Hundreds of roofs in informal settlements of Gujarat have been painted in a reflective, white coating over the last two months. The effort, which involves 400 households in Ahmedabad, is part of a global scientific trial to study how indoor heat impacts people’s health and economic outcomes. 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. In the Vanzara Vas slum in the Narol area of the city, which has more than 2,000 dwellings, most of them airless, one-room homes, residents that are part of the project say they have already noticed a difference. \”My refrigerator doesn’t heat up any more and the house feels cooler. I sleep so much better and my electricity bill is down,\” said Nehal Vijaybhai Bhil, whose roof was painted in January. The trial 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.