The Hindu Business Line : Rain deficit in northwest, northeast; surplus elsewhere

Thiruvananthapuram, Sept. 10 With the end of the four-month southwest monsoon just 20 days away, the contours of overall spatial and temporal distribution of seasonal rainfall are emerging with northwest India (-11 per cent) and northeast India (-1 per cent) running up varying deficits.

The position is irreversible in the case of the former with the monsoon having all but begun to withdraw from the region, but the ongoing weak phase with the monsoon trough in close proximity might just help the latter to consolidate position to some extent.

In contrast, and true to the predictions made on the basis of a positive Indian Ocean Dipole (IOD) phenomenon, the southern peninsula (+21 per cent) and central India (+5 per cent) have recorded surplus rainfall. This has, in turn, helped prop up the overall area-weighted rainfall to 2 per cent surplus till date (September 5), as per an assessment by India Meteorological Department.

A positive IOD year sees a warming anomaly making its presence felt in the western Indian Ocean and helps boost the organised convection regime in the region with a beneficial impact on the Indian monsoon, irrespective of what a prevailing El Nino/La Nina may or may not bring to bear.

OVERALL FIGURES

Overall, the monsoon has been in excess over 31 per cent of the landmass, normal in 57 per cent; deficient in 12 per cent; and scanty in 4 per cent. A district-wise analysis returns the following statistics: excess in 30 per cent; normal in 40 per cent; deficient in 26 per cent; and scanty in 4 per cent.

According to Mr J. V. Singh, scientist with the Ministry of Earth Sciences, the fate of deficient Met subdivisions of Himachal Pradesh, Punjab, Haryana, West Uttar Pradesh and east Madhya Pradesh may have been sealed already. Whatever ran an odd western disturbance may manage to bring to the region would just not measure up to drastically alter the situation.

Why rains failed

There are two possible reasons why the rains may have failed these areas, some of which are fortunately well-irrigated, reasoned Mr Singh. One, interactions of incoming western disturbances in the middle troposphere and monsoon easterlies in the lower levels were far and few between. The northwest region gets most of its share of monsoonal rainfall from these interactions.

Also, the few westerlies that managed to set up an interaction were less intense in nature and lacked the latitudinal depth required to cause largescale precipitation witnessed in the past few years.

Going forward, the withdrawal process will gain momentum despite the feeble resistance offered by the Bay of Bengal. The ‘ridge’ (high-pressure zone) is making its inexorable march into northwest India and would, sooner than later, take its semi-permanent position in the region from where it will oversee the advent of winter two months from now.

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