailableonlyunderAR4,otherGCMs
rechargerateswereusedasboundaryconditionsforgroundwatersim- underAR5wereexploredinordertobeselectedtorepresentthefuture
ulationsinthewatershedscale.TherechargezonesintheSEAWAT climateoftheCHLBforthelatestAssessmentReport.TenoftheGCMs,
modelwereclassifiedbylanduse,soiltype,andbytopographicslope includingCNRM-CM5,MIROC-ESM,FGOAL-s2,MPI-ESM-LR,CESM1-
asshowninFig.5.Thesoilprofileandpropertieswereassignedasa BGC,CCSM4,CanESM2,HadGEM2-CC,andGFDL,havebeenwidely
soilcolumnintheHELP3model(Table2).Ninerechargezoneswere usedinThailand(Chaowiwatetal.,2017).TheseareincludedinIPCC
assignedtorepresenteachzone.TheresultsfromtheHELP3model AR5andwereselectedtoevaluateasuitableclimatemodel.There-
wereusedasinputsforeachzoneinSEAWATmodel. cordedtemperatureandprecipitationdatafromtheCHLBandfrom
thetenGCMSduringthebaselineperiod(2006–2015)wasstatistically
3.2.Futureclimatescenarios analyzedbythesamemethodusedforSEACAM.Theresultsfromthevi-
sualcomparisonsandthestatisticalmeasurementsindicatedthatthe
Toexaminetheprojectedimpactofclimatechangeinthenearfu- CanESM2wasshownthebestcorrelationwhencomparedtotheothers,
ture,thefutureclimateoftheGCMsundertheIPCCFourthandFifthAs- withcoefficientsofdetermination(R2)of0.67and0.68foraverage
sessment Report (AR4 and AR5) were considered. For AR4, the monthlytemperatureandtheaveragemonthlyamountofprecipitation,
SoutheastAsiaClimateAnalyses&Modeling(SEACAM)regionalclimate respectively.Incontrast,otherGCMsexhibitedcoefficientsofdetermi-
modelingexperimentprovideshighresolution(25km)informationon nation(R2)at0.23–0.46and0.19–0.49fortheaveragemonthlytemper-
futureclimateprojectionsfortheSoutheastAsia(SEA)regionuptothe atureandtheaveragemonthlyamountofprecipitation,respectively.
endofthiscentury.Thiswascarriedoutbythedynamicaldownscaling Therefore, it was found that CanESM2 was reasonably reliable in
oftheMetOfficeHadCM3Qensemble-basedGCMs,whichwerere- representingthefutureclimateoftheCHLBasshownintheresults
trievedfromtheCMIP3,andbyusingtheMetOfficePRECISmodel fromthestatisticalmeasurementsinTable3.ThesecondgenerationCa-
(SEACAM,2014).TheSEACAMclimatemodelwasselectedtoexamine nadianEarthSystemModel(CanESM2)consistsofthephysicalcoupled
Table2
Rechargezone,soilprofiles,andotherinputparametersforestimatingofgroundwaterrecharge.
Zone Layer Depth Soiltexture- Ø FC WP Ks(cm/s) Slope Landuse EZD LAI
(cm) (vol/vol) (vol/vol) (vol/vol) (%) (cm)
17A1-(0–2) 1 0–20 Loamyfinesand 0.49 0.28 0.14 5.0×10−5 1.00 Rice 56 3
Lowlandsoil,paddyfield,slope0–2% 2 20–65 Silt 0.48 0.30 0.10 1.9×10−6 – – – –
3 65–130 Siltyloam 0.49 0.28 0.14 1.9×10−6 – – – –
4 130–200 Siltyclay 0.49 0.38 0.22 1.3×10−8 – – – –
40A1-(0–2) 1 0–40 Loamysand 0.50 0.35 0.20 5.0×10−5 1.50 Rice 56 3
Uplandsoil,paddyfield,slope0–2% 2 40–90 Siltloam 0.35 0.32 0.20 1.0×10−7 – – – –
3 90–120 Clay 0.475 0.378 0.256 1.0×10−9 – – – –
4 120–200 Siltyclayloam 0.445 0.393 0.277 3.8×10−8 – – – –
40A2-(0–2) 1 0–200 Sandyloam 0.453 0.19 0.085 7.5×10−5 1.50 SugarCane 102 4
Upland,fieldcrop,slope0–2% 2 150–200 Siltyclay 0.479 0.371 0.251 6.15×10−8 – – – –
40A2-(2−10) 1 0–90 Sandyloam 0.45 0.30 0.09 3.85×10−6 5.00 SugarCane 102 4
Upland,fieldcrop,slope2–10% 2 90–200 Gravel 0.45 0.032 0.013 3.0×10−1 – – – –
40F-(2–10) 1 0–90 Siltysand 0.501 0.284 0.135 1.9×10−5 5.00 Forest 102 7
Upland,forest,slope2–10% 2 90–120 SiltysandandLaterite 0.463 0.232 0.116 3.5×10−6 – – – –
3 120–200 Clay 0.475 0.378 0.265 3.0×10−9 – – – –
61A1-(0–2) 1 0–150 Sandyloam 0.453 0.19 0.085 1.0×10−5 1.75 Rice 102 7
Highlandsoil,paddyfield,slope0–2% 2 150–200 Siltyclay 0.479 0.371 0.251 3.15×10−8 – – – –
61F-(N10) 1 0–100 Loamysand 0.437 0.105 0.047 1.7×10−3 15.00 Forest 102 7
Highlandsoil,forest,slopeN10% 2 100–150 Gravel 0.397 0.032 0.013 1.0×10−1 – – – –
3 150–200 Clay 0.475 0.378 0.25 2.73×10−8 – – – –
Waterbody –
Urban –
Remarks:leafareaindex(LAI),evaporativezonedepth(EZD),totalporosity(Ø),fieldcapacity(FC),wiltingpoint(WP),andsaturatedhydraulicconductivity(KS).
K.Pholkernetal./ScienceoftheTotalEnvironment633(2018)1518–1535 1527
Table3 et al., 2016; Pratoomchai et al., 2014; Saraphirom et al., 2013a;
AsummaryofthestatisticsoftheobservedandsimulatedhistoricaldatafortheCHLBdur- JyrkamaandSykes,2007).Theimpactonthegroundwaterresources
ingtheperiod2006–2015.
forthisstudywasinvestigatedbyexaminingthechangesingroundwa-
Monthlyaverage Monthlyaverage terrecharges,levels,flowpatterns,andsalinityasindicatorsofground-
temperature(°C) precipitation(mm) waterstorage,waterlogging,andsalinitydistribution.
SEACAM CanEMS2 SEACAM CanEMS2 During the period from 2010 to 2015, the models, HELP3 and
SEAWAT,werecalibratedandvalidatedwiththeobservedgroundwater
SD,Obs 2.49 2.49 110.99 110.99
SD,Sim 3.63 2.85 84.83 95.94 levelsandsalinitylevels.Simulationsofgroundwaterflowandsalt
Mean,Obs 26.98 26.98 105.72 105.72 transportunderthefutureclimatedataof4SEACAMscenariosand3
Mean,Sim 28.36 27.99 87.15 111.56 CanESM2scenarioswereprojectedforthenext30years.Theclimate
Median,Obs 27.80 27.80 66.53 66.53
datawasusedastheinputdataintheHELP3modeltoestimatethe
Median,Sim 29.34 28.66 60.08 67.90
R2(coefficientofdetermination) 0.72 0.67 0.63 0.68 netrechargefrom2016to2045.Thentheprojectedgroundwaterre-
charge for each scenario was used as the recharge input for the
SEAWATmodelinordertosimulatethegroundwaterlevels,flowpat-
atmosphere-oceanmodel(CanCM4)coupledwithaterrestrialcarbon terns,andsalinitydistributions.
model (CTEM) and an ocean carbon model (CMOC) (Chylek et al., Theimpactofclimatechangeonthegroundwaterresourceswas
2011). GCM precipitation and temperature were downloaded and classifiedintermsofgroundwaterquantityandquality.Thedifferences
downscaledusingthePRECISmodel.TheGamma-gamma(GG)trans- ingroundwaterstoragevaluesfromtheaquiferbalancebetweenthe
formation with the optimizing parameter method was adopted to baselineandfutureperiodswereutilizedtoassesstheimpactupon
downscalethetemperatureandtheprecipitationfromtheglobalscale groundwaterquantity.Differenceswerefoundinareasinwhichthe
totheriverbasinscale.Thecharacteristicsofthegammacumulative depthsofwatertablecanmoveupwardtowardsthesoilsurfaceand
densityfunction(CDF)wereusedtoremovethebiasesfromtheRCM cancausetheaccumulationofsalt(waterlogging).Moreover,ground-
precipitationdata(Chaowiwatetal.,2017)andtoprovideinformation watersalinitychangesbetweenthebaselineandfutureperiodswere
withhigherresolution(10km)forfutureclimateprojections. usedtoassesstheimpactongroundwaterquality.Thewaterlogging
Four of SEACAM downscaled climate scenarios of HadCM3Q3, andsalinitydistributionswereevaluatedbymeansofthearealdistribu-
HadCM3Q10,HadCM3Q11,andHadCM3Q13wereselectedinorderto tionofthewatertabledepthsandtheexpansionofthesalineground-
investigatethepotentialimpactoffutureclimatescenariosonground- waterboundaries.
wateranditsconsequencesonwaterloggingandsalinitydistribution
intheCHLB.IncapturingtheAsianmonsoons,theHadCM3Q3model 4.Resultsanddiscussion
showed the lower degree of temperature change, while the
HadCM3Q13modelshowedthehigherdegreeoftemperaturechange 4.1.Baselinegroundwaterflowsituation
fortheSEAregions.Duringthewetseasons,theHadCM3Q10model
showedincreasesinrainfall,whiletheHadCM3Q11modelindicatedde- ThegroundwaterconditionoftheCHLBinthebaselineperiod(2006
creasesinrainfall. to2015)wassimulated.Thehydraulicheadsandsalinityofthe89wells,
TheCanESM2downscaledclimatescenarios,whichwereusedtoin- distributedinsixaquifersintheCHLB,weremeasuredfromSeptember
vestigatetheimpactofgroundwaterontheCHLB,weretheRepresenta- 2014toDecember2015andwereusedascalibrateddata.Themodel
tiveConcentrationPathways(RCPs)4.5and8.5whichwerepresented wasvalidatedwith33observationwellswhichhadbeenmonitored
intheAR5ofIPCC.TheRCP8.5isthehighestemissionthatisconsidered duringtheyearsfrom2010to2012.Themodelperformancewaseval-
tobeconsistentwiththefutureofnopolicychangestoreduceemis- uatedbymakingvisualcomparisonsofthegroundwaterlevelsandsa-
sions.ItwasdevelopedbytheInternationalInstituteforAppliedSystem linityintermsofTotalDissolvedSolid(TDS)betweentheobserved
AnalysisinAustriaandischaracterizedbyincreasinggreenhousegas versusthesimulatedbothgroundwaterlevelandTDSandbyusing
emissionsthatleadtohighgreenhousegasconcentrationsovertime. the Root Mean Square error (RMSE) and the Normalized RMSE
TheRCP4.5representstheintermediateemissionsdevelopedbythePa- (NRMSE) as statistical measurements (Table 5 and Fig. 6). Major
cificNorthwestNationalLaboratoryintheUS.Here,radiativeforcingis groundwaterflowdirectionshavebeenreplicatedforthetopographic
showntobestabilizedshortlyafter2100,whichisconsistentwiththe terrainaspresentedinthehydrogeologicmap(Fig.6).Thecomparison
futureofrelativelyambitiousreductionsinemissions. ofsimulatedandobservedhydraulicheadsandTDSisreasonable.Sen-
Selectedfutureclimatescenariosinthisstudywassummarizedin sitivityanalysesofthegroundwaterflowandsalttransportmodel,the
Table4. SEAWATmodel,werecarriedoutinordertostudythesensitivityof
therechargerates,thehydraulicconductivity,thestoragecoefficients,
3.3.Climatechangeimpactsongroundwaterresourcesassessment thedispersivity,andtheeffectiveporosityofthegroundwaterlevel
andsalinity.Theresultsindicatedthattherechargerateshadbeenthe
Theimpactofclimatechangeongroundwaterresourcesaffectsre- mostsensitiveparametersforthegroundwaterlevel(Fig.7(a)),while
chargerates,patterns,andtiming;decreases/increasesingroundwater thedispersivityhadbeenthemostsensitiveparameterforgroundwater
levels;andthedeteriorationofgroundwaterquality(e.g.,Shrestha salinity(Fig.7(b)).Thewaterbalancein2015showedthatwaterinflow
Table4
Selectedfutureclimatescenariosinthisstudy(SEACAM,2014;vanVuurenetal.,2011).
Model IPCC Downscale Scenarios Description
resolution
SEACAM AR4, 25km×25 HadCM3Q3 SimulateslowerdegreeoftemperaturechangeinthefutureinSEAregion,HadCM3GCManddownscalingbyPRECIS
CMIP3 km HadCM3Q13 SimulateshigherdegreeoftemperaturechangeinthefutureinSEAregion,HadCM3GCManddownscalingbyPRECIS
HadCM3Q10 SimulatesrainfalldecreasesinthefutureinSEAregion(dry),HadCM3GCManddownscalingbyPRECIS
HadCM3Q11 SimulatesrainfallincreasesinthefutureinSEAregion(wet),HadCM3GCManddownscalingbyPRECIS
CanESM2 AR5, 10km×10 RCP4.5 Stabilizationwithoutovershootpathwayto4.5W/m2atstabilizationafter2100,CanESM2GCManddownscalingby
CMIP5 km PRECIS
RCP8.5 Risingradiativeforcingpathwayleadingto8.5W/m2in2100,CanESM2GCManddownscalingbyPRECIS