Assessing climate change effects on streamflow and paddy production in the Bharathapuzha Basin Kerala

In humid tropical regions, where paddy production is heavily reliant on monsoon rainfall and regulated streamflow, climate variability remains a major threat to agricultural sustainability. Using projections from three CMIP6 climate models under two shared socioeconomic pathways and the Soil and Water Assessment Tool (SWAT), this study examines how climate variations may affect hydrological processes and paddy yield in the Bharathapuzha River watershed in Kerala, India. The SWAT model was calibrated and validated against observed streamflow and district-level yield statistics, achieving NSE = 0.74 (monthly) for streamflow and NSE = 0.80 (RSR = 0.45) for Palakkad and NSE = 0.68 (RSR = 0.57) for Alathur for paddy yield. .Results indicate significant increases in rainfall variability and temperature across the CMIP6 models, leading to altered streamflow regimes characterized by intensified flood peaks and heightened dry-season stress. Projected paddy yields show consistent declines, ranging from 23 to 33% by 2035 to as much as 68-74% by 2100 under SSP5-8.5. The Alathur block exhibits greater near-term sensitivity, while the Palakkad block faces stronger late-century declines. These results highlight the vulnerability of Kerala's paddy cultivation systems to changing climatic conditions and underscore the importance of adaptive measures-including climate-resilient crop varieties, optimized planting schedules, and improved irrigation management-to ensure long-term regional food security.