What’s happening to the monsoon?

still Hopeful: The contribution of July rainfall to the annual rainfall showed a marked decline.

still Hopeful: The contribution of July rainfall to the annual rainfall showed a marked decline.   | Photo Credit: — Photo: PTI

N. Gopal Raj

Researchers are noticing changes in the established patterns of monsoon rainfall.

Last year, heavy rains in southern India led to the south-west monsoon ending with above-average nationwide rainfall. In striking contrast, this year large parts of the south as well as Maharashtra and Gujarat are suffering a drought. While June ended with surplus rains for the country as a whole, poor rains in July have pushed the national average into a deficit.

Upto July 15 this year, the south had received 34 per cent less rain than usual while central India had a deficit of three per cent, according to the India Meteorological Department (IMD). The north-western States, which fared badly last year, had a surplus of 77 per cent by mid-July. The eastern parts of the country too have been getting ample rain.

Rain is never evenly distributed across the country during the monsoon. Indeed, as has happened this year, parts of the country can be flooded after receiving too much rain while other places bake in the sun. Predicting how various regions of the country will fare during a monsoon is hugely problematic. But over long periods of time, some typical patterns emerge. The north-eastern states and the west coast, for instance, usually get plenty of rain each year while places like Rajasthan get far less of it and are drought-prone.

However, some researchers are noticing changes in the established patterns of monsoon rainfall.

India receives about three-quarters of its annual rainfall during the south-west monsoon. Data for the last 100 years shows that close to one-third of the nationwide monsoon rainfall occurs in July. August gets around 29 per cent of all the monsoon rain while June and September each receive about 19 per cent.

But when P. Guhathakurta and M. Rajeevan of the IMD’s National Climate Centre closely analysed the rainfall distribution between 1901 and 2003, they found that the contribution of June and August to the annual rainfall exhibited “significant increasing trends”. The contribution of July rainfall, on the other hand, showed a marked decline.

In addition, there were strong regional patterns to this change. The contribution of June rainfall had gone up all along the western side of the country while it had fallen in some central and eastern parts. The contribution of July rainfall had reduced in central and west peninsular India, covering much of Karnataka and Maharashtra, the Konkan-Goa region, and eastern Madhya Pradesh. Interestingly, the same regions were receiving more rain than before in August.

Over the last 10 years or so, July rainfall has often been below par, remarked Dr. Rajeevan, who recently moved to the National Atmospheric Research Laboratory at Tirupati in Andhra Pradesh. But neither the annual rainfall nor the rains during the south-west monsoon for the country as a whole showed any clear trend either of increase or decrease, he added.

However, Dr. Guhathakurta and Dr. Rajeevan noted in their paper that Jharkhand, Chhattisgarh and Kerala were now getting significantly less rain than before during the south-west monsoon. On the other hand, much of West Bengal, west Uttar Pradesh, Jammu & Kashmir, Konkan and Goa as well as parts of Maharashra and Andhra Pradesh were getting more rain during the monsoon.

Meanwhile, K. Krishna Kumar of the Indian Institute of Tropical Meteorology in Pune is finding that the annual cycle of rainfall is beginning some two weeks earlier than before across much of northern India in the last two to three decades.

“Places where the monsoon used to set in only at the end of June now regularly get rain much earlier in the month,” he told The-Hindu. This year was a classic case of many places in northern India receiving a lot of rain in June itself.

Prominent shifts

In many northern states, the May-June rainfall has been increasing in recent decades while the July-August rainfall has declined. These shifts have been particularly prominent in the north-western and eastern parts of the country, he added.

Dr. Krishna Kumar is working with Balaji Rajagopalan of the University of Colorado at Boulder in the United States to try and understand why these changes are occurring. Global warming by itself does not appear to explain the changes, observed Dr. Krishna Kumar.

Research carried out for a Master’s thesis at the Indian Institute of Science too indicated that the annual cycle of rainfall could be changing in central India over the last two decades. In her thesis, Charu Singh used mathematical techniques to define the rainy period and its salient characteristics. Her work suggested that the rainy period in central India could be ending earlier and that the duration of the rains might therefore be somewhat shorter than before. These, however, were only preliminary findings and more work was being done to make sure of their robustness, cautioned her thesis supervisor, V. Venugopal.

Whatever be the underlying reasons, as Dr. Krishna Kumar points out, such changes in rainfall patterns will have profound implications for farmers and the crops they are able to grow.

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