2018 S-W Monsoon - Northeast Deficit and Overall Rainfall

What is the issue?

Severe rainfall deficiency in the Northeast has caused an overall deficiency in the country at the end of the current south west monsoon season.

How was rainfall this monsoon?

• Northeast - Northeast region witnessed a severe rainfall deficiency of 24% this southwest (S-W) monsoon season.
• India Meteorological Department said that it was “very rare” for such a large deficiency in the Northeast.

• In the 116-year period from 1901 to 2017, only in 4 years (1992, 2005, 2009 and 2013) has the deficiency in the Northeast exceeded 20%.

• Northeast deficiency has caused an overall 9% rainfall deficiency in the country at the end of the season.

• Others Regions - The distribution of rainfall across Northwest, Central India and Southern Peninsula was “satisfactory”.
• The deficiency in these areas was marginal with 2% each in Northwest and Southern Peninsula, and 7% in Central India.
• So if the Northeast had received normal rainfall, the all-India rainfall would have been 96% of the Long Period Average.
• Long Period Average (LPA) is the average annual rainfall for the period 1951-2000.

What is the cause for deficiency?

• Starting from the extreme south-western tip of the peninsula, the Southwest monsoon progresses inland.

• But the monsoon trough that usually moves towards the Northeast did not happen this year.
• Sea surface conditions over the Equatorial Pacific (El Niño conditions) did not have any adverse effect on the rainfall.
• The IMD has thus planned a detailed scientific analysis on the causes by the end of December 2018.

Why is 2018 S-W monsoon unique?

• Rainfall - The 2018 monsoon has been characterised by “large day-to-day variability” within the season.
• Many cities in the country received almost their entire rainfall of the season within a short time.
• This added up to just a few days to a few weeks within the four-month season (June 1 to September 30).
• E.g. in 22 cities with sizeable populations, 95% of the monsoon precipitation occurred over 3 days to 27 days on average.
• Many intense rainfall events during the season have led to flooding like the Kerala floods.
• The season also witnessed formation of a large number of low pressure systems over Bay of Bengal and their westward movement across central India.
• Water in dams - The spatial distribution of this year’s rainfall is also reflected in the storage capacity of the country’s reservoirs.
• Country’s major reservoirs at present have 117% of the live storage of the corresponding period last year.
• This is 105% of the average water storage over the last 10 years, as said by the Central Water Commission (CWC).
• Of the five regions, storage in reservoirs in Northern, Eastern, Central and Southern regions is higher than last year.
• Storage in the Western region is less than the storage of last year and also less than the 19-year average storage.
• Agriculture - The overall crop acreage during the kharif season is higher by 2.6%.
• This is in comparison to the country’s highest ever acreage/record food production during 2017.
• The resultant acreage is largely the result of a good soil moisture distribution across the country.
• Adequate soil moisture available over northern parts of India may help the rabi crop during 2018-19.

Source: Indian Express