New Delhi, Oct 30 The Southwest Monsoon recently concluded with "below normal" rainfall to the tune of 94 per cent of the long-period average (LPA) against the forecast of 96 per cent with an error margin of plus and minus four per cent, says an analysis.
However, increasing variability of rainfall continued to dominate the four-month-long season.
July was the best performer and a saviour from a possible disaster. It recorded 13 per cent excess rainfall, which was the second highest since 2005. The month compensated for the underperformance of June that had ended with a deficit of 10 per cent rainfall.
Halfway through the season, August, the core monsoon month, collapsed completely with 36 per cent rainfall deficiency.
The country was plunging into despair with drought threats looming large on account of building El Nino in the Pacific Ocean.
However, the oceanic phenomena of Indian Ocean Dipole (IOD) and Madden Julian Oscillation (MJO), both associated with increasing rains over India, turned the tables by triggering back-to-back monsoon low-pressure systems over the Bay of Bengal in September.
With this, the timely revival of the monsoon saved the country from the scare of yet another potential drought.
Out of 36 meteorological subdivisions in the country, 26 subdivisions recorded normal rainfall, constituting 73 per cent of the area of the country.
Meanwhile, seven subdivisions recorded deficit rainfall that covers 18 per cent of the area of the country. Only three subdivisions witnessed excess rainfall amounting to an area of seven per cent.
A look at the district-wise distribution of rainfall through the four months of monsoon offers a glimpse of how distorted the picture of “normalcy” really is. An analysis of the daily district rainfall sheets from June up to the last week of September suggests barely any sense of normalcy in the distribution of rainfall. About six per cent of the 81,852 district rain days during the monsoon analysed by Carbon Copy and Climate Trends registered normal rainfall.
Analysis of daily district-level rainfall through the four-month season reveals the volatile nature of “normalcy” -- over 60 per cent of the district-level daily rainfall observations registered large deficits or no rain while almost 20 per cent of the observations showed large excesses.
It is understood that normal rainfall data has been averaged out over several years and cannot be expected to indicate the consistency of rainfall, but the relatively miniscule number of “normal” rainfall days experienced by India’s 718 districts does reflect a reality of being swung between extremes.
Days registering “large excess” (where excess is over 60 per cent of the LPA) rainfall was the next most prevalent category, indicating the violent shifts between dry and wet through the season.
August was the worst performing month, with over 76 per cent of district rain days registering large deficits or no rain. The week-by-week rainfall performance assessment of India’s 36 meteorological sub-stations over 17 weeks of the monsoon reveals that almost half of all weekly observations experienced rainfall deficits of at least 20 per cent. This denotes that almost two-thirds of the district rainfall days either registered large deficits or no rain, raising a question on the definition of seasonal normalcy.
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