Quantifying shifts in extreme rainfall events in Uttarakhand, India, using GEV distribution modeling and CORDEX RCM projections under RCP scenarios

Extreme precipitation in the Himalayan region has intensified under recent warming, yet long-term distributional shifts and future changes in multi-day rainfall extremes in Uttarakhand, India, remain insufficiently quantified. This study assesses historical trends (1901-2023) and future projections using India Meteorological Department (IMD) gridded rainfall data, CORDEX South Asia regional climate simulations, Expert Team on Climate Change Detection and Indices (ETCCDI)-based precipitation indices, and generalized extreme value (GEV) modeling. Results reveal spatial heterogeneity. Intensification of extremes is evident across northern and south-eastern districts, where maximum 5 and 1 d precipitation amounts (RX5day and RX1day) increased by approximately 4-10 mm decade -1 and 2-6 mm decade -1 , respectively, accompanied by increasing values of R95p and R99p (indices of very wet and extremely wet days). In contrast, south-western districts and parts of northwest Uttarakhand show weaker or declining trends with increasing dry spells. GEV analysis of RX5day across successive 30 yr periods shows rightward shifts in probability density peaks, indicating increasing rainfall intensity, particularly in high-elevation regions. Enhanced variability, clustering of high-magnitude events, and upper-tail amplification suggest a likelihood of rare extremes. Return-level estimates highlight spatial contrasts, with 100 yr RX5day return levels ranging from ~524 mm in the south to ~342 mm in the north. Future projections show scenario dependence: under RCP4.5, extremes partially stabilize, whereas under RCP8.5, intensification persists with rightward shifts, increased variability, and greater rainfall magnitudes by the end of this century. These findings emphasize the need for climate-informed risk assessments in planning, infrastructure design, and disaster preparedness.