Shifting Rainfall Patterns and Associated Hydroclimatic Risk Across the Northwestern Himalayas: A Multi-Decadal Perspective

Abstract Precipitation patterns in the northwestern Himalayas have shifted markedly over the past four decades. Using MERRA-2/GEOS reanalysis data (1983–2022) coupled with non-parametric trend analysis, Sen’s slope estimates, and Intensity–Duration–Frequency (IDF) modeling, we document a significant increase in annual and monsoonal rainfall across southern and mid-altitude belts, alongside persistently low but increasingly variable precipitation in high-altitude cold deserts such as Ladakh. The Seasonality Index (0.46–1.26) indicates growing temporal clustering of rainfall, heightening flood and drought exposure. IDF-curves reveal the most severe short-duration extremes in orographically enhanced monsoon catchments, highlighting heightened flash-flood risk, while arid zones face sporadic but impactful extremes. Although reanalysis products can underestimate localized extremes in steep terrain, especially cloudburst-like events, the four-decade consistency of MERRA-2 provides robust regional-scale diagnostics of changing rainfall variability. These findings support region-specific adaptation strategies, including resilient infrastructure design and early-warning systems, for these ecologically sensitive mountain landscapes.