Beyond Temperature: Humidity’s Hidden Impact on Heatwaves

With summer approaching in many regions, temperatures are already rising to higher levels, indicating that this season will be hotter than usual, mainly because of the expected El Niño effect.

However, with rising temperatures and the potential of heatwaves (a period of abnormally hot weather), a basic question arises: Does temperature alone accurately reflect how hot it feels?

While temperature is an important factor, there’s more to the equation. Have you ever wondered why coastal destinations like Goa and Chennai feel hotter in the summer, even when the thermometer reads only 35°C, compared to blistering Delhi, where temperatures can reach 45°C?

The answer lies in a less obvious factor: humidity levels, a hidden factor that greatly influences how we perceive heat.

As the temperature rises, our bodies rely on sweating to cool down, which evaporates and provides a cooling effect. But this sweating mechanism loses efficiency in high-humidity environments, which makes it more difficult for our bodies to naturally cool down and intensifies the sensation of heat.

Yet another question arises: Is there a more precise way to measure this sensation? Yes, there is. It’s called the apparent temperature or heat index. This metric considers both temperature and humidity, providing a more accurate representation of how hot it truly feels to the human body.

When humidity is factored in, the heat index can be significantly higher than the actual air temperature. The table below shows the apparent temperature, or heat index, based on air temperature and relative humidity.

Let’s compare Chennai and Delhi on May 15, 2023. According to the heat index chart, Chennai’s temperature of 35°C and 60% humidity result in a heat index of approximately 46°C.

In comparison, Delhi’s heat index stays at 41°C with 20% humidity. This shows that, despite Chennai’s lower temperature, it seems hotter due to increased humidity.

In dry, low-humidity environments, humans can survive temperatures up to around 54°C. However, in high-humidity conditions, this threshold drops significantly to as low as 31–35°C.

Effect of climate change on Humidity levels
Rising global temperatures as a result of global warming and climate change cause water to evaporate quicker from our oceans and waterways, increasing humidity.

According to the Lethal Humidity Global Council, for every 1°C rise in global temperature, humidity rises by about 7%.

Higher humidity levels have serious consequences, including reduced economic growth and productivity. Furthermore, health crises caused by increased core body temperatures, can result in serious results such as heart attacks, strokes, and even death.

Given the reality of climate change, it is critical for governments and leaders across the world to address rising humidity levels and associated threats to protect both human health and the environment.

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