NEW DELHI: There has been a major shift in the pattern of rainfall during the southwest monsoon season (from June to September) in recent years. This is one of the findings of an analysis by scientists at the India Meteorology Department's National climate Centre at Pune.

Another is that rainfall over Kerala, Chhattisgarh and Jharkhand is showing a significant decreasing trend, while that over coastal Andhra Pradesh, Rayalaseema, north interior Karnataka, Madhya Maharashtra, Konkan, Goa, Jammu and Kashmir, west Uttar Pradesh and Gangetic West Bengal is showing a significant increasing trend.

While the contribution of July rainfall to the overall monsoon exhibited a significant decreasing trend, the contributions in June and August exhibited a significant increasing trend.

In a report published recently, the scientists have noted that decrease in the contribution of July rainfall was particularly prominent in central and west peninsular India. The decline was especially significant in south interior and north interior Karnataka, Konkan and Goa, Madhya Maharashtra, Vidarbha, Marathwada, and east Madhya Pradesh. But, at the same time, contribution of the August rainfall is increasing in all these sub-divisions.

The findings are significant in the context of the global phenomenon of climate change.

The southwest monsoon is very crucial considering that on an average it accounts for 74.2 per cent of the country's annual rainfall. Within the monsoon period, rainfall during July is all the more important as it has a great bearing on agricultural activity in the country.

The mean rainfall of July is the highest at 286.5 mm, while that of June is the lowest at 163.1 mm. The mean rainfall of August and September fell in between, at 250.84 mm and 167.8 mm respectively.

The study also found that rainfall is decreasing in almost all meteorological sub-divisions, barring Himachal Pradesh, Jharkhand, and Nagaland, Manipur, Mizoram, and Tripura during the winter season from January to February and over most parts of central India during the pre-monsoon season from March to May.

However, rainfall was found to be increasing for almost all sub-divisions during the post-monsoon season from October to December. The increasing trend was found to be particularly significant over the Rayalaseema area.

Difficult to attribute

Speaking to The Hindu over phone, the Director of the Centre, M. Rajeevan, said that though the shifts in the rainfall pattern were significant, it could not be conclusively attributed to the global climate change. "One must remember that monsoon rainfall is known for its natural variations. Given that fact, it is very difficult to say whether the shifts were due to global climate change or not.''

(The study was conducted by Dr. Rajeevan and Head of Hydrometeorology Division at IMD, Pune, P. Guhathakurta. The study was conducted by analysing the rainfall data for 1,476 rain gauge stations spread across the country.

The data set covered a little more than 100 years, from 1901 to 2003.)

As a follow-up to the study, the Centre has undertaken an analysis to see whether there has been any changes in intensity of daily rainfalls over different parts of the country. That study should give a clue as to whether global climate change has begun to have an impact on Indian monsoon or not. The report on the study was expected to be ready in about a month, he said.

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