The India Meteorological Department (IMD) is strategizing on how to implement a ‘heat index’ warning system in Delhi and other regions in India. This proposal comes after a study they conducted on the impact of meteorological factors on heatwaves and the country’s “heat wave hazard zonation”. According to the IMD’s “Hot Weather Analysis over India,” the way heat affects humans is sophisticated, involving interactions between temperature, radiation, wind, and humidity. There is substantial experimental evidence suggesting that high temperatures cause more significant physiological stress when the humidity is also high.
About the Proposed Heat Index
The proposed Heat Index aims to combine temperature and humidity levels to give a more accurate measure of the perceived temperature. In the United States, a color-coded heat index system offers warnings based on heat impact. The IMD plans to introduce a similar mechanism in India. The Heat Index is especially significant because of its implications for human body comfort. The body starts to sweat or perspire to cool off when it gets too hot. If this perspiration doesn’t evaporate, the body can’t regulate its temperature—evaporation cools, effectively lowering the body’s temperature when perspiration evaporates. High atmospheric moisture content or high relative humidity slows the rate of evaporation from the body, making us feel warmer. Conversely, we feel cooler in arid conditions as low relative humidity increases perspiration rate. Therefore, there’s a direct correlation between air temperature, relative humidity, and the heat index.
An Overview of Heatwaves
A heatwave is an unusually long period of extremely high temperatures, common in India during May-June, and in rare instances, extending into July. The term ‘heatwave’ applies when a location’s maximum temperature reaches at least 40°C for Plains and 30°C for Hilly regions. To mitigate the impact of heatwaves, the National Disaster Management Authority (NDMA) outlined comprehensive guidelines in 2016 for devising national-level strategies.
Factors Contributing to Delhi’s Comparedly High Temperatures
There are several reasons why temperatures in Delhi often feel higher than recorded levels. One of these is the Urban Heat Island Effect, where concrete, buildings, and asphalt absorb and retain heat, making the temperature seem hotter. Additionally, high pollution levels from stubble burning in Punjab and Haryana, vehicular emissions, and construction dust can trap heat and create a blanket effect, resulting in a warmer city. Delhi’s high humidity can further elevate air pollution levels. Additionally, Delhi’s inland location deprives it of the cooling influence of large water bodies like seas or lakes, contributing to hotter perceived temperatures.