New Delhi: Central and northwestern parts of India are witnessing a spike in both the frequency and duration of heat waves, shows a study that analysed daily temperatures for the last 50 years.
The study conducted by Indian scientists and published in Scientific Reports, one of the Nature Publishing Group’s journals, also said that further warming of the tropical Indian Ocean and more frequent El Nino events may lead to even more frequent and longer spells of heat waves across the India.
The study said that in northwest India, the frequency of heat waves has increased by one event in 20 years and that the average duration of heat waves has risen by two days per decade.
For the study, the researchers analysed a gridded daily temperature data set for the period between 1961 and 2013 to find trends in heat waves across the country.
Several other studies have already pointed to an increase in the frequency, duration and intensity of heat waves over land regions across the globe.
The India-specific heat wave trend could improve heat wave predictions in the future, according to one of the co-authors of the study.
In India, heat waves have caused more deaths than any other natural hazard. In May 2015, severe heat wave in parts of south-eastern India, Telangana and Andhra Pradesh killed 2,500 people.
In this study, the scientists showed that the frequency, total duration of heat waves per season and maximum duration of heat waves are increasing in India during the April to June summer season.
“A heat wave event usually lasts for five to seven days and there are supposed to be 2-3 spells in a year. But that frequency has now increased to four events a year on an average,” said M. Rajeevan, co-author of the study and secretary, ministry of earth sciences.
“The time series of frequency, duration and maximum duration clearly suggests a link between the El Nino events and heat wave events over India,” said the study.
The years that record above-normal heat wave activity in India are also the years that follow El Nino events, such as 2016.
Sea surface temperature in the Indian and Pacific Oceans play a large role in the creation of heat waves, suggests the study, adding that increases in greenhouse gase emissions can also lead to further warming of the oceans.
“With warming of the tropical Indian Ocean and increasing frequency of extreme El Nino events, more frequent and long lasting heat wave events are likely over the Indian sub-continent in near future,” concluded the study.