Does Delhi feel hotter than it is? IMD to give answers soon

This summer, Delhi could have a similar colour-coded warning system in place that can provide information on the possible impact of the heat index and suggest actions.

IMD scientist Kuldeep Srivastava said, “We expect that this summer, we will be able to do a heat hazard analysis for the country. We may initially begin with Delhi and then expand to other parts of the country. Our temperature here in Delhi may be close to 40 degrees, but it feels hotter. This is because of high relative humidity levels, that is moisture is higher in the atmosphere and sweat is unable to evaporate, meaning that discomfort is higher.”

In Delhi, the heat index is likely to be available for the Safdarjung weather station, since long-term data on temperature, wind and humidity are available for this observatory. “We are also collecting more data and this will be expanded. It may be map-based. There has been a demand for this sort of index over the past few years. This is being planned but could take some time to be operational since it needs more study. We hope to make it operational by around May or June this year. It will be like a warning, possibly a colour-coded one on what sort of impact the heat index can have and what actions are to be taken,” Srivastava said.

Humidity levels in Delhi rise around June and July. When the monsoon sets in, easterly winds bring moisture from the Bay of Bengal.

On being asked about the heat index in July last year, IMD Director General Mrutyunjay Mohapatra told The Indian Express, “This type of index we are developing based on past data. That will be available, perhaps, next year. Based on historical data on temperature, humidity, wind speed etc, we are preparing an index. Based on the index, we will be able to find out the heat hazard proneness of various districts. Most probably, by the next heatwave season, we will have this.”

Srivastava pointed to a recent study by IMD scientists on the impact of different meteorological factors on heat waves and the “heat wave hazard zonation” of the country.

The study, ‘Hot weather analysis over India,’ by IMD scientists Akhil Srivastava, Naresh Kumar, and M Mohapatra, said, “The mechanism by which heat impacts humans is complex; it is a result of the interactions between temperature, radiation, wind, and humidity. There is strong experimental evidence that physiologic stress from high temperatures is greater if humidity is higher. However, heat indices developed to allow for this have not consistently predicted mortality better than dry-bulb temperature. Further few studies have demonstrated that metrics which are thought to be better predictors of physiological heat stress by considering several weather conditions simultaneously may not be better at predicting heat-related mortality, which has significant implications in the heat wave and health warning systems.”