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Detection of hydrological changes in Blue Nile Basin, Ethiopia: a modeling approach

Detection of hydrological changes in Blue Nile Basin, Ethiopia: a modeling approach. Solomon Gebreyohannis Gebrehiwot Department of Aquatic Sciences and Assessment, SLU, Box 7050, 750 07 Uppsala; Kevin Bishop

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Detection of hydrological changes in Blue Nile Basin, Ethiopia: a modeling approach

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  1. Detection of hydrological changes in Blue Nile Basin, Ethiopia: a modeling approach Solomon Gebreyohannis Gebrehiwot Department of Aquatic Sciences and Assessment, SLU, Box 7050, 750 07 Uppsala; Kevin Bishop Department of Aquatic Sciences and Assessment, SLU, Box 7050, 750 07 Uppsala; and Department of Earth Sciences, Uppsala University, Villavägen 16, 752 36  Uppsala Annmieke Gärdenäs Department of Soil and Environment, SLU, Box 7014, 750 07 Uppsala; Jan Seibert Department of Geography, University of Zurich – Irchel, Winterthurestrasse 190, CH-8057 Zurich, Switzerland; Per-Erik Mellander Research Officer, Agricultural Mini-Catchment Programme, Teagasc, Johnstown Castle Environmental Research Centre, Co. Wexford, Ireland

  2. INTRODUCTION • Hydrological change detection • Statistical analysis • Change detection – modeling • Pair watershed approach • model parameter changes in a single watershed

  3. Study Site – Blue Nile Basin Forest change history Koga Gilgel Abbay Rf ~ 1500 mm Birr Upper-Didesa Rf ~ 2000 mm Area = 260 (Koga) – 1900 km2 (Upper-Didesa

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

  5. Model Application - HBV Snow routine parameters:

  6. Periodic classification

  7. METHODS - Change detection • Parameter comparison • Comparison of the distribution of 50 best parameter sets • Using Wilcoxon signed-rank test • Residual comparison • Using parameter sets from P1 then simulating rainfall in P2 and P3 • Then calculating residuals for all 3 periods and comparing them • Simulation comparison • Parameter sets from P1, P2 and P3 simulated for the driest and wettest years, and compare the simulations

  8. RESULTS Parameter comparison

  9. Table. Medians of model parameter values with test results. Groups in a column colored red are significantly different at ρ 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 .

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

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

  12. Discussion and conclusion • Specific parameters are significantly changing • Residuals are significantly changing from the reference period – Period 1 (1960-1975)

  13. Discussion and conclusion • Though parameters were said significantly changing, the response of the watersheds to flow remains less/no change • The masking of parameter changes in simulations • Scale issue • Parameter compensation • The impacts of parameter changes might be seen at smaller scale • We recommend analysis of relation of model parameters to specific watershed characteristics in the future

  14. Acknowledgment! Swedish International Development Agency (SIDA)

  15. Thank You!

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