RESERVOIR PERFORMANCE UNDER CLIMATE CHANGE ON MEGECH WATERSHED

Abstract

Now a days the sign of climate change and its impact is revealing on different natural and man-made systems, in one or other ways. Accordingly, this impact is significant on the water resource system. This study mainly deals with assessment of the reservoir performance under climate change impact on the Megech reservoir which is found in Lake Tana Sub-Basin, using the reliability, resilience and vulnerability indices. To evaluate the impact of climate change, climate change scenario of evapotranspiration and precipitation were developed for three period (base, short term and long term) using output of CMIP5 with RCP for RCP4.5 emission scenarios and they are used to develop the future climate change scenario. A hydrological model, HBV, was used in order to simulate the current and future inflow volume to the reservoirs. The performances of the model were assessed through calibration and validation process and the result shows NSE 0.72 during calibration and 0.69 during validation at the gauge station. The projected future climate variable shows an increasing trend .Tmax 0.23 o c and 2.73 o cin short and long term respectively and Tmin 1.68 o c and 2.13 o c in short and long term respectively and but precipitation also shows decreasing by 0.84% and 1.2% in short and long term respectively. Relative to the current condition, the average annual open water evaporation for Megech reservoir will increase by 1.01% and 1.03% in short and long term respectively. Relative to the current condition, the simulated future period average annual inflow volume shows a decrease of 1.15% and 1.58 % in the period of 2021 -2030 and 2061-2070 respectively from the base period. On average, the time based reliability of Megech reservoir shows a value of above 90 %. However, the resilience shows value less than 50% in the two periods. This shows that, the reservoir needs long time to recover itself from failing to meet the demand. The dimensionless vulnerability, below 50% in all period. This Shows that the Reservoir have no shortage of Flow to meet the Demand in all periods. A reservoir simulation model, MODSIM, was used to simulate the amount of release potential of the reservoirs and to determine the reservoirs operation rule curve. The future period average annual Release will decrease by 1.2% and 1.19% for both short and long term in comparison to the base period.