Comparison of drought indices for appraisal of drought characteristics in the Ken River Basin

Abstract

Drought indicesareusedtomonitordroughtconditionsofaregion.Variousdroughtindices(DIs)have been proposedinpastfewdecades,butsomeofthoseareregionspecific andhavelimitationsofap- plicability inotherclimaticconditions.Also,multipletimestepsofDIsmakeithardtodecidethatwhich time stepisthebesttoshowthedroughtcondition. Present studyaimstocompareStandardizedPrecipitationIndex(SPI),EffectiveDroughtIndex(EDI), statistical Z-Score,China Z-Index(CZI),RainfallDeparture(RD),RainfallDecilebasedDroughtIndex (RDDI) fortheirsuitabilityindroughtpronedistrictsoftheKenRiverBasin,locatedincentralIndia, where therainfallisconcentratedinthemonsoonseason(June–September)andfrequentoccurrenceof severedroughteventsarecommon.AllselectedDIswithmultipletimestepsareappliedtocomputethe severity for five timestepsof1,3,6,9,and12-month,andcomparedwitheachotherandEDI. The studyrevealsthat(1)1-monthtimestepinallDIsmayproduceerroneousestimatesofdrought duration. (2)Thedroughtindicescomputedfor9-monthtimesteparebestcorrelatedwitheachother. However,thedroughtdurationandthedroughtfrequenciesestimatedusingRDandRDDIareindis- agreement withotherDIs,therefore,thesearenotsuitableforthisareawherethesummerconcentration of precipitationisveryhigh.(3)TheDIsarehighlycorrelatedatsametimestepsandcanalternativelybe used. However,theyarepoorlycorrelatedatdissimilartimesteps,whichmakesithardtoassesswhether the droughtoccurredornot.(4)Becausetherearenoobjectiverulestoselecttheappropriatetimestep, and theidentified droughtdurationvariestoomuchwithdifferenttimesteps,itisveryhardagainto assess whenthedroughtoccurred. However,EDI,thathasself-defined timestepinitself,andfreefromtimestepproblem,(1)iscor- relatedbetterwithotherDIsforalltimestepsandeffectiveonlongandshortdroughttogether,with highest correlationat9-monthtimesteps,(2)identifies thedroughtconditionearlierthananyother indices, therefore,(3)isfoundtobemoresuitabledroughtindexforthestudybasin.Thisisinagreement with theresultofEDIapplicationinKorea,Japan,Turkey,AustraliaandIranthoughthemethodsofits testing aredifferent.