The Hindu : Southwest monsoon has no bearing on northeast

Online edition of India's National Newspaper
Saturday, Oct 12, 2002

Southern States

Southern States - Tamil Nadu

Southwest monsoon has no bearing on northeast

By T. Ramakrishnan

CHENNAI OCT. 11. This year's southwest monsoon turned out to be a `washout' for Tamil Nadu, like it was for the rest of the country, but it does not mean rainfall during the northeast monsoon also will be deficient.

A senior Meteorological department official says the past record of rainfall pattern reveals that there is no correlation between an adverse southwest monsoon (June-September) and the northeast monsoon (Ocotober-December).

Since 1961, the State has recorded deficit rainfall only once (in 1980) during both the monsoons.

In all the other years, the rainfall was either excess or normal.

However, last year it was quite close.During the southwest monsoon, the deviation from the anticipated rainfall was minus 19 per cent (which, in meteorological parlance, is normal) and during the northeast monsoon, it was minus 21 per cent.

As per meteorological standards, if the departure is in the range of minus 19 per cent-plus 19 per cent, it is called normal; plus 20 per cent and more — excess; minus 20 per cent to minus 59 per cent — deficient; and minus 60 per cent to minus 99 per cent — scanty.

Between June and September this year, as against an anticipated rainfall of 32 cm, the State received 17 cm, a shortfall of 45 per cent.

Statistics apart, the characteristics of the two monsoons differ so much that there is little possibility of the southwest monsoon having any bearing on the northeast monsoon, the official points out.

While the southwest monsoon covers the entire country, the northeast monsoon benefits mainly Tamil Nadu, besides the adjoining portions of coastal Andhra Pradesh, Rayalaseema, south interior Karnataka and Kerala.

Meanwhile, the focus is on the onset of the northeast monsoon, expected to take place around October 20, plus or minus seven days.

The official does not want to hazard a guess on its intensity, as no mechanism is available.

But for the southwest monsoon, 16 well-established parameters are studied before making an assessment.

During this year's southwest monsoon, Chennai was the only district in the `normal' category, though the city received, in actual terms, less rainfall than the anticipated precipitation.

It recorded 36 cm, whereas 44 cm was expected, a shortfall of minus 19 per cent.

As many as 23 other districts fell in the category of `deficient', including Tirunelveli (6 cm and minus 50 per cent), Coimbatore (11 cm and minus 41 per cent), Madurai (actual: 17 cm and departure from normal: minus 37 per cent), Tiruchi (19 cm and minus 28 per cent), and Salem (21 cm and minus 57 per cent).

Thanjavur and Nagapattinam, forming part of the Cauvery basin, received 19 and 15 cm, a shortfall of minus 40 and minus 42 per cent.

Of the districts in the `scanty' category, Kanyakumari recorded 83 per cent shortfall, registering only 8 cm against the anticipated 46 cm, Theni (6 cm and minus 69 per cent), Ramanathapuram (5 cm and minus 64 per cent), Tiruvarur (12 cm and minus 61 per cent) and Tuticorin (3 cm and minus 61 per cent).

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