Large parts of India have warmed, hit by frequent hot days, say climate scientists

  • Over 60 percent of India, except for the Indo Gangetic plains, has experienced significant warming in the 1951-2015 period, a study has said. A climatic shift has also been noted with a pronounced increase in frequency of hot days in the last four decades, according to another study.
  • From 1951 to 2015, the summer of 2010 was the hottest summer in the arid, cold, and temperate regions of India and it was linked to human actions. Due to human-induced warning, India is likely to experience summers like the hottest summer more often.
  • Before the 1976 climate shift (i.e., during 1951-1975) the eastern and southern parts of India experienced marked rise in the frequency of hot days; whereas, after the 1976 climate shift hot days have significantly increased over the northwestern parts and along the western coast.
  • The researchers said adaptation and mitigation, including education, will play a crucial role in reducing the adverse impacts of climate change in the short and long-term.

As India gears up for warmer than normal summer temperatures in 2020, climate scientists say large parts of India, except for the Indo-Gangetic plains, have experienced significant warming in the last 60 years due to human-induced climate change. A climatic shift has also been noted with a pronounced increase in frequency of hot days in the last four decades, scientists said.

The India Meteorological Department recently said the March-April-May (MAM) season average temperatures are likely to be warmer than normal over most of the meteorological subdivisions of northwest, west and central India and some subdivisions from south India. Near normal temperatures are likely in the remaining subdivisions.

The World Meteorological Organisation in a Statement on State of the Global Climate 2019 released on March 10, 2020, said 2015-2019 are the five warmest years on record, and 2010-2019 the warmest decade on record. Since the 1980s, each successive decade has been warmer than any preceding decade since 1850.

“We find that more than 60 percent of India has experienced significant warming during the 1951-2015 observed record. The rise in summer temperature is already more than one degree in the last 60 or so years,” Vimal Mishra of the Water and Climate Lab at Indian Institute of Technology (IIT)-Gandhinagar told Mongabay-India referring to his latest study that taps into India Meteorological Department’s observed data as well long-term simulations of 2,000 years that helps understand the future changes.

Mishra and colleagues identified the hottest summer in the observed record (1951 to 2015) across five climatic regions in India. 

“The hottest summers in the observed record occurred once in 60 or so years and had lasting impacts on public health, water availability, agriculture, and labour efficiency. Due to anthropogenic warming, we will witness the summers like the hottest summer more often, which will affect various aspects of socio-economic well being,” explained Mishra.

For instance, a study of health impacts on construction workers in Gandhinagar, Gujarat, showed that heat stress levels were higher than those prescribed by international standards, highlighting the need for revision of work practices, increased protective measures, and possible development of indigenous work safety standards for heat exposure.

Expanding on his latest study, Mishra said the five regions classified in the study are: arid regions, which includes both arid and semi-arid regions in the northwestern parts of India and rain shadow regions in the Indian peninsula; cold regions, which encompass all the Himalayan states of the country; tropical monsoon forest regions that includes the western coast of India and the southern parts of the northeastern states where the southwest monsoon hits the earliest in the country.

The tropical Savannah regions that comprise the tropical regions in India; and temperate dry summer regions, which encompass the Gangetic and Brahmaputra plains and the narrow belt in Punjab-Haryana plains that receives moderate rainfall during the summer monsoon season are the other two regions.

“Hottest summers in different climatic regions can be linked to natural climate variability as well as anthropogenic climate change. The hottest summers of 1979 and 1973 are not linked with anthropogenic warming rather those were caused by natural climate variability,” noted Mishra.

However, the study identifies the summer of 2010 as the hottest summer in the arid, cold, and temperate regions during the observed record period and it was found to be directly associated with warming linked to human actions.

India experienced one of the worst heatwave spells in the last several decades. Map Source: NASA.

“Further, our analysis shows that if the global mean temperature increases to two degrees from the pre-industrial level (1861-1890), the chances of getting the summers like the observed hottest summer will increase by about seven times,” said Mishra, adding that climate change mitigation can help reduce the rise in global mean temperature but it is unlikely to limit the warming under two degrees by the end of the 21st century using the best possible mitigation measures.

The observed cooling over the Indo-Gangetic Plain in IMD data can be attributed to irrigation and the presence of atmospheric aerosols. Intensive irrigation over the Indo-Gangetic plain results in cooling of the surface as well as air temperature as reported in the previous studies, the authors said.

Mishra said said adaptation and mitigation will play a crucial role in reducing the adverse impacts of climate change in the short and long-term.

Agreeing with the study findings, Krishna AchutaRao, professor, Centre for Atmospheric Sciences at Indian Institute of Technology Delhi, who was not associated with the research, said the increases in risk ratio are not uniform across the country.

“So the action required will have to take this into account and produce specific
plans for specific regions. This will definitely help policymakers,” AchutaRao told Mongabay-India in response to a query on research feeding into policy.

Another study suggesting a climatic shift has shown that most of India, except the Indo-Gangetic plains, has experienced more frequent hot days having higher temperatures in recent years (1976 to 2018).

“Our results provide compelling evidence that large parts of India, except the Indo-Gangetic plains, have experienced more occurrences of hot days (upsurge by 24.7 percent) having higher temperatures in the recent period (1976–2018), compared to the past (1951–1975), which suggests a shift in climate,” said corresponding author M.K. Joshi of the Indian Institute of Tropical Meteorology (IITM), Pune.

Joshi and colleagues Archana Rai (IITM), Ashwini Kulkarni (IITM), and Fred Kucharski, at International Center for Theoretical Physics, Trieste, Italy, diagnosed the change in characteristics (i.e., frequency and intensity) of hot extremes over India before and after the 1976 climate shift.

The scientists used IMD dataset (gridded temperature data) developed using the daily maximum temperature of 395 quality control stations all over India. Because grids in extreme north and northeast regions have inconsistent data, these grids are excluded from the analysis and set to as missing values.

The study indicated a geographical shift in the uptick in the frequency of hot days.

“Before the 1976 climate shift (i.e., during 1951-1975) the eastern and southern parts of India experienced marked rise in the frequency of hot days; whereas, after the 1976 climate shift (i.e., during 1976-2018) hot days have significantly increased over the northwestern parts and along the western coast indicating a spatial shift of significant increasing trends in frequency of hot days,” Joshi said.

They also explored the driving mechanisms (including atmospheric patterns, local factors, and natural variability associated with El Nino/Southern Oscillation) responsible for such hot extremes that can help in mitigation and adaptation.

El Nino and the Southern Oscillation, also known as ENSO is a periodic fluctuation in sea surface temperature (El Niño) and the air pressure of the overlying atmosphere (Southern Oscillation) across the equatorial Pacific Ocean.

“Based on preceding ENSO, the periodic fluctuation in sea surface temperature and the air pressure of the overlying atmosphere across the equatorial Pacific Ocean, hot extremes over India can be potentially anticipated in advance and this will help society to prepare for such extremes,” Joshi told Mongabay-India in an email in response to questions.

Joshi said since soil moisture also has a role in controlling severely hot days, practices such as those involving the selection of environment-friendly building materials and expansion of vegetation, can help maintain soil water levels.

“The building materials used in urban spaces are water-resistant surfaces and don’ allow water to flow through surfaces. So, without the cycle of flowing and evaporating water, these surfaces can’t cool automatically. Planting more trees for shade will prevent solar radiation from reaching surfaces that absorb heat. In addition to this,  evapotranspiration from plants cools the air around it,” Joshi added.

Local weather labs

Stepping up climate change education is also a key mitigation tool and the UNESCO states education is an essential element of the global response to climate change. One such educational initiative that has unfolded in the cold Himalayan states involves setting up school weather labs.

In Sikkim, which has recently seen harsh summers and has introduced climate change studies in its school curriculum, efforts are on to train students into maintaining and monitoring school-based local weather stations, set up under a climate change initiative run by Indian Institute of Public Administration (IIPA) and SEEDS, in collaboration with Sikkim State Disaster Management Authority (SSDMA). The lab builds on pilots in Leh, Chamoli, and Gangtok.

At the recent launch of the Sunny Weather Lab, in a government-run school in Soreng, West Sikkim, eight-year-old Nancy Rai, who is from a school in East Sikkim enthusiastically explained the equipment that measure atmospheric pressure, temperature and several other parameters, to students who would be running the weather station in Soreng. Rai is experienced with the weather lab in her school, a laboratory set-up installed in schools for children to record daily weather conditions.

“In the weather lab set up at our school, we are learning to measure and document daily weather through six parameters. They are temperature, humidity, atmospheric pressure, wind speed, wind direction, and rainfall. The weather changes from valley to valley in Sikkim and a dense network of stations are needed,” Rai told Mongabay-India during the launch of the weather lab in March 2020.

School students discuss the working of a weather station in Sikkim. Photo from SEEDS.

According to Vinod Sharma, a senior professor of disaster management at IIPA and vice-chairperson, SSDMA, extreme weather events are common in Sikkim.

“Summers are very harsh since the last few years. Rainfall has not changed but rainy days have reduced. The size of the rain droplets has expanded. More thunderstorms, hailstorms, cloudbursts are observed each year which increases the frequency of landslides,” Sharma told Mongabay-India, adding that crops such as cardamom and oranges have been hit by climate change. A recent study on the Teesta river basin in Sikkim shows a clear sign of an increase in rainfall and temperature in the 21st century.

IITM’s Joshi believes such school weather stations can help in data gathering for documenting a changing climate but data has to be collected for the long-term for a climate change perspective and maintenance of equipment should be ensured.

India experienced a prolonged heatwave in 2019. According to a McKinsey Global Institute (MGI) report released in January 2020, most of the increase in direct impact from climate hazards to date has come from greater exposure to hazards rather than from increases in the mean and tail intensity of hazards. In the future, hazard intensification will likely assume a greater role. Outdoor labour productivity is also expected to be impacted, reducing the effective number of hours that can be worked outdoors, the report states. By 2030, the average number of lost daylight working hours in India could increase to the point where between 2.5 and 4.5 percent of GDP could be at risk annually, according to the report estimates.


Nanditha, J. A., van der Wiel, K., Bhatia, U., Stone, D., Selten, F. M., & Mishra, V. (2020). A seven-fold rise in the probability of exceeding the observed hottest summer in India in a 2° C warmer world. Environmental Research Letters.

Joshi, M. K., Rai, A., Kulkarni, A., & Kucharski, F. (2020). Assessing changes in characteristics of Hot extremes over india in a Warming environment and their Driving Mechanisms. Scientific reports10(1), 1-14.

Banner: People beat the summer heat by covering up in scarves. Photo by Sankara Subramanian/Flickr.


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