Diurnal Pattern of Heat Stress Over South Asia: A Wet Bulb Globe Temperature‐Based Analysis From 1984 to 2023

ABSTRACT Assessing the diurnal characteristics of heat stress is crucial for understanding its daily dynamics and impacts. This study evaluates various diurnal characteristics of heat stress using the Wet Bulb Globe Temperature (WBGT) over South Asia from 1984 to 2023. The Copernicus Climate Change Service hourly ERA5 dataset was used to calculate the WBGT using the Liljegren method to assess the hourly and daily heat stress, heatwave events, duration and diurnal range for different WBGT thresholds. The results revealed significant disparities in heat stress in different South Asian regions. The western and southeastern regions are more susceptible to extreme WBGT (≥ 32.2°C), while severe WBGT (≥ 31.1°C and < 32.2°C) predominantly affected central and eastern Pakistan and southern India. The western part of South Asia experiences an average of 5.8 heatwave events, with a cumulative total of 580 h. The diurnal range indicated a WBGT range of more than 8°C in western and southeastern regions. Conversely, the areas with no heat stress are predominantly located in the Himalayas and northern Afghanistan. The average annual extreme WBGT hours in western South Asia increased by 120 h between the early (1984–2003) and late (2004–2023) periods, while the extreme WBGT days increased by 15 days. Other characteristics of WBGT also increased in the recent decades compared to 1984–2003, suggesting the implementation of measures to mitigate future WBGT increases. These findings highlight the urgent need for adaptive strategies to address escalating heat stress in the region, especially in vulnerable and highly populated areas of South Asia.