Environment, Geography, GS-1, Uncategorized

Explained: Why is Chennai under water?

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While stormwater drains are supposed to be planned on the basis of detailed topographical data, their linkage with water bodies, construction along their course, and the design of roads have rarely been seen as part of a whole. As a result, drains constructed over the past decade have repeatedly proved inefficacious — and showed up problems of poor urban planning nearly every monsoon.

Across Chennai, illegal construction has been making neighbourhoods unrecognisable — what may have been a tank, lake, canal or river 20 years ago, is today the site of multistorey residential and industrial structures.

An exceptionally strong El Niño, along with a rare “coincidence of various factors”, has resulted in the heavy rain in Tamil Nadu this northeast monsoon season. The El Niño phenomenon — an unusual warming of surface waters in the equatorial Pacific Ocean — is “intensely strong” at present. “In a strong El Niño year like the present one, the summer (southwest) monsoon is adversely affected, while the northeast monsoon or the winter monsoon is favourably affected.”

The 2015-16 El Niño could turn out to be the strongest ever recorded — in fact, by one measure, it has already reached that milestone. In mid-November, the sea surface temperature in the central tropical Pacific was 3 degrees Celsius warmer than normal, the largest positive deviation in recorded history. To officially beat the 1997-98 El Niño as history’s worst, sea surface temperatures must stay at these levels for three months.

Other than the El Niño, a strong upper air divergence and high moisture content at lower levels, have contributed to the rain. “These two factors, along with formation of low pressure systems have resulted in the heavy rainfall,” .

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