Context:
The India Meteorological Department (IMD) has predicted an “above normal” monsoon rainfall for India between June and September this year. Remarkably, this is the first time in a decade that the IMD has forecasted “above normal” rainfall at the initial stage, nearly 45 days ahead of the onset of the four-month monsoon season. This early prediction provides valuable insights for farmers, policymakers, and the general public, allowing them to better prepare for the anticipated weather conditions and potentially benefiting agricultural productivity and water resources management across the country.
Relevance:
GS I: Geography
Dimensions of the Article:
- IMD’s Rainfall Prediction for 2024
- La Niña
- El Niño
- Indian Ocean Dipole (IOD)
IMD’s Rainfall Prediction for 2024
Overall Rainfall Prediction:
- Above Normal Rainfall:
- The country is expected to receive 106% of the long period average (LPA) rainfall.
- Long Period Average (LPA):
- LPA is the average rainfall received over the past 50 years, specifically the average from 1971-2020.
- Classification of Rainfall:
- Normal: 96% to 104% of LPA
- Deficient: Less than 90% of LPA
- Below Normal: 90% to 95% of LPA
- Above Normal: 105% to 110% of LPA
- Regional Distribution:
- Except for some regions in the northwest, east, and northeast, nearly the entire country is likely to receive good rainfall.
India’s Normal Rainfall:
- India typically receives 870 mm of rainfall during the monsoon season.
Factors Indicating Above Normal Rainfall:
El Nino and La Nina:
- Weakening of El Nino: A contributing factor to the good rainfall forecast.
- Development of La Nina: Expected during the second half of the season (August-September), also contributing to the positive forecast.
Indian Ocean Dipole (IOD):
- Positive IOD: Another factor indicating above normal rainfall for the season.
La Niña
- La Niña is a coupled ocean-atmosphere phenomenon that is the colder counterpart of El Niño, as part of the broader El Niño–Southern Oscillation (ENSO) climate pattern.
- is a coupled ocean-atmosphere phenomenon that is the colder counterpart of El Niño, as part of the broader El Niño–Southern Oscillation (ENSO) climate pattern.
- During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 3 to 5 °C (5.4 to 9 °F).
- An appearance of La Niña persists for at least five months.
- It has extensive effects on the weather across the globe, particularly in North America, even affecting the Atlantic and Pacific hurricane seasons, in which more tropical cyclones occur in the Atlantic basin due to low wind shear and warmer sea surface temperatures, while reducing tropical cyclogenesis in the Pacific Ocean.
- La Niña is a complex weather pattern that occurs every few years, as a result of variations in ocean temperatures in the Equatorial Pacific.
- It occurs as strong winds blow warm water at the ocean’s surface from South America across the Pacific Ocean towards Indonesia.
- As this warm water moves west, cold water from the deep sea rises to the surface near South America.
- As a result, it is considered to be the cold phase of the broader El Niño–Southern Oscillation weather pattern, as well as the opposite of El Niño weather pattern.
- La Niña impacts the global climate and disrupts normal weather patterns, which as a result can lead to intense storms in some places and droughts in others.
El Niño
- El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (between approximately the International Date Line and 120°W), including the area off the Pacific coast of South America.
- The ENSO is the cycle of warm and cold sea surface temperature (SST) of the tropical central and eastern Pacific Ocean.
- El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific.
- During the development of El Niño, rainfall develops between September–November.
- The cool phase of ENSO is La Niña, with SSTs in the eastern Pacific below average, and air pressure high in the eastern Pacific and low in the western Pacific.
- The ENSO cycle, including both El Niño and La Niña, causes global changes in temperature and rainfall.
Indian Ocean Dipole (IOD)
- The Indian Ocean Dipole (IOD), sometimes referred to as the Indian Nino, is a phenomenon similar to El Nino.
- It occurs in a relatively smaller area of the Indian Ocean, between the Indonesian and Malaysian coastline in the east and the African coastline near Somalia in the west.
- In the IOD, one side of the ocean along the equator becomes warmer than the other.
- A positive IOD occurs when the western side of the Indian Ocean, near the Somalia coast, becomes warmer than the eastern Indian Ocean.
- Conversely, a negative IOD indicates cooler temperatures in the western Indian Ocean.
Negative IOD
- Air circulation in the Indian Ocean basin moves from west to east near the surface and in the opposite direction at the upper levels.
- Warmer waters from the western Pacific cross into the Indian Ocean, causing a slight temperature rise in that region.
- During normal years, this leads to the rising of air and helps maintain the prevailing air circulation.
- In years when the air circulation becomes stronger, more warm surface waters from the African coast are pushed towards the Indonesian islands, resulting in a warmer western Indian Ocean.
- Hotter air rises, reinforcing the cycle of a negative IOD.
Positive IOD
- Air circulation becomes weaker than normal, and in rare cases, it may even reverse direction.
- As a result, the African coast becomes warmer, while the Indonesian coastline experiences cooler temperatures.
- Positive IOD events often occur during El Nino periods, while negative IOD is sometimes associated with La Nina.
- The cooling effect of El Nino on the Pacific side of Indonesia contributes to the development of a positive IOD in the Indian Ocean.
-Source: Indian Express, PIB
