A recent study has revealed that the hot and humid conditions characteristic of India's monsoon season could prolong the duration of uncompensable heat stress typically associated with summer, especially under a global warming scenario of 2 degrees Celsius. The findings, published in the journal American Geophysical Union (AGU) Advances, emphasize a significant surge of uncompensable heat stress (UHS) during the monsoon months from July to October as the climate continues to warm.
Understanding Uncompensable Heat Stress
Uncompensable heat stress occurs when the human body is unable to cool itself through sweating or other mechanisms due to extreme heat and humidity. This sustained accumulation of heat can lead to severe health consequences, including heat-related illnesses, organ failure, and even death. Researchers from the Indian Institute of Technology (IIT) Gandhinagar, along with scientists from Stanford and Purdue universities in the United States, conducted the study. They warn that prolonged UHS across both summer and monsoon seasons could pose critical challenges to public health, labor productivity, and climate resilience in densely populated and vulnerable regions of India.
Increasing Frequency and Area Affected
The study analyzed data from 1979 to 2021 and found that uncompensable heat stress has become more frequent and is affecting significantly larger areas of India. In the 1980s, UHS impacted less than 0.01 million square kilometers, but by 2020, this area had expanded to 0.04 million square kilometers. During the summer months of March to June, UHS affects about eight percent of India's land area and is strongly correlated with annual heat-related mortality. In contrast, only about one percent of the country was impacted by UHS during the monsoon season historically.
Projected Expansion Under Climate Warming
However, the research projects a rapid increase in monsoon-season UHS with climate warming. Under a 2 degrees Celsius warming scenario relative to preindustrial levels, the area affected by UHS during the monsoon could reach 53 percent of India's land area, nearly equivalent to the 60 percent affected during summer. The total population potentially exposed to uncompensable heat stress could range between 0.8 and 1.2 billion, depending on future population projections and warming levels.
Data Sources and Spatial Patterns
The team utilized population and density data from the Gridded Population of the World dataset, while heat-related mortality data for Indian states from 1980 to 2019 was obtained from the National Disaster Management Authority (NDMA) and the India Meteorological Department (IMD). Spatially, summer UHS primarily occurs in the Indo-Gangetic plain and coastal regions, driven by high temperatures and inland moisture transport from the Bay of Bengal via pre-monsoon winds. In contrast, monsoon-season UHS is predominantly humid and occurs within a narrower air temperature range of 35 to 38 degrees Celsius. The study identified Punjab in northwestern India as a region where monsoon UHS has already been observed.
Mechanisms and Hotspots
High humidity during the monsoon, combined with moderately high air temperatures—especially during monsoon breaks—creates favorable conditions for extreme heat stress events. The Gangetic Plain, northwestern India, and eastern coastal regions are hotspots for summer UHS. However, under a warming climate, northwestern and Gangetic plain regions are expected to experience more frequent UHS during the monsoon than in summer, according to the authors.
Implications for Policy and Resilience
The findings underscore the urgent need for adaptive measures to protect vulnerable populations from prolonged heat stress. As climate change intensifies, the extended duration of uncompensable heat stress could exacerbate public health crises, reduce labor capacity, and strain infrastructure. The study calls for enhanced climate resilience strategies, including early warning systems, urban planning to reduce heat islands, and improved access to cooling and healthcare in affected regions.
