Uneven Rainfall in the Northeast a Result of Climate Change: Experts

GUWAHATI: Rainfall distribution during monsoon months in the northeast region has been affected by climate change, although the total amount of rain received has mostly remained unchanged, says experts.

This change in uniform distribution of rainfall in the northeast during monsoon months has resulted in consecutive dry days for a prolonged time and shorter wet days, experts said on the eve of World Environment Day.

Research conducted by Assam Agricultural University (AAU) on rainfall patterns revealed a decreasing trend of annual rainfall by 66.4 mm/decade during 1986-2015 in the Brahmaputra valley of Assam. Decrease in monsoon rainfall by 53.4 mm/decade contributed largely to this decrease of annual rainfall in the valley, while there was a statistically significant shortfall of September rainfall in the upper (39 mm/decade) and central (35 mm/decade) parts of the valley and July rainfall in the lower (77 mm/decade) part of the Brahmaputra valley.

Head at Agricultural Meteorology department of AAU, Prof. Rajib Lochan Deka said, “Consecutive dry days increased by 6.5 days/decade while consecutive wet days showed a significant decreasing trend in Brahmaputra valley that covers vast parts of Assam. This is an impact of climate change,”

He noted a decreasing trend in the monsoon rainfall pattern in the region, while during post-monsoon it displayed an increasing tendency. “The contribution of June, August and September rainfall to annual rainfall exhibited a decreasing trend while the contribution of July and October rainfall marked a rising trend,” he said.

Upon analyzing rainfall data of 30 stations of northeast, there was an indication that rainfall decreased during monsoon months of July to August whereas, data from more stations revealed increasing rainfall during the April-May months or pre-monsoon period and October-November (post-monsoon), indicating a shift in inter-seasonal rainfall without the annual total recording much changes.

“Number of rainy days was found to have positive trends in March-May and negative trends in September-December,” Deka said, adding that, of late, there was an impact on agriculture in the region from such distribution patterns of uneven and changing rainfall.

Upon conducting separate studies on spatial assessment of rainfall data, it was also disclosed that post-monsoon rainfall in Guwahati showed significant increasing tendencies, along with pre-monsoon rainfall in Imphal and Tezpur and winter rainfall in Cherrapunjee and Umiam in Meghalaya displaying similar tendencies during the last few decades.

NE India experiences a humid sub-tropical climate characterized by high rainfall and high humidity due to its unique geographical location and extensive water bodies and these weather conditions are mainly influenced by the south-west monsoon coming in from the Bay of Bengal.

The annual average rainfall is 2162 mm over the northeast, varying from about 2352 mm in Assam to 4275 mm in Meghalaya, and further to 2250 mm in Nagaland.

While the monsoon season contributes the highest amount of annual rainfall at about 65%, the pre-monsoon rainfall contributes 25%, post-monsoon 7% and winter seasons contributes about 3% to the annual rainfall of the region.

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