While tornadoes mostly occur in India's eastern states, some have been reported in the northwest regions as well
Photo for representation: iStock Around 3:30 pm on March 31, 2024, a deadly tornado struck the Mainaguri area of Jalpaiguri district of West Bengal for 10 minutes and killed five people and injured over a 100.
In recent years, an increasing number of tornadoes have formed across India and caused destruction. A warming Bay of Bengal and land, along with anomalous wind patterns could be a reason behind this.
A tornado is a land-based vertical column of violently rotating air that forms from a thunderstorm to the ground. It can have wind speeds in the range of 105-322 kilometres per hour, according to the National Weather Service (NWS) of the United States. The system itself can be stationary or can move at a speed of around 97 km / hr.
These extreme storms are rare in India and have mostly been reported in the eastern states of West Bengal, Odisha and Jharkhand during the pre-monsoon period. But there is evidence of some of them having formed in northwest India as well.
A research paper published by India Meteorological Department (IMD) scientists in 2016 provides different records for possible tornadoes in eastern India. They collated the data from various sources, including media reports and research papers published on tornadoes.
The highest number was reported in a 1981 paper that documented 51 possible tornadoes across Bengal, out of which 18 killed 10 people or more.
Twelve of these tornadoes occurred during 1838-1963 and 24 during 1968-81.
The paper also recorded 15 tornadoes during 1903-2012 in northwest India. Twelve of these took place during 1976-2010, which means their frequency could have increased in later years. Most of these tornadoes occurred in March and a few in April.
Tornadoes are the most common in the United States, Argentina and Bangladesh. In the US, they are monitored by the meteorologists at NWS, who generate tornado watch and tornado warning based on data from satellites and radars.
In India, there is no official monitoring of tornadoes though IMD recorded the recent West Bengal tornado in its press release.
“Any collision of warm, moist air with dry, cool air in the presence of a low pressure system like a trough causes thunderstorms and tornadoes,” Raghu Murtugudde, a climate scientist at the Indian Institute of Technology, Bombay and University of Maryland, United States told Down To Earth.
In the case of West Bengal, IMD, in its March 30 press release, stated that a cyclonic circulation lay over sub-Himalayan West Bengal where Jalpaiguri is located.
In its March 31 press release, the weather agency announced that a cyclonic circulation was positioned over northeast Assam and a north-south trough was observed running from east Bihar to north Bay of Bengal.
Specifically, “tornadoes need warm air and humidity and a seed has to be put down in terms of rotation.The cool northeast winds can push on top of warm, moist ocean air and cause these tornadoes,” explained Murtugudde.
In India they should not get so strong as the land is not homogenous and the distances that it can travel is short. But wind patterns over many parts of India, including the eastern region, have been showing changes.
“The warm ocean and the warming land with the anomalous wind patterns are beginning to let the seeds sprout into tornadoes,” noted Murtugudde.
Other factors include weak background winds during the pre-monsoon season, which allow tornadoes to persist, and lower speeds of vertical winds, which allow them to grow.
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