‘break periods’ are normal every season; but this time, there is a difference

Currently, the monsoon trough has not even reached its normal position; hot winds flowing in from the Arabian Peninsula and the Arabian Sea could be responsible, say experts

An image of the cumulative rainfall for June shared by IMD, including the anomaly (last map)

An image of the cumulative rainfall for June shared by IMD, including the anomaly (last map)

The Bay of Bengal branch of the southwest monsoon has been stalled since May 31, a day after the onset of the monsoon simultaneously over Kerala and Northeast India. That is a stalling period of 19 days as of June 19, one of the longest in recent time, according to data from the India Meteorological Department (IMD).

The Arabian Sea branch of the monsoon has been stalled since June 10, which is a stalling period of nine days.

The onset of the monsoon was two days earlier than normal for Kerala and six days earlier than normal for the Northeastern region.

The stalled monsoon has led to an all India deficit in monsoon rainfall of 20 per cent between June 1 and June 18, heralding a sluggish start to the season responsible for 70 per cent of the country’s total rainfall.

It is also one of the reasons for the late heatwaves in most of north India and many parts of west, central and eastern India since the beginning of June. In many places like Delhi, temperatures are also not reducing at night. This is leading to warm night conditions and no respite for people even at night.

On June 18, Delhi recorded a night time temperature of 35.2°C, its highest June temperature since 1969, according to media reports. This was a staggering 8°C above the normal. Delhi also suffered from a huge rainfall deficit of 94 per cent between June 1 and June 18.

Across regions, the largest deficit rainfall is in northwest India at 69.9 per cent. It is followed by central India at 31.3 per cent. The east and Northeast India region has received 14.7 per cent less rainfall than normal, despite the region suffering from floods since the beginning of the season.

Some states like Sikkim, Arunachal Pradesh and Assam have also witnessed flash floods and landslides due to sudden heavy rainfall events in the last few days. Southern India has been the only region with ample rainfall during the first three weeks of June. It recorded an excess of 15.7 per cent between June 1 and June 18.

‘Break periods’ are a normal characteristic for the monsoon. But some of the recent breaks have been much longer than normal. The season is usually said to be on a break when the monsoon trough moves towards the foothills of the Himalayas.

During this period, it starts raining heavily in the Himalayan and the northeastern states while the rest of the country remains dry, especially what the IMD defines as the ‘core monsoon zone’. The core monsoon zone stretches from Gujarat in the west to West Bengal and Odisha in the east.

The monsoon trough is an elongated low pressure region that causes the rainfall during the monsoon season over the country. This normally happens once or twice during the season once the monsoon trough has settled into its normal position.

Currently, the monsoon trough has not even reached its normal position. Therefore, this stalling is different from the regular break period of the monsoon.

The current stalling of the monsoon comes after an early onset which occurred due to the progression of Cyclone Remal in the Bay of Bengal in the last week of May. Such a quick progress and stalling after cyclonic activity had also occurred in 2021.

Cyclones Tauktae in the Arabian Sea and Yaas in the Bay of Bengal had propelled the monsoon winds. But then, the winds remained stalled for 24 days.

“The early break in monsoon is not so unusual in the beginning of the season except that 2023-24 are unique because of the warming and thus we are having heatwaves very late in the season as well,” Raghu Murtugudde, professor of climate studies at the Indian Institute of Technology, Bombay and emeritus professor at the University of Maryland told Down To Earth.

Hot winds flowing in from the Arabian Peninsula and the Arabian Sea, causing heatwaves in northwest India, may in fact be responsible for stalling of the monsoon trough.

“The main question I would ask is whether the intrusion of dry hot air in the north-northwest is impeding the trough from moving forward,” said Murtugudde.

“Some droughts are caused by the trough stalling over the middle of the country. But sometimes, you can get moisture supply from the northwest when the trough gets stuck. So the northern moisture supply is what is missing this year,” he explained.

The IMD expects the monsoon trough to start advancing further in the next two to three days, according to its latest press release.

“We may be seeing the impacts of warming on the monsoon evolution as a whole. So, we have to see if this is an indicator of new mechanisms that will play out as warming continues,” it read.

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