Evaluation of basin level climate change impacts on streamflow and reservoir operations -

Abstract

Global climate change is known to trigger local and regional hydrologic variations like changes in precipitation patterns, surface temperatures and streamflows. Apt and efficient water management is extremely important as climate change can considerably affect the water supply-demand balance. Focusing on reservoirs and their management, it is very important to study climate change impacts on streamflow input and reservoir operations with a proper analysis. Targeting on that, this study was conducted as a case study on the Deduru Oya reservoir, Sri Lanka. The impacts of climate change on the Deduru Oya basin were reviewed and two main parameters of climate indices, rainfall and temperature were identified using the findings from the previous literature. The prediction of the future streamflow data was carried out using a rainfall-runoff based hydrological model developed in Hydrologic Engineering Centre’s Hydrologic Modeling System, version 4.3 (HEC-HMS) software, with the aid of the identified climatic parameters. Furthermore, prediction of the reservoir operation data was accomplished using a water balance based hydrological model developed in Hydrologic Engineering Centre’s Reservoir System Simulation, version 3.1 (HEC-ResSim) software, with further emphasis on reservoir hydrology and adaptation methods. It has been observed that there is an increase in the total annual rainfall by 21% - 24% for the 20s (2011-2040) and 42% - 75% for the 50s (2041-2070) while the average annual temperature indicates 0.08% - 0.14% increase for the 20s and 0.28% - 0.43% increase for the 50s under IPCC emission scenarios A2 and B2. Annual streamflow has shown a 62% -77% increase for the 20s and it has increased further in the 50s while the reservoir releases also indicate increased amounts on an annual basis. On a monthly basis, the rainfall, streamflow and reservoir releases in wetter months will get increased further, but in drier months those amounts will get reduced slightly. Because of the increased release rates from the reservoir, it is needed to exert more attention to the increased downstream basin vulnerability to floods. While increased release rates add pressure to reassure the safety of existing structures, the ability to produce energy, cope with the agricultural and drinking water demand and maintain the ecological flow can be ensured by better water management practices in the future.