Context:
The U.N. Office for the Coordination of Humanitarian Affairs (OCHA) has characterized the recent floods in Somalia and neighboring East African countries as a once-in-a-century event. The floods, triggered by torrential rainfall and influenced by climatic factors like El Niño and the Indian Ocean Dipole, have displaced hundreds of thousands of people. The impact extends beyond Somalia, affecting regions in neighboring Kenya, leading to 15 reported deaths and posing significant challenges in areas like Mombasa, Mandera, and Wajir.
Relevance:
GS I: Geography
Dimensions of the Article:
- Indian Ocean Dipole (IOD)
- El Nino Southern Oscillation (ENSO)
- Impact of Indian Ocean Dipole (IOD)
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.
El Nino Southern Oscillation (ENSO)
- The El Nino Southern Oscillation (ENSO) is a climate phenomenon that affects the Pacific Ocean and has global weather implications.
- In a normal year, the eastern side of the Pacific Ocean near the northwestern coast of South America is cooler compared to the western side near the islands of the Philippines and Indonesia.
- This temperature difference arises due to prevailing wind systems that move from east to west, pushing warmer surface waters toward the Indonesian coast.
- As the warm surface waters are displaced, relatively cooler waters from deeper levels rise up to replace them.
- During an El Nino event, there is a weakening of the wind systems, resulting in less displacement of the warmer waters.
- This causes the eastern side of the Pacific Ocean to become warmer than usual. The opposite occurs during La Nina.
- El Nino and La Nina are two phases of ENSO.
- Both El Nino and La Nina have widespread effects on weather patterns globally.
- In India, El Nino has the impact of suppressing monsoon rainfall.
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.
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.
- It 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 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.
Impact of Indian Ocean Dipole (IOD)
- The Indian Ocean Dipole (IOD) exhibits an ocean-atmosphere interaction that resembles the fluctuations observed during El Nino events in the Pacific Ocean. However, the IOD is relatively less powerful than El Nino, resulting in relatively minimal impacts.
- During a positive IOD event, rainfall increases along the African coastline and over the Indian subcontinent, while rainfall is suppressed over Indonesia, Southeast Asia, and Australia. The impacts are opposite during a negative IOD event.
Past Events:
- In 2019, an IOD event developed during the late monsoon season. It was so strong that it compensated for the deficit rainfall experienced during the first month of the monsoon season (June, which had a 30% rainfall deficiency that year).
- The deficit in June 2019 was also attributed to a developing El Nino, but the El Nino weakened and did not have a significant impact later on.
-Source: Indian Express
