Rainfall Variability, Extremes, and Drought Risk in Kerala (1951–2020): Trends, Anomalies, and Policy Implications

This study examines long-term rainfall variability, extremes, and drought risks across 14 districts of Kerala, India (1951–2020) using a suite of climatological and statistical approaches. Monthly rainfall data were analyzed to construct district and state-level climatology curves, revealing the characteristic double monsoon regime with a dominant Southwest Monsoon (June–September) and a secondary Northeast Monsoon (October–December) peak. Annual and decadal trends were assessed using linear regression (mm/decade) and anomaly analysis (baseline 1951–1980). Results indicate a statistically significant decline in Wayanad (–163 mm/decade, p < 0.001) and consistent downward trajectories in Thrissur and Trivandrum, while Idukki and Ernakulam exhibit marginal, nonsignificant increases. Kerala-wide anomalies reveal a transition toward frequent rainfall deficits since the 1980s, accompanied by increased interannual variability in recent decades. Extreme rainfall analysis employed 95th percentile thresholds and Weibull return-period estimation, revealing a reduction in extreme months after 2000, although rare high-magnitude events continue to have a significant impact (e.g., the 2018 flood). Drought risk, quantified using the Standardized Precipitation Index (SPI-12), highlights southern and midland districts (Trivandrum, Thrissur, Kottayam, Ernakulam) as particularly vulnerable. A composite risk index integrating extremes and droughts identifies Idukki, Malappuram, Ernakulam, Thrissur, and Palakkad as the most climate-sensitive districts. The study demonstrates that Kerala faces dual water risks, structural drying in several districts, and persistent exposure to episodic flood extremes. Embedding rainfall-based drought and extreme weather indices into climate adaptation policy is crucial for strengthening water security, agricultural resilience, and disaster preparedness in Kerala.