Steady increase in hot days in Northwest and Southeast India in recent years: claims study

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The 2019 Indo-Pakistani heat wave across north India and Pakistan( Credit: NASA Earth observatory/ Wikimedia Commons)

According to a study conducted by the researchers from Indian Meteorological Department (IMD) and the Indian Institute of Technology, Delhi (IITD), there was a steady increase in the occurrence and duration of hot days in the Northwestern and Southeastern regions in India in the recent years. Analyzing weather data from 1951 to 2015 to understand the incidence and duration of heatwave conditions in India, the study found that the average heat wave duration in the Northwestern and Southeastern regions of India has increased during this period. 

However, the average duration of hot days has decreased over most parts of India from 1951 to 2015, except in the northwest and southeast regions. According to the researchers, this may be due to the increase in average heatwave duration in the Northwestern and Southeastern regions during the same period as hot days could be upgraded to the heatwave category as temperature soars.

 

During the period, the eastern region of the Gangetic plains witnessed a consistent decrease in the number and duration of hot days, heat waves and severe heat waves. The presence of aerosols in the atmosphere in the region during the period might have contributed to this as per the researchers. Aerosols are solid or liquid particles suspended in the atmospheric air due to natural causes (like water vapour) or human-induced reasons (like soot from pollution or emitted particulate matter from coal mines/etc.).

 

Published in the journal ‘Climatic Change’, the study also examined potential heatwave conditions in two simulated scenarios where the average temperature in India rises by 1.5 °C and 2.0 °C. Using simulation models which help to predict future scenarios and using existing observed weather data, the study found that there will be a significant increase (as compared to the past) in the frequency, duration and area spread of the heat waves.

 

Extended Heatwave events likely in the future

As per the study, if the average temperature rises by 2.0 °C, significant heatwave events in certain areas in India may extend up to 30 to 40 days. Presently, the longest large heatwave event in the 1951-2015 period occurred for 15 days in 2014, as per the IMD weather data. However, the simulations show that there will not be a significant increase in the highest temperatures in these scenarios. “The highest temperatures in the +1.5 °C and+2.0 °C (scenarios) are not substantially larger and do not exceed 47 °C”, says the study.

 

As the nature of heatwave conditions changes, other weather events like Monsoons and the resulting humidity may contribute to the condition further. “The probability of heatwave days is highest in the months of May and June with larger increases in the + 1.5 °C and + 2.0 °C futures, compared to historical simulations. Although this study does not address the issue of humidity in heat events, the increased probabilities during June and July are of particular concern as these are monsoon months when the humidity is quite high, which can lead into high heat-index”, says Dr Arulalan T, a scientist with IMD and IITD who was part of the study team.

 

However, the simulations used in the study indicate that more regions in India will be prone to heatwaves in the future. The study claims that future heat wave events are going to be longer in duration and wider in terms of affected areas.

“Our findings show that the heatwaves over India, the area likely to experience long duration events in future, extends into regions previously not prone to such events, leading to the emergence of new heatwave-prone zones in India; especially over some parts of the east and west coastal regions”, says Arulalan. According to him, new regions in the states of Gujarat, Odisha, West Bengal and Tamil Nadu may be prone to such instances. In addition, he says, plains like central Maharashtra and the interiors of Karnataka along with Indo-Gangetic plains may also turn out to be more prone to heatwave conditions in the future.

Need for new adaptation mechanisms

According to the researchers, the findings call for new policy initiatives to formulate adaptation mechanisms for long-duration heat wave conditions. “The effects of prolonged heat waves could have far-reaching implications for managing the impacts on a wide range of sectors from health to agriculture, electricity, and industry.” cautions the study. The present mechanisms are in the form of disaster management plans meant for localized events. This may be inadequate in the future, say the study.  Krishna Achuta Rao and Ambuj D Sagar affiliated with IITD, were also part of the study team.