The southwest monsoon is expected to officially start withdrawing from India on October 6-7, set to mark a hat-trick in the delayed retreat, with recording normal rainfall to the tune of 99 per cent of the long-period average.
The countrywide cumulative rainfall for the overall season from June 1 till September 30 was recorded at 874.6 mm against the normal rains of 880.6 mm.
However, the journey of monsoon, vital for farmers, had been quite abnormal even though it appears that the country met its rainfall targets for the year.
This year’s monsoon has been a season of extremes, from exceptionally low to exceptionally high rainfall, traditionally rain-fed areas reeling with dry weather and vice-versa.
Climate experts say some erratic and anomalous patterns witnessed this season.
The core months of July and August together record four low-pressure areas, while September alone saw five low-pressure areas.
The deficit rainfall pockets — West Madhya Pradesh, East Rajasthan, and Marathwada and Vidarbha regions of Maharashtra — are all surplus, while the rainiest pockets — Kerala, Odisha and Northeastern pockets — struggled to meet their average rainfall quota.
The Council for Energy, Environment and Water (CEEW) says more than 75 per cent of districts are exposed to extreme climate events.
Subsequently, over 40 per cent have experienced climatic disruptions such as a shift from being flood-prone to being drought-prone, or vice-versa.
With 24 per cent deficit rainfall, August — the prime month of monsoon season — made history as the worst performance this monsoon.
While it has been the sixth driest August since 1901, it is the first since 2009, which was a drought year owing to El Nino conditions.
Experts attribute this to absence of the monsoon weather systems, which then kept the monsoon trough north of its normal position, bringing torrential rains across Himachal Pradesh, Uttarakhand and foothills of Himalayas like East Uttar Pradesh and Bihar.
Also, these monsoon systems keep activating the semi-permanent off-shore trough along the West Coast. However, in the absence of these weather systems the trough remained weakened.
The Indian Ocean Dipole — often called the Indian Nino — too remained negative for most of the month.
“Barring a few days, the countrywide cumulative rain deficiency on a daily basis has been 30-40 per cent. Prolonged dry spells from August 4 to 25 had pushed the country towards drought-like conditions. Usually, we see four low-pressure areas during the month, but 2021 saw just two of them which were also feeble ones. Besides this, typhoon activity in the Pacific Ocean was also less, whose remnants usually travel across the Bay of Bengal and gain strength,” said G.P. Sharma, President (Meteorology and Climate Change), Skymet Weather.
The withdrawal month of September saw what can be termed as a miraculous recovery of monsoon across India.
“From extreme failure in August to extreme recovery in September is nothing short of a miracle. The month on its own was able to pull the countrywide rainfall from ‘below normal’ to ‘normal’ category,” Sharma said.
“Oceanic parameters — Indian Ocean Dipole, Madden Julian Oscillation and evolving La Nina — are to be given credit, which aligned all together for the first time to save the falling monsoon. All these conditions led to the formation of back-to-back monsoon low-pressure areas.”
Besides, the Arctic sea-ice loss in summer has also led to late season rainfall extremes.
Raghu Murtugudde, an earth system scientist at CMNS-Atmospheric and Oceanic Science, said “Reduced sea-ice in the Arctic during summer, especially over the Kara Sea, leads to high sea-level pressure over Western Europe and Northeastern China, which steer planetary waves southeastward instead of their eastward trajectory. And these waves enter India late in the season to produce circulation anomalies in the upper atmosphere, resulting in heavy rainfall in September.”
The core monsoon months — July and August — have failed to perform.
Meteorologists have attributed this to the absence of low-pressure areas that account for 60 per cent of the seasonal total rainfall.
The withdrawal of monsoon this time strikes a hat-trick in the delayed retreat after 2019 and 2020.
While 2020 saw the process of withdrawal of monsoon commencing on September 28, it was 2019 which started bidding farewell to monsoon rains on October 9, making it the most delayed retreat of the monsoon since 1975.