India may lose south-west monsoon in 150 yrs: Study

Last Updated: Sunday, September 6, 2009 - 11:37

New Delhi: India may lose one of its crucial
lifelines -- the south west monsoon, which brings rains across
the country during the summers, in the next 150 years, warns a
new study by Indian Institute of Tropical Meteorology.

The phenomenon is the result of global warming which has
led to increase in the rate of temperature rise over Arabian
Sea, researchers say.

This rise is reducing temperature difference between
land and sea, known as Temperature Gradient (TG), responsible
for attracting rain causing winds from Arabian Sea towards
Indian mainland.

"For climatology, 30 years variations are considered.
The decreasing trend (of TG) is highly significant and in
another 150 years or so, it may tend to zero," lead author SM
Bawiskar, a scientist at the Pune-based institute, said.

Once the gradient becomes zero, Bawiskar warns, the
monsoon winds will be replaced by dry easterly winds thus
disturbing the flow of south-west monsoon.

He found that average temperature over Arabian Sea was
18.77 degrees Celsius during 1948-77 but it has increased by
0.87 degrees to touch 19.64 degrees during 1979-2008.

The results published in the Journal of Earth System
Science show that rate of temperature increase over sea is
higher than land which has narrowed the Gradient by 1.11
degrees during the said period.

The below normal rains during the current season are
also an indication of the changes taking place in the
temperature over the Arabian sea.

The Indian Meteorology Department has shown a 23 percent reduced rain activity during the present season, which
may be an indication of this phenomenon.

"With decreasing TG, monsoon current over Arabian sea
would become weak. This will lead to reduced rainfall activity
over Indian Peninsula. The break like circulation will prevail
for a longer period of time, which we are already experiencing
during this monsoon," Bawiskar said.

Global warming, which is increasing the average
temperature across the planet, is also behind the increasing
temperature over the Arabian sea, the study says.

During monsoon, Arabian sea and Indian peninsula are
under the grip of Westerlies (winds coming from west) in the
lower troposphere.

These winds are mainly responsible for bringing rains
over the Indian land mass and are established during the
monsoon due to the Temperature Gradient.

Bureau Report



First Published: Sunday, September 6, 2009 - 11:37

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