Heatwaves are the new normal. Study the hazards

  • The most effective way to reduce the negative impacts of a heatwave is to develop a comprehensive response plan that combines individual strategies into an integrated approach
With unabated global warming, the probability of compound extremes such as the simultaneous occurrence of drought and heatwaves is also likely to increase. (Sanjeev Kumar /HT Photo) PREMIUM
With unabated global warming, the probability of compound extremes such as the simultaneous occurrence of drought and heatwaves is also likely to increase. (Sanjeev Kumar /HT Photo)
Published on May 16, 2022 09:20 PM IST
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It is well-known that global warming is sparking extreme temperature events, such as heatwaves, across the world. For India, April was the hottest in 122 years and followed the hottest March on record, and reportedly 25 people have died already. On Sunday, Delhi-NCR set a new record with the mercury passing the 49 degree mark at Mungeshpur (northwest Delhi) near the Haryana border, while neighbouring Gururgam registered the day’s high at 48 degrees, also the highest since May 1966.

In India, a heatwave is declared when the maximum temperature is over 40 degrees Celsius and 4.5 degrees above normal. A severe heatwave is declared when the temperature is above 40 degrees Celsius and 6.5 degrees above normal. Heatwaves usually occur during the March-June season over central and northwest India (heatwave zones), and coastal Andhra Pradesh and Odisha. In this region, the heatwave frequency is slightly lower than what is witnessed in north India.

On average, two heatwave events occur during the season in the heatwave zones, lasting between five and seven days. However, the frequency of heatwaves, their duration, and the maximum duration increase due to global warming. Over India’s heatwave zones, the total duration of heatwaves has increased by about 2.5 days over the last 30 years. The Intergovernmental Panel on Climate Change (IPCC) projections suggest an increase of about two heatwave events (12-18 days) by 2060. Heatwaves may also spread to southern India.

With unabated global warming, the probability of compound extremes such as the simultaneous occurrence of drought and heatwaves is also likely to increase. Unless we do an in-depth attribution study, it is tough to attribute a heatwave event to human influence. However, the 2003 heatwave in Europe and the 2010 Russian heatwave have been unequivocally attributed to human influence. Recent heatwaves in March and April in north India are in line with IPCC’s projections.

Heatwaves affect human health and air quality, increase energy consumption, reduce crop yields, increase water loss, and intensify droughts. In addition, exposure of crops to temperatures beyond a critical threshold can lead to crop failure. Heatwave events also raise temperatures in buildings and cities (urban heat islands); induce disruptions in critical infrastructure networks, affect the economy through reduced labour productivity; and exacerbate the consequence of other climate-related hazards such as droughts or wildfires.

Heatwaves have caused more deaths than other natural hazards in India, except tropical cyclones. During March and June, they also lead to dry weather with reduced humidity. However, heat stress due to increased humidity and temperatures can significantly threaten human life. Unfortunately, there is hardly any research on such heat stress episodes in India.

The most effective way to reduce the negative impacts of a heatwave is to develop a comprehensive response plan that combines individual strategies into an integrated approach, including cultural, institutional, technological, and ecosystem-based adaptations.

For example, the institutional plan might include weather forecasting, monitoring, and education and awareness. Adequate outreach can ensure the health and safety of city dwellers during heatwaves, especially vulnerable groups such as older adults, children, people who work outdoors, and low-income communities.

Due to the efforts taken up by the ministry of earth sciences, a reliable heatwave warning system is now available in India, which provides critical information at least one week in advance. In addition, there is a good synergy between the India Meteorological Department, and central and state disaster management authorities, which culminated in the development of heatwave action plans by a few states.

However, more collaborative work is needed on heatwave impacts.

We need to establish evidence-based thresholds to develop and activate different responses. For example, we need to develop strategies for raising education and awareness among the public; improving energy efficiency to reduce stress on electrical systems to avoid power outages and reducing heat island effects; constructing cool shades and shelters (such as cyclone shelters); and developing evidence-based forewarning systems to reduce crop damages.

M Rajeevan Nair is former secretary, ministry of earth sciences 

The views expressed are personal

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Monday, July 04, 2022