NEW DELHI: The Indian
Meteorological Department has forecast a “near-normal” monsoon rainfall
this year, between 96% and 104% of the long-term average.
The long-term average is arrived at by collecting rainfall data between
the year 1941 and 1990.
“Quantitatively, monsoon season rainfall is likely to be 99% of the
long period average with a model error of +- 5%. The long period
average rainfall over the country as a whole for the period 1941-1990
is 89 centimetres,” the Union minster of state for science and
technology and ocean development Kapil Sibal said on Wednesday.
“The monsoon is expected to hit Kerala tentatively on May 20,” Sibal
added.
IMD will update the forecast in June this year as a second part of
forecasts to include seasonal rainfall over the four geographical
regions of India. Last year’s monsoon rainfall was measured at 106% of
the long period average against the IMD forecast of 95%.
This year’s monsoon is being helped by the movement of the cold water
currents of the central Pacific towards the coast, director, National
Climate Centre at IMD, M Rajeevan said. The La Nina condition, as it is
called, was observed in August last year.
The forecasts indicate that La Nina will become weak and then persist
for the next three months, Rajeevan said. “The monsoon this year would
have been even better had La Nina not shown the signs of retrieval,” he
added.
The IMD has this year changed its definitions of normality parameters
from 98%-102% of the long period average as “near normal” to 96%-104%
this year.
“Looking at the long-term data between the 1901 and 2005, we felt that
the 98%-102% range was too narrow and needed to widen it,” Rajeevan
said.
IMD has also considered data collected using the “dynamic” model for
peninsular and north-eastern India, instead of going purely by the
statistical model, Kapil Sibal said.
“The statistical model was working fine for predicting rainfall for
most parts of the country, except the peninsular and the north-eastern
regions. Thus, the IMD has also collected information using the dynamic
model for these regions on an experimental basis, and has correlated it
with data gathered using the statistical model and has made necessary
corrections,” Sibal said.
There is increased possibility of using the dynamic models formally and
incorporating the data or information thus collected into the
forecasts, Rajeevan said.
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