- The ongoing La Nina phase of the equatorial Pacific Ocean is expected to last at least another six months, making it one of the longest La nina episodes ever recorded. It is also only the third episode since 1950 to run for a third year in a row.
- On August 31, the World Meteorological Organization (WMO) stated that La Nina would span three consecutive northern hemisphere winters for the first time this century, resulting in a ‘triple dip’ La Nina.
- This is likely to have far-reaching consequences for weather events around the world in the coming months, potentially exacerbating both floods and droughts in various regions.
GS Paper 1: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc
Drought has been designated as a disaster due to its geographic scope, duration, slow onset, and long-term effects on vulnerable populations. Discuss the mechanisms for preparedness to deal with likely El Nino and La Nina fallouts in India, with a focus on the National Disaster Management Authority’s (NDMA) September 2010 guidelines. (250 Words)
What exactly is ENSO (El Nino Southern Oscillation)?
- ENSO is one of the most important climate phenomena on the planet because of its ability to alter global atmospheric circulation, which influences temperature and precipitation around the world.
- El Nino = [Warm water in the Eastern Pacific + cold water in the Western Pacific].
- SO = [Low Pressure in the Eastern Pacific + High Pressure in the Western Pacific]
- ENSO = [Warm water in the East Pacific + Low Pressure in the East Pacific] + [Cold water in the West Pacific + High Pressure in the West Pacific].
- In ENSO, the formation of an El nino [Circulation of Water] is linked with a pattern of Pacific Ocean circulation known as the southern oscillation [circulation of atmospheric pressure].
- Though ENSO is a single climate phenomenon, it can exist in three states or phases:
- An increase in sea surface temperatures (SST) above average in the central and eastern tropical Pacific Ocean.
- The accumulation of warm water causes the thermocline in the eastern Pacific Ocean to drop, cutting off the upwelling of cold deep ocean water along Peru’s coast. The fishing industry has been impacted.
- It is linked to lower-than-average monsoon rainfall in India.
- It is associated with a cooler ocean surface, or lower-than-average SSTs, in the central and eastern tropical Pacific Ocean, as well as a comparatively better monsoon rainfall in India.
- There is no El Nino or La Nina, and tropical Pacific SSTs are frequently close to average.
- El Nino and La Nina episodes typically develop between March and June and last between nine months and a year.
- They are strongest during the winter (November-January in the northern hemisphere), then weaken or dissipate by March or April the following year.
- However, El Nino and La nina events are not mirror images of one another. They differ in terms of length and strength.
- El Nino episodes are more common and are usually associated with more severe weather events. El Nino is more likely to be a one-time event.
- La Nia, on the other hand, has a longer track record. As a result, multi-year La nina events (those lasting more than a year) are becoming more common.
La Nia’s ‘Triple Dip’
- Extensive phases: These El nino and La nina episodes can sometimes last for months.
- In recent years, the El nino of 2015-16 was one of the longest on record, lasting 19 months, and was dubbed ‘Godzilla’ due to its sustained high intensity.
- Current situation: ‘Triple Dip’ La nina is a period in which the La nina period lasts for up to three consecutive winters and results in multiyear cooling of the equatorial Pacific Ocean’s surface temperature.
- For example, the current La nina episode began in September 2020, has lasted 24 months, and is expected to last another six months, classifying it as a ‘triple dip’ La Nia.
- La Nina duration: According to a study, nearly half (six out of 13) of all La nina events since 1950 have lasted two years (double dip La Nina), with three, including the current one, lasting three years.
- El Nino comparison: In comparison, more than 75% of El nino events (15 of 20) ended within a year. No El nino has ever lasted a third year.
- The current ‘triple dip’ La nina episode is notable: While prolonged La nina episodes are not uncommon, the current one differs significantly from the previous two triple-year events.
- Both earlier events, one between 1973 and 1976 and the other between 1998 and 2001, were preceded by a strong El Nio, and the longer heat dissipation time resulted from the higher amount of accumulated heat in the oceans.
- In the absence of a strong El Nio, the cause of the current La nina episode is unclear at the moment.
Considering the likely impact on India
- In India, La nina is associated with abundant rainfall during the monsoon season. This is the inverse of El Nio, which is known to reduce monsoon rainfall.
- As a result, another year of good, or normal, monsoon rainfall could be expected if La nina persists.
- India has received 740.3 mm of rainfall this year, which is 7% more than the seasonal average through August 30.
- One of the following factors: However, despite its strength, the ENSO condition is not the only factor influencing monsoon rainfall in India, and there is no one-to-one correlation between the ENSO condition and the amount of rainfall.
- Additionally, ENSO has a global impact. At the local level, rainfall varies greatly, which is being exacerbated by climate change.
- Effects on other regions
- La Nia, for example, is associated with extremely dry winters in most parts of the United States. The recent widespread drought in the United States is also a result of La Nina.
- The National Oceanic and Atmospheric Administration (NOAA) of the United States recently declared that August 2022 will be the sixth hottest August in the last 143 years.
- La nina is expected to bring more rain to Australia and Indonesia, as well as the rest of the tropical region. For example, this year’s flooding in eastern Australia.
- La nina can also be blamed for the excessive rainfall in Pakistan, which is experiencing its worst flooding disaster.
- According to the World Meteorological Organization (WMO), the persistence of La nina will almost certainly worsen Africa’s drought.
- Experts predict that as a result of this triple dip, the world will experience an active Atlantic hurricane season in 2022.
The Climate Change Connection
- Incomplete records: Because there are no long-term historical records, the natural variability of ENSO is not well understood. Furthermore, no conclusive evidence has been found linking ENSO events to global warming.
- Inconsistent variability: The erratic occurrences of El nino and La Nia, for example, sometimes occurring every two years and other times spanning seven years, result in ambiguous natural variability. As a result, quantifying the impact of global warming is difficult.
- The role of trade winds in ENSO: Although some experts believe that climate change is increasing the frequency and intensity of El nino and La nina events, there is no conclusive evidence.
- This is because trade winds play a significant role in triggering ENSO events, and changes in trade wind strength are not easily explained by global warming.
- Notable link: There is evidence of another type of link between global warming and ENSO events, as follows:
- Colder surfaces allow the oceans to absorb more heat from the atmosphere during La nina years. As a result, air temperatures tend to fall, producing a cooling effect.
- However, according to the World Meteorological Organization, La Nia’s cooling influence is temporarily slowing the rise in global temperatures, but it will not halt or reverse the long-term warming trend.
- In addition, average global temperatures were found to be about 0.9 degrees Celsius higher than the 20th century average.