Monsoon starts withdrawing from India, eight days after normal date
India has received 796.4 mm of rain during this monsoon season so far, compared to a normal of 843.2 mm, representing a deficit of 6%
Monsoon started withdrawing from India on Monday (September 25), eight days behind the normal date of September 17, the India Meteorological Department (IMD) said.
“The southwest monsoon has withdrawn from parts of southwest Rajasthan today, September 25, 2023, against its normal date of withdrawal from southwest Rajasthan of September 17,” it said in a statement. This is the 13th consecutive year to have witnessed delayed monsoon retreat.
The withdrawal of monsoon from northwest India marks the beginning of its retreat from the Indian subcontinent. Any delay in the monsoon’s retreat means a longer rainy season, which can significantly impact agricultural production, particularly for northwest India where monsoon rainfall plays a crucial role in the Rabi crop production.
Typically, the southwest monsoon makes its onset over Kerala by June 1 and covers the entire country by July 8. It starts retreating from northwest India around September 17, withdrawing entirely by October 15.
According to the IMD, the withdrawal of monsoon from extreme north-western parts of the country is announced based on three major synoptic features after September 1 – no rainfall activity over the region for five days on the trot, the establishment of anticyclone in the lower troposphere (850 hPa and below) and a considerable reduction in moisture content as inferred from satellite water vapour imageries and tephigrams.
Below normal monsoon
India has received 796.4 mm of rain during this monsoon season so far, compared to a normal of 843.2 mm, representing a deficit of 6%. Rainfall between 94 per cent and 106 per cent of the long-period average (LPA) is considered normal.
Normally, the country receives an average of 870 mm of precipitation during the four-month monsoon season (June to September).
In a pre-monsoon briefing, the IMD had predicted a normal monsoon for India, albeit on the lower side of normal. It had, however, cautioned that El Nino -- warming of waters in the Pacific Ocean near South America -- might influence the latter half of the southwest monsoon.
El Nino results into weaker monsoon winds and drier conditions in India. However, normal cumulative rainfall over the country during the monsoon season doesn’t mean even spatial and temporal spread of precipitation.
The Indian monsoon refers to inherent fluctuations and changes that occur over time due to various natural factors. This is called natural variability. However, research shows climate change is making monsoon more variable. Increased variability means more extreme weather and dry spells.
Rainfall deficit in June
This year, India experienced a rainfall deficit in June but saw excessive precipitation in July due to consecutive western disturbances over northwest India and a favourable phase of the Madden-Julian Oscillation (MJO), known for increasing convection in the Bay of Bengal and the Arabian Sea.
MJO is a large-scale atmospheric disturbance originating in tropical Africa and travelling eastward, typically lasting 30 to 60 days.
August 2023 marked the driest month since 1901 and the hottest ever recorded in India, attributed to the strengthening of El Nino conditions.
However, September brought excess of rain due to multiple low-pressure systems and the positive phase of MJO.
(With agency inputs)