Rain-deficient Tamil Nadu pins hope on December

With the northeast monsoon playing truant this year, water situation in many parts of the State looks very bleak

November 27, 2016 12:00 am | Updated December 02, 2016 05:51 pm IST - CHENNAI:

In discussions on monsoons that wet this country, the northeast monsoon comes off as a poor cousin to its ferocious southwest monsoon. In fact, the northeast monsoon is known as the ‘post-monsoon’ season or ‘retreating southwest monsoon’ as if it does not have a character of its own.

However fickle and temperamental it is, the northeast monsoon is the lifeline for Tamil Nadu, which receives an estimated average 48 per cent of its rainfall between October and December.

Last November, the State, particularly the coastal districts of Chennai and Cuddalore, battled one of the most devastating monsoon showers of the century. In less than a week, it will be the first year anniversary of the December deluge that parts of the State witnessed, which left a trail of destruction. But, this November, which is normally the wettest month of the year, the State stares at a bleak northeast monsoon and is struggling with nearly 70 per cent deficient rainfall since October 1.

Because of the State’s reliance on the rains of the northeast monsoon for its water requirements, Tamil Nadu is often prone to drought when the ‘winter monsoon’ fails. While prolonged dry spells are considered ‘normal’ in the course of the monsoon, the delayed onset and weak weather systems have been a cause for concern. The impact of the failed monsoon on the storage levels in water bodies and agriculture, which has left farmers doubly disappointed with Cauvery water flow, is likely to be devastating.

Driest month

The data of the Meteorological department indicates that all districts are grappling with deficit rainfall with only a variation in percentage. Cuddalore and Chennai are among the worst-hit districts with a shortfall of over 80 per cent so far this month. With the department forecasting that there may not be much rain till November-end, as there is no strong weather system to trigger monsoon activity, November is likely to end up as one of the driest months in the past few decades.

S.Balachandran, Director of Area Cyclone Warning Centre, Chennai, said: “We are likely to have largely a dry weather for the next four days across the State. Chilly weather will continue to prevail over most parts of the State because of clear skies. The minimum temperature may dip by three or four degree Celsius in the north western parts of the State because of the same reason.”

It may be recalled that the Met department had predicted that the State would receive 90 to 100 per cent of its average rainfall. Some weather models showed that the monsoon may end on a negative note. Mr. Balachandran said the northeast monsoon is ‘complicated’, and it is known to bring in an intense spell of rainfall in a short time too. As it happened in 2015, when nearly 30 cm of rainfall fell on December 1 alone in Chennai, a record-breaking event.

The State, thus, is justified in continuing to pin its hope on December, believing the monsoon is likely to revive.

However, the question of whether the rainfall will bridge the shortfall remains to be answered. S.B.Thampi, Deputy Director General of Meteorology, Regional Meteorological Centre, Chennai, said: “We are expecting rains to revive from the first week of December. The intensity of rainfall will increase from the second week of December. Long-range forecast is sometimes not very reliable. Numerical weather models indicate that the monsoon may wind up on negative side. But, we may have to wait till the year-end to know the amount of deficiency and to see if the December rains will compensate for the loss so far.”

Signs not good

Elaborating on the monsoon pattern, Mahesh Palawat, chief meteorologist, Skymet Weather Services, a private weather forecasting agency, said usually the weather systems formed in central and southeast Bay of Bengal move in a westerly/northwesterly direction and reach the Tamil Nadu coast, Andhra Pradesh, and recurve to other regions.

“The sea surface temperature must be 29 degree Celsius or more to develop weather systems. This year, there is poor chance for Tamil Nadu to end with good rainfall. It may record only less than 50 per cent of its average rainfall. Some southern parts may get good rains,” he said.

While it is difficult to decipher the exact reasons for failure or good monsoon year given its complexity, Mr.Palawat noted that El Nino, the global weather phenomenon, has favoured copious rainfall whenever it was active after 1976. However, during La Nina years, like 2006 and 2007, the State has had only normal or deficit rainfall. “We cannot directly link monsoon performance to only a few weather phenomena and much more research is needed,” he added.

Going by the current rainfall deficit over the State, this year could be one of the worst northeast monsoons of the century. Y.E.A.Raj, former deputy director general of meteorology, Chennai, recalled that the State saw a severe drought in 1974 when the rains were inadequate by nearly 60 per cent. Tamil Nadu records an average of 438.2 mm of rainfall during this season.

“This century has witnessed seven poor monsoon years with below 40 per cent rainfall. Unlike the southwest monsoon or summer monsoon, when convective activity too brings evening showers, this season needs easterlies and moisture to come from the Bay of Bengal to induce rains,” he said.

At present, there is more northerly wind, which denotes cold, dry wind, blowing over the region. Normally, three or four weather systems form over the Bay of Bengal in November. So far, there is no strong system to bring heavy spells this time.

“In 1974 there was a massive drought. There was no water supply at the Egmore railway station to be filled in trains then. There were talks of cloud seeding operations, and drought mitigation efforts like desilting water bodies were taken on a large scale then. However, the drought did not last long as rains in 1975 solved the problem,” he recalled.

Bloggers’ view

Meanwhile, independent weather bloggers claim that Tamil Nadu is headed for one of the worst monsoons in 150 years if December does not compensate for the loss. K.Srikanth of Chennaiyil Oru Mazhaikalam points out that the State has recorded 11 cm against the normal of 33 cm in October and November. Overall, 1876 holds the record of the worst-ever monsoon performance with lowest cumulative rainfall of 12 cm. Given the unpredictable and chaotic nature of the northeast monsoon, will December showers bridge the shortfall? It could, because that is also in the nature of the monsoon.

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