Warmer nights during Indian summers may be more dangerous than heatwaves, and this is a critical issue that demands our attention. While most discussions about extreme heat in India focus on peak daytime temperatures and heatwaves, the growing concern is that warmer nights pose a greater health risk, especially for those in low and middle-income housing. The human body needs cooler evenings and nights to recover from daytime heat, but when nighttime temperatures remain high, the body cannot recoup, leading to prolonged and sustained heat exposure. This is particularly challenging in small, poorly-ventilated spaces without air conditioning.
A study by Climate Trends in Chennai revealed that occupants of low and middle-income housing units frequently slept in temperatures exceeding 32°C, with some nights reaching 35°C, similar to peak daytime temperatures. This indoor heat exposure has not been widely studied in India, but global research suggests that nighttime warming could significantly contribute to heat-related deaths. The India Meteorological Department's recent data confirms that nighttime temperatures are rising faster than daytime temperatures, and this trend is more pronounced in urban areas due to the urban heat island effect.
The urban heat island effect occurs when concrete, roads, bricks, and metal absorb heat during the day and radiate it at night. The lack of green spaces and natural ventilation in many urban homes exacerbates this effect. As cities expand, this issue is likely to worsen. The study in Chennai highlighted the need for immediate relief measures, such as reflective roof coatings and natural ventilation, to mitigate the impact of indoor heat exposure.
The correlation between higher nighttime temperatures and increased mortality rates is significant. According to former director of the Indian Institute of Public Health, Dileep Mavalankar, all-cause mortality rates in Ahmedabad rise dramatically when nighttime temperatures exceed 30°C. This trend is not limited to Ahmedabad; at least 23 states and over 200 cities have heat action plans, but most focus on heatwave-like situations, which are less frequent and specific than the perennial issue of extreme heat and rising nighttime temperatures.
To address this, heat action plans should emphasize long-term measures to reduce the impact of heat on urban infrastructure, low-cost housing, and green spaces. In the meantime, passive cooling solutions like reflective roof coatings and natural ventilation can provide immediate relief to those in cramped households. As the world grapples with the effects of climate change, understanding and addressing the risks of warmer nights in Indian summers is crucial for public health and well-being.
In my opinion, the focus on daytime heatwaves often overlooks the more insidious threat of warmer nights. As the climate continues to warm, we must prioritize research and action to protect vulnerable populations from the health risks associated with prolonged heat exposure. The future of public health in India may depend on our ability to adapt to and mitigate these changing conditions.
