The City That Never Cools
The core of the problem lies in a phenomenon known as the Urban Heat Island (UHI) effect. During the day, the materials that make up our cities—concrete buildings, asphalt roads, and other dense infrastructure—act like massive sponges for solar radiation.
Unlike natural landscapes with vegetation and soil that stay cooler through shade and evapotranspiration, these man-made surfaces absorb and store vast amounts of heat. This causes city temperatures to be significantly higher than in surrounding rural areas. Studies show that this effect is particularly pronounced in India's rapidly expanding urban centres.
Concrete's Night-Time Secret
What happens to all that heat absorbed during the day? It doesn't just disappear. As the sun sets and the outside air begins to cool, concrete and asphalt start to release the thermal energy they've stored. This process is incredibly slow, acting like a 'thermal flywheel' that radiates warmth back into the environment throughout the night. That’s why your terrace or balcony can still feel warm to the touch hours after sunset. This slow release prevents the city from cooling down effectively, keeping nighttime temperatures uncomfortably high.
Humidity: The Insulating Blanket
Humidity is the game-changer during the monsoon. While rain can offer a temporary drop in temperature, it loads the air with moisture. This water vapour acts like an insulating blanket, trapping the heat that is being radiated from the ground and buildings. The moist air holds heat more effectively than dry air, preventing it from escaping into the upper atmosphere. This trapped heat leads to a smaller temperature difference between day and night, contributing to persistently warm and muggy nights. Recent studies highlight an alarming rise in dangerously humid days and warm nights across the Indo-Gangetic plain, linked to warmer oceans pushing more moisture inland.
Why You Feel Even Hotter
It’s not just your imagination—high humidity makes the heat feel more intense. Our primary way of cooling down is through sweat, which removes heat from the body as it evaporates. However, when the air is already saturated with moisture, this evaporation process slows down dramatically. Sweat clings to the skin instead of vanishing, making our natural cooling system inefficient. This is why the 'feels like' temperature, or heat index, is often much higher than the actual reading on the thermometer during the monsoon. You feel sticky, uncomfortable, and hotter because your body is struggling to regulate its temperature.
