This summer: Most number of heatwave days and still counting

Odisha registered as many as 27 heatwave days between  March 1 and June 9, IMD data shows. This was the highest number for any state in the country. Rajasthan recorded 23 heatwave days while Haryana, Delhi and UP had at least 20 days each. Even Jammu and Kashmir experienced six days of heatwaves.

Heatwaves have a very specific temperature-dependent definition. In general, a heatwave is declared when the maximum temperature in at least two stations in an area goes either above 45 degrees Celsius, or is above 40 degrees Celsius and at least 4.5 degrees Celsius above normal.

This condition must be met for at least two consecutive days. For hilly or coastal locations, the temperature threshold for heatwaves is 30 and 37 degrees Celsius, respectively.

Heatwaves are declared only in the officially designated summer season that stretches from March to June. So, last year, heatwave-like conditions had prevailed as early as February in some parts of the country, but could not be declared as such.

“The summer season is not yet over, so we do not have complete data. But I don’t think there is any doubt that heatwaves this year have been one of the most intense ever, if not the most intense. Part of the reason could be that this year follows an El Nino season. We have seen earlier as well that the year following an El Nino had produced more intense heatwaves. An example is 2010. But that is only one factor influencing this. Several other factors are also at play,” said M Rajeevan, former Secretary in the Ministry of Earth Sciences.

Under El Nino, the eastern Pacific Ocean warms up more than usual setting off global temperature hikes.

Rajeevan said the impacts of heatwaves on public health were now well-acknowledged and work had been done by IMD, National Disaster Management Authority, state governments and other agencies to minimise the health impacts. But there were other consequences as well, he said.

“Heatwaves are going to become more frequent, more prolonged and more intense going forward. There are implications for water resources, our energy supplies, our agriculture. The economy as a whole is going to be impacted. Some of these impacts are not very well understood. So we need to work a lot towards adapting to these heatwaves,” he said.

As many as 23 states and union territories in the country are considered vulnerable to heatwaves. Each one of them now has a heatwave action plan to deal with the situation. Almost each one of them experienced heatwaves this year, the only exception being the states in the Northeastern region.

Heat-related deaths are widely acknowledged to be going down in the last one decade, but the quality of this data has been called into question. In any case, the heatwave deaths have been showing an upward trend in the last couple of years.

The spread of heatwaves has also been increasing.

“Till a few years ago, heatwaves were mostly restricted to the northern plains and central part of the country. Coastal Andhra Pradesh and Telangana used to be affected but the southern peninsula by and large did not see heatwaves. Not a prolonged or intense heatwave in any case. But now almost the entire country is experiencing heatwaves, even hilly states like Himachal Pradesh or Uttarakhand, and southern states like Tamil Nadu and Kerala,” said K J Ramesh, former director of IMD.

“Also, these are beginning early in the season, in March itself. Traditionally, April and May have been the hottest months. They still are. But increasingly, we are seeing large temperature anomalies in March, and even in February as was seen last year,” he said.