• India is experiencing one of the worst heatwave spells it has faced in the past few decades with about 200 deaths already recorded this year. Now, a recently published study has warned that poor urban neighbourhoods are more vulnerable to the extended effects of heat.


• People in densely built, low-income neighbourhoods, with no open green spaces, remain unsheltered from heat even at night.


• As heat action plans evolve for a few Indian cities, they should take into account thermal indices, not just temperature thresholds, recommends the study.


• Climate-smart city design can help alleviate the burden of a rise in temperature caused by climate change.

As India stares at one of the longest heatwaves in three decades, which so far has claimed over 200 lives, experts warn that the spell will impact people in poor urban neighbourhoods for weeks after the scorcher is over.

In a study published in the journal Science of the Total Environment in April 2019, researchers mapped and compared exposure to heat between low-income and other neighbourhoods in Delhi (India), Dhaka (Bangladesh) and Faisalabad (Pakistan).

While high and low income neighbourhoods both have heat going up during the day, one’s ability to afford air conditioning (AC), avoid strenuous activities outdoors and presence of shade make a difference in coping with the heat exposure, said co-author Christian Siderius of the Wageningen University and Research (WUR).
But people in densely built, low-income neighbourhoods, with no open green spaces, remain unsheltered from heat even at night. Because, at night, these neighbourhoods, tend to trap the heat of the day and stay warmer.

“And due to a combination of factors when the heatwave is over, poor people will be exposed to extremely high night-time temperatures for many more weeks or even months,” said Siderius, adding that this creates an ongoing health risk.

Instead of just tracking urban heat island or air temperature, researchers assessed the exposure to heat in outdoor microclimatic conditions in terms of thermal indices. They advocated that heat action plans (HAP) be based on thermal indices so as to include factors such as humidity, not just temperature thresholds.

Heat is more than just high temperature and it is influenced by several other factors such as humidity, wind, direct or indirect radiation from the sun and indices take into account these factors and give an idea of how hot one really feels.

“Cities are hotter than rural areas around them (we see differences of up to eight degrees Celsius), especially at night. In dense urban areas where the poor live it is even more so. Then they don’t have AC or well-insulated houses so they can’t escape the heat,” said Siderius, also associated with London School of Economics (at the Grantham Research Institute).

“And finally, while temperatures go down a bit with the onset of the monsoon, humidity increases which means heat indices generally stay high. So it’s not so much an emergency situation, but more of an ongoing health risk,” he said.

Hem Dholakia of Council on Energy, Environment and Water(CEEW), who was not associated with the study, agreed about the increased impact of heat in poorer urban areas.

“Let us say that a poor person living in a tin shed, with little or no ventilation, experiences, on an average, a temperature that is two degrees higher indoors, than the outside temperatures. On a heatwave day, when the outside temperature is 41 degrees Celsius, this person is exposed to a temperature of nearly 43 degrees Celsius,” Dholakia elaborated.

“Once the outside temperature drops to 38 degrees (i.e. the heat wave has passed) the person may still experience 40 degrees indoors. Thus, the exposure for the poor may be prolonged based on housing characteristics. This will drive health impacts,” Dholakia told Mongabay-India.

Additionally, differences in heat exposure mostly depended on where in the city, slums or low-income neighbourhoods are situated.

For example, in Delhi, which recorded its highest ever June temperature, 48 degree Celsius, and where urban parts cover roughly half the total city area of 1500  square kilometres, poor neighbourhoods tend to be found all over the city and also close to the centre of the city.

“Here the influence of all the surrounding concrete, which cools down slowly during the night, is highest. In Pakistan’s third largest city of Faisalabad, poor neighbourhoods are now developing on the outskirts of the city, close to agricultural fields which cool down quicker at night which influences the outdoor temperature to some extent,” Siderius said. In Dhaka, in some slum areas close to water, which – if it flows – can cool down temperatures a bit.