Emergence of strong trends in humid heat intensity and duration in recent decades over South Asia

Abstract South Asia experiences the hottest temperatures in the pre-monsoon season, followed by intense humid heat during the early summer monsoon. We examine trends and drivers of humid heat extremes in both seasons. We find that since early 2000s, monsoon season humid heat extremes have warmed twice as fast as the long-term rate since the 1950s, with their duration increasing from ∼2 days in the 1950s to several weeks in present-day climate. This intensification in parts of South Asia is driven by peak humidity occurring ∼2 weeks earlier since 2000, coinciding with higher temperatures. Pre-monsoon humid heat extremes have increased across most areas, except Western South Asia, where they have declined since 2000. Declining humidity levels drive pre-monsoon trends, while elevated humidity during precipitation events that precede humid-heat events explain their monsoon season intensification. Our findings call for targeted responses to escalating humid heat that threatens health, productivity, and the economy.