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Some parts of east and North East India may be staring at a deficient monsoon season and perhaps even a possible drought. This is because the India Meteorological Department (IMD) has forecast less-than-normal rainfall in these areas for August and September, continuing the below normal trend from June and July.
Most parts of the region received below normal rainfall in June and July as well, in spite of major floods in North East India. In fact, the region as a whole received the lowest July rainfall in 2022 in the past 122 years at 44.7 per cent less rains than normal, according to IMD.
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The southern peninsula received 60 per cent excess rains in July while central India received 43 per cent more rains than normal. Northwest India also fared decently well with almost 11 per cent excess rains. Overall, India received 17 per cent more rains than normal.
The IMD has predicted normal rainfall (94-106 per cent) for the country as a whole in August and September. But for many parts of the western coast and some parts of east central, east and North East India, it has predicted less-than-normal rains.
The IMD’s monthly forecast for August also predicted below normal rainfall for many areas in east, east central and North East India.
One of the reasons for this decrease in rainfall could be the development of a negative Indian Ocean Dipole (IOD) event which generally has a dampening impact on monsoon rainfall.
The IMD’s depiction of the monsoon in July
During a negative IOD event, the temperatures of the sea surfaces in the western Indian Ocean are cooler than the eastern Indian Ocean.
Due to this, the trade winds over the region get disrupted and start flowing towards Australia, causing more rainfall there and generally decreasing the monsoon rainfall over India.
A negative IOD event during the monsoon season had also decreased rainfall in August 2021 as only one low pressure area had formed in the Bay of Bengal during the month. Such low pressure areas in the Bay of Bengal and Arabian Sea bring most of the rainfall to central and western India during the monsoon season.
This is exactly what happened in July this year, with four low pressure areas forming in the month and bringing a lot of rainfall to central and western states, according to the IMD. The excessive rainfall even induced floods in Gujarat, Rajasthan and Maharashtra.
Normally, three low pressure areas form in July, with an average period of activity of 14 days. The total period of activity of these four low pressure areas was longer in duration by a week at 21.
One of the reasons for below normal rainfall in central and western India in June 2022 was also the complete absence of low pressure areas in the Bay of Bengal and Arabian Sea during the month. Normally, three low pressure areas form in June, with an average period of activity of 11 days.
Research on low pressure areas during the monsoon season suggests that they have been decreasing over the Bay of Bengal, where 60 per cent of them form.
Studies predict a 50 per cent decrease in stronger low pressure areas that form over the Bay of Bengal in the future, according to a study by Sandeep Sukumaran, assistant professor at the Centre for Atmospheric Sciences at Indian Institute of Technology, Delhi.