How a coat of paint is protecting the health of some of this city’s poorest residents

A new approach in an Indian slum is already making a difference

Liquid-applied membrane is applied to roofs in the Vanzara Vas slum in Narol (Reuters)

In Ahmedabad, India, hundreds of roofs gleam white in a large slum, a new defence against the approaching summer heat.

The initiative, covering 400 households, is part of a global scientific trial exploring the impact of indoor heat on health and economic outcomes in developing countries, and the potential of "cool roofs" to mitigate these effects.

"Traditionally, home is where people have come to find shelter and respite against external elements," explains Aditi Bunker, an epidemiologist at the University of Heidelberg leading the Wellcome Trust-backed project.

"Now, we're in this position where people are living in precarious housing conditions, where the thing that was supposed to be protecting them is actually increasing their exposure to heat."

Climate change has intensified India's summers, with Ahmedabad experiencing temperatures exceeding 46C in recent years.

The Vanzara Vas slum in Narol, comprised of over 2,000 dwellings, mostly airless single-room homes, is one area where the project is underway.

Residents participating in the trial, like Nehal Vijaybhai Bhil, report already feeling a difference thanks to the reflective white coating applied over the last two months.

Ajit Thakor, a field supervisor, climbs down from a one-room house after measuring its temperature (Reuters)

“My refrigerator doesn't heat up any more and the house feels cooler. I sleep so much better and my electricity bill is down.”

The project aims to understand how these extreme temperatures, exacerbated by inadequate housing, affect residents' lives and how simple interventions like cool roofs can offer relief.

Across the world, heatwaves that, prior to the industrial revolution, had a one-in-10 chance of occurring in any given year are nearly three times as likely, according to a 2022 study in the journal Environmental Research Letters.

By painting roofs with a white coating that contains highly reflective pigments such as titanium dioxide, Ms Bunker and her team are sending more of the sun's radiation back to the atmosphere and preventing it from being absorbed.

"In a lot of these low socioeconomic homes, there's nothing to stop the heat transfer coming down - there's no insulation barrier from the roof," Ms Bunker said.

Aditi Bunker, an epidemiologist, speaks with Manisha Barot and Roshani Barot, whose one-room house's rooftop has been coated with liquid-applied membrane (Reuters)

Before joining Ms Bunker's experiment, Arti Chunara said she would cover her roof with plastic sheets and spread grass over them.

Some days, she and her family sat outside for most of the day, going into the house only for two to three hours when the heat was bearable.

The trial in Ahmedabad will run for one year, and scientists will collect health and indoor environment data from residents living under a cool roof - and from those who do not.

Other study sites are in Burkina Faso, Mexico and the island of Niue in the South Pacific, spanning a variety of building materials and climates.

Early results from the Burkina Faso trial, Ms Bunker said, show that cool roofs reduced indoor temperature by between 1.2 C in tin- and mud-roofed homes, and 1.7 C in tin-roofed homes over two years, which subsequently lowered residents' heart rates.