Heat Waves:- Scorching daytime temperatures due to the intense heat wave sweeping large parts of India and Pakistan are not the only problem facing tens of millions of people in cities.

A new study warns that hotter nights and rising humidity levels are worsening heat stress on tens of millions of people, posing a growing health hazard.

The study by the New Delhi-based Center for Science and Environment (CSE) points out that cities are not cooling down at night as much as they used to. It looked at six of India’s megacities, Delhi, Mumbai, Kolkata, Hyderabad, Chennai and Bengaluru over 23 years.

“The temperature difference from morning to night used to be about 12 degrees Celsius or more two decades ago. That is not happening anymore in cities,” according to Avikal Somvanshi at the Center for Science and Environment. “If you see Delhi for example, the city does not cool down more than six to seven degrees Celsius in the peak summer season.”

Somvanshi says hot nights are as dangerous as midday peak temperatures because people get little chance to recover from day-time heat. “This is a public health crisis, especially for the elderly and those who work outdoors.”

In the Indian capital, rising nighttime temperatures are a double whammy for thousands of street vendors who brave the sizzling sun to ply their trade. Atma Prakash Singh, who sells rice and a lentil curry on a city pavement, takes care to park his cart under the shade of a tree. Still he says he gets frequent headaches and his feet ache at night. “Even standing here on this road is a problem. What to do? I have to survive the heat to earn a living,” he says.

A study by Lancet Planetary Health has warned that the mortality risk on days with hot nights could be 50% higher than on days when nights are not so hot.

Sunday, more than 30 cities recorded temperatures of over 45 degrees Celsius, mostly in northern, central and western India. That included parts of the capital New Delhi.

Ice cream vendor, Jai Singh, does not need studies to tell him it has been a sizzling summer. He works from about noon to midnight on the roadside. “I get skin rashes. I keep eating cucumber and drinking water to stay cool,” he says. The nights provide little respite, he says.

Pointing out that the sun is not the only source of heat in cities, experts cite many reasons for rising nighttime temperatures. Concrete spaces, emissions from air conditioners and cars generate heat. When the sun sets, polluted air traps the heat instead of letting it radiate out.

Rising humidity in cities is also exacerbating the impact of heatwaves — for example Delhi, located in the dry northern plains, has been 8% more humid in the last ten years compared to the previous decade according to the study. It blames it on “uncontrolled urban sprawl.”

People buy air coolers from a roadside vendor on a hot summer afternoon in New Delhi on May 20, 2024, amid the ongoing heatwave.

Many Indian cities have seen green spaces shrink as they race to build new homes and offices to accommodate a growing population and an expanding economy.

The study cites the case of the southern city of Chennai where the green cover has shrunk by nearly 14% in the last two decades, while what it calls “concretization” has doubled.

Experts say even if global warming stops below 1.5 degrees Celsius, climate induced heatwaves are here to stay.

“There has been a shift in seasons. Summers have become extended,” points out Abinash Mohanty, Sector Head, Climate Change and Sustainability at research firm IPE Global. “Earlier the onset of the monsoon in June or July calmed the weather. Now the summer persists into the post monsoon season also, with high temperatures and high humidity.”

The extreme temperatures in northern and central India have coincided with a six-week-long general election that concludes this week. However, the impact of the intensifying heat and the need for cities to adapt to it in a hot, tropical country of 1.4 billion people did not figure as an issue on the campaign.

“Talk on the need for climate adaptation has not really started in India because of poor understanding of what is happening, whether it is in political circles or the wider public,” points out Somvanshi. “While there is some talk about climate change, there is no recognition that even if we control global warming, heat waves will not go away. They are the new reality.”

It may not be talked about, but the heat did leave its mark on the election. A month ago, Nitin Gadkari, minister of Road Transport and Highways, fainted on stage at a campaign rally. He blamed the episode on the high temperature. Questions are also being asked whether a lower voter turnout compared to 2019 elections can be blamed on the intense heat or on voter apathy.