September shows positive departure for three consecutive years from normal rainfall

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During the southwest monsoon 2021, India received 874.6 mm rainfall, about 99.32% of the normal southwest monsoon rainfall. The country received "normal" rainfall during the four-month monsoon season from June to September, IMD said. September recorded a positive departure of 34.96% rainfall due to circulations contributed from the Bay of Bengal, ending with Cyclone Gulab which helped to fill the deficit formed during the months of July and August.

According to IMD, the season also saw the formation of 12 cyclonic circulations— low pressure (LP), well-marked low-pressure area (WML), depression, deep depression, and cyclone—which are critical during the rainfall period. June saw one LP, July recorded two LP and one WML. August recorded two LPAs. However, September recorded one cyclone (Gulab), one deep depression and two WML, and one LP. 

Deep depression was formed during 12-15 September and cyclonic storm Gulab was formed during 24-28 September.  

The withdrawal of the southwest monsoon from some parts of northwest India is likely to begin from October 6, said IMD. The normal date for the withdrawal of monsoon from the country is September 17. Last year, the withdrawal of the monsoon from northwest India began on September 28.

Onset of Southwest Monsoon

The southwest monsoon made an onset over Kerala on June 3 and covered the entire country on July 13- five days later than usual.  The monsoon normally covers the entire country by July 8, however, the trend was different last year, when it covered the entire country by June 26.

According to IMD, the formation and movement of the cyclone Tauktae, over the Arabian Sea (during 14-19 May) and severe Cyclonic storm Yaas over the Bay of Bengal (during 23 to 28th May) helped to increase cross-equatorial flow and the onset of monsoon. 

 

In the last five years, the maximum delay to cover the entire country was recorded in 2018, moreover, the same year recorded the earliest onset of the monsoon. Apart from 2018, the early onset of the monsoon was also recorded in 2017 and for the rest, it was usually delayed (except 2020), during the past five years.

Three consecutive years of normal/above normal rain

India received 867.8 mm of rainfall during the southwest monsoon which is 99% of its long period average (LPA).  LPA is the average of rainfall received by India over a 50-year period between 1951 and 2001. The current LPA of all southwest monsoon rainfall is 880.6 mm.

While 2019 recorded the highest percentage (110%) of its LPA followed by 2020, this year’s LPA is the third highest in the last five years. 

According to the India Meteorological Department (IMD), the country received "normal" rainfall during the four-month southwest monsoon season from June to September. This is for the third consecutive year that the country has recorded rainfall in the normal or above-normal category. Rainfall was above normal in 2019 and 2020. 

Rainfall over the northwest and central region was normal while the south peninsula region recorded above normal rainfall. However, it was below normal over the east and northeast regions. 

The south peninsula has been receiving normal or above normal rainfall for the last three years, while the east and northeast region has been receiving normal or below normal rain for the past five years.

September shows positive departure for three consecutive years

While the current rainfall number (99% of LPA) seems to suggest normal rainfall, in reality, the rainfall varied widely across the four monsoon months. 

The rainfall over the country as a whole was 110% in June, 93%, and 76% in July and August respectively. However, the shortfall of July and August was compensated in September which recorded rainfall 135% of the LPA. 

India recorded the maximum departure in September (+34.96%) and the minimum in August (-24.13%). September has been showing a positive departure from the normal rainfall (170.2 mm) for the last three years, recording the maximum positive departure in 2019 (+52%). 

On the other hand, August has recorded the maximum negative departure this year in comparison to the last five years. Last year August recorded excess rainfall (+26.6%) and in the previous four years, it observed normal rainfall.

Trends of southwest monsoon in meteorological subdivisions

According to IMD, out of the total 36 meteorological subdivisions, 20 subdivisions received normal seasonal rainfall, 10 subdivisions received excess rainfall and six subdivisions received deficient seasonal rainfall.

Nagaland, Manipur, Mizoram & Tripura, Assam and Meghalaya, Arunachal Pradesh, Jammu & Kashmir and Ladakh, West Uttar Pradesh, and Lakshadweep are the six divisions that received deficient rainfall. Out of these six subdivisions, three lie in northeast India. 

The number of rainfall-deficient regions has increased by 200% this year as compared to 2019. It has been increasing for three consecutive years, with 2018 observing the most rainfall-deficient regions (11).

Additionally this year 10 regions received excess rainfall which is more than that observed in 2016, 2017 and 2018. West Rajasthan, Haryana, Delhi, Andhra Pradesh, Telangana, north interior Karnataka, Gangetic West Bengal, Konkan and Goa, Marathwada and Andaman and Nicobar recorded excess rainfall during the monsoon season.