Recently, Indian Ocean Research Vehicle (IORV) Sagar Nidhiv as part of India- US expedition seeking to find answers to vagaries of Bay of Bengal fed South-West Monsoon was set out in Indian Ocean.

Monsoon forecasting in India

• IMD adopted new methodology to forecast monsoon in India. The new methodology, called dynamical forecasting, breaks away from the century-old tradition of using the British-developed statistical system for forecasting.
• The dynamic modelling used by India has been sourced from the US and is being tweaked according to the Indian monsoon.
• Ministry of Earth Sciences (MoES), Government of India had launched 'National Monsoon Mission' (NMM) in 2012 with a vision to develop a state-of-the-art dynamical prediction system for monsoon rainfall on different time scales. Major objectives of the mission are:

1. To setup a state-of-the-art dynamical modeling frame work for improving prediction skill of Seasonal and extended range prediction system; and Short and medium range prediction system
2. To setup the infrastructure and manpower required to improve the prediction skill at all time scales (long, seasonal, extended, medium and short range) over Indian region
3. To build a working partnership between the Academic / Research & Development Organizations and the Operational Agency to improve the monsoon forecast skill

Dynamic Weather Prediction Model

A dynamic weather prediction model involves 3D mathematical simulation of the atmosphere on computer. Dynamic models are especially useful for predicting rainfall over smaller spatial and temporal scale, which is not possible in the statistical forecasting system. With dynamic models, we will be able to provide monthly forecasts for every state.

Dynamic models have several advantages.

• The dynamic model, also known as the Coupled Forecast System, is based on faster computing to improve shortrange forecasts. It provides the flexibility to upgrade forecasts for specific regions and enables collation of data on local as well as global weather patterns to simulate a forecast for a specific duration.
• They can be used along with agriculture and hydrological models. They can be used for many more purposes than rainfall prediction. One can get real-time information on wind, temperature and humidity in digitised format.

Earlier system and its limitations

India earlier used statistical forecasting system. Statistical models require lengthy calculations to track the southwest monsoon. The model uses historical relationships between rainfall and six to eight predictors such as sea-surface temperatures and south-easterly winds over the Indian ocean.

• Failure in prediction: For instance, IMD couldn’t predict the oncoming droughts in the years 2002, 2004 and 2009. Also, from 1988 to 2010, the IMD has been able to successfully predict the monsoon only nine times which translates to a success rate of a mere 40 percent.
• It gives forecasts for the country as a whole and five regions, though does not give separate ones for the country's 29 states. Because of India's size, one national forecast is of little help to farmers spread across diverse climatic zones.

Benefits

• Weather forecast systems under the National Monsoon Mission (NMM) will be extended up to the block level across the country by 2019. It would help the farmers, policy makers, administrators and all concerned alike.
• It will be possible to predict droughts. Fallout of droughts like those of 2004 and 2009 could be prevented if we’re able to warn farmers in advance.
• Better forecasting could help India raise its farm output by nearly 15 percent, by helping farmers tweak the best time to sow, irrigate or apply fertilizer to crops and if rains fail plan state-wide measures.
• Also, better forecasts resulting in better farm outputs can stabilise the inflation level and thereby provide for effectual transmission of monetary policies in the economy.

Why it is difficult to forecast monsoon in India?

• Huge variability of monsoon: Many factors seem to affect the duration and intensity of monsoon, which include:

1. El Nino Southern Oscillation (ENSO): A climatic phenomenon associated with warming up of eastern Pacific Ocean. Other factors temper or boost the impact of El Nino such as the Indian Ocean Dipole (IOD) which is the difference in the Sea Surface Temperature between the western Indian Ocean near Arabian Sea and the Eastern part near the Bay of Bengal. A warmer western pole leads to a positive IOD that can act as a neutralizing factor to El Nino and result in normal rainfall. Other factors include - Equatorial Indian Ocean Oscillation (EQUINOO), Madden Julian Oscillation etc. Moreover, they share complex relations between themselves thus further complicating the scenario.
2. Anthropogenic Emissions affect rain patterns: Warmer atmosphere has direct correlation with greater variability in the monsoon.
3. Air Pollution: complicates the rainfall variability as aerosols such as black carbon interact with sunlight resulting in either scattering or absorbing sunlight. Scattering prevents the light from warming the earth surface while absorbing causes the particles to warm the air around them which ultimately alters the heating pattern of atmosphere and heating up of the land relative to Ocean.
4. Forest Cover: in August and September around a quarter of the precipitation in the large basin of eastern India comes from land surface, mainly through the evapotranspiration in the forests. Large scale deforestation around the world can lead to an 18% decrease in the Indian Monsoon.
5. Other factors: for instance dust over North Africa and the Arabian Peninsula absorbs sunlight, warms the air and strengthens wind carrying moisture eastwards which later cause heavy rainfall in India. Similarly, climate change further complicates the phenomena.

• Monsoon Depressions: these are the depressions formed over Bay of Bengal and are known for producing heavy rainfall during monsoons. In recent years, these are reducing due to anomalous moisture convergence over the western Indian ocean due to rapid sea surface warming.

• Need for better understanding the role of Jet streams: During monsoon, strong winds known as low level monsoon jet stream appear around the southern part of India at an altitude of about 1.5 Km above the ground. Similarly, around 14 Km altitude (very near to stratosphere) there is another jet stream from the East. The speed, along with the North South movement of these two Jet streams controls the distribution of rainfall over the Indian region.