Heat stress due to working outdoors may have caused a 10 % decline in productivity among migrant workers in India over the past four decades, a study has estimated.
Researchers, including those from the Indian Institute of Technology Gandhinagar, also show that during 1980-2021 rural-to-urban migration hotspots in north, east and south India saw a significant increase in humidity, pointing to a higher heat stress experienced by the section of society indoors.
Mumbai, Delhi, Kolkata, and Hyderabad are the top four urban areas experiencing the highest inflow of migrants, with total population estimated to be up to 10 million, they said.
The study, published in the journal Earth’s Future, projects that with each additional degree of global warming, migrant workers could experience a substantial increase in heat stress — both indoors and outdoors — and a lowered capacity to engage in physical labour.
Migrant workers in India move from rural to urban areas for work and make up a large, growing part of the country’s population.
Studies suggest 42 % of the total population could be migrant workers. A 2020 study, published in The Indian Journal of Labour Economics, cites 450 million internal migrants according to the 2011 Census.
Working physically demanding jobs and often long hours outdoors, migrant workers are vulnerable to heat stress — where one’s body is unable to regulate its temperature — due to high temperatures.
Climate change has been shown to produce higher heat stress, impacting productivity and incomes of outdoor workers, including migrant workers.
The researchers said the season of extreme heat stress is projected to lengthen, posing challenges for the overall well-being and labour capacity of migrant workers.
However, little is known about how an increase in heat stress in urban regions affects migrant workers’ ability to work, they added.
The team analysed data from 2011 Census, global climate models, focussing on top 50 urban areas in India to study the impacts of heat in areas where large numbers of people are less likely to be able to escape.
“We show that during 1980-2021, most rural-to-urban migration hotspots in north, east, and southern India witnessed a significant rise in (wet bulb temperature), indicating (an) elevated indoor heat stress,” the authors wrote.
“Over that interval, outdoor heat stress has considerably increased and led to a (nearly) 10 % decline in labour capacity in these hotspots,” they said.
Nearly all urban areas in India could start seeing a high heat stress indoors if global warming exceeds 2 degrees Celsius since pre-industrial levels, the team projected.
Typical labour capacity is projected to reduce to 71 % and 62 %, under 3 degrees Celsius and 4 degrees Celsius of global warming, compared to 86 % in a scenario in which current warming trends continue.
Productivity loss of up to 35 % have been noted in outdoor workers engaging in moderate or heavy workload in Chennai and parts of West Bengal if wet bulb temperature exceeds 28 degrees Celsius, the researchers said.