As per a report by PTI, selecting a heatwave index is crucial for identifying dangerous conditions across varied geographies and weather. This was according to a study that found many existing indices failed to capture the severity of heat waves, including those in India.

Heatwaves have become more frequent and intense as the planet warms, emerging as a significant contributor to heat-related deaths.

Furthermore, in the study, published in the journal Nexus, the researchers from The Hong Kong Polytechnic University analysed six available heat wave indices, including the Wet Bulb Globe Temperature (WBGT) index and Canada's humidex.

WBGT index was first developed in the 1950s by the United States (US) military to prevent heat-related illnesses in training camps.

The authors found that five failed to identify dangerous heat stress days during the heatwaves of Spain and the US in 2022 and those in 2023 in India's West Bengal and Uttar Pradesh.

Because of low humidity, the air was largely dry during these heat waves, even as these regions registered record-breaking temperatures, they said.

How lethal a heat wave is depends not only on temperatures recorded but also on humidity in the air, the researchers said.

Moreover, the authors found that of the six indices they studied, only one — the 'lethal heat stress index' — was able to account for these countering effects of dry air, and therefore, performed better in identifying days with dangerous heat wave conditions.

The lethal heat stress index is based on temperature and humidity for identifying conditions that could likely lead to human death, as opposed to others that use labels such as 'extreme danger' and 'heat stroke imminent', the authors said.

"The lethal heat stress index applies a correction factor to relative humidity, which means that it is better at predicting dangerous heat conditions in regions which have very low humid conditions compared to the other indices," said first author Pir Mohammad, an earth scientist at The Hong Kong Polytechnic University.

Besides that, the recent study's results emphasise the limitations of available heat indices in detecting dangerous heatwave conditions, especially when humidity in the air is low, the authors said.