Historical and future extremes of cauvery basin analysed using cmip6 models and ETCCDI indices.

Climate change has intensified temperature extremes and altered precipitation patterns, impacting water resources, agriculture, and ecosystems. The Cauvery Basin, a crucial water source for southern India, is highly vulnerable to these changes. This study validates and ranks 13 CMIP6 models against IMD gridded observations using Multi-Criteria Decision-Making (MCDM) techniques for projecting extreme events in the Cauvery region. INM-CM5-0 for Precipitation, INM-CM4-8 for Tmax, and ACCESS-CM2 for Tmin emerged as top performers for projections. ETCCDI analysis revealed significant variations in temperature and precipitation extremes. Historical trends (1951-2023) indicate moderate but statistically significant increases in key temperature extremes, with TXx ranging from mid-30s for TXx and mid-teens for TNn, though recent decades witnessed increases in SU35 and TN90p. Temperature-related projections suggest TXx will rise by 1.5-2.0 °C under SSP245 and exceed 3.5 °C under SSP585 by 2076-2100, with SU35 projected to surpass 90 days annually under SSP585, alongside increases in TX90p and decreases in DTR, indicating intensified heat stress. Precipitation trends showed high interannual variability, with PRCPTOT between about 770-1230 mm and RX5day historically around 200 mm. Future precipitation-related projections indicate RX5day could exceed 300 mm, R95p may approach 450 mm, and SDII could rise to 16 mm/day, while CDD is expected to remain above 70 days, pointing to alternating flood and drought risks. These findings highlight the urgent need for targeted adaptation strategies that integrate climate-smart agriculture and adaptive water management, ensuring resilience of agriculture, water resources, and ecosystems in the Cauvery Basin.