An analysis of South Asia’s biggest cities found that if current warming trends continued, wet bulb temperatures — a measure of heat and humidity indicating when the body can no longer cool itself — will become so high people directly exposed for six hours or more would die.
NEW DELHI — On a sweltering Wednesday in June, a rail-thin woman named Rehmati gripped the doctor’s table with both hands. She could hardly hold herself upright, the pain in her stomach was so intense.
She had traveled for 26 hours in a hot oven of a bus to visit her husband, a migrant worker here in the Indian capital. By the time she got here, the city was an oven, too: 111 degrees by lunchtime, and Rehmati was in an emergency room.
The doctor, Reena Yadav, did not know exactly what had made Rehmati sick, but it was clearly linked to the heat. Yadav suspected dehydration, possibly aggravated by fasting during Ramadan. Or it could have been food poisoning, common in summer because food spoils quickly.
Yadav put Rehmati, who is 31 and goes by one name, on a drip. She held her hand and told her she would be fine. Rehmati leaned over and retched.
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Extreme heat can kill, as it did by the dozens in Pakistan in May. But as many of South Asia’s already-scorching cities get even hotter, scientists and economists are warning of a quieter, more far-reaching danger: Extreme heat is devastating the health and livelihoods of tens of millions more.
If global greenhouse-gas emissions continue at their current pace, they say, heat and humidity levels could become unbearable, especially for the poor.
It is already making them poorer and sicker. Like the Kolkata street vendor who squats on his haunches from fatigue and nausea. Like the woman who sells water to tourists in Delhi and passes out from heatstroke at least once each summer. Like the women and men with fever and headaches who fill emergency rooms. Like the outdoor workers who become so weak or so sick that they routinely miss days of work, and their daily wages.
“These cities are going to become unlivable unless urban governments put in systems of dealing with this phenomenon and make people aware,” said Sujata Saunik, who served as a senior official in the Indian Ministry of Home Affairs and is now a fellow at the Harvard University School of Public Health. “It’s a major public-health challenge.”
Indeed, a recent analysis of climate trends in several of South Asia’s biggest cities found that if current warming trends continue, by the end of the century, wet bulb temperatures — a measure of heat and humidity that can indicate the point when the body can no longer cool itself — would be so high that people directly exposed for six hours or more would not survive.
In many places, heat only magnifies the more thorny urban problems, including a shortage of basic services, like electricity and water.
For the country’s National Disaster Management Agency, alarm bells rang after a heat wave struck the normally hot city of Ahmedabad, in western India, in May 2010, and temperatures soared to 118 degrees Fahrenheit: It resulted in a 43 percent increase in mortality, compared with the same period in previous years, a study by public health researchers found.
Since then, in some places, local governments and the Natural Resources Defense Council, an advocacy group, have put in place simple measures. In Ahmedabad, city-funded vans distribute free water during the hottest months. In the eastern coastal city of Bhubaneswar, parks are kept open in afternoons so outdoor workers can sit in the shade. Some cities that had felled trees for construction projects are busy trying to plant new ones.
The science is unequivocally worrying. Across the region, a recent World Bank report concluded, rising temperatures could diminish the living standards of 800 million people.
Worldwide, among the 100 most populous cities where summer highs are expected to reach at least 95 degrees Fahrenheit by 2050, according to estimates by the Urban Climate Change Research Network, 24 are in India.
Rohit Magotra, deputy director of Integrated Research for Action and Development, is trying to help the capital, Delhi, develop a plan to respond to the new danger. The first step is to quantify its human toll.
“Heat goes unreported and underreported. They take it for granted,” Magotra said. “It’s a silent killer.”
On a blistering Wednesday morning, with the heat index at 111 degrees, he and a team of survey takers snaked through the lanes of a working-class neighborhood in central Delhi. They measured temperature and humidity inside the brick-and-tin apartments. They spoke to residents about how the heat affects them.
“Only by 4 a.m., when it cools down, can we sleep,” a woman named Kamal told him. Her husband, a day laborer, suffered heatstroke this year, missing a week’s work — and a week’s pay.
A shopkeeper named Mohammed Naeem said that while he managed to stay cool in his ground-floor space, his father’s blood pressure rose every summer, as he sweltered in their top-floor apartment all day.
A woman named Abeeda told Magotra that she helped her husband cope during the summer by stocking glucose tablets in the home at all times. Her husband works as a house painter. Even when he is nauseated and dizzy in the heat, he goes to work, she said. He cannot afford not to.
Across town, workers covered their faces with bandannas as they built a freeway extension for Delhi’s rapidly growing number of cars. The sky was hazy with dust. Skin rash, dry mouth, nausea, headaches: These were their everyday ailments, the construction workers said. It got so debilitating that every 10 to 15 days, they had to skip a day of work and lose pay.
Ratnesh Tihari, a 42-year-old electrician, said he felt it getting hotter year by year. And why would that be surprising? He pointed his chin at the freeway extension he was helping to build. “It’s a fact. You build a road, you cut down trees,” he said. “That makes it hotter.”
Worldwide, by 2030, extreme heat could lead to a $2 trillion loss in labor productivity, the International Labor Organization estimated.
Delhi’s heat index, a metric that takes average temperatures and relative humidity into account, has risen sharply — by 0.6 degrees Celsius in summer and 0.55 degrees during monsoons per decade between 1951 and 2010, according to one analysis based on data from 283 weather stations across the country.
Some cities are getting hotter at different times of year. The average March-to-May summertime heat index for Hyderabad had risen by 0.69 degrees per decade between 1951 and 2010. In Kolkata, a delta city in the east, where summers are sticky and hot anyway, the monsoon is becoming particularly harsh: The city’s June-September heat index climbed by 0.26 degrees Celsius per decade.
Joyashree Roy, an economist at Jadavpur University in Kolkata, found that already, most days in the summer are too hot and humid to be doing heavy physical labor without protection, with wet-bulb temperatures far exceeding the thresholds of most international occupational health standards.
And yet, walk through the city on a stifling hot day in June, and you will find people pedaling bicycle rickshaws, hauling goods on their heads, constructing towers of glass and steel. Only a few people, like herself, Roy pointed out, are protected in air-conditioned homes and offices. “Those who can are doing this. Those who can’t are becoming worse,” she said. “The social cost is high in that sense.”
Researchers are tinkering with solutions.
In Ahmedabad, city funds have been used to slather white reflective paint over several thousand tin-roofed shanties, bringing down indoor temperatures.
In Hyderabad, a similar effort is being tested. A pilot project by a team of engineers and urban planners covered a handful of tin-roofed shacks with white tarpaulin. It brought down indoor temperatures by at least 2 degrees, which was enough to make the intolerable tolerable. Now they want to expand their cool-roof experiment to a 1-square-kilometer patch of the city, installing cool roofs, cool walls and cool sidewalks, and planting trees.