Monsoon deficiency drops to 4% due to September rains: IMD

Currently, the monsoon is in the “normal” category which is 104% to 96% of the long period average, the IMD said.
Tourists protect themselves from rain at Red Fort in Agra on September 17. (PTI)
Tourists protect themselves from rain at Red Fort in Agra on September 17. (PTI)
Updated on Sep 20, 2021 12:27 AM IST
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ByJayashree Nandi

There has been a 4% deficiency in monsoon rains till Sunday in comparison to the 9% deficiency at the end of August, even as more showers are expected till the end of this month, India Meteorological Department (IMD)’s extended range forecast revealed.

Currently, the monsoon is in the “normal” category which is 104% to 96% of the long period average.

Monsoon rains have been extremely skewed this year with 9.6% excess at the end of June, 6.8% deficiency in July, 24% deficiency in August and 28.7% excess in September till Sunday. Instead of July and August, September has been the most active monsoon month this year.

According to the north Indian Ocean’s extended range outlook, a cyclonic circulation is likely to form over east-central Bay of Bengal around September 23-24 with a near similar pattern of movement as the one that is presently over Madhya Pradesh. The cyclonic circulationlikely to form over Bay of Bengalis expected to bring widespread rains over central and parts of northwest India.

“The monsoon trough is very active right from the northern parts of the country to the western Pacific. The favourable position of Madden Julian Oscillation (MJO) is supporting convective activity. Though a cyclonic circulation is weaker in intensity than a low pressure system, it is likely to bring rainfall over many parts of the country till the end of the month,” Sunitha Devi, in charge of cyclones at IMD, said.

The MJO is an eastward moving disturbance of clouds, rainfall, winds and pressure that traverses the planet in the tropics and returns to its initial starting point in 30 to 60 days on average, according to the National Oceanic and Atmospheric Administration. Its location and amplitude strongly modulates the intensity of tropical convection and features like low pressure systems over the north Indian Ocean.

In September, the monsoon season changed so abruptly that districts which were “severely” and “extremely” dry as per the IMD’s drought monitoring from June to August, have now turned “mildly dry” as per the standard precipitation index (SPI).

The SPI is an index used to monitor drought -- it is negative for drought and positive for wet conditions.

For the period June to August, 129 districts were found to be in moderately/severely/extremely dry conditions or moderately/severely arid conditions, and 43 districts under dry conditions in all the three drought indices (rainfall, aridity and SPI monitored by IMD). These 43 districts remained under severe water-stressed conditions till the end of August.

The maximum number of districts which faced dry/arid conditions were in Gujarat, but are now in wet condition following widespread and heavy rain this month. Almost all of northeast India and Jammu and Kashmir and Himachal Pradesh continue to remain dry.

“There is a sudden revival in the dry states which is good because there were drought conditions in Gujarat and parts of Odisha. This will help in groundwater recharge ahead of winter crops,” Pulak Guhathakurta, head of climate research division at IMD Pune, said.

“Power of the #monsoon! Rainfall deficit at the end of August (left) turning to rainfall surplus in mid-September (16th, right). Red colors showing drought and green wet areas! Entire scenario changed due to rainfall in a few days! Regions face both drought and wet extremes!!” tweeted Vimal Mishra, associate professor, civil engineering and earth sciences at IIT Gandhinagar, with maps of soil moisture.

Normally, five to six depressions form during the monsoons (June- September) whichenhances rain in the core monsoon zone when they travel in the west-northwest direction. However, the first depression of this monsoon formed in September over northwest Bay of Bengal. It intensified into a deep depression on September 13 and moved across Odisha and north Chhattisgarh during September 13 and 14, and weakened into a well-marked low pressure area over northeast Madhya Pradesh on September 15. A cyclonic circulation also formed over east central Bay of Bengal on September 16 which moved to Odisha and another cyclonic circulation was over south Gujarat at the same time.

“A cyclonic circulation formed yesterday, which is lying over northwest Bay of Bengal and adjoining areas of north Odisha-West Bengal-Bangladesh coasts, will travel and bring rain. Another is expected to form next week. There is likely to be active monsoon conditions till the end of month. This is mainly because of the location of MJO and active northwest Pacific. The remnants of systems forming in the Pacific also help in development of low pressure areas and cyclonic circulations over Bay of Bengal. We had forecast this early this month,” IMD director general M Mohapatra explained.

The withdrawal of monsoons from northwest India has already been delayed by three days. The IMD’s extended range forecast indicates widespread rainfall till October 7.

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Monday, November 29, 2021