Monsoon to revive briefly but rain deficiency to stay

The drought indicator of the India Meteorological Department showed large parts of India under mild to moderately dry conditions.

After the driest August since record keeping began, the south-west monsoon is likely to revive briefly for 2-3 days this week, but weaken again after that, weather experts said.

There is a gradual increase in break monsoon days in recent years, according to long-term data maintained by the Met department (HT Archive)

There is an 11% deficiency in monsoon rainfall over the country, with 12% deficiency over central India; 14% deficiency over the peninsula; and 18% deficiency over the east and northeast as on Sunday. The drought indicator of the India Meteorological Department showed large parts of India under mild to moderately dry conditions.

August was the driest and warmest for the entire country since weather records began in 1901, HT reported on August 31. There were 20 break monsoon days in the month compared to 16 such days in 2005, which was the previous record for highest break days, when the monsoon is extremely weak.

There is a gradual increase in break monsoon days in recent years, according to long-term data maintained by the Met department. In 2005, it accounted for 25% deficiency in August while this year, the figure is 36%.

“A cyclonic circulation is lying over northeast Bay of Bengal. Under its influence, a low-pressure area is likely to form over northwest and adjoining west- central Bay of Bengal in the next 48 hours,” the weather bureau said on Sunday.

It added: “The monsoon trough, an elongated low-pressure area, at mean sea level continues to run along the Himalayan foothills. Its eastern end is likely to shift southwards to its normal position from Monday and to the south of its normal position after that. This would result in active monsoon conditions over north peninsular India, Odisha and Chhattisgarh in next 2-3 days. There is likely to be an increase in rainfall with isolated heavy rain over northeast India, Madhya Pradesh and Maharashtra as well from September 5”.

Before 2016, the 11% deficiency in monsoon rainfall would have been called an all India drought, according to Roxy Mathew Koll, climate scientist at Indian Institute of Tropical Meteorology. “District-wise maps show widespread deficit across India, except northwestern districts of Gujarat and Rajasthan,” he posted on X (formerly Twitter) on September 1.

The nomenclature from drought to deficient was changed in 2016 by the weather office, which now considers monsoon rainfall between 96% and 104% of the long-period average as normal. Rainfall of 90% to 95% is considered below normal category, while less than 90% is considered deficient.

The weather office’s cumulative standard precipitation for the period between June 1 and August 30 shows most districts in India are mildly to severely dry. Around 13% of the area is moderately dry; around 5% area is severely and extremely dry, and around 40% of country’s area is mildly dry as per the index.

The Standardized Precipitation Index (SPI) is the most commonly used indicator worldwide for detecting and characterizing meteorological droughts. The SPI is used for estimating wet or dry conditions based on precipitation variable. It reflects soil moisture and rainfall conditions for a particular location.

“Rainfall deficit pattern of 2023 is similar to the long-term declining trend of the monsoon, both denoting a weak monsoon circulation in response to El Niño/Indian Ocean warming,” Koll said, referring to findings of a 2015 paper led by IITM, which found that there is a significant weakening trend in summer rainfall during 1901-2012 over the central-east and northern regions of India, along the Ganges-Brahmaputra-Meghna basin and the Himalayan foothills, where agriculture is still largely rain-fed.

The paper had found that the land-sea thermal gradient over South Asia has been decreasing due to rapid warming in the Indian Ocean and a relatively subdued warming over the subcontinent. Enhanced Indian Ocean warming potentially weakens the land-sea thermal contrast, dampens the summer monsoon circulation, and reduces the rainfall over parts of South Asia.

“With the formation of the low-pressure area over Bay of Bengal, there is likely to be rainfall over Bihar, Jharkhand, West Bengal, Odisha, east Uttar Pradesh, Chhattisgarh for next 2-3 days. There may be some rainfall over Telangana, Vidarbha and Marathwada also, but thereafter monsoon conditions will weaken again,” said Mahesh Palawat, vice-president of climate and meteorology at Skymet Weather Services, a private forecaster. “There will also be no rainfall over western parts of the country during next 2-3 days. Rains will be limited to east- central parts. After this spell, monsoon will gradually move towards the withdrawal phase so we are not expecting any major rainfall activity thereafter.”

The favourable phase of Madden Julian oscillation may help monsoon during the first half of September but not after that, said M Rajeevan, former secretary, ministry of earth sciences. The oscillation characterised as an eastward moving pulse of cloud and rainfall near the equator that typically recurs every 30 to 60 days.

“At present things are not good. They are close to drought conditions at many places, even though we cannot liberally use the term drought. Almost 40 % of districts is under the deficient category. It’s not a good sign,” he said.

“But with the ensuing active phase things will improve substantially, especially over central and northern parts. There is a possibility of active spell over central India during next 10 days or so. But a weak spell may be expected during the second half of September,” Rajeevan added.

Isolated very heavy rainfall is likely over coastal Andhra Pradesh on September 4-5 and over Telangana on September 3-5, the Met office said on Sunday. Over central India, light to moderate and widespread rainfall, thunderstorm and lightning with isolated heavy rainfall is likely over western Madhya Pradesh on September 6-7; eastern Madhya Pradesh and Vidarbha during September 5-7 and over Chhattisgarh during September 3 -7.