The uncertain dance of the Indian monsoon

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Photo courtesy: NOAA

The growing uncertainty of El Nino conditions during the Indian monsoon is keeping the weather agencies on the tenterhooks across the globe, according to skymetweather.com

According to the website, the earlier consensus of a likely strong La Nina has shifted now to a state of divided opinion. Accordingly, whether more favourable conditions will actually form or appear in time for monsoon rains, is a contentious issue, it said.

The current El Nino phenomenon is possibly one of the longest and strongest on record, wherein the Pacific temperature has remained above normal by more than 2˚C from fall of 2015 till now.

As oceans are not good conductor of heat, they neither absorb nor release the heat quickly. More often, the declining trend of temperature is very gradual. In the last two weeks, Nino indices in the Pacific have dropped marginally, the website said, adding that the mixed layer depth (MLD i.e. Sea surface to 50 meters below) and the thermocline (50 to 150 meters below sea surface) continue to be very warm.

According to the El Nino and the Indian Monsoon rains are inversely related. Trade winds coming from South America normally blow westward towards Asia during Southwest Monsoon. Warming of the Pacific Ocean results in weakening of these winds. Therefore, moisture and heat content gets limited and results in reduction and uneven distribution of rainfall across the Indian sub-continent.

Skymet said the most prominent droughts in India, six of them, since 1871 have been triggered by El Nino, including the recent ones that occurred in 2002 and 2009. Nevertheless, it is important to note that all El Nino years do not lead to drought in India, tit said, adding that he year 1997-98 is a stark reminder as it was a strong El Nino year but that did not cause drought in India, in fact, rainfall was in excess. On the other hand, a moderate El Nino in 2002 resulted in one of the worst droughts.

“Going by historical data of 135 years from 1880 to 2014, about 90 percent of all evolving El Nino years have led to below normal rainfall and 65 percent of evolving El Nino years have brought droughts. From this fact, one thing is clear that El Nino years adversely affect the weather in India in terms of Monsoon rain, with very few exceptions. During an El Nino year, the rainfall is generally below the normal average, which has its negative bearing on crop production.”

 

 

 

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