Rains lash Chennai
Rains lash Cnennai waterlogging many areas.IANS

Heavy rains witnessed in Andhra Pradesh and Tamil Nadu over the past few days have given rise to questions whether El Nino, the phenomenon often linked to poor monsoon rainfall, is the reason for the excessive downpour.

In the week ending 18 November, Chennai recorded an above-normal rainfall of 329%, while Vellore saw 572% more than normal rainfall, according to India Meteorological Department (IMD).

In 1997 too, when Tamil Nadu saw heavy rains, the El Nino was recorded as the strongest in decades.

However, not enough research is available to ascertain the impact of El Nino on winter rain or Northeast Monsoon in India.

"During El Nino extreme rainfall occurs in Ecuador, Peru, and southwest US. The impact on winter rain is not as well documented, but in 1997, rainfall over Tamil Nadu was really high. Averaged over all El Nino, the winter monsoon is indeed higher than average," Mint quoted Wenju Cai, a principal research scientist specialising in El Nino modelling at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia's national scientific agency, as saying.

After starting on a promising note in June this year, the monsoon rainfall weakened from late July due to El Nino effect and ended in deficit for the second consecutive year.

Further, this year's October was recorded as the hottest October in the past 136 years, according to a report from the US National Oceanic and Atmospheric Administration (NOAA).

The El Nino this year has already resulted in "extreme weather patterns" across the world. The World Meteorological Organization forecasts it to get even stronger by the end of 2015.

"The El Nino is still growing, and is approaching the intensity of the 1997. It is possible to grow stronger than the 1997 (one)," said Cai.

The growing strength of El Nino has raised doubts whether it is responsible for heavy rains in Tamil Nadu, which caused huge damage to lives and property in the state.

"There is no such relation regarding conversion, but generally it is seen that disturbances such as depression, low pressure systems and cyclones are more during post monsoon and pre-monsoon season. But during El Nino years, such systems in the Bay of Bengal have a typical feature that they move westward, while in other years they move eastward. This causes heavier rainfall in Tamil Nadu and other such coastal areas," Live Mint quoted D.S. Pai, Chief of Long Range Forecasting Division of IMD.

"It is because of this typical feature that we had predicted above average rainfall this Northeast Monsoon season. Another problem is also that the heavy rainfall is concentrated in a few days," Pai added.

NOAA said that the global sea surface temperature in October was 0.85°C above the 20th century average of 15.9°C, which was recorded as the highest for the month.

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