Solomon Gebreyohannis GebrehiwotDepartment of Aquatic Sciences and Assessment, SLU, Box 7050, 750 07 Uppsala; Kevin BishopDepartment of Aquatic Sciences and Assessment, SLU, Box 7050, 750 07 Uppsala; and Department of Earth Sciences, Uppsala University, Villavgen 16, 752 36 UppsalaAnnmieke GrdensDepartment of Soil and Environment, SLU, Box 7014, 750 07 Uppsala; Jan SeibertDepartment of Geography, University of Zurich Irchel, Winterthurestrasse 190, CH-8057 Zurich, Switzerland;Per-Erik MellanderResearch Officer, Agricultural Mini-Catchment Programme, Teagasc, Johnstown Castle Environmental Research Centre, Co. Wexford, Ireland*

INTRODUCTIONHydrological change detectionStatistical analysisChange detection modelingPair watershed approachmodel parameter changes in a single watershed

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Study Site Blue Nile Basin*Area = 260 (Koga) 1900 km2 (Upper-Didesa

Subsistence farming, soil erosion and land use change, seasonal water availability*

Snow routine parameters: Model Application - HBV*

Periodic classification*

METHODS - Change detectionParameter comparisonComparison of the distribution of 50 best parameter setsUsing Wilcoxon signed-rank testResidual comparisonUsing parameter sets from P1 then simulating rainfall in P2 and P3Then calculating residuals for all 3 periods and comparing themSimulation comparisonParameter sets from P1, P2 and P3 simulated for the driest and wettest years, and compare the simulations

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Parameter comparison*

*Table. Medians of model parameter values with test results. Groups in a column colored red are significantly different at 0.05 with Wilcoxon signed-rank test, and those do not are non-significantly different, IN shows that the parameters respective to each watershed were insensitive .

FCLPBETAK1K2MAXBirrP11208.20.211.150.220.131.96P21386.60.171.100.250.122.41P31604.60.281.100.210.122.73Upper-DidesaP2773.00.313.250.060.082.21P3714.90.221.540.140.063.04Gilgel AbbayP1195.60.862.400.05IN2.24P2227.00.941.680.08IN2.54P3217.10.951.800.09IN1.89KogaP11413.20.361.150.140.062.19P21637.00.441.220.150.082.17P31670.50.501.280.110.053.07

Model residuals comparison*Annual medians of relative residuals; filled circles showed significant differences and open ones, non significant. + indicates the average medians.

Extreme climate simulation comparison*Simulations for the driest and wettest years of the four watersheds with parameter sets from the three periods.

Discussion and conclusionSpecific parameters are significantly changing*Residuals are significantly changing from the reference period Period 1 (1960-1975)

Discussion and conclusion*Though parameters were said significantly changing, the response of the watersheds to flow remains less/no changeThe masking of parameter changes in simulationsScale issueParameter compensationThe impacts of parameter changes might be seen at smaller scaleWe recommend analysis of relation of model parameters to specific watershed characteristics in the future

*Swedish International Development Agency (SIDA)

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