The Dark Side Of Heat: Concrete Cages, Sweltering Nights; Examining The Urban Heat Island – Analysis

Nights in India’s capital, Delhi, of late, became uncomfortably and dangerously hot, as the world’s most populous nation grappled with relentless heat. Northern India has experienced an intense summer, with one part of Delhi hitting 49.9°C (121.8°F) in late-May, marking the highest temperature ever recorded in the city. However, the intense heat did not subside even after sunset.

According to a report by the Centre for Science and Environment (CSE) tracking urban heat stress in Delhi, the city cools down by only 8.5°C at night. In contrast, urban outskirts see a more significant drop of 12.2°C.

Scientists warn that hotter nights are a result of the climate crisis, increasing the health risks associated with heat stress. Research indicates that higher nighttime temperatures make it harder to fall asleep and reduce deep sleep and rapid eye movement (REM) sleep, both crucial for the body’s nighttime repair and refreshment.

Exposure to heat waves during pregnancy may lead to adverse outcomes, such as pre-term birth, as noted in a 2019 study. Older adults may experience higher heart rates and more stress when sleeping in warmer conditions. Deaths due to mental and behavioral disorders increased during heat waves, especially among older adults, as reported by CNN quoting a 2008 Australian study.

The rise in nighttime temperatures—particularly noticeable in such cities as Delhi, Mumbai and Bangalore, besides other metropolitan cities—is due to the urban heat island (UHI) effect. These places are much hotter than their surrounding rural areas.

In a UHI, heat is generated not just from the sun, but also from the energy consumed by people, cars, buses and trains. UHIs are common in areas with high activity levels and dense populations. There are many causes for UHIs. When homes, stores and factories are built close together, UHIs can form. The materials used in these buildings often trap heat, making the areas around them warmer.

‘Waste heat’ also contributes to the UHI effect. Human activities—such as driving cars, exercising, running factories, or simply going about daily chores—consistently release energy. This energy typically escapes as heat. When a large number of people is concentrated in one area, a significant amount of heat is generated.

Urban areas are highly populated. These areas are also densely built. When urban areas run out of space to expand outward, engineers construct taller buildings, resulting in skyscrapers. All this construction generates waste heat and the heat that escapes from insulation has no place to dissipate. It remains trapped in and around the buildings, contributing to the UHI effect.

At night, UHIs have higher temperatures because buildings, sidewalks and parking lots prevent ground heat and pollutants from escaping into the cold night sky. This traps the heat at lower levels, making it warmer.

UHIs can experience poorer air and water quality compared to their rural counterparts. The air quality in such areas is frequently compromised due to a higher presence of pollutants, which are emitted from vehicles, industries and human activities. Water quality is also adversely affected in urban heat islands. The influx of warm water from a UHI into nearby streams poses a challenge for indigenous species that are accustomed to living in cooler aquatic environments.

Researchers are examining the potential contribution of UHIs to the phenomenon of global warming, which encompasses the ongoing increase in Earth’s temperature.

In times of extreme heat, individuals often seek relief by turning on their fans or air-conditioning units, particularly in urban regions impacted by the presence of UHIs. Urban heat islands exert pressure on energy resources by increasing the demand for energy during summer. Power outages, commonly known as ‘rolling blackouts’, are a recurrent occurrence in UHIs. The utilization of electric fans and air conditioning systems actually adds to the overall heat of the urban heat island, exacerbating its temperature.

When utility companies cannot meet the energy demands of their customers, they initiate ‘rolling blackouts’ as a measure to cope with the shortfall. During a ‘rolling blackout’, specific areas or groups of customers are intentionally and temporarily deprived of electricity for a predetermined period of time, typically on a rotational basis, in order to balance the energy supply and demand.

To mitigate the adverse consequences mentioned above, experts propose that urban residents, architects and designers collaborate to minimize human activities’ impact on urban areas. One effective strategy to combat the negative effects of UHIs is the implementation of green roofs, where rooftops are covered with vegetation.

Green roofs have the ability to absorb carbon dioxide, a major pollutant, while also reducing the ambient temperature of the surrounding areas. Additionally, using lighter-coloured materials for buildings can contribute to cooling effects. Light colours reflect sunlight and minimize heat absorption, as highlighted by National Geographic.