HYDROLOGICAL DROUGHT ANALYSIS UNDER CLIMATE CHANGE SCENARIO FOR UPPER BLUE NILE BASIN, ETHIOPIA (A CASE STUDY OF KESSIE SUB-BASIN)

Abstract

This paper revises the hydrological drought under future climate change scenarios. The most part of the Kessie sub-basin is exposed to a drought; shared sources of water such as reservoirs, rivers and groundwater for wells are in danger of running dry. An analysis of drought in Kessie sub basin based on daily data from 1983-2012, in 11 stations over the study area were obtainable using SWAT model. These changes of the climate variables were applied to SWAT hydrological model to simulate future water availability. General Circulation Models (GCMs) which are considered as the most important tools for estimating future climate change scenarios operate on coarse resolutions. Climate change scenarios of precipitation and temperature were developed at Bahir Dar, Debre Markos and Motta stations of the Basin for three periods namely; 2011-2040, 2041-2070 and 2071-2099 and their respective changes were determined as deltas (for temperature) and as percentages (for precipitation) from the base period values. The outputs of HadCM3 coupled atmosphere-ocean GCM model for the A2 and B2 SRES emission scenarios were used to produce the future scenarios. The study found that there is an overall increasing trend in annual temperature and significant variation of monthly and seasonal precipitation from the base period level. SWAT was calibrated with fifteen years of data (1985-1999) to assess the possible impact of climate change in the Basin. Stream flow model efficiency by regression coefficient and Nash-Sutcliffe was 0.713 and 0.664 for calibration and 0.83 and 0.62 in validation respectively. The future climate variables as an output from the GCM model and downscaled by the SDSM model and directly as an input to the SWAT model. As a result of the average total annual flow at the outlet of the study area might decrease up 11.13% and 10.24% for both A2a and B2a scenario respectively at 2013-2040 period, 14.43% and 23.46% for both A2a and B2a scenario respectively at 2041-2070 and 27.15% and 22.11% for both A2a and B2a scenario respectively at 2071-2099.The decrease in the future flow of 2013-2040 periods might be unsatisfactory in some months to meet future demands for the water of the ever growing population within and around the basin. The future possible volume of deficiency or hydrological drought appears below the Q 70 line, it indicates the hydrological drought. According to the output, in this study area the hydrological drought was observed 313 months within 1044 months for both A2a and B2a scenarios.