El Niño has become the buzzword this northeast monsoon and is said to be the cause ofthe torrential downpour across the State.
While admitting that this is a strong El Niño year, weather experts pointed out that this was not the only global weather phenomenon that affects the monsoon.
Tamil Nadu has so far received average rainfall of 39 cm, an increase of 32 per cent. Weather experts note that this is a defining El Niño year with the sea surface temperature going above normal. This has favoured an intense northeast monsoon in the State.
El Niño and La Niña are complex weather patterns that result from variations in ocean temperatures in the equatorial Pacific Ocean. While El Niño is generally said to favour good northeast monsoons, La Niña leads to poor rainfall.
However, there have been years when Tamil Nadu has received scant rainfall during El Niño years and excess rainfall when the La Niña factor is strong, meteorological department officials said. Global weather factors that influence weather patterns across the world were documented as early as 1950s, weather experts said. However, more people became aware of the climatic phenomenon and its impact only after the Internet era set in in the1990s.
Y.E.A. Raj, former deputy director general of meteorology, Chennai, recalled that meteorologists who visited the United States used to bring tapes filled with data to research the impact of these global weather factors. “We cannot deny El Niño’s impact on excess rainfall this year. But, the State and Chennai can get excess rains in northeast monsoon even without El Niño. A classic example is 2005 when the state got 79 per cent more than its average of 43 cm of rainfall,” he said says.
Quoting from a study of data of northeast monsoon between 1961 and 2015, he said that the State received excess rains by at least 20 per cent during the nine years when neither El Niño nor La Niña factors were strong. The latest was in 2011.
Years of no impact
While El Niño contributed to a good monsoon in 17 years, it failed to have any influence in 1982, 1986 and 2002, when the State received less than 20 per cent of normal rainfall.
This year, too, a combination of factors, including El Niño, Southern Oscillation and Siberian High, has been the driving force behind torrential downpour.
