Assessing Impact of Climate Change on Streamflow of Koyna River, India

The Koyna River basin, situated in the ecologically sensitive and biodiverse Western Ghats of India, exhibits heightened vulnerability to the dual pressures of climate variability and land use/land cover (LULC) changes. In this study, the hydrological dynamics of the basin were modeled using the advanced ArcSWAT tool, which is well-suited for simulating the influence of climatic and land use changes on streamflow. The analysis incorporated historical LULC data from 1996 and 2016 and climate change scenarios represented by RCP4.5 and RCP8.5 pathways. The model was meticulously calibrated and validated using observed hydrological data spanning 1978 to 2016. Performance metrics such as the coefficient of determination (R²), Nash-Sutcliffe Efficiency (NSE), and percent bias (PBIAS) indicated robust model with high reliability and accuracy. Future climate projections were developed using six Regional Climate Models (RCMs) which were refined through bias correction with the CMhyd tool to minimize discrepancies between simulated and observed climatic variables. The analysis integrates historical data from 1978 to 2016 and future projections derived from the CNRM-CM5 climate model under RCP4.5 and RCP8.5 scenarios for three timeframes: early (2025–2050), mid (2051–2075), and end century (2076–2100). Key parameters, including rainfall, temperature, and hydrological responses, were used to simulate streamflow variations and assess the basin's hydrological sensitivity to changing climatic conditions. Results reveal significant increases in streamflow under both RCP scenarios, with RCP8.5 indicating the most pronounced impacts by the end of the century. Monsoonal months (June–September) dominate streamflow contributions, with projections of heightened peak flows and prolonged discharge during these periods. Streamflow during the monsoon season is expected to nearly double under RCP8.5, increasing the risk of flooding. Monsoon rainfall, a pivotal driver of the basin's hydrology, accounts for over 85% of the annual runoff, with future projections pointing to intensified monsoonal discharges and an increase in extreme weather events. Conversely, drier months show marginal increases, signalling potential changes in seasonal water availability. The study also highlights the synergistic effect of land use and land cover (LULC) changes on hydrology. Analysis of LULC datasets from 1996 and 2016 indicates increased streamflow driven by urban expansion and reduced vegetation. These shifts amplify runoff, particularly under future precipitation increases. This evolving hydrological regime highlights the urgency for adaptive management strategies tailored to the region’s unique climatic and ecological context. Sustainable land use planning and proactive water resource management are essential to mitigate the risks associated with these changes. The insights from this research are vital for stakeholders, including policymakers, agronomists, and water resource managers, enabling them to formulate evidence-based strategies for climate adaptation and mitigation.