El Nino and La Nina are all terms referring to a major ocean-current together called as El Nino Southern Oscillation (ENSO). This is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific, including off the Pacific coast of South America. Fishermen in Peru were the first to notice irregular cycles of rising ocean temperatures because the fish disappeared when the water warmed. They named this as El Nino (Spanish for the little boy) since they often occur around Christmas time. La Nina (little girl) results when the eastern tropical Pacific cools.
Climatologists determined that El Niño occurs simultaneously with the southern oscillation. The southern oscillation is a change in air pressure over the tropical Pacific Ocean. When coastal waters become warmer in the eastern tropical Pacific (El Niño), the atmospheric pressure above the ocean decreases. Climatologists define these linked phenomena as El Niño-Southern Oscillation (ENSO). The ENSO cycle, both El Niño and La Niña, cause global changes of both temperatures and rainfall.As El Niño brings rain to South America, it brings droughts to Indonesia and Australia. These droughts threaten the region’s water supplies, as reservoirs dry and rivers carry less water. Agriculture, which depends on water for irrigation, is threatened.
Developing countries that depend on their own agriculture and fishing, particularly those bordering the Pacific Ocean, are usually most affected. Modern day research and reanalysis techniques have managed to find at least 26 El Niño events since 1900, with the 1982–83, 1997–98 and 2014–16 events among the strongest on record.El Niño events of 1982-83 and 1997-98 were the most intense of the 20th century. Since 2000, El Niño events have been observed in 2002–03, 2004–05, 2006–07,2009–10, 2014-16, and2019.
An especially intense El Niño event in 1998 caused an estimated 16% of the world's reef systems to die. The event temporarily warmed air temperature by 1.5 °C, compared to the usual increase of 0.25 °C associated with El Niño events.
It has been observed that E1 Nino is having severe impacts on climatological conditions of Odisha. During the El Nino event 1997-98 we experienced sunstroke in the year 1998 and Super Cyclone in 1999. Similarly El Nino 2014-16 gave us tropical cyclones Phailin and Hudhud. Recently during the ongoing El Nino 2019, we faced again another super cyclone Fani which has devastated a vast area covering three districts of the State. Further, it may affect also the regular monsoon causing severe draught in our State. Alternatively it may intensify the monsoon causing severe flood.
Extreme weather conditions related to the El Niño cycle correlate with changes in the incidence of epidemic diseases. For example, the El Niño cycle is associated with increased risks of some of the diseases transmitted by mosquitoes, such as malaria, dengue fever, and Rift Valley fever.
Cycles of malaria in India, Venezuela, Brazil, and Colombia have now been linked to El Niño. Outbreaks of another mosquito-transmitted disease, Australian encephalitis (Murray Valley encephalitis—MVE), occur in temperate south-east Australia after heavy rainfall and flooding, which are associated with La Niña events. A severe outbreak of Rift Valley fever occurred after extreme rainfall in north-eastern Kenya and southern Somalia during the 1997–98 El Niño.
ENSO conditions have also been related to Kawasaki disease incidence in Japan and the west coast of the United States, via the linkage to tropospheric winds across the North Pacific Ocean.
El Nino influences global climate as well as extreme weather events such as floods, droughts and tropical cyclones leading to large societal impacts.
(Dr Senapati Dean, Biju Patnaik University of Technology, Odisha Professor and Head Department of Chemistry, Trident Academy of Technology Bhubaneswar-751024)
