Delhi’s hot nights as a public health challenge

This is called the urban heat island (UHI) effect, and it is a bigger and more serious problem. The climate crisis and increasing urbanization are making Delhi hotter, more energy-intensive and potentially more vulnerable to public health disasters. The United Nations Office for Disaster Risk Reduction (UNDRR) describes the UHI effect as the phenomenon where buildings, roads and other infrastructure absorb and retain heat, causing urban areas to become significantly warmer than surrounding rural areas. During the day, glass, asphalt and concrete surfaces absorb a lot of solar energy. This heat is slowly released into the atmosphere at night, keeping temperatures high after sunset. Therefore, the results are adequate for a metropolitan area of ​​more than 30 million people. Summer is no longer just a seasonal problem. This is a new problem that affects energy demand, productivity, urban planning and public health.

There are many reasons for the UHI effect and Delhi has many of them together. The biggest loss of green space is in crowded cities. Trees provide shade and also reduce surface temperatures and cool the air through evapotranspiration. Green corridors, urban forests and parks can significantly reduce local temperatures. However, during rapid urbanization, natural cooling systems have often been sacrificed. Delhi still has much green cover compared to many other Indian cities but the vegetation is unevenly distributed. Some neighborhoods have plenty of trees to provide shade from direct sunlight, while others do not.

The physical construction of the city also plays a big role. Higher density development, increasing road networks and larger paved surfaces increase heat absorption. In cities, buildings built close together can block airflow, reducing the flow of cool air and trapping heat. This means that temperatures often remain high after the sun goes down. Another major element is human-generated waste heat. Lakhs of cars ply on Delhi’s highways every day. Industrial clusters in the National Capital Region also contribute to thermal emissions. Air conditioners are important for safety and comfort in extreme heat, but they also radiate heat into the surrounding air, making cities even hotter. As cooling demand increases, a feedback loop occurs where higher temperatures mean more energy use, which in turn generates more heat. The effect of the combination appears to be increasing with temperature trends. A steady rise in land surface temperatures has been observed in many parts of Delhi over the last ten years. The continued occurrence of heatwaves and an increase in extremely hot days is evidence that urban warming is becoming a structural problem rather than a sporadic weather phenomenon.

When people talk about heat waves, the one thing they talk about most is the day temperature. But night-time heating can be equally important. Cool nights help the human body recover from the heat of the day. When the temperature is high after sunset, the physical stress caused by intense heat persists for a long time. This can increase the chances of dehydration, cardiovascular stress, sleep disturbances and heat-related illnesses.

Vulnerable populations are particularly badly affected. Individuals with prior medical conditions, young children, workers who work outdoors, and the elderly are often less resistant to prolonged exposure to heat. Many low-income families also face inadequate home insulation, cramped living quarters, and limited access to air conditioning. These clusters are uncomfortable not only on hot nights. This can become a major health hazard. International studies have found that higher temperatures at night have been linked to higher mortality rates during heatwaves. The absence of recovery time between hot days can increase physical stress and place additional strain on health care systems. Even a small increase in heat-related health problems can have a major impact on a large number of people in a densely populated city like Delhi.

The UHI impact is bigger than you might think. This is interacting with broader climate changes that are altering rainfall and temperature patterns in South Asia. Long ago, climate experts warned that heat waves in the region were becoming more frequent, longer and hotter. As global temperatures rise, the likelihood of extreme heat events also increases, and changes in atmospheric circulation may affect the duration and intensity of heatwaves.

Another layer of complexity can come from climate variability, for example through events such as El Niño. These events can influence the behavior of the monsoon, increasing dry periods and reducing rainfall in some areas. In urban environments that are already prone to heat retention, reduced rainfall could increase the duration of thermal stress in cities. That means the dangers are coming together. Climate change is increasing basal temperatures; Urban development patterns are increasing local heat retention. Together they make life difficult for the local people.

Indian governments have begun creating heat action plans to reduce heat-related deaths and improve preparedness to meet these challenges. Delhi has several heat management strategies including public awareness campaigns, emergency response plans and relief assistance during severe weather events. These initiatives are important and have the potential to reduce existing threats.

But adaptation cannot simply be an emergency response. Vulnerable people need respite during extreme heat, and cities need easy access to cooling centres. There should be more public drinking water infrastructure in markets, transport hubs and other high traffic areas. Outdoor workers need better workplace protections, such as regular rest periods, access to shade and hydration during the hottest parts of the day. The capacity of health care systems to identify and manage heat-related illnesses also needs to be strengthened. Heat exhaustion, dehydration, and heatstroke should be viewed as regular public health threats, not anomalies. The serious issue is that local governments lack better systems to monitor the effects of heat. Better data collection can help policymakers identify at-risk neighborhoods and better target interventions.

Emergency actions save lives during particular heat waves, but urban design choices will determine long-term resilience. Cool roofing is one of the most promising treatments. Reflective roofing materials can significantly reduce indoor temperatures and energy consumption. When deployed widely, there could be significant cooling benefits at the city scale, as rooftops account for a large portion of the urban surface area.

Another major goal is to increase the amount of green space in our cities. Trees, parks and green spaces support biodiversity, air quality and general urban liveability as well as improving thermal comfort. It is important to preserve existing green areas as well as create new ones. Water bodies can also play a big role in cooling cities. Lakes, ponds and wetlands also help the ecosystem by regulating local temperatures as well as cutting heat. Many urban water bodies in NCR have been encroached upon or degraded over time. Restoring them could be an important part of strategies for climate adaptation. We also need to change the building codes. Future urban development should incorporate climate-sensitive design ideas such as improved ventilation, shading systems, and materials that reduce heat absorption. Population growth is not the only factor to consider when building infrastructure; Rising temperatures also need to be taken into account.

Citizens can build heat resilience through actionable steps such as limiting direct heat exposure, improving home ventilation and supporting neighborhood green projects. Community groups, schools and resident welfare associations can all play an important role in raising awareness and implementing actions at the neighborhood level. However, the scale of the problem will require individual actions. Urban heat is truly a systems problem that requires a coordinated response from communities, public health agencies, planners, and governments.

As urbanization and the climate crisis drive environmental changes, Delhi’s hot nights offer a glimpse of what many cities may face in the future. The only challenge was dealing with it in hot weather. It’s about keeping cities safe, healthy and liveable in a warming world. The future consequences of heatwaves depend on the decisions we make about urban design, environmental protection and climate adaptation: they will either be tolerable or pose more serious threats to public health and economic resilience.

(Views exchanged are personal)

This article is written by columnist and climate researcher Anushrita Dutta and Dilip Pandey, co-in-charge of Aam Aadmi Party, Uttar Pradesh.