Monsoon Forecast in India

5 min read

News: The Monsoon Mission Coupled Forecast Model, developed under the Monsoon Mission has failed to accurately forecast the excess rainfall in August-September 2019.

Facts:

Monsoon Forecast in India:

  • The IMD issues operational forecast for the southwest monsoon seasonal (June to September) rainfall for the country as a whole in two stages. The first stage forecast is issued in April and the second stage forecast is issued in June.
  • These forecasts are prepared using state-of-the-art Statistical Ensemble Forecasting system (SEFS) and using the dynamic coupled Ocean-Atmosphere global Climate Forecasting System (CFS) model known as the Monsoon Mission Coupled Forecasting System (MMCFS)

Statistical Ensemble Forecasting system (SEFS):

  • IMD has been using the ensemble statistical model to predict monsoon since 2007.
  • It relies on arriving at a prediction based on historical monsoon data coupled with data on sea-surface temperatures and winds.

Monsoon Mission Coupled Forecasting System (MMCFS):

  • It has been developed by the National Centres for Environmental Prediction (NCEP) and NOAA National Weather Service, USA.
  • It is a coupled ocean-atmosphere modelling system that combine data from ocean, atmosphere and land for providing long range forecasting.
  • As part of the Monsoon Mission project, the Indian Institute of Tropical Meteorology (IITM) has developed the indigenous strategy of the model.

Additional Information:

National Monsoon Mission:

  • The National Monsoon Mission was launched in 2012.
  • It aims to develop a state-of-the-art dynamical prediction system for monsoon rainfall on different time scales.
  • The mission falls under the aegis of Ministry of Earth Sciences.
  • The responsibility of execution and coordination of the mission is bestowed upon the Indian Institute of Tropical Meteorology (IITM), Pune.
  • Climate Forecast System (CFS) of NCEP, USA has been identified as the basic modelling system for providing long range forecasting (seasonal prediction of Indian Monsoon). Further, the Unified Model (UM), developed by the United Kingdom Meteorological Office (UKMO), UK has been identified for short to medium range prediction.

Climate Models:

  • Climate models are computer programs made up of mathematical equations that quantitatively describe how factors like atmospheric temperature, air pressure, winds, water vapour and clouds respond to the heating of the Earth‘s surface.
  • Coupled climate models have equations describing three-dimensional oceanic circulation (the large-scale movement of waters across the Earth’s oceanic basins), and how it transports the absorbed solar energy around the Earth, how it exchanges heat and moisture with the atmosphere.

Rainfall Distribution on All India Scale

  • Normal percentage departure of realised rainfall is within ± 10 % of the Long Period Average (LPA)
  • Below Normal percentage departure of realised rainfall is < 10% of the Long Period Average (LPA)
  • Above Normal percentage departure of realised rainfall is > 10% of the Long Period Average (LPA)

Note: LPA is the 50 year average of monsoon rains in India and is pegged at 89 cm.