Analysing fresh water inputs to Indian Ocean could be key to forecasting the South Asia monsoon and understanding climate changes

The Indian Ocean contains a distinctive layer of fresh water from rain and rivers which may influence the South Asian monsoon, scientists have said

Map of monsoon forecast and major rivers entering the Bay of Bengal

Meteorology officials in South Asia  have been slow to consider the role of fresh waters.They are already struggling to forecast monsoon rains due to a range of factors including climate change. Monsoons account for 70% of the rainfall in India and neighbouring countries between June and September. But longer dry periods and heavy rainfall within a short space of time during monsoon season in recent years have caused concern in South Asia. And this is already being seen this year, with higher rainfall than normal in June – whereas July and August are predicted to have lower than normal rainfall.  Some meteorologists based in the region believe the freshwater element could be a vital missing link. Major rivers such as the Ganges, Bramhaputra and Irrawaddy flow into the Bay of Bengal.

A team of international scientists are currently researching the issue. Freshwater inputs from both rivers and a large amount of rainfall make the Bay of Bengal a rather unique place, and that is not properly being taken into account in the monsoon forecast models, said Professor Eric A. D’Asaro, an oceanographer at the University of Washington, who has been researching the Bay of Bengal with scientists from India and the US. That’s one of the reasons they are not able to forecast what are known as monsoon breaks – in other words the variations on monthly time scales through the monsoon season. The fresh water makes the surface layer of the ocean water much thinner and lighter and that reacts with the monsoon clouds more strongly whereas saline water would do so more slowly and that would have less effects on the monsoons. Researchers with the Ocean Mixing and Monsoon project say they have found a  sharp separation between river water and seawater on scales ranging from 100m to 20km.

The buoy contains sensors that measure the salinity and temperature of the sea

Further information

BBC News

Research Highlight: US  and Indian Research Centers Take Part in Multinational Effort to Understand a Key Monsoon Variable