HYDROLOGICAL IMPACT OF CLIMATE CHANGE ON KOGA RESERVOIR OPERATION

Abstract

Nowadays the sign of climate change and its impact is revealing on different natural and man-made systems, in one or other ways. This impact is significant on water resource systems. Therefore impact of climate change on different sectors need to be evaluated in order to understand the extent of the impact and to propose possible adaptation measures to reduce the expected future consequences. This study mainly deals with hydrological impact of climate change impact on Koga reservoir operation which is found in Upper Blue Nile Basin, using the reliability, resilience and vulnerability indices. The hydrological models, HBV were utilized to simulate the water balance inflow of the reservoir. The model result shows good performance with R 2 =0.853 and NSE=0.744. The projected future climate variables has two future time series (2031-2040 and 2091-2100), in which the annual percentage change of PET with respect to the base period (1991-2000) ranges between +4.68% and +10.30%. The annual precipitation shows reductions which range between 1.69 to 5.93% with in the two time series and annual runoff shows a 14.04% reduction in the first time series and 9.75% on the second time series. Two seasons (FMAM and JJAS) shows high reduction of runoff in both future time series (-16.52% to -26.76%) and (-13.84% to-25.51%) respectively. The reservoir simulation model,HEC-ResSim was used for release and rule curve development and in general it is observed that no significant changes on release and rule curve for future condition. From reservoirs operational performance indices on average it was generally observed that the reliability index (time based and volumetric basis) in the Koga reservoirs for all climate scenarios reveals above 80%, hence the reservoir has high capability to meet the required target demand in the next century. The resilience of the reservoir on average has an index of less than 50% for all climate scenarios as result the reservoir will not able to recover rapidly from failure to safe state. The vulnerability of the reservoir has an index of less than 50% for all climate scenarios hence the reservoir has no shortage of flow to meet the demand in the next century. Finally from results of performance indices the Koga reservoir has very good potential to irrigate the required area under future climatic condition.