How Heat Waves Are Impacting Health And Agriculture In India

The early heat waves of 2022 that began on 11 March have impacted 15 Indian states and Union Territories as of now, according to data from the India Meteorological Department (IMD).

Rajasthan and Madhya Pradesh have suffered the most among the states, with 25 heat waves and severe heat wave days each during this period.

Gujarat, Goa, Delhi NCR, Haryana, Odisha, Himachal, Uttarakhand, Maharashtra, Jammu and Kashmir, Jharkhand, Uttar Pradesh, Bihar and Punjab are other states and Union Territories which have witnessed heat waves in the country, as per the data analysed by Down To Earth.

The IMD says a heat wave happens when the temperature of a place crosses 40 degree C in the plains, 37 degree C in coastal areas, and 30 degree C in the hills. The weather agency declares a heat wave when a place registers a temperature that is 4.5 to 6.4 degree C more than the normal temperature for the region on that day. If the temperature is over 6.4 degree C more than the normal, the IMD declares a ‘severe’ heat wave.

What have been the impacts of heat waves?

Heat waves exert enormous impacts on health, agriculture and availability of water — all often related to each other in complex ways. Even though the number of deaths due to heat waves in India has decreased over the years, research shows that the general physical and mental wellbeing of people does get affected by extreme temperatures.

On the other hand, agricultural yields get impacted as well. For instance, the wheat crop in the current rabi season in Punjab, Haryana and Uttar Pradesh has been impacted by heat waves. Many farmers have reported losses between 20 per cent and 60 per cent in these states. This happened because the heat waves arrived early this year and the temperatures affected the wheat crop during their growth stage, leading to shrivelled grains which fetch lower prices in the market, resulting in losses. To reduce agricultural losses due to heat waves, heat-tolerant varieties of wheat need to be developed.

Similarly, heat-resistant varieties of other rabi crops also need to be developed. Apart from direct heat, agricultural yields may also get impacted by droughts or drought-like conditions that are often associated with heat waves. This mainly occurs because of non-availability of water for irrigation during drought conditions.

The unlikely impact of the current heat waves would occur in the Himalayan regions of Himachal Pradesh, Jammu and Uttarakhand that are not used to heat waves and not well adapted to the extreme temperatures. One major impact in these regions would be on the accelerated melting of glaciers due to extreme temperatures which are the main source of water for the people living there.

The IMD also uses another criteria to declare a heat wave which is based on absolute recorded temperatures. If the temperature crosses the 45 degree C mark, the department declares a heat wave; when it crosses 47, a ‘severe’ heat wave is declared.

Surprisingly, after Rajasthan and Madhya Pradesh, the mountainous state of Himachal Pradesh has been the most affected by heat waves this year — with 21 heat waves and severe heat wave days.

D Sivananda Pai of the Kottayam-based Institute for Climate Change Studies says that anti-cyclones over western parts of Rajasthan in March and the absence of rain-bearing western disturbances had triggered the early and extreme heat waves. Anti-cyclones cause hot and dry weather by sinking winds around high pressure systems in the atmosphere.

Raghu Murtugudde, a climate scientist at the University of Maryland explains that a north-south pressure pattern, associated with the La Nina phenomenon in eastern and central Pacific Ocean that happens during winters in India, has persisted longer than expected and interacted with warm waves coming in from a rapidly warming Arctic region, leading to the heat waves.

The sea surface temperatures over the east and central Pacific Ocean become cooler-than-average during La Nina. This affects the trade winds flowing over the ocean surface through changes in wind stress. The trade winds carry this weather disturbance elsewhere and affect large parts of the world. In India, the phenomenon is mostly associated with wet and cold winters.

Therefore, the current impact of La Nina on the spring and summer season in India is completely unexpected. Murtugudde says that the heat waves may continue till at least the monsoon season begins in June.

What global evidence do we have of heat waves happening across the world?

In the first installment of the ‘sixth assessment report’, the IPCC asserted that human activities have warmed the planet at a rate never seen before in the planet’s long history, and the Earth’s global surface temperature has warmed by 1.09 degree C compared to the pre-industrial period of 1850-1900. Human influence is the main driver of hot weather extremes (which have become more frequent and intense since the 1950s).

Improvements in climate models and analytics have enabled scientists to identify “fingerprints” of human influence on climate change by observing records of rainfall, temperature, and other factors. In the past two decades, scientists have published more than 350 scientific papers and assessments analysing the role of anthropogenic GHG emissions in individual extreme events.

The IPCC report says that every additional 0.5 degree C of warming will increase hot weather extremes, along with extreme precipitation and drought. Heat waves in India are likely to “last 25 times longer by 2036-2065” if carbon emissions remain high and push global temperature rise to 4 degree C by the end of the century, according to an international climate report published 28 October 2021, covering the G20 countries.