ã2017CaliforniaInstituteofTechnology.Governmentsponsorshipacknowledged.

NISAR:TheNASA-ISROSARMission

DroughtandGroundwaterWithdrawalDuringdroughts, surfacewater flowdeclines, rivers runlow, streams dry up, and reservoir inventories decline.Facedwith little or no supply ofwater from runoff and

snow melt, communities and businesses turn to analternative source: aquifers, i.e., the undergroundreservoirsofwaterstoredinwater-bearingrock.

DroughtandtheRapidlyChangingLandscape

Droughtsareaccompaniedbyahostoftroubles.Thereducedsurfacewatercaptureandsupplyresultsinmoregroundwaterwithdrawal,whichinturnleadstogroundsubsidencethatcanimpactinfrastructureandevenexacerbatefuturefloodingintheveryareashardesthitbythedrought.

Recent Drought in the United States

Droughtistheconsequenceofabnormallylowprecipitation,reducingthesurfacewatersupply.In2016~22%ofthecontinentalU.S.experiencedmoderatetoextremedrought,andmuchofCaliforniawasclassifiedintheevenmoresevere‘exceptional’droughtcategory[U.S.DroughtMonitor].AlthoughthewesternU.S.washardesthit,droughtsarebynomeansexclusivetothewesternstates.Thenortheast,areasofthesouth,andpartsofnorthernGeorgiaexperiencedthesameexceptionaldroughtin2016thatplaguedCalifornia.Infact,mostofthesouthernstateshaveexperienceddroughtinrecentyears.Manyareas,includingtheGeorgiaandCalifornia,haveimposedwaterrestrictionstosafeguarddwindlingwatersupply.Agricultureisoftenhardhitbydrought,becausesupplyingdrinkingwateristhehighestpriority.

TheNISARMission–Reliable,ConsistentObservations

The NASA–ISRO Synthetic Aperture Radar (NISAR) mission, a collaborationbetween the National Aeronautics and Space Administration (NASA) and theIndian Space ResearchOrganization (ISRO),will provideall-weather,day/nightimagingofnearlytheentirelandandicemassesoftheEarthrepeated4-6timespermonth.NISAR’sorbiting radarswill imageat resolutionsof5-10meterstoidentifyandtracksubtlemovementoftheEarth’slandanditsseaice,andevenprovideinformationaboutwhatishappeningbelowthesurface.Itsrepeatedsetofhighresolutionimagescaninformresourcemanagementandbeusedtodetectsmall-scalechangesbeforetheyarevisibletotheeye.Productsareexpectedtobeavailable1-2daysafterobservation,andwithinhoursinresponsetodisasters,providingactionable,timelydataformanyapplications.

Photo:Ca.Dept.ofWaterResources

Photo:USGS

Photo:Ca.Dept.ofWaterResources

Photo:Va.WaterResourcesResearchCenter

ã2017CaliforniaInstituteofTechnology.Governmentsponsorshipacknowledged.

Cont.fromfrontpage

The water in the aquifers, called groundwater, is anextremelyvaluableresource,likeawatersavingsaccountthatcanbedrawnonwhentimesarehard.Thewaterintheaquifersoriginallywasprecipitationthatmadeitswaydownthroughthesoilandrockviacracksandpores.Allaquifersarenotcreatedequal:aquiferscanholdsmallorvastamountsofwaterandrecharge,orreplenish,quicklyor slowlydependingupon the typeof rock,both inandabove the aquifer. For example, clays hold very littlewaterandwater transfersvery slowly through them, solayers of clay will separate aquifers which have verydifferentrechargingrates.Infact,itiscommonforanareato have multiple aquifers at different depths. Shallowaquifers of saturated soil and rock in contact with thesurface are called unconfined aquifers, and their waterstore depends upon recent activities, i.e., sources (e.g.,rainfall) and sinks (e.g., pumping via wells, drainage tostreams). Recharge is slow in deeper aquifers that areisolated from the surface by less permeable material.Theseconfinedaquiferscollectwatermainlyaroundtheedgesoforthroughholesintheoverlyingrock.Fortheseaquifers, recharge can take hundred to thousands ofyears.Groundwaterisavaluableandrenewablesourceofwaterthat can be tapped throughwells, rechargeable by rainand surface water runoff. However, pumping can havebothimmediateandlongtermimpact.Thepumpingcan

causegroundsubsidencethatleadstocracksinroadsandbridges,lowerleveewalls,andcanevenchangethepathofrunoff,leavingtheareaathigherriskofflooding.Over-pumping can cause collapse of the aquifer pores,permanently reducing the water storage capacity. Forslowly recharging aquifers, the effectivewater supply isreducedsimplybecauseittakessolongforsurfacewatertoreachtheaquifer.Inthiscase,restorationispossible,simplynotonthescalethatisneededforapracticalwatersupply. Consequencescanbeadevastating lossof landviabilityforagriculturalorhabitation.Sustainable, low impact groundwater extraction ispossible,though,giveninformationabouttheaquiferandthe surface changes associated with pumping. This iswhere imaging by satellite radars capable ofmeasuringchanges in surface elevation, likeNISAR, has immediateandpracticalvalue.NISARwillimagegloballandareasonrepeated orbits, providing a time series of the surfaceuplift and subsidence. This information shows both thelong-termdeclineinsurfaceelevation,whichcorrespondstounrecoverable loss or slow rechargeof groundwater,and a seasonal cycle of uplift and subsidence thatcorrelatestoasustainablebalancebetweenprecipitationandwithdrawals.Armedwiththisinformation,userscanprotectthisvaluablerenewablewaterassetoverthelongterm, avoiding the terrible consequences of permanentlossofwatersupply.

NationalAeronauticsandSpaceAdministration Formoreinformation,visithttp://nisar.jpl.nasa.gov/applications

JetPropulsionLaboratory/CaliforniaInstituteofTechnology/Pasadena,California/www.jpl.nasa.gov

TheCaliforniaAqueductsupplieswateroriginatinginnorthernCaliforniaandthecentralCaliforniamountainrangestoresidentsandbusinessesthroughoutmuchofcentralandsouthernCalifornia.Theover400-milelongwaterconveyancesystemisacornerstoneofCalifornia’swatersystem,sustainingitspopulaceandeconomy.In2014,asCaliforniaenteredthesecondyearofextremedrought,groundwaterpumpingincreasedtoreplacethemissingsurfacewater.Thefiguretotherightshowstheconeofdepressiontypicalofnewpumpingfromdeepconfinedaquifers.Inthiscase,thesubsidencebowlextendedacrosstheCaliforniaAqueduct,whichatitsnearestis0.5mifromthecenterofthedepression.Theextensivesubsidencecausedtheclosestpartsofthestructuretosinkmorethan12”.

Radar-derivedmapofgroundsubsidenceintheCentralValley,California,associatedwithgroundwaterpumping[Farretal.,2015]. UAVSAR,anairborneprototypeoftheNISARinstrument,wasusedforthestudy.

Unintended Consequences: Drought Impact to the California Aqueduct