Hydrological Response and Reservoir Operation Strategy under Climate Change - A Case Study of Simly Dam

Abstract

Climate change is reality now and fresh water resources are under threats in this context. The assessment of impacts of climatic variabilities on available water resources is necessary to identify adaptation strategies. Simly dam a key source of drinking water for Islamabad city is likely to be affected by such type of changes. In this study ERDAS IMAGINE and HEC-HMS were employed for land use classification and hydrological assessment of the catchment, respectively. Climate change projected precipitation data, derived under the medium and high emission scenarios namely RCP4.5 and RCP8.5, respectively, was extracted for Simly dam catchment from dataset developed by Himalayan Adaptation Water and Resilience (HI-AWARE) for Indus, Ganges and Brahmaputra (IGB) River basins. Bias correction of projected data was performed using delta technique and corrected daily precipitation data wa used as input of HEC-HMS model to evaluate potential impacts of climate change on storage of water at Simly reservoir. For ease of understanding, analyses were carried out for three future time windows named as 2025s (2010-2040), 2055s (2041-2070) and 2085s (2071-2100). Frequency analysis was carried out to predict change in frequency of precipitation events. Initially three probability distributions Normal, Log-Normal and Gumbel distributions were considered, and finally best fit distribution was selected based on Chi-squared (X2) and probability plotting test. HEC-HMS model was used to assess hydrological response of the catchment and sustainability of the reservoir to withstand against rainfall events of different return periods under present and future climate change conditions. Reservoir simulations were performed using HEC-ResSIM model, to address potential impacts of climate change on existing operational strategy of Simly reservoir. For this purpose, HEC-HMS generated inflows for above mentioned climate change scenarios were used as input of HEC-ResSIM model. Performance of the system was evaluated in terms of reliability, resilience, vulnerability and water use efficiency. Modification in current operational rule curves was applied and reservoir levels were simulated against projected inflows into Simly reservoir. It is anticipated that system performance would enhance under changing climate by adopting proposed changes in current operational rules curves.