On emerging circulation patterns driving the continued rise in heavy rains across western India

Abstract Over the past half-century, evolving Indian summer monsoon environment has led to an east–west asymmetric rainfall trend over the subcontinent. This emerging asymmetry is shaped by a marked rise in heavy rainfall events across western India. However, the mechanisms underlying this prominent signal of the changing regional hydroclimate are not well understood. Using self-organizing maps, this study identifies two dominant atmospheric circulation patterns linked to a significant increase in the frequency of these extreme events over western India during 1970–2022. The first pattern is marked by a large-scale mid-level cyclonic vortex spanning the subcontinent and strong easterly anomalies over the equatorial Indian Ocean (EIO). The pattern results from extensive synoptic low-pressure activity across central monsoon zone of India, reinforced by zonal sea surface temperature gradient at the EIO and associated dynamic forcing. In contrast, the other pattern is manifested as a localized cyclonic vortex centered over western India, featured by an isolated synoptic low-pressure system. Moisture recycling from antecedent wet soil in Northwest India catalyzes this local pattern during periods of subdued remote forcing. Our analyses link the rising frequency of heavy rains over western India to the combined effects of zonally differential warming across the EIO and progressive soil moistening in semi-arid northwest India. Examining the complex interactions among extreme weather patterns, large-scale oceanic forcings, and local land–atmosphere coupling, this study highlights the need for an improved understanding of multi-scale interactions that reshape monsoon hydrological extremes in a changing climate.