Extreme heat is pushing some of India’s poorest workers further into poverty, with income losses of up to 9% for outdoor workers, new research has found.

Analysis done by the International Institute for Environment and Development (IIED), and shared exclusively with the Guardian, found that extreme heat is acting as a “poverty multiplier” for hundreds of millions of workers in India’s informal sector.

Researchers found that those working in highly physical jobs in sectors such as agriculture, construction and transport lost on average 6.6% of their salaries in 2024 due to extreme heat. Outdoor workers suffered the most, losing close to 9% of their salary in 2024, amounting to £112 ($151).

The economic loss was the highest in the arid desert region of Rajasthan, an area with prolonged heatwaves and a rising death toll due to extreme heat. Informal workers in the region lost equivalent to 8.3% of their income, due to the gruelling effects of extreme heat on the body making them unable to work.

The IIED research estimated that each year, 21.1 working days were lost in India due to extreme heat, an unaffordable loss for many of the 550 million workers in the informal sector.

Ritu Bharadwaj, climate finance director at the IIED, said the research showed how extreme heat was deepening poverty and worsening existing structural inequalities in India, which is aiming to be a developed nation in the next two decades.

She said: “Heat is quietly pushing these families deeper into poverty.

“As the heat rises, their efficiency goes down, so they earn less. With lower income their food intake falls. And because they cannot afford to stop, they keep working through it, doing lasting damage to their health. They are paying for a crisis they did nothing to cause, with their health and with their savings.”

Inder Kumar, 25, hails from Chattarpur, Madhya Pradesh, and works as a contract labourer. He recently endured over a week of fever brought on by heat stress. Photograph: Smita Sharma/The Guardian

Human-caused climate breakdown is making every heatwave in the world more intense and more likely to happen. India, a country where nine out of 10 work in the informal economy, could become one of the first places where heatwaves break the human survivability limit, a World Bank report said.

The research estimates that heat could cost the Indian economy at least £58bn – equivalent to 2% of its GDP – in a combination of wages lost due to reduced productivity, worksite closures and long-term losses from heat-related illnesses.

The analysis accounts for three ways heat exposure reduces hours worked: heat-related illnesses, a reduction in the capacity of work or maintaining normal productivity, and time lost when workplaces suspend their operations.

Informal workers include some of the most socially and economically marginalised people, who lack employment security, obliging them to work through illness and tolerate unsafe conditions.

Inder and Laxmi Kumar. ‘We kept working because if we stopped, we wouldn’t be paid,’ said Laxmi. Photograph: Smita Sharma/The Guardian

Access to drinking water, shade, rest areas, sanitation and medical support at the worksite was poor, said the report. Many workers then returned to homes that provided “no relief from heat”.

Eight construction workers who spoke to the Guardian all said they had repeatedly fallen ill over the past four months because of the heat, forcing them to miss work and lose income. Some had collapsed and sustained serious injuries but were given no compensation by employers. Some were even refused pay.

Inder and Laxmi Kumar, a husband and wife toiling on a dusty construction site in Gurugram, a satellite city outside Delhi, said they had both been confined to bed with fever, body aches and exhaustion. But after losing eight days’ wages, they could no longer afford to stay at home.

“I felt like I would collapse, like my body was on fire,” Laxmi said. “We kept working because if we stopped, we wouldn’t be paid.”

Satyam Kumar, 5, the son of Inder Kumar and Laxmi, drinks water at a construction site in Sector 92, Gurgaon. He doesn’t go to school and stays at the site while his parents work as labourers. Photograph: Smita Sharma/The Guardian

Doctors told the couple they were suffering from dehydration and heat exhaustion and advised them to rest.

The couple earn 800 rupees (£6) each a day, supporting their two young sons and four other family members back in their home village in Madhya Pradesh. They start around 9am and spend eight to 10 hours a day mixing cement, carrying construction materials and laying bricks, with hardly any breaks and little shade beyond the unfinished structure itself. Their five-year-old son plays in the rubble.

In the past three months alone, they have fallen ill three times, losing nearly four weeks of work and spending much of their income on medicines.

“We had no choice but to come back,” Inder said. “Whatever we manage to save is spent the next time we fall sick. We hardly have anything left to send home. I just pray this heat ends. It’s torture.”

Inder said he did not know a single labourer at the site who had escaped illness this summer. The extreme heat often spoiled the food they made for lunch, making them sicker.

The family’s home is a 2.5 metre (8ft) square of tarpaulin shelter inside the unfinished building. In the evening, a fan stops when the diesel generators are switched off just an hour after they return from work, leaving them to sleep in the stifling heat.

“When I get home, my whole body aches,” said Laxmi. “But my son becomes restless in the heat and keeps crying. Then I still have to cook, and the room gets even hotter.

“It feels like we work and sleep inside an oven.”

Kumkumari, 35, and her two-year-old daughter stand outside their makeshift tent at a construction site in Sector 92, Gurgaon. Photograph: Smita Sharma/The Guardian

For female labourers, the burden is often heavier. Many spend their working day also caring for young children.

Beside a water tanker on a construction site, 35-year-old Kumkumari poured water over her two-year-old daughter. “This is the only way to cool her down,” Kumkumari said. “She falls sick often, and when that happens I have to look after her instead of working.”

The makeshift tent where Kumkumari, 35, lives with her family is built of plastic with no ventilation, it relies on a small temporary fan for cooling. Photograph: Smita Sharma/The Guardian

Prolonged exposure to heat and dehydration over time increases the risk of developing chronic kidney disease. The IIED research estimated that over years of repeated exposure to heat, one in 20 informal workers in India could develop chronic kidney disease – equivalent to more than 26 million workers.

Among them was 38-year-old Sattavir, who stood on the roadside in Gurugram, hoping for a contractor to offer him a day of labour work.

In the past two months, he could only work for eight days after he developed a kidney infection, brought on by working in extreme heat and repeated dehydration.

Daily-wage labourers wait at Badshahpur market, Gurgaon, to be picked by contractors for construction work. Photograph: Smita Sharma/The Guardian

“The heat is killer,” he said. “In the last two months, I earned barely 7,000 rupees but spent around 9,000 rupees on medicines and treatment. I’m already in debt, but I’m still looking for work even though doctors say I need treatment for my kidneys.”

After waiting for several hours in the sun, Sattavir was not picked for work – the third consecutive day he returned home empty-handed. “When people see you’re weak, they don’t hire you,” he said.