Hot after hours: Why Delhi won’t chill at night anymore

Residents of the national capital are finding no relief even after sunset, with night-time temperatures soaring and turning the city into what experts are calling a classic case of the urban heat island effect, ToI reported. This April has already recorded two unusually warm nights. On Thursday, the minimum temperature was 25.7 degrees Celsius, while Friday followed closely at 25.6 degrees. Earlier in the month, on April 9 and 10, the city saw similar conditions with minimums at 25.6 and 25.9 degrees, respectively.

Experts believe the intensity of heat during the night is proving more harmful than high daytime temperatures. Mitashi Singh, programme manager for the sustainable habitat programme at the Centre for Science and Environment (CSE), told ToI the causes go beyond weather patterns. She linked it to poor urban planning, shrinking green spaces, vanishing water bodies, and materials used in construction. “Our cities, which were once able to cool themselves off during the nighttime, cannot do so anymore. Among the major reasons are concretisation, loss of green cover and fewer water bodies. The heat sinks are gone. We keep on trapping radiation throughout the day and releasing it at night. That precisely is the urban heat island effect,” she said.

According to her, Delhi’s ever-increasing concrete footprint and the use of thermally poor materials like tin sheets or galvanised iron for roofing have compounded the situation. She added, “There is a global pattern. Bigger cities mean more population, cars and buildings. Thus, anthropogenic activities are the bigger factors contributing to heat in the cities. This is also in line with the fact that approximately 70% of greenhouse gases come from cities. Issues like more car-centric mobility, urban waste landfills, air pollution and buildings are prevalent. Delhi has these issues; there are three landfills too.”

Mitashi recommended adopting indigenous building methods such as insulated bricks, cool roof techniques, and constructing low-rise residences with canopy trees to bring some respite.

The damage from these warm nights is not only to the body but also to the economy. A CSE report pointed out that “India is projected to lose 5.8% of working hours in 2030, a productivity loss that is equivalent to 34 million full-time jobs due to global warming.” High night-time heat pushes people to use more cooling equipment like air conditioners, which in turn release more heat, thus feeding into a vicious cycle of rising power demand and rising temperature.

According to a report by the International Water Association, water bodies and green spaces can make a noticeable difference in reducing this heat load. However, as those vanish from the city, the consequences worsen.

Dr Prasoon Singh, a fellow at the Centre for Climate Change Research at TERI, pointed to the lack of respite. Last June, Safdarjung’s base weather station recorded a night temperature of 35.2 degrees Celsius. “Since the temperatures in the daytime are very high consistently and there is no cooling taking place, the heat is cascading to the next day. Night heat is harmful, even more than the daytime, since the body needs comfort with the cooling of the environment,” said Singh. For now, he said, low humidity has kept the worst impacts at bay, but the high temperatures continue unabated.

(with ToI inputs)