A primer on monsoon and Mettur Dam water

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New Delhi, June 3: The flow into the Mettur Dam has improved from 72 cusecs to 222 cusecs on Sunday as the catchment areas in Salem and Dharmapuri districts experienced incessant rains in the last three days.

The districts have been experiencing rain following the advancement of south-west monsoon in neighbouring Kerala.

The water level on Sunday stood at 18.43 feet against full level of 120 feet. The inflow was only 22 cusecs yesterday and the discharge was 600 cusecs.

Though Karnataka did not release the Cauvery water, rain in the past three days in catchment areas in the two districts improved the inflow. The inflow could raise the storage level and ease drinking water problem.

The catchment area of entire Cauvery Basin is 81,155 sq. km. The principal tributaries of Cauvery in Karnataka are the Harangi, the Hemavathy, the Lakshmanathirtha, the Kabini, the Shimsha, the Arkavathi and the Suvarnavathy.

Meanwhile, the monsoon is expected to advance to parts of Tamil Nadu and drought-hit states of Karnataka and Andhra Pradesh over the next two days.

Arriving in Kerala two days ahead of schedule, the monsoon has boosted farming prospects and raised hopes in the cotton and sugar growing belt.

onset-of-monsoon

What is South-west monsoon?

The southwest maritime winds bring rains to most of the country from June to September and the northeast, or retreating monsoon is active in October and November.

Nearly 80 percent of the country receives most of its rainfall from the southwest monsoon.

The southwest monsoon comes in from sea to land and breaks on the west coast early in June and covers South Asia by the first week in July.

Scientists have attributed monsoons to thermal changes in the Asian landmass. Contemporary theory cites other factors--the barrier of the Himalayas and the sun's northward tilt (which shifts the jet stream north).

The hot air that rises over South Asia during April and May creates low-pressure areas into which the cooler, moisture-bearing winds from the Indian Ocean flow.These changes bring in moisture-rich air from the southern seas and resultant monsoon.

The southwest monsoon has two branches, the Arabian Sea monsoon and the Bay of Bengal monsoon. They move west and eastwards, covering most of the India by July.

The withdrawal of the monsoon is a far more gradual process than the arrival. The retreating monsoon covers states of Tamil Nadu, Karnataka, and Kerala.

Assam and West Bengal are extremely wet and humid. The southeastern part of Meghalaya has the world's highest average annual rainfall at 10,900 millimeters.

In the Peninsula region, the Western Ghats and the adjoining coast receive heavy rains during the southwest monsoon. The Eastern Ghats receive less rainfall than the western coast. Rainfall there ranges between 900 and 1,300 millimeters annually.

The northern Deccan region, bounded by the Western Ghats, the Vindhya Range and the Narmada River to the north, and the Eastern Ghats, receives most of its annual rainfall during the summer monsoon season. The southern Deccan area is in a rain shadow.

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