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India is witnessing a steady rise in nighttime temperatures due to climate change, rapid urbanisation, and changing land-use patterns. Unlike daytime heat, rising night temperatures prevent the atmosphere from cooling adequately after sunset, leading to prolonged heat stress for humans, agriculture, and ecosystems. This trend has become more pronounced in recent years, especially in urban areas affected by the urban heat island effect. Increasing nighttime temperatures not only worsen heatwaves but also impact public health, energy demand, crop productivity, and overall climate resilience in India.
| Table of Content |
| What is meant by nighttime temperature? What are the reasons behind rising nighttime temperature? What are the impacts of rising nighttime temperatures? What needs to be done? |
What is meant by nighttime temperature?
- Nighttime temperature refers to the atmospheric temperature recorded during the night, usually after sunset and before sunrise. It generally represents the minimum temperature experienced in a day.
- Global mean temperatures have risen by more than 1.3°C since 1850, with nighttime temperatures increasing even more rapidly than daytime temperatures.
- Rising nighttime lows are often a clearer signal of global warming than rising daytime highs, as warmer nights can increase heat stress on humans and crops.
What are the reasons behind rising nighttime temperature?
- Changes in the Planetary Boundary Layer: The planetary boundary layer is the lowest part of the atmosphere – the air directly influenced by the Earth’s surface. This layer changes shape between day and night, which accelerates nighttime warming:
- The Daytime Layer: During the day, solar heating causes the air to mix vigorously, expanding this boundary layer up to several kilometers high. The heat is distributed through a massive volume of air.
- The Nighttime Layer: At night, the ground cools and the boundary layer shrinks, becoming very thin and stable – often just a few hundred meters thick.
- When that trapped heat is compressed into a much shallower nighttime layer, the same amount of warming energy causes a greater temperature increase than during the day.
- Greenhouse Gas Emissions: CO₂, methane, and other greenhouse gases trap heat in the atmosphere around the clock. While the sun drives daytime warming, these gases prevent heat from escaping at night — making nights warm faster than days.
- Increased Atmospheric Moisture (Water Vapor): As the planet warms, evaporation increases, and the atmosphere can hold more moisture (about 7% more moisture for every 1°C of warming). Humid air holds onto heat far better than dry air. When nighttime humidity is high, it prevents the air temperature from dropping significantly, resulting in persistently hot nights.
- The Urban Heat Island Effect: Cities are significantly hotter than surrounding rural areas at night due to:
- Concrete and asphalt: Absorb heat during the day and release it slowly at night.
- Dark surfaces: Low albedo (reflectivity) means more solar energy is absorbed.
- Lack of vegetation: Fewer trees means less evaporative cooling
- Waste Heat: Air conditioners, vehicles, and industrial machinery run around the clock in cities, pumping literal “waste heat” directly into the nighttime environment.
- Deforestation: Trees provide shade and release moisture through transpiration, cooling the air at night. Clearing forests removes this natural cooling mechanism, leading to warmer nights in affected regions.
- Cloud Cover Changes: Clouds trap heat beneath them at night (similar to greenhouse gases). Changes in cloud patterns due to climate change are contributing to warmer nights in many regions.
- Land Use Changes: Converting forests and wetlands into farmland or urban areas reduces natural cooling. Irrigated farmland can increase humidity, which in turn traps more heat at night.
What are the impacts of rising nighttime temperatures?
- Impact on Human Health: During heatwaves, high nighttime temperatures are actually more dangerous than daytime peaks. If the temperature doesn’t drop enough at night, the human body can’t cool down and recover from the daytime heat stress. For vulnerable groups (such as the elderly, infants, outdoor workers, and people with heart or kidney disease) this lack of nighttime relief drastically increases the risk of heatstroke and cardiovascular failure.
- Impact on Agriculture:
- Many crops and plants require a period of cooler nighttime temperatures to rest and regulate their metabolism.
- High nighttime temperatures have been directly linked to lower yields in major global staples like rice, corn, and wheat. For example, research shows that for every 1°C increase in nighttime minimum temperatures, rice yields can drop by roughly 10%.
- Like humans, dairy cows, pigs, and poultry rely on cool nights to shed daytime heat. Persistent nighttime heat causes severe heat stress in animals, leading to lower milk production, reduced fertility, and higher mortality rates.
- Economic Costs:
- Demand for air conditioning surges through the night, straining power grids and increasing electricity costs. This relentless demand deprives power grids and transformers of the cool night hours they need to cool down mechanically, leading to a higher frequency of brownouts, blackouts, and equipment failures.
- Buildings, roads, and bridges experience more thermal stress as they get less nighttime cooling, accelerating wear and tear.
- Urban infrastructure designed for historical temperature ranges becomes increasingly inadequate.
- Intensified Wildfires: As nights warm, the relative humidity stays low, preventing the nighttime moisture recovery that used to naturally dampen fires. Wildfires now remain aggressively active through the night, making them much more unpredictable and dangerous to combat.
- Ecosystem Imbalance: Many nocturnal animals, insects, and pollinators are adapted to specific nighttime temperature ranges. Warmer nights alter their hunting patterns, reproductive cycles, and geographical ranges, throwing entire local food webs out of sync.
- Aggravated Air Pollution: Rising nighttime temperatures can trap pollutants close to the ground. When the night stays warm, it alters the stability of the lower atmosphere, preventing the dispersion of ground-level ozone and particulate matter (PM 2.5). This creates stagnant, toxic air in the urban areas.
What needs to be done?
- Emission Reduction: To permanently slow down the rise of nighttime temperatures, global society must rapidly transition away from fossil fuels and toward renewable energy, halting the accumulation of carbon dioxide and methane that traps infrared heat at night.
- Redesign Cities to Combat the Heat Island Effect:
- Cool Pavements and Roofs: Replacing traditional dark asphalt and roofing with highly reflective materials (cool roofs and cool pavements) prevents surfaces from absorbing solar radiation during the day.
- Massive Urban Greening: Planting trees, creating pocket parks, and installing green roofs. Plants naturally cool the air through evapotranspiration and provide shade that prevents the ground from heating up in the first place.
- Wind Corridors: Designing city layouts with building heights and spacings that encourage natural wind flow. This helps flush trapped heat out of urban centers after sunset.
- Revising Heatwave Definitions: Weather bureaus must issue heat warnings based on minimum nighttime temperatures, not just daytime peaks. A day that hits 38°C followed by a 28°C night is far more dangerous than one followed by a 20°C night.
- Smart Grid Management: Power companies must fortify the electrical grid to handle 24/7 peak demand, incorporating large-scale battery storage to handle the relentless overnight air conditioning load without blackouts.
- Agriculture Adaptations:
- Develop and promote heat-tolerant crop varieties that can withstand warmer nights.
- Use night-time irrigation techniques to cool soil and crops during warm nights.
- Shift planting schedules to align with changing temperature patterns.
- Install automated misting systems and fans in barns that trigger specifically at night to help dairy cows and livestock shed daytime heat stress.
- Cooling Shelters & Infrastructure: Cities need to provide 24-hour cooling shelters for those without AC at home, as well as cool bus stops and public water kiosks where people can access relief at any hour.
| UPSC GS-1: Geography Read More: Indian Express |
