Topic : Monsoons to be well distributed in India: IMD
Topic in Syllabus: General Studies Paper 2: Indian Geography
The India Meteorological Department (IMD) recently forecast that the coming south west monsoon season is likely to be near normal, with a rainfall of 96 per cent of the long period average with a model error of plus or minus five per cent.
More about on news:
- The country was expected to have a well distributed rainfall scenario during the four month season from June to September.
- There was a weak El Nino condition and it was likely to prevail through the season, though the intensity could reduce from July onwards
- The sea surface anomaly over equatorial Pacific Ocean region, which is responsible for El Nino, is at present between 0.5 degree and one degree Celsius. This could have some impact at the beginning of the season. But, it would gradually reduce as the season progressed.
- The existence of the weak El Nino condition has been accounted for in the forecast.
- IMD issues operational forecast for the south west monsoon season in two stages.
- The second forecast will be issued in June, when more information on various parameters that affect the monsoon will be available.
- IMD issues operational forecast for the south west monsoon season in two stages. The second forecast will be issued in June, when more information on various parameters that affect the monsoon will be available.
Five predictors are used in the statistical system for the first stage forecast:
- Sea surface temperature gradient between north Atlantic and north Pacific for the period from December to January
- Equatorial south Indian Ocean sea surface temperature in February;
- East Asia mean sea level pressure during February-March;
- North west Europe land surface air temperature during January; and
- Equatorial Pacific warm water volume during February-March.
Rainfall distribution categories:
IMD maintains five rainfall distribution categories on an all-India scale. These are:
- 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
About on El Nino:
- El Niño is the name given to the occasional development of warm ocean surface waters along the coast of Ecuador and Peru.
- When this warming occurs the usual upwelling of cold, nutrient rich deep ocean water is significantly reduced.
- El Niño normally occurs around Christmas and usually lasts for a few weeks to a few months.
- Sometimes an extremely warm event can develop that lasts for much longer time periods. In the 1990s, strong El Niños developed in 1991 and lasted until 1995, and from fall 1997 to spring 1998.
How often do El Niños occur?
- El Niños occur every three to five years but may come as frequently as every two years or as rarely as every seven years.
- El Niños occur more frequently than La Niñas. Each event usually lasts nine to 12 months.
- They often begin to form in spring, reach peak strength between December and January, and then decay by May of the following year.
- Their strength can vary considerably between cycles.
- One of the strongest in recent decades was the El Niño that developed the winter of 1997-98.
- El Niño was originally named El Niño de Navidad by Peruvian fishermen in the 1600s.
- This name was used for the tendency of the phenomenon to arrive around Christmas.
- Climate records of El Niño go back millions of years, with evidence of the cycle found in ice cores, deep sea muds, coral, caves and tree rings.
During El Nino year:
- In an El Niño year, air pressure drops over large areas of the central Pacific and along the coast of South America.
- The normal low pressure system is replaced by a weak high in the western Pacific (the southern oscillation). This change in pressure pattern causes the trade winds to be reduced Weak Walker Cell. Sometimes Walker Cell might even get reversed.
- This reduction allows the equatorial counter current (current along doldrums) to accumulate warm ocean water along the coastlines of Peru and Ecuador.
- This accumulation of warm water causes the thermocline to drop in the eastern part of Pacific Ocean which cuts off the upwelling of cold deep ocean water along the coast of Peru.
- Climatically, the development of an El Niño brings drought to the western Pacific, rains to the equatorial coast of South America, and convective storms and hurricanes to the central Pacific.
How El Nino impacts monsoon rainfall in India:
- El Nino and Indian monsoon are inversely related.
- The most prominent droughts in India – six of them – since 1871 have been El Nino droughts, including the recent ones in 2002 and 2009
- However, not all El Nino years led to a drought in India. For instance, 1997/98 was a strong El Nino year but there was no drought (Because of IOD).
- On the other hand, a moderate El Nino in 2002 resulted in one of the worst droughts.
- El Nino directly impacts India’s agrarian economy as it tends to lower the production of summer crops such as rice, sugarcane, cotton and oilseeds.
- The ultimate impact is seen in the form of high inflation and low gross domestic product growth as agriculture contributes around 14 per cent to the Indian economy.
Impact on Agriculture:
- The rains are critical because nearly half of all Indians depend on a farm-based income and 60% of the country’s net-sown area does not have any form of irrigation.
- Millions of farmers wait for the rains to begin summer (or monsoon) sowing of major crops, such as rice, sugar, cotton, coarse cereals and oilseeds.
- Half of India’s farm output comes from summer crops dependent on these rains.
- Robust summer rains, which account for 70% of India’s total annual rainfall, spur rural spending on most items and increase demand in other sectors of the economy.
- Rural sales, for instance, account for about 48% of all motorcycles and 44% of television sets sold annually if the monsoon is normal, according to consumer sales data from the Citibank Research.
- Patchy rains tend to stoke food inflation..
- For good farm output, the rains have to be not just normal but also evenly spread across states.
- The monsoon also replenishes 81 nationally-monitored water reservoirs critical for drinking, power and irrigation.
- India, still the world’s fastest-growing major economy, saw annual growth slip to 6.6% in the December quarter from 7% in the previous quarter, making this the slowest growth rate in five quarters.
What lies ahead?
- El Nino has been generally known to suppress monsoon rainfall in India while La Nina increases it.
- El Niño years tend to be drier than average, but one of the strongest El Nino of the century (1997-98) produced a monsoon season with above-average rainfall for India (see table).
- Researchers also believe that even the location of the warming in the Pacific may possibly have an influence on the monsoon.
- Anomalous warming in the Central and East Pacific (Nino 3.4 region) could have a more profound adverse impact on the monsoon than when the warming shifts to the adjoining Far East Pacific (Nino 3. region).
- Current conditions (March, 2019) suggest that the warming is pronounced (+0.98 degree Celsius) in the Nino 3.4 region than the Far East Pacific (+0.74 degree Celsius), which could suggest a weaker monsoon this year.
- The official forecast from the India Meteorological Department (IMD) is eagerly awaited.
- Scientists claim there may be other factors that combine with the prevailing Pacific conditions to decide the fate of the monsoon. Progressive heating of the land during April-May-June is one.
- Warming up of the West Indian Ocean boosts a prevailing monsoon, and vice-versa.
- International and domestic weather agencies expect that this year, the Indian Ocean dipole could be either ‘neutral’ or weakly positive.
What do you understand by El Nino? Discuss How El Nino impacts monsoon rainfall in India?