Abstract:
Droughtsi nEthiopiacauseagreathumansufferingsandlosso flife .Suchconsequencesnotonly
resultfrominsufficienttota lrainfallamountbutalsofiomlon gdryspellswithi ntherain y
season.Henceassessingthevariabilityo fextremerainfal leventsi noverthebasiniscrucial.The
aimo fthispaperisevaluatingthevariabilityo frainfal landtrendso fextremerainfal levents
overBlueNilebasin.Thevariabilityo frainfal lislessi nthemainrainyseasona scomparedto
thesmallrainyseason.Andi ntheKiremtseasonalmostal lthestationshavecoefficientso f
variationlessthan20%.Trendsi nheavyrainfall ,totalrainfall,thenumbero fdrydays,
maximum5daysconsecutiverainfalltotalsandsimpledailyintensityindex(SDII )havebeen
analysedusingdailyrainfal lrecordsat26stations.BelgandKiremtseasonswereconsidered
separatelyfortheperiodo f1980-2002.Heavyrainfal lisdistincta stheOO" 'percentileo fdaily
rainfalli nthetw oseasons.Themagnitudeo ftrendswasdeterminedfiomYueetal2002andthe
statisticalsignificaqjceweredeterminedbyMann-Kendaltest.Increasingtrendsi nheavyrainfal l
andtotalrainfallhaveoccurredduringtheKiremtseason,butonly10-20%o fthestationshave
statisticallysignificanttrends.Morenumbero fstationsshowssignificantincreasei ntrendso f
heavyprecipitationii nBelgseasonthani ntheKiremtseason.Thegreatestsignificanti nheavy
rainfallfrequencyhasoccurredi nthesoutheastandwesternparto ftheBlueNileBasin.
Trendso fwetanddrydecadewereanalysedoverthebasin.Theresultshowsnearly75%o fthe
driestyearsarefiom1981-1990whichagreeswiththedriestyearsthatoccurredoverthecountry
lik e1984and1987.Thefrequencyo fthewettestyearsdecreasesfiom42%during1970-1980
and1981-1990to17%during1991-2002.
