QUANTIFYING SURFACE WATER AVAILABILITY AND DEMAND ANALYSIS IN THE POORLY GAUGED CATCHMENTS OF JEMMA SUB-BASIN, ABBAY/UPPER BLUE NILE BASIN, ETHIOPIA

Abstract

The socioeconomic activities and environmental changes with respect to the spatiotemporal variation of streamflow in the catchment intricates the supply and demand management system. Assessment of the surface water potential and demand analysis at a sub-basin level was aimed at estimating escalating demands of the catchments and meeting the society's needs without causing potential negative consequences on the ecological balance of the catchments. To quantify the surface water availability of the catchments, the soil and water assessment tool (SWAT) model was used after the sensitive analysis, calibration, and validation of the model was done by SWAT-CUP. The annual total demands was anlysed in water evaluation and palanning (WEAP) model after the surface water potenial was quantified. Different‘’what if” scenario was developed to forecast future water demand, supply requirement, and unmet demands in 2022-2035. The model showed the mean annual flow depth in Beressa and Robigumer catchments was 174.4mm and 166.91mm, respectively and contirbutes to 37MCM and 149.05MCM surface water potential, respectively. From the mean annual precipitation recieved in the Beressa and Robigumer catchments, 48% and 43% was lost through evapotransipiration, respectively. The model performace showed satisfactory result with a value of 0.89(R2 ), 0.87(NS), and 0.76(R2 ), 0.74(NS) in calibration, and 0.71(R2 ), 0.70(NS), and 0.72(R2 ), 0.66(NS) in validation in the Beressa and Robigumer catchments, respectively. The CROPWAT 8.0 model was used to determine the irrigation water requirement of selected crops. The total consumptive water demand in 2022 was 11MCM(29.7%) and 8.1MCM(5.4%) of the total surface water potential of the Beressa and Robigumer catchments, respectively. The total water demand in projected irrigation area scenario was 125.64MCM(84.05%) of the surface water potential of the Robigumer catchment in the year 2035. The EFR was significant parameter to maintain the ecological balance of catchments. In the two last scenarios the total water demand were beyond the surface water potential of the Beressa catchment. To mitigate the future water stress and scarcity in the catcments, dopting rainwater harvesting, other potential sources, and integrated water resources management options are importannt