Monsoon season was 0.58 degree C warmer this decade than long-term average
Anumita Roychowdhury, CSE’s executive director (research and advocacy), called this a very disturbing trend as policy preparedness to mitigate rising heat due to climate change is nearly absent in India
The June to September monsoon season has been 0.3-0.4 degrees Celsius hotter than pre-monsoon seasons in the decade from 2012 to 2022, according to a new Centre for Science and Environment (CSE) analysis based on India Meteorological Department (IMD)’s long-term data.
Anumita Roychowdhury, CSE’s executive director (research and advocacy), called this a very disturbing trend as policy preparedness to mitigate rising heat due to climate change is nearly absent in India. “Without heat action plans, rising air temperature, radiating heat from land surfaces, concretisation, heat-trapping built structures, waste heat from industrial processes and air conditioners, and erosion of heat dousing forests, urban greens, and water bodies will worsen public health risks,” she said in a statement. “This requires an urgent time-bound mitigation.”
The decadal average temperature for the pre-monsoon or summer period was 0.49 degrees Celsius hotter than long-term normal (1951-80 baseline). This is a significant increase but not as much as that for the other three seasons.
The post-monsoon period from October to December has been hotter by 0.73 degrees Celsius than the long-term normal. The winter season from January to February, as per IMD classification, has been warmer by 0.68 degrees Celsius, and the monsoon by 0.58 degrees Celsius.
HT on March 22 reported that there has been a sharp upward trend in average temperatures across seasons in the country since 1991 compared to the average surface air temperature baseline recorded between 1981 and 2010. The trend is more evenly pronounced during the monsoon and post-monsoon seasons.
The seasonal average air temperature for this summer from March to May was 1.24 degrees Celsius warmer than the baseline trends between 1971 and 2000. This was warmer than the 1.20 degrees Celsius anomaly noted in 2016 summer. But it is lower than the 1.45 degree anomaly recorded in 2010 summer. Land surface temperature anomaly has been extreme this summer with a 1.46-degree Celsius increase compared to the baseline (1971-2000).
Institute of Climate Change Studies director DS Pai said the temperature anomalies are increasing mainly because of less clouding on a higher number of days. “So, if rainy days are reducing, cloudless or less cloudy days will increase. If we analyse the overall increase in maximum and minimum temperatures during these two seasons [monsoon and post-monsoon] we can also find out if there is an incursion of warm air from other regions.”
Pai said the rise in average temperatures is mainly linked to global warming. “We cannot link less cloudy days in monsoon and post-monsoon seasons to global warming directly but there may be indirect effects of climate change on cloud and rain patterns.”
The CSE said that the average daily maximum temperature this year for March and April in northwest India was almost 4 degrees Celsius above the normal compared to its baseline of 1981-2010. “This is almost twice as much as the increase observed at all India levels and it holds true for even average daily minimum, daily mean, and land surface temperatures. Temperatures became relatively closer to normal during the month of May.”
CSE cited National Crime Records Bureau data and said 2,137 people reportedly died due to heat strokes in northwest India between 2015 and 2020. “...the southern peninsula region... reported 2,444 deaths due to excessive environmental heat with Andhra Pradesh alone accounting for over half of the reported casualties.” It added Delhi reported only one death for the same period. “Most deaths have been reported among working-age men (30-60), usually not considered highly vulnerable to temperature anomalies. The understanding of the public health impacts of meteorological conditions like the heat waves is still weak in India.”
The seasonal average temperatures of Delhi, Mumbai, Kolkata, and Hyderabad were 1-2-degree Celsius higher than the all-India average due to the urban heat island phenomenon. “Due to excessive hard and dark surfaces, cities tend to absorb the heat coming from the sun during the day; a city also generates a lot of waste heat due to human activities which adds to the natural heat. This extra heat should dissipate after sunset, but due to pollution and continuing generation of waste heat the city fails to cool down, leading to warmer condition compared to rural areas,” said the CSE analysis.
It added that temperature and humidity data suggested massive variations in temperature within the cities.
In terms of absolute air temperature, Hyderabad, with a 7.1-degree Celsius variation (difference between hottest and coolest part of the city), had the most pronounced heat islands. Kolkata, with just 1.3 degree Celsius, had the least pronounced ones. Delhi had a 6.2-degree Celsius variation and Mumbai 5.5. Some urban or metropolitan areas were significantly warmer than their surrounding rural areas or areas with more green cover. The phenomenon is referred as Urban Heat Island effect.
Avikal Somvanshi, a senior programme manager with CSE’s Urban Lab, said understanding the overall temperature anomaly, extreme heat conditions, and the mixed trends in heat patterns across India has become necessary to assess the emergent risk. “Currently, the attention is largely on the maximum daily heat levels and extreme conditions of heat waves. But it is equally important to pay attention to the overall rising temperature and humidity trends in different regions to understand the gravity of the problem.”
CSE sourced the intracity temperature variation data from the Continuous Ambient Air Quality Monitoring Stations and surface air from NASA’s Goddard Institute for Space Studies.