Monsoon Forecast Models

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Monsoon Forecast Models

• Monsoon has always been critical for India’s economy. 
• If variations in monsoon rainfall are known well in advance, it would be possible to reduce the diverse impacts related to excess or deficient rainfall. 
• A reliable monsoon forecast with sufficient lead time is essential for policy makers and farmers for planning and sowing of crops, as well as making long-lead plans for the future.
• There are several methods to assess the likelihood of Monsoon  rainfall.
• Currently, IMD relies on an ensemble model for forecasting monsoon. This traditional model uses a statistical technique.
• It uses an average of 6 meteorological values correlated to the monsoon such as sea surface temperatures in the Pacific, and North Atlantic sea level pressure.
• These meteorological values are traditionally derived from century-old meteorological data linked to the historical performance of the monsoon.
• This model equates relationships of physical parameters, such as for instance sea surface temperatures, snowfall, the temperature of landmass etc with the actual observed rainfall in the past.
• India currently operates a global model on a 12-km grid size — that is,  information is gathered every 12 km. This is the highest resolution ensemble system, and at present India has the best model in the world. 
• However, this traditional approach has failed to predict monsoon recent decades (for instance in 2002 and 2004) leading meteorologists to call for a new, modern forecasting system.

LPA Method

• LPA of rainfall is the rainfall recorded over a particular region for a given interval (like month or season) average over a long period like 30years, 50-years etc.
• It acts as a benchmark while forecasting the quantitative rainfall for that region for a specific month or season. 
• For example, LPA of south west monsoon rainfall over Kerala for the months June, July, August and September are 556mm, 659mm, 427mm and 252mm respectively. 
• Current LPA of all India south west monsoon rainfall based on the average rainfall over the period 1961 -2010 is 880.6mm.

Indian Monsoon Mission (NMM): 

• The accurate prediction of monsoon rainfall remained a challenge for decades. The conventional forecast in use so far is based on the statistical approach and is low skilled in forecasting rainfall anomalies. 
• Several new approaches (high resolution, super parameterizations, data assimilation etc.) developed in recent times have shown that the variability in tropics can be reasonably resolved
• The National Monsoon Mission (NMM) was envisaged in 2012 by the Ministry of Earth Sciences (MoES) to develop a dynamical coupled prediction system specially suited for the Indian region.
• The main objectives of NMM are to improve Seasonal and Intra-seasonal Monsoon Forecast and to improve Medium Range Forecast.

To achieve its objectives the NMM envisages to:

• Build a working partnership between the academic research and development organisations and the operational agency to improve the monsoon forecast skill;
• Set up a dynamical modelling framework for improving prediction skill of seasonal and extended range prediction system, and short and medium range prediction system; and,
• Set up the infrastructure and train manpower required to improve the prediction skill in all time scales.

Megha-Tropiques satellite: 

• The main objective of the Megha-Tropiques mission is to study the convective systems that influence the tropical weather and climate.
• The satellite was launched in 2011 into a non-sun synchronous orbit (Low Earth Orbit), unlike other IRS spacecraft. 
• Megha-Tropiques provides scientific data on the contribution of the water cycle to the tropical atmosphere, with information on condensed water in clouds, water vapour in the atmosphere, precipitation, and evaporation.
• The Megha-Tropiques is a unique satellite for climate research that also aids scientists seeking to refine prediction models.
• It is operated as part of a joint programme between the Indian Space Research Organisation (ISRO) and France′s Centre National d′Etudes Spaciales (CNES). 
• This Megha-Tropiques satellite carries four payloads namely, MADRAS-a microwave imager, SAPHIR-scanning radiometer instrument, SCARAB-scanner for radiative budget and GPS occultation receiver for atmospheric studies.

New models

• The India Meteorological Department (IMD) may introduce new monsoon models this year to better forecast changes in rainfall. 
• Three different models would be tested this year. Two of them were dynamical models and one a statistical model. 

The three models under consideration are: 

• 12 global circulation models (dynamical) : The outputs these models would be combined into a single one
•  a model that gauges rainfall based on the sea surface temperature in the tropics (developed by Prof. Sumant Nigam, University of Maryland, U.S.) and 
• the statistical model based on climate variables observed during the pre-monsoon. 

All of them are ‘ensembles’ meaning smaller models are combined to arrive at an average value.