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Enyew BD, Van Lanen HAJ and Van Loon AF
Droughts are common natural phenomenon in Ethiopia which has been affecting food insecurity and imposing other complex problems. Severe droughts happened once every 10 years in the north and north east Ethiopia, now becoming more frequent and covering areas that never experience drought before, in the southern parts of the country. According to IPCC droughts will become more intense, frequent and severe in the future due to the impact of climate change. This thesis presents the assessment of projected impact of climate change on hydrological drought in the Lake Tana basin in Ethiopia, which is the headwater for the Blue Nile River. The rainfall-runoff HBV model was calibrated and validated against historical data to obtain a reference situation to the possible impact of climate change on hydrological drought in four sub-basins and the Lake Tana basin. Datasets obtained from the EU- ATCH project for three General Circulation Models (CNCM3, IPSL and ECHAM) were used as an input to the HBV model, which was recalibrated for the same historic period to obtain an assessment to what local downscaled, bias-corrected GCM can be used as a forcing data for hydrological drought assessment. Next the GCM outputs with the recalibrated HBV model were used to simulate future streamflow for two future time windows (2021-2050 and 2071-2100) and for one future emission scenario A2. The variable threshold level method combined with a 10-day moving average streamflow was used to detect hydrological drought characteristics.