Heightened Adaptability Challenges from Extreme Humid Heat Stress for South Asia

While the explosive increase in extreme humid heat stress exposure from 2000’s over South Asian monsoon region is challenging human adaptability leading to productivity and mortality loss, factors responsible remain poorly constrained. Here, we unravel that the disruptive regional climate change of decadal-mean maximum Humidex exceeding 45°C to be the primary cause. Over Northeast India, it results in the exposure of extreme heat-stress during the monsoon season rising fourfold to 80 days or 800 ± 278 hours and makes the longest annual extreme moist heat-spell duration increase threefold to 30 days in the 2020’s. The adaptation crisis arises from the average length of spells doubling to 10 days while the average gap between spells decreasing to 3 days. Our findings of changes in characteristics of moist heat spells holds for a large fraction of South Asia, and highlight the urgent need for data on impact of long-spells of continued exposure on human physiology for appropriate advisories and policy interventions.