The ‘End of the Season – Southwest Monsoon 2020’ recently released gives a picture of the performance of Southwest monsoon across the country. For UPSC the data can be used as supplement information while writing answers.
- Key findings of the report
- The seasonal (June-September) rainfall over the country as a whole was 109% of its Long Period Average (LPA) in 2020.
Long Period Average (LPA) is the average rainfall recorded during the months from June to September, calculated during the 50-year period between 1951 and 2001. It is kept as a benchmark while forecasting the quantitative rainfall for the monsoon season every year.
IMD maintains five rainfall distribution categories on an all-India scale-
- Normal or Near Normal: When per cent departure of actual rainfall is +/-10% of LPA, that is, between 96-104% of LPA
- Below normal: When departure of actual rainfall is less than 10% of LPA, that is 90-96% of LPA
- Above normal: When actual rainfall is 104-110% of LPA
- Deficient: When departure of actual rainfall is less than 90% of LPA
- Excess: When departure of actual rainfall is more than 110% of LPA
- It was the third highest after 112% of LPA in 1994 and 110 % of LPA in 2019.
- Seasonal rainfalls over Northwest India, Central India, South Peninsula and Northeast (NE) India were 84%, 115%, 130% and 106% of their respective LPA.
- Out of 36 meteorological subdivisions,
|Number of subdivisions||Area covered||Rainfall|
|2||5% of the total area||Large excess rainfall|
|16||45%||Normal seasonal rainfall|
|5||15%||Deficient season rainfall|
- Monthly rainfall over the country as a whole was 118% of LPA in June, 90% of LPA in July, 127% of LPA in August, and 104% of LPA in September.
- Southwest monsoon current reached south Andaman Sea and Nicobar Islands on 17th May 2020 (5 days ahead of its normal date), but further advance was sluggish.
- It set in over Kerala on 1st June, covering the entire country on 26th June 2020; 12 days before its normal date (8th July).
- The formation of two low pressure areas in the month of September led to an active monsoon trough which delayed the withdrawal of monsoon.
- The withdrawal of monsoon commenced on 28th September from some parts of west Rajasthan and Punjab, against its normal date of 17th September with the establishment of an anti- cyclonic circulation in the lower tropospheric levels over western parts of northwest India.
- The Southwest Monsoon withdrew from the entire country on 28th October 2020.
- During the season, one Severe Cyclonic Storm “NISARGA” formed during 1st to 4th June.
- The year 2020 witnessed absence of monsoon depression during the season.
- The forecast for monsoon onset over Kerala for this year was correct, which is the fifteenth consecutive correct forecast for the event (except for the year 2015) since issuing a forecast for the onset over Kerala started in 2005.
- The forecasts for the rainfall over the country as whole during the season, forecasts for the seasonal rainfall over three broad homogeneous geographical regions (Central India, Northeast India and South Peninsula) and forecast for August rainfall and for rainfall of second half of the monsoon season for the country as a whole were found to be underestimated with respect to the actual rainfall.
- The forecasts for the rainfall for the country as whole during July and forecast for the seasonal rainfall for Northwest India were found to be overestimated as compared to the actual rainfall.