Excess heat stress is making India’s cities unlivable, making it crucial to design ways to adapt to high urban temperatures. The problem is especially acute in low-income communities in India, where houses are often constructed with materials that absorb heat and require more energy to cool down. These households often use cooling fans and air coolers for hours a day in the summer, raising their energy bills.

These homes, by shifting to passive cooling, could better adapt to days of extreme heat, making households less vulnerable to weather impacts and improving their resilience against climate change risks.

Tata Centre for Development (TCD) at UChicago, Energy Policy Institute at the University of Chicago (EPIC-India), and University of Chicago Energy and Environment Lab partnered with the Mahila Housing SEWA Trust (MHT) to evaluate the effectiveness of using heat-reflective paint on roofs in lowering indoor temperatures. While these paints are widely used, there is little rigorous evidence on their effectiveness outside of small-scale pilots.

MHT is painting the roofs of households with heat-reflective paint in a resettlement colony in Delhi. The researchers at the University of Chicago are working with MHT to evaluate the impact of the paints on indoor temperatures, energy expenditures, and overall well-being. This project was one of the winning ideas in the Delhi Innovation Challenge—a joint initiative of TCD and the Dialogue and Development Commission of Delhi.

This intervention, under which 540 households have been covered, could prove effective during Delhi’s summer. Decreasing indoor temperatures will make life a little more comfortable for slum dwellers, and help the community become resilient to climate change as well.

Using a randomized control trial design, implemented in a slum in India’s capital city of Delhi, we tested the impact of painting roofs with reflective paints on both indoor temperatures and a host of household outcomes and cooling behaviors. Households in the study population are poor and use a combination of water and electricity to cool their homes, with air conditioning being rare. Many households own swamp coolers (desert coolers) which work by blowing air through a wet mesh. As air flows over the water, it evaporates, simultaneously cooling the air which then blows out of the device. An even cruder technique – also common in our sample – is to simply throw water on the floor and turn on an ordinary ceiling or floor fan. This produces a similar result, albeit less effectively. Either way, while exploiting evaporation, the rate of consumption of water becomes a critical determinant of how much indoor temperatures reduce.

We find precisely estimated, near zero reductions in the indoor temperatures of painted households. These results are in sharp contrast to both previous field evidence. Although painted households did not grow appreciably cooler, we find evidence suggesting that this might be because households responded to better passive cooling by reducing active cooling inputs, in particular water. This suggests that paints may increase household welfare, but not by delivering any of the benefits – social or private – associated with reducing exposure to high temperatures.

For this project, the Energy Policy Institute gratefully acknowledges generous research support provided by the Tata Centre for Development (TCD) at UChicago.