Why in news?

Warmer nights may pose a greater health risk than daytime heatwaves during Indian summers, especially for people living in low- and middle-income housing. While daytime heat receives most attention, nighttime temperatures in India are rising even faster, increasing the danger of prolonged heat exposure.

Normally, cooler nights allow the human body to recover from daytime heat, but persistently high night temperatures prevent this recovery, leading to continuous physiological stress. The risk is particularly severe in poorly ventilated homes without air-conditioning, where people remain trapped in hot indoor conditions for hours.

A recent Climate Trends study in Chennai found many households experiencing indoor nighttime temperatures above 32°C, sometimes even crossing 35°C, comparable to peak daytime heat.

Though research in India is limited, global studies suggest that warmer nights could significantly increase heat-related deaths, making indoor heat exposure an emerging public health concern.

What’s in Today’s Article?

• Rising Night-Time Temperatures: An Emerging Heat Risk
• Heat Beyond Heatwaves: The Hidden Danger of Warm Nights

Rising Night-Time Temperatures: An Emerging Heat Risk

• India’s average temperature increased by about 0.7°C between 1901 and 2018, according to the 2020 climate assessment for the Indian region.
• While both daytime and nighttime temperatures have risen, their rates differ.
• By the end of the century:
  • Warmest day temperatures may rise by 4.7°C
  • Coldest night temperatures may rise by 5.5°C
• This indicates that nighttime temperatures are likely to rise faster than daytime temperatures, a trend already visible in recent IMD data.
• Urban Heat Island Effect
  • The rise in nighttime temperatures is particularly severe in cities due to the urban heat island effect.
  • Causes - Urban materials such as: Concrete; Roads; Bricks; Metal structures, absorb heat during the day and release it at night.
  • This effect is intensified by: Lack of vegetation and green spaces; Loss of water bodies; Dense clusters of high-rise buildings; Growing use of air-conditioners that release hot air outdoors.
  • As a result, nighttime temperatures in dense urban areas can be 4–6°C higher than in city outskirts.
• Impact on Urban Residents
  • The problem is especially acute in urban India, where many people live in: Small houses; Poorly designed structures; Homes with inadequate ventilation.
  • This leaves residents with little nighttime relief from heat.
  • Persistently warm nights can lead to: Sleep discomfort; Restlessness; Physical exhaustion; Reduced energy levels; Lower productivity the following day.
  • Experts warn that the full scale of health impacts is still being studied, but the risks are likely to be significant.

Heat Beyond Heatwaves: The Hidden Danger of Warm Nights

• Evidence suggests that high night-time temperatures may significantly increase mortality.
• Public health experts highlighted that when daytime temperatures exceeded 45°C but night temperatures stayed below 28°C, daily deaths remained close to the normal average of 100.
• However, when nighttime temperatures rose to 28–30°C, daily deaths increased to around 165, and when they crossed 30°C, mortality surged to nearly 265 deaths per day.
• This indicates a strong correlation between warmer nights and increased health risks.
• Limitations of Current Heat Action Plans
  • India has heat action plans in at least 23 states and over 200 cities, but these largely focus on managing heatwave events, which occur only when specific temperature thresholds are met and may happen only a few times a month.
  • However, extreme summer heat and rising night-time temperatures are a persistent reality, suggesting that existing responses may be too narrowly focused on episodic heatwaves rather than continuous heat exposure.
• Need for Long-Term Structural Measures
  • Experts stress the need to strengthen the long-term components of heat action plans, including:
    • Improved urban infrastructure
    • Better low-cost, heat-resilient housing
    • Expansion of green spaces
    • Better urban planning to reduce heat stress
• Immediate Relief Measures
  • For vulnerable households, especially those in cramped living conditions, simple low-cost solutions can offer quick relief.
  • The Climate Trends Chennai study suggests measures such as:
    • Reflective roof coatings
    • Whitewashed roofs and walls
    • Improved natural ventilation
  • These passive cooling interventions can help reduce indoor heat exposure and lessen health risks from increasingly warmer nights.