Implications of climate change on water storage and filling time of a multipurpose reservoir in India

Reservoirs are measures to maintain balance between regional water supply and demand during surplus as well as water-scarce conditions that are expected to increase because of changing climate especially in subtropical regions. Therefore, inclusion of reservoir demand and storage characteristics in climate change impact analysis on a catchment may help to improve the understanding of changes in future water availability. This study addresses the climate change impact on demand supply characteristics of a reservoir in a subtropical region of India. Calibrated and validated HEC-HMS model, fed with bias corrected eight GCM projections under two RCPs (4.5 and 8.5), is used to simulate climate change effect on three future time (2006-35, 2036-65 and 2066-95) reservoir inflow with respect to baseline period (1976-2005). To avoid uncertainty of individual GCM projections, multi-model ensemble (MME) of streamflow is also estimated. Six out of the eight models projected an increased streamflow whereas two showed possible reduction in future streamflows. MME projected an increased annual streamflow of about 6.7-23.8% under RCP 4.5 and 11.73-20.93% under RCP 8.5 with respect to the baseline period. Also, MME analysis shows possible volumetric shift in streamflow, increasing towards the post-monsoon months. Further, interannual variations of reservoir water availability causing demand and storage time deficits are estimated, respectively, to be a maximum of 53% and 70% while MME does not show any increased deficits in future. Simultaneously, change in reservoir filling period under both the RCPs for MME, varying from -1 to 7 days, gives an insight of shift in streamflow. Overall, future hydrologic projections indicating increased streamflow variability vis-a-vis perplexed demand and supply of reservoir, emphasize the need for revising the reservoir operation policies for sustainable basin management.