The Hindu Business Line : Model limitations blamed for rain figure disparity

Monsoon showers recorded in May during years of early onset should logically go into cumulative area-weighted rainfall account but the temptation to employ them for verifying a specific weather model should be resisted.

"This is so because the monsoon model that we follow takes into account an integrated four-month season of rainfall starting June 1," clarified Dr Akhilesh Gupta of the Department of Science and Technology (DST). Logically speaking, the pre-June showers must go into the monsoon account.

MODEL NOT AGREEABLE

But the specific weather model does not agree, since it is tuned to record the June to September rainfall only. This explains why official statistics have refused to consider the rainfall received from May 26 to June 1 this year, torrential by normal monsoon standards.

If the six days of rain leading up to June 1 is included, the cumulative area weighted deficit up to July 12, amounts to no more than 3.5 per cent for the country as a whole. But official statistics made available have assessed the deficit as 10 per cent.

There have been years when the monsoon has started much earlier than it did this year, and also when it spilled into October, well beyond the time when the model calls an end of the season. But the rain event has been recorded as having fallen on either side of the monsoon mean - pre-monsoon or post-monsoon (if not northeast monsoon).

Pointing out another dichotomy, Dr Gupta said monsoon sets in over the Andamans, which is well within the Indian territorial waters, by May 20, but this is not reflected in official rainfall statistics.

In real terms, monsoon starts here, although it rains out over ocean waters for a number of days before crossing the mainland along Kerala by June 1.

Meanwhile, the `low' over south-east Uttar Pradesh merged with the seasonal trough on Wednesday. A forecast by the National Centre for Medium range Weather Forecasting (NCMRWF) said the rainfall over Central India and the Indo-Gangetic plains would continue for another three to four days.

A fresh upper air cyclonic circulation has formed over Jharkhand and adjoining West Bengal. This is expected to cause widespread rainfall with heavy to very heavy rains over Orissa, Jharkhand and Chhattisgarh for the next two days.

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