Dry spell, Westerlies and anti-cyclones above Arabian Sea behind heatwave in plains of north-west India

“Wind is consistently coming from desert area. It should be reverse, coming from Bay of Bengal towards Delhi. But this hasn’t happened,” IMD scientist Dr RK Jenamani said

Dry spell, Westerlies and anti-cyclones above Arabian Sea behind heatwave in plains of north-west India

Ashlin Mathew

This year Delhi recorded the hottest March since 1901 and the maximum temperature in the national may touch 45°C by April 29. The Indian Meteorological department has issued an orange alert (‘be prepared’) for Delhi and the plains of north-west India, and the heatwave is expected to intensify over the weekend.

The ongoing heat wave has affected the harvest season. Above-average scorching temperatures have damaged crops in Rajasthan, Punjab and Uttar Pradesh, and some reports suggest that it could lead to inflation and shortage of stock after wheat supplies stopped from war-hit Ukraine.

The severe heat in the country has been prevailing since mid-March, with the average temperature at 32.65°C, as against 31.24°C.

The ongoing heat wave has been continuing for the last nine days in Delhi. In Maharashtra’s Vidarbha and western parts of Rajasthan, the temperatures have remained between 40°C and 45°C for the last one-and-a-half months.

When temperature rises, the risk of heat strokes and deaths also rise. Maharashtra public health data stated that 14 deaths had happened due to heatstroke in the first fifteen days in the state. Officials were expecting the numbers to rise by the end of the month. Other states have not disclosed the death figures due to heat stroke.

On Wednesday, several regions in north-west and Central India recorded 45°C. “These high temperatures will last for the next three-four days. Temperature is likely to cross 44°C in parts of Delhi. We have issued an orange alert till May 2, 2022, for north-west and Central India, which calls for preparedness. In eastern India, we have issued an alert till April 30, 2022,” said Dr RK Jenamani, IMD scientist.

Pockets of Delhi touched 44°C on Wednesday. “The temperature in Delhi is five degrees above normal and temperatures are expected to reach 43°C and 44°C in many parts of Delhi. Whenever the temperature is more than five degrees above normal, it is categorised as a heat wave. As the weather will remain almost dry, the heat wave conditions are expected to continue,” said Mahesh Palawat, vice president of SkyMet Weather.

This year there hasn’t been heat wave conditions in south India and north-eastern India as pre-monsoon activities continued.

Explaining the reasons for the heat wave, Jenamani pointed out that the hot winds from Rajasthan and Afghanistan are the reasons for the consistently high temperatures in Delhi, central and north-west India. This has been caused by the dry spell, absence of rain, Westerlies and anti-cyclones above Arabian Sea. All of this gives rise to dry and warm winds. March was entirely dry and on April 21 and 25, there were mild dust storms.

“At the lower level atmospheric level, the wind is consistently from the desert area. It should be reverse and should be Easterlies. This means it should be coming from the Bay of Bengal across Lucknow, Banaras and then towards Delhi. But, this hasn’t happened,” Jenamani said.

Breaking it down further, Dr S Pai of the Institute of Climate Change Studies, said that in Delhi, when there is a heatwave, there will be clear skies. Only when the Westerlies are passing, will there be cloudy skies. Where there are clear skies, solar radiation will hit the surface directly, but if clouds are there, they will reflect it back. This increases the surface heat. These winds coming from warmer regions bring warmer air and heat from the radiation is causing the heat wave.

The changes in the atmospheric pattern too have added to the heat in the region. There is an anti-cyclone being formed above Gujarat and the Arabian Sea, which is causing the north-westerly winds over north-west India and Delhi.

Delhi is currently witnessing high temperatures both in the morning and the evening and the reason is the hot winds from the desert region. IMD has also predicted dust storms in some part of north-west India.

“The urbanisation in Delhi will add to the heat and will cause heat islands to form in the region. This happens in many cities. Another cause for this heat wave is the extensive period with no rainfall. This also causes the surface to heat up. If there had been some rainfall a day or two before, then that would have helped to cool down the surface,” added Pai.

As per IMD’s complete analysis, this rise in temperature was unusual for March. In 2020 and 2021, Jenamani pointed out, there had been no heat wave. Delhi had the last major heat spell in April 2019.

“We had regular thunderstorms in the last two years during these months. This year there has been no thunderstorm since February 24. That means the dry spell has continued for 65 days,” said Jenamani.

Temperature has touched 45.5°C in Rajasthan and which is likely to go up to 46/47°C. In Delhi, it is likely to touch 44/45°C. Some respite is likely from May 2, said the IMD scientist.

Palawat predicted that dry Westerlies from Central Pakistan, Baluchistan and the Thar Desert will continue. “By May 4/5, we think that pre-monsoon activities such as dust-storm, thunderstorm and mild thunder shower activities occur in north Rajasthan, parts of Haryana, Punjab, Delhi and western part of Uttar Pradesh. These pre-monsoon activities will lead to a drop in temperatures and between May 4 -7, pre-monsoon thunder showers are expected. In the month of May, there are higher chances of pre-monsoon activities than March or April,” forecasted Palawat.

In addition to this, climate change has caused incremental warming all around, but global warming cannot be the sole reason for the heat wave, said scientists. Every year, a few climate records are being broken.

“This March was the hottest in terms of the average maximum temperature since 1901. For the first fifteen days of April, this year was the hottest since 1951. In April 2010, there were 11 heat wave days in Delhi. But now, we have already seen nine heat wave days until Wednesday. There are chances of the heat wave on Thursday, Friday and Saturday. This will mean 12 heat wave days,” added Palawat.

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