New Delhi: Even as the monsoon has made its footfalls felt across the country, there seems to be little respite from the searing heat – aided by steep rises in humidity levels -- in many pockets. The heat waves lashing India this summer are symptomatic of the anomalous temperature trends that are expected to worsen with growing climate change impacts.

Since 2016, the summer of 2022 has been the second hottest after the summer of 2010. Megacities including Delhi, Mumbai, Kolkata and Hyderabad are much hotter than the larger region around them due to heat island effects caused by surface absorption of heat and local waste heat generated by traffic, industry and air conditioning (among other urban activities). A new country-wide analysis by the Centre for Science and Environment indicates while extreme heat waves in the states of the northwest -- as per the classification of the India Meteorological Department -- draw maximum public attention, the increase in overall anomalous temperature in other regions of the country have been largely neglected.

“This is 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 waterbodies will worsen public health risks. This requires urgent time-bound mitigation,” says Anumita Roychowdhury, executive director, research and advocacy, CSE.

“Understanding the overall temperature anomaly, extreme heat conditions, and the mixed trends in heat patterns across different regions of 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,” says Avikal Somvanshi, senior programme manager, Urban Lab, CSE.

The Urban Lab of CSE has analysed the temperature trends in India from January 2015 to May 2022. An effort has been to understand the warming trends by covering all three dimensions of heat stress -- surface air temperature, land surface temperature, and relative humidity -- at the national, regional and local levels. The trends in the metropolises of Delhi, Mumbai, Kolkata and Hyderabad have also been assessed.

The analysis has studied the temperature anomaly. A positive anomaly indicates that the observed temperature was warmer than the baseline, while a negative anomaly says the observed temperature was cooler. It is generally used to report monthly, seasonal, annual, or decadal temperature changes. Heatwaves are also anomalous temperature events, but of much shorter duration and are defined in comparison to an absolute temperature threshold in addition to departure from the normal.