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

Abstract South Asia’s climate features the hottest temperatures in the pre-monsoon season followed by intense humid heat after the onset of the summer monsoons. Here, we examine trends and drivers of humid heat extremes during the monsoon and pre-monsoon season Since the early 2000s, humid heat extremes in the monsoon season have warmed two times faster than the rate observed since the 1950s. In addition, the average duration of monsoon season humid heat extremes has increased from ~2 days in the 1950s to several weeks in the recent decades across South Asia, a region with high population density. The intensification of humid heat extremes is driven in part by peak humidity in the monsoon season occurring nearly two weeks earlier since 2000 compared to the mid-20th century baseline. and coinciding with higher temperatures. Humid heat extremes during the pre-monsoon season are also increasing across most of the region. The exception is Western South Asia, the hottest and driest region, that experienced remarkably strong cooling trends during the pre-monsoon since the 2000s. We find that rising precipitation-induced humidity levels explain the intensifying trends in humid heat extremes in the monsoon season, while declining humidity levels drive the decreasing trends in the pre-monsoon season. Our findings emphasize the need for policies and adaptations and mitigation measures to align with the substantial escalation in humid heat intensity and duration that threatens public health, labor productivity, and the economy.