solomon gebreyohannis gebrehiwot department of aquatic sciences and assessment, slu, box 7050, 750...

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, Villavägen 16, 752 36 Uppsala

Annmieke GärdenäsDepartment 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

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INTRODUCTIONHydrological change detection

Statistical analysisChange detection – modeling

Pair watershed approachmodel parameter changes in a single watershed

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Study Site – Blue Nile Basin

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KogaGilgel Abbay

Birr

Upper-Didesa

Forest change history

Rf ~ 1500 mm

Rf ~ 2000 mmArea = 260 (Koga) –

1900 km2 (Upper-Didesa

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

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Snow routine parameters:

Model Application - HBV

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Periodic classification

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METHODS - Change detection

Parameter comparisonComparison of the distribution of 50 best parameter setsUsing Wilcoxon signed-rank test

Residual comparisonUsing parameter sets from P1 then simulating rainfall in P2

and P3Then calculating residuals for all 3 periods and comparing

themSimulation comparison

Parameter sets from P1, P2 and P3 simulated for the driest and wettest years, and compare the simulations

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Parameter comparison

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  FC LP BETA K1 K2 MAX

Birr            

P1 1208.2 0.21 1.15 0.22 0.13 1.96

P2 1386.6 0.17 1.10 0.25 0.12 2.41

P3 1604.6 0.28 1.10 0.21 0.12 2.73

Upper-Didesa  P2 773.0 0.31 3.25 0.06 0.08 2.21P3 714.9 0.22 1.54 0.14 0.06 3.04

Gilgel Abbay  P1 195.6 0.86 2.40 0.05 IN 2.24P2 227.0 0.94 1.68 0.08 IN 2.54P3 217.1 0.95 1.80 0.09 IN 1.89

Koga  

P1 1413.2 0.36 1.15 0.14 0.06 2.19

P2 1637.0 0.44 1.22 0.15 0.08 2.17

P3 1670.5 0.50 1.28 0.11 0.05 3.07

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 .

Model residuals comparison

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

Extreme climate simulation comparison

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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

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Residuals are significantly changing from the reference period – Period 1 (1960-1975)

Discussion and conclusion

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Though parameters were said significantly changing, the response of the watersheds to flow remains less/no change

The masking of parameter changes in simulationsScale issueParameter 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

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Swedish International Development Agency (SIDA)

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