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IMD to strengthen modelling systems to accurately capture extreme rainfall events

Between June to September months, the country receives a seasonal rainfall of 880mm, but it can vary from year-to-year. Being an agrarian country, rainfall during these months is crucial for India's economy, water and reservoir management, and overall agriculture output.

Written by Anjali Marar | Pune |
January 18, 2021 1:50:08 pm
The India Meteorological Department (IMD) stands at the Ministry of Earth Sciences complex in New Delhi (Photographer: Prashanth Vishwanathan/Bloomberg)

Starting from the Southwest monsoon 2021 season, the India Meteorological Department (IMD) will have an expanded bouquet of weather models and be better equipped, particularly to capture and issue timely forecasts ahead of extreme rainfall events during the season.

Between June to September months, the country receives a seasonal rainfall of 880mm, but it can vary from year-to-year. Being an agrarian country, rainfall during these months is crucial for India’s economy, water and reservoir management, and overall agriculture output.

Extremely heavy to very heavy rainfall (115mm to 204mm in 24 hours) occurring over a short span of time, leading to flash floods, urban floods, landslides, and large-scale destruction is increasingly becoming a common phenomenon during the June to September monsoon season over the country. These include recent events over Maharashtra (2019), Kerala (2018), Chennai (2015), Srinagar (2014) and more.

Last year alone, over 600 people died due to heavy rainfall and related incidents across India, the Statement on ‘Climate of India during 2020’, released by IMD said.

IMD issues a Long Range Forecast (LRF) ahead of an upcoming monsoon season in two stages — April and in June. The April forecast mentions overall quantum rainfall (in per cent) for the Long Period AVerage for the country as a whole. Its updated version, issued in June, gives the probable rainfall over the four broad homogenous regions — North, East and Northeast, Central and South Peninsular India for the four-month period.

Presently, the IMD depends upon the Monsoon Mission Coupled Forecasting System (MMCFS), which is a coupled (ocean and atmosphere) dynamic model that was developed during the first phase of the Monsoon Mission. The latest and high-resolution version is run on supercomputers installed at the Indian Institute of Tropical Meteorology (IITM), Pune. The Met department also considers model output generated by indigenously developed Statistical Ensemble Forecasting System (SCFS) and Principal Component Regression Model (PCR) models, ahead of issuing the comprehensive seasonal forecast.

Since the Southwest monsoon is a highly complex weather system influenced by global factors, some of them including the Madden Julian Oscillation (MJO), El Nino Southern Oscillation (ENSO) in the Pacific Ocean, sea surface temperatures of the Indian Ocean, weather models capable to process these global weather parameters are needed for preparing accurate predictions.

” The MMCFS is over sensitive to the Pacific Ocean conditions, especially La Nina, which influences the rainfall during the Southwest monsoon season. We need to further improve our weather models, so that extreme weather events get captured,” said Dr D Sivanand Pai, head, LRF and Climate Services and Research at IMD. He was speaking on ‘Seasonal Forecast of Monsoon 2020 : Success, Problem areas and Plan for 2021’ during the virtual workshop ‘Monsoon 2020’ on Monday.

Last monsoon, heavy rainfall events recorded over the West and Central India were not captured by the MMCFS, he said.

Inputs received from the coupled model contributed by IMD’s Noida-based sister institution, the National Centre for Medium-Range Weather Forecasting (NCMRWF), could be referred to in the monsoon forecasts for 2021, Dr Pai said.

In addition to the present weather models, the monsoon forecasters will take guidance from three independent types of weather models — including one developed by IMD,Pune, at the time of monsoon forecasts for this year.

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