Shifting monsoon patterns
- Posted By
26th Sep, 2022
The monsoon patterns in India are experiencing a shift which is possibly triggered by triple dip El Nina effect. This is also affecting the sowing of the summer crops.
Withdrawal of Monsoon
- Withdrawal of the monsoon is a more gradual process. The withdrawal of the monsoon begins in north-western states of India by early September.
- By mid-October, it withdraws completely from the northern half of the peninsula. The withdrawal from the southern half of the peninsula is fairly rapid.
- By early December, the monsoon has withdrawn from the rest of the country. The islands receive the very first monsoon showers, progressively from south to north, from the last week of April to the first week of May.
- The withdrawal takes place progressively from north to south from the first week of December to the first week of January. By this lime the rest of the country is already under the influence of the winter monsoon.
Criteria for the declaration of monsoon withdrawal
- Monsoon is said to withdraw from a region when the following criteria are met:
- Rainfall activity ceases over the area for five continuous days;
- An anticyclone establishes in the lower troposphere around 1.5 kilometers above sea level, and
- Moisture content reduces.
- Similar criteria are followed for the declaration of monsoon withdrawal from the country.
- The wind patterns over the country change from a south-westerly direction to a more westerly direction when the monsoon retreats.
How climate change is altering Indian monsoon?
- Monsoon in India has undergone several changes over the years, especially on account of climate change. The Indian Meteorological Department (IMD) has clearly sighted that 2022 has seen the second highest extreme events since 1902.
- The change can be observed in shift in the track of monsoon systems, like low pressure and depression travelling south of their position and flash floods are a result of this change.
- Factors contributing to it:
- Persistence of intense La Nina conditions
- the abnormal warming of East Indian Ocean
- negative Indian Ocean Dipole (IOD)
- southward movement of most of the monsoon depressions and
- Lows and pre-monsoon heating over the Himalayan region are melting glaciers.
When does the monsoon withdraw?
- The monsoon begins its withdrawal from the last State it reaches, which is Rajasthan. Around September 15, cyclonic systems from the Arabian Sea and the Bay of Bengal that fuel the monsoon from June-September are replaced by an ‘anti-cyclone’
- After that dry, windless conditions start to prevail over western and northern India.
- In other words, the withdrawal is a cessation of rainfall activity over northwest India for five straight days, an anticyclone establishing itself in the lower troposphere, and a marked reduction in moisture content.
How has the monsoon been in recent times?
- Monsoon rainfall in India has been surplus by around 7% in the year 2022, though with extreme inequity.Central and southern India saw a sharp surge in rainfall.
- Rains in Central India were surplus by 20% and in southern India by 25%, with the last month seeing several instances of flooding in Kerala, Karnataka, and Madhya Pradesh. On the other hand, large parts of U. P., Bihar, and Odisha have seen large deficits.
- The east and northeast of India have reported a 17% shortfall and the northwest 2%.
What led to excessive rains in southern and central India?
- These heavy rains are premised on a La Nina, the converse phenomenon of the El Nino and characterized by cooler than normal sea surface temperatures in the central Pacific.
- El Ninois linked to reduced rains over India, whereas La Ninaindicates surplus rainfall.
- India is seeing an extended spell of the La Nina, called a ‘triple dip’ La Nina which is a phenomenon lasting across three winter seasons in the northern hemisphere.
- This is only the third time since 1950 that a triple-dip La Nina has been observed. This, in part, is why for the third year in a row, India is seeing surplus rain in September, particularly in a month when the retreat of the monsoon us on the card.
Are monsoon patterns changing?
- Since 2019, monsoon in India has returned surpluses, barring a slight dip last year.This year the monsoon is already in surplus by about 6%.
- Three years of above-normal rain in a block of four years is unprecedented in more than a century of IMD’s database.
- The impact of La Niña is that India can expect a longer period of Monsoon this year. The La Niña months are known to provide heavy rainfall and this year also India has received 740.3mm of rainfall which is 7 per cent higher than the average.
- The worst affected states are Assam, Uttar Pradesh, Bihar and Manipur, Karnataka, and Odisha where heavy rainfall and floods were witnessed. Maharashtra is also being battered by rain in the month of September.
Impact on the sowing of crops
- This uneven spread of monsoon has impacted the sowing of the Kharif, or summer crop.
- Paddy planting has been impacted with sown area 5.51% lower than last year, according to the Agriculture Ministry.
- The Centre is expecting a minimum of six-million tons shortfall in rice production and this is likely to elevate inflation.