Multi-scenario assessment of climate change impacts on water resources (runoff and recharge) in the periyar river basin and their implications for sustainable water management

Understanding the impacts of climate change on hydrological processes is essential for sustainable water resource management, particularly in monsoon-dominated river basins. This study presents a multi-scenario assessment of future runoff and groundwater recharge in the Periyar River Basin under four Shared Socioeconomic Pathway (SSP) scenarios derived from CMIP6 climate projections. The ABCD hydrological model was employed to simulate basin-scale runoff using projected rainfall and potential evapotranspiration (PET). The interrelationship between rainfall and runoff was examined using wavelet coherence analysis and transfer entropy (TE) to capture both temporal scale dependence and directional information flow. Groundwater recharge was estimated using a water balance approach under each SSP scenario. Results indicated that SSP5–8.5 exhibits the highest projected runoff and groundwater recharge, primarily due to comparatively higher rainfall and PET. Wavelet coherence analysis revealed strong positive coherence between rainfall and runoff with particularly pronounced information transfer from rainfall to runoff under SSP5–8.5, especially during the monsoon month of June. Projected groundwater recharge under SSP5–8.5 was estimated at 0.1858 mm month⁻¹, representing a 76% increase compared to SSP1–2.6 (0.0024 mm month⁻¹). Furthermore, a Nash equilibrium-based optimisation framework grounded in game theory identified SSP1–2.6 as the most sustainable pathway from a water management perspective. Overall, the findings highlighted increased variability in hydrological processes under high-emission scenarios and underscored the critical importance of mitigation strategies to ensure long-term water sustainability in the Periyar River Basin.