Validation of SWAT simulated streamflow in the Eastern Nile and sensitivity to climate change

Abstract

Abstract. The hydrological model SWAT was calibrated with daily station based precipitation and temperature data for the whole Eastern Nile basin including the three subbasins: the Blue Nile, Baro Akobo and Tekeze. The daily and monthly streamflow was calibrated and validated at six outlets in the three different subbasins. The model performed very well in simulating the monthly variability of the Eastern Nile streamflow while comparison to daily data revealed a more diverse performance for the extreme events. Of the Eastern Nile average annual rainfall it was estimated that around 60% is lost through evaporation and estimated runoff coefficients were 0.24, 0.30 and 0.18 for Blue Nile, Baro Akobo and Tekeze subbasins, respectively. About half to two-thirds of the runoff could be attributed to surface runoff while the remaining contributions were from groundwater. The annual streamflow sensitivity to changes in precipitation and temperature differed among the basins and the dependence of the response on the strength of the changes was not linear. On average the annual streamflow responses to a change in precipitation with no temperature change was 19%, 17%, and 26% per 10% change in precipitation while the average annual streamflow responses to a change in temperature and no precipitation change was −4.4% K−1, −6.4% K−1, and −1.3% K−1 for Blue Nile, Baro Akobo and Tekeze river basin, respectively. While we show the Eastern Nile to be very sensitive to precipitation changes, using 47 temperature and precipitation scenarios from 19 AOGCMs participating in IPCC AR4 we estimated the future change in streamflow to be strongly dependent on the choice of climate model as the climate models disagree on both the strength and the direction of future precipitation changes. Thus, no clear conclusions can be made about the future changes in Eastern Nile streamflow.