New Delhi: Next year, India’s annual summer monsoon forecast may be made by a supercomputer running a dynamical model.
The
Secretary, Ministry of Earth Sciences (MoES), Madhavan Rajeevan, said
the dynamical model, being tested at the Indian Institute of Tropical
Meteorology, (IITM) Pune for a decade was “ready for operational
purposes next year.” A dynamical monsoon model works by simulating the
weather on powerful computers and extrapolating it over particular
timeframes.
Though this method is normally effective in
forecasting weather over a few days, using it to forecast the annual
monsoon over 3 or 4 months has proved difficult.
While such
models have been used for research purposes for long, the India
Meteorological Department (IMD) has never integrated them into its
operational forecast. “We hope to be able to launch it next year though
discussions are still ongoing,” Mr. Rajeevan said, on the sidelines of
an Earth Sciences Ministry foundation day event on Wednesday. The IMD, a
division of MoES, is the official national weather forecaster. Mr.
Rajeevan clarified that statistical models would still be in use next
year. The IMD Director-General, L.S. Rathore, said, “We are ready to use
the dynamical model, but this doesn’t mean one is abandoned for the
other. Both have their role and we must use what’s best.”
The IMD
relies on an ensemble model, a statistical technique that uses an
average of six meteorological values correlated to the monsoon such as
sea surface temperatures in the Pacific, and North Atlantic sea level
pressure. These values are derived from century-old meteorological data
linked to the historical performance of the monsoon.
Prediction failures
This
traditional approach in recent decades has failed to predict monsoon
failures — in 2002 and 2004 for instance — leading to calls by
meteorologists for a new, modern forecasting system.
Though the
dynamical model, called the Coupled Forecast System version 2, has so
far achieved only 60 per cent accuracy in forecasting the monsoon,
Rajeevan says it is good enough for now. “No doubt it needs to improve
and the aim is to make that 77 per cent but we have to start somewhere,”
he added. A confidence boost came when the dynamical model and the
ensemble technique correctly signalled a drought in 2015.
While
the IMD has for some years put out the dynamical model’s forecast along
with the traditional one, its plans to give prominence to the dynamical
model signals a new approach. This is a precursor to giving monsoon
predictions over India’s 36 sub-divisions rather than only four broad
geographic regions that encompass them. A dynamical approach can also be
more easily tuned to account for rapidly changing global weather
conditions.