Monsoon Forecasts by IMD

Operational long range forecasts issued for south west monsoon by IMD and other agencies have underestimated the realized seasonal quantum of rainfall for the period June-September, 2011and hence the seasonal forecast assessments went wrong. However, forecast of the onset of monsoon over the south Kerala coast, that signifies the beginning of the principal rainfall season for the country, was found to be correct not only for 2011 but continues to be accurate for the successive 7th year since the beginning of such forecasts from 2005.

Most of the models used for seasonal prediction of monsoon rainfall currently are poorly represented in terms of treating the non-linear response/feedback of ocean-atmospheric interactions, such as prevalence of La Nina (cooling over the equatorial Pacific Ocean) conditions that has direct bearing on the enhancement of rainfall over Indian sub-continent.

All global parameters, that are identified to have strong bearing with the seasonal quantum of monsoon rainfall over India as whole, are monitored very closely by IMD during pre-monsoon season (March-May) and their ever changing statistical relationships are accounted fully in the current suite of long range forecast models. Since the prevalent La Nina conditions of monsoon-2010 have gradually weakened and dissipated by around middle May 2011 have reemerged during the second half of the monsoon season of 2011(that was not accounted in the operational suite of models), the seasonal assessments of monsoon rainfall got underestimated.

Currently, IMD uses a suite of statistical models for prediction of seasonal monsoon rainfall over India. Such a mechanism is continued to be used due to non-availability of a suitable coupled ocean-atmospheric model with a proven performance of capturing the realistic monsoon rainfall variability over India.

It is expected to put in place a most representative dynamical framework for monsoon rainfall prediction in coming years through following initiatives started with the commissioning of the high-performance computing system recently,

i) Evaluating the performance of an adopted coupled ocean-atmospheric model of National Oceanic and Atmospheric Administration (NOAA), USA for monsoon seasons of 2010 and 2011 in terms of capturing locations of excess and deficient rainfall on monthly and seasonal time scales that has established demonstrable skill.

ii) Efforts are being organized under the National Monsoon Mission initiative to develop a most representative and advanced dynamical model framework for India for forecasting monsoon rainfall and its variability in various space and time scales by involving all relevant organizations and research institutes of India and NOAA.

This information was given by the Minister of State in the Ministry of Science and Technology and Earth Sciences Shri Ashwani Kumar in a written reply to a question by Prof. Anil Kumar Sahani in Rajya Sabha today.

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