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Friday, September 17, 2021

Weak monsoon spell in August pushes all-India rainfall to 10% below normal

Of the four-month long monsoon, July and August account to nearly 70 per cent of the country's seasonal rainfall.

Written by Anjali Marar | Pune |
Updated: August 26, 2021 7:08:12 am
IMD officials pointed out that an extended subdued rainfall period was due to the weak monsoon spell this month. (File)

A prolonged weak monsoon spell witnessed throughout August this year has pushed the all-India rainfall to 10 per cent below normal as on Wednesday.

Of the four-month long monsoon, July and August account to nearly 70 per cent of the country’s seasonal rainfall. This year, the all-India July rainfall had ended with 1 per cent rainfall deficiency and it appears that August, too, shall follow suit with an even greater deficiency margin. As on Wednesday, it stood at -10 per cent.

There is no immediate revival likely as the India Meteorological Department (IMD) on Wednesday said that subdued rainfall will continue over central, north-west and along the west coast regions of the country till August 30.

IMD officials pointed out that an extended subdued rainfall period was due to the weak monsoon spell this month. Favourable weather systems — either in the form of a low pressure formed in the Bay of Bengal or an off-shore trough in the Arabian Sea along the west coast — were largely absent.

Normally, both of these aid the monsoon currents and cause rainfall over the Core Monsoon Zone covering Gujarat, Maharashtra, Madhya Pradesh, Chhattisgarh, Jharkhand and Odisha. The two-low pressure systems, formed earlier in this month, were not strong enough.

Till July 31, the country had recorded 449 mm and in the subsequent 25 days till Wednesday, the amount of rainfall added to this total was merely 154.1 mm. In July, rainfall over 12 states or union territories was ‘deficient’ in comparison to 14 states or UTs this month. Last month, 18 states or UTs ended up receiving ‘normal’ rainfall while 21 are in this category in August.

With extended dry conditions lasting for over three weeks now, the Standardised Precipitation Index (SPI) values are growing negatively, indicating increasing dryness during monsoon season. SPI is a value assigned to measure the dryness in a locality solely based on precipitation and is used to forecast possible droughts.

Gujarat, Odisha, Jharkhand, west and east Madhya Pradesh, Nagaland, Manipur and northern Maharashtra are witnessing extremely dry conditions with SPI values about -1.99, the IMD data (till August 18) showed. Along with south and central Rajasthan, Himachal Pradesh and Punjab, these large geographical areas are experiencing mild to severe dry conditions, with SPI values ranging between – 0.99 and -1.49.

Among the most rain deficient states or UTs are Manipur (- 58 per cent), Ladakh (- 51 per cent), Gujarat (-48 per cent), Chandigarh (- 38 per cent), Lakshadweep (-35 per cent), Odisha (-31 per cent), Jammu and Kashmir (-29 per cent), Kerala and Mizoram (-28 per cent, each), Nagaland (-25 per cent), Arunachal Pradesh (-24 per cent), Punjab (-21 per cent), Himachal Pradesh and Assam (-20 per cent, each).

Till the end of this month, rainfall is expected to largely remain concentrated over east and northeast India regions.

“With the likely formation of a low-pressure system in the Bay of Bengal on Thursday, strong southerly and south-easterly winds would prevail. This will cause rainfall over Sub-Himalayan West Bengal, Sikkim and the northeast region till Saturday,” the IMD’s forecast stated.

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