Climate crisis transformed Indian summer; the worst, say experts, is yet to come
Indian summer or what the India Meteorological Department (IMD) calls “pre-monsoon season” in March-April- May has seen a very clear shift in its intensity since 1998. Even as IMD warned of a harsh summer this year with high probability of very hot days and warm nights, long-term data 1971 onwards suggests a shift to considerably warmer than normal summers since 1998 and more than double the number of deadly heatwave events.
The year 2010 recorded the worst summer since 1971with its mean temperature recorded as nearly 29 degrees Celsius compared to the average 27.6 degrees Celsius according to IMD’s climate diagnostic bulletin. Interestingly, last year was the least warm summer since 1998. “El Niño conditions associated with warm summers had started weakening in the summer of 2020. You can see that effect. Also, rainfall data shows there was rainfall and a lot of related activity along the Himalayan foothills during the period which helped bring down temperatures. So, 2020 stands out for not being so warm,” explained DS Pai, senior climate scientist at IMD Pune.
But the outlook for 2021 is worrying. According to IMD’s Monsoon Mission Coupled Forecasting System (MMCFS), the forecast suggests above-normal seasonal maximum and minimum temperatures are likely over most of the subdivisions of north, northwest and northeast India, few subdivisions from eastern and western parts of central India and few coastal subdivisions of north peninsular India. Over the Indo-Gangetic Plains region there is a 60% to 70% probability that maximum temperatures are likely to be 0.56 degrees Celsius to 0.71 degrees Celsius above normal, while minimum temperatures are likely to be about 0.12 degrees Celsius above normal. But it also indicates that La Niña (a global weather phenomenon which has a cooling effect) conditions are likely to prevail from March to May.
“After 1998, there has been a shift in summer temperature patterns compared to the 70s and 80s when summer temperatures were mostly below normal. This is a climate change signal. But even during the above-normal summer temperature epoch, there is decadal variation. Models are telling us summers are going to get even warmer,” added Pai.
IMD is now working on new policies for better preparedness during summer. It will issue heatwave warnings valid up to five days every day, which will be updated four times by the national weather forecasting centre. Impact-based heatwave warnings will also be issued wherein the general public will be advised how to protect themselves. For example, if a severe heatwave is likely to persist for more than two days or the total number of continuous heatwave days is over six, then vulnerable people will be asked to take extreme care. There could be a high likelihood of all age groups developing heat illness and heat strokes during such conditions. IMD will also provide meteorological support to states and districts for preparation of heat action plans, according to a statement by the department.
Though summer’s mean temperatures are rising, they often mask the impact of heatwaves. There are two parameters for recording of heatwaves—when the maximum temperature is at least 40 degrees Celsius and departure from the normal is 4.5 degrees Celsius to 6.4 degrees Celsius. A heatwave is also declared when maximum temperature is over 45 degrees Celsius for two stations in a sub-division for two days.
The frequency, total duration and maximum duration of heatwaves during the hot summer months (April–June) are increasing over central and northwestern parts of India. The increase in the number of intense heatwaves between March and June in India over the last decade was attributed to the presence of an upper-level cyclonic anomaly over the west of North Africa and a cooling anomaly in the Pacific, according to a report by the Ministry of Earth Sciences released last year titled Assessment of Climate Change over the Indian Region.
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A paper titled “An assessment of long-term changes in mortalities due to extreme weather events in India: A study of 50 years’ data, 1970–2019” led by scientists from the Ministry of Earth Sciences published in Science Direct journal on February 26 reveals that the number of heatwave events increased by 9.90 per year between 1980-99 to 23.55 between 2000 and 2019. Mortality associated with heatwaves increased from 19.46 per event between 1980-99 to 23.54 between 2000 and 2019.
But there is likely to be gross under-reporting of deaths due to heatwaves. “States will have to be ready with heat action plans. The National Disaster Management Authority along with Indian Institute of Public Health will be reviewing preparedness of states next week. This year, summer has arrived early so we have to be prepared,” said Dileep Malvankar, director, Indian Institute of Public Health, Gandhinagar, adding, “States should monitor all cause mortality and compare it with the data for the last five years during heatwave periods. Hospital admissions with heat-related complications will also have to be monitored. People should be alerted in advance and advised on how to avoid health effects of heat stress. In the long run, we need greening of cities, cool-roofing and staggered work hours, especially for outdoor activities.”
The frequency of summer (April–June) heatwaves over India is projected to be three or four times higher by the end of the twenty-first century under the RCP8.5 scenario (wherein greenhouse gas emissions remain uncontrolled), as compared to the 1976–2005 baseline period. The average duration of heatwave events is also projected to double, the MoES has cautioned in its 2020 assessment report.
The average total duration of summer heatwaves in India is likely to be about 25 and 35 heatwave days per season during the mid- and end-twenty-first century respectively, if global emissions are not curbed dramatically. The CORDEX ensemble shows that mean change in the frequency of heatwaves for the mid- and end-twenty-first century are likely to be higher over northwest India (more than three days per summer season) compared to other parts of India.