Though there were 32 days of cyclone trough last year, there were no wet spells in the State, with Tamil Nadu facing a 20 per cent deficit in the annual rainfall in 2013.
The State’s average annual rainfall is usually 92 mm, but this time, it was short of 18 mm, according to Y E A Raj, deputy director general of Meteorology, Regional Meteorological Centre (RMC), Chennai.
Raj attributed it to the cyclones which moved away faster to Andhra Pradesh, resulting in a single wet spell.
“On an average, the State has 12 to 13 days of cylone or trough, but last year it had nearly 32 days of cylone. This could have a huge rainfall potential. But then the tropical cyclones, which are heat engines powered by the release of latent heat when water vapor condenses into liquid water, are hurt by wind shear,” he said.
The delicate balance of inflowing low-level winds and outflowing upper-level winds that ventilated the storm got disrupted due to this phenomenon, said Raj.
He also said that the prevalence of a positive southern oscillation, the atmospheric component of El Nino, a prolonged warming of sea surface temperature, could be the reason for the lesser rainfall.
Interestingly, the El Nino factor was neutral during the October-December period. As such, it did not benefit the NE monsoon. Raj said more studies had to be done in this regard.
He also said that it was the Southwest monsoon that saved the city from a massive deficit. The city received more rainfall during the South West monsoon than the North East.
“It is a rare phenomenon although it may have occurred twice or thrice. “This year, the city received 60mm of South West monsoon, while the NE monsoon was around 45 mm. Normally, it is the other way around. During the South West monsoon, the city receives 45mm of rains and during NE monsoon it recieves 85mm of rains,” said Raj.
Interestingly, this is being considered to be one of the five poorest north-east monsoons since 1969.This time, the annual rainfall in the city crossed 100 mm. This is considered to be better than last year. The annual rainfall from 2004 has been good except for 2012 and 2013, he said.
T S Sridhar, additional chief secretary and commissioner of revenue administration (Disaster Management and Mitigation), said that though the rainfall was better than last year, the State Government would look at the yield and crop condition before declaring 2013 as a year of drought. The year 2012 was considered one of drought and the government gave away more than Rs 830 crore as aid to farmers.
Source - http://www.newindianexpress.com/
