Abstract:
Thestudyarea,theAbayachamoBasinisasubbasinoftheEthiopianRiftValleylake s
Basin.ItcomprisestwolakesAbayaandChamo,perennialrivers,andotherephemeral
riversareenteringatChamoandanoverflowfro mchamojoin sSermalerivertojoi n
Segenriver,whichinturnendsupinLakeChew-bahiratborderofEthiopiawith
Kenya.Thestudythu sinvestigate sEvapotranspiration(ET)ofthebasinwhichisamajor
componentofthehydrologiccycle.
Asoneofuniversallyacceptedandwellunderstoodevaporationestimationmethod,it
hasbeenassumedtha tFACPenman-Monteithmethodperformbettertha nother
availablemethod.Thusinthisstudy.Inordertosynchronizeestimatesfro mvarious
evaporationmethodstheconceptofPenmanequivalentestimate(PEE)isintroduced .
Naturally,dueto^thedifferenceinth econceptualizationanditsintende doriginaluse,
differentevaporationmethodsgivedifferentestimates.TheconceptofPEEiscoinedto
reducepartoferrorintroduce dasaresultofusingdifferentevaporationmethodsin
estimationofasingletimeseriesofevaporation.Inthisregard ,estimatesfro mvarious
methodswerestandardizedtopenmanmethodbyintroducin gregressioncoefficientto
eachmethod.Therefore,inthisstudyastandardizedvalueofth ePEEisusedinthe
estimationoftheEvapotranspirationofthebasin.
ThemeanDailyestimatesofEvapotranspirationbyFACPenman-Monteithwas
obtainedas3.7mm/dayatHageremariamto4.5mm/dayatMirabAbaya.Aftermethods
(HargreavesandBlanney-Criddle)havebeenregressedwithpenmanestimate
improvemen testimatearedoneforstations.ForMirabAbaya,Dila,Arbaminchand
Konsotheimprove destimatefo rHargreavesproducesR ^valueof0.98,0.96,0.98and
0.93respectively.Calibrationwithth eFACPenman-Monteithwasdonebyimprovin g
theKhscoefficientoftheHargreavesequation.Similarlycalibrationwithth eFAC
penman-Monteit hwasdonebyimprovin gthePvalueoftheBlaneyandCriddle equation
