Most parts of India, including those in peninsular India and the coasts will see an increase in duration of heatwave by 12-18 days by 2060, a new report from the India Meteorological Department (IMD) released Tuesday said, recommending a comprehensive response plan for heatwaves which includes cultural, institutional, technological and ecosystem-based adaptation strategies.
The recommendations of the report titled “Heat and Cold Waves in India Processes and Predictability” include: improving India’s buildings through ventilation and insulation; raising awareness about heat stress; changing work schedules; providing early warning; and creating cool shelters.
Heatwaves have claimed more lives in India than other natural hazards, with the exception of tropical cyclones, IMD said in its report. It has used data from 1961-2020 to decipher heat wave climatology and occurrence.
A heatwave is declared by IMD when the maximum temperature is above 40 degrees Celsius and 4.5 degrees above normal. A severe heat wave is declared when the temperature is above 40 degrees Celsius and 6.5 degrees above normal. Heatwaves usually occur in the period from March to June in central and north-western India (heatwave zone) and in the coastal areas of Andhra Pradesh and Odisha. In this region, the frequency of heat waves is slightly lower than in northern India.
On an average more than two heatwave events occur over northern parts of the country and coastal Andhra Pradesh and Odisha. In some pockets, heatwave frequency even exceeds four in a season. Most IMD stations show increasing trends of heatwave events during the 60-year period in terms of heatwave duration; frequency and severity. The authors provide maps to show how these trends are rising over most of IMD’s meteorological stations.
“There are on average two to three heatwaves in a year; the total duration of heatwaves has increased by three days over the last 30 years. In future we expect an increase in two heatwaves per year which would mean 12-18 heatwave days by 2060. Most importantly, peninsular India and coastal regions where heatwaves are not common will also record heatwaves in future scenarios,” said M Rajeevan, former secretary, ministry of earth sciences and co-author of the report.
Over central and northwestern India and coastal Andhra Pradesh, the longest heatwave exceeds 10 days at many stations. Over the far northwest of India, the longest even exceeded 15 days. The longest severe heatwave generally lasts more than five days in central and north-western India, while it is less than that over the southern peninsula including the Andhra Pradesh coast, the report found.
Global models referred to by the report suggest an increase of about two heatwaves and an increase in duration of heat waves by 12-18 days over the period 2020-2064, due to global warming.
The future increase in heat waves will be supported by the strengthening of the mid-tropospheric high and the associated subsidence over central and northwest India. Land surface processes such as soil moisture depletion and increased sensible heat fluxes are also responsible for the increase in heatwaves, the report said.
Studies referred by the report suggest the frequency of severe heat waves will increase by 30 times the current climate by the end of the 21st century if the global average temperature is limited to 2 degree C above pre-industrial conditions.
“Based on an ensemble of high-resolution climate change simulations, the study found that wet bulb temperature (35 degree C) extremes in South Asia are likely to approach and exceed this critical threshold in a few places by the end of the 21st century under the business-as-usual scenario of future greenhouse gas emissions. The greatest risk from extreme heatwaves is in the densely populated agricultural regions of the Ganges and Indus River basins,” the report said.