Thursday, 23 August 2012

Fresh water 'swamping' increases tropical storm's intensity by up to 50%, new research says

Phenomena could increase with climate change.

pic source: NASA
Large amounts of fresh water dumped into sensitive areas of oceans around the world are making tropical revolving storms (TRS) - commonly called typhoons, cyclones or hurricanes - up to 50% more intense and deadly, says research published in the National Academy of Sciences Early Edition (PNAS). The organisation, set up in 1914, claims to be one of the world's most-cited multidisciplinary scientific publications, and says it brings into focus "cutting-edge research reports" in biological, physical, and social sciences. 

Their analysis, a collaborative effort between scientists based in China, the US and elsewhere, says that the possibility of the two synchronous events- a TRS and the affected ocean being swamped with fresh water- are relatively small, at between 10 and 23 percent, but the outcome is significant in terms of the large effect they can have on storm systems.  They can also have a huge impact on human populations, according to Karthik Balaguru at the US Department of Energy’s Pacific Northwest National Laboratory, the scientist who authored the report. “Sixty percent of the world’s population lives in areas affected by tropical cyclones,” he says, adding, “Cyclone Nargis killed more than one hundred and thirty eight thousand people in Burma in 2008." Examples of areas particularly at risk from fresh water swamping include the Indian Ganges River system in the Bay of Bengal, the Amazon River system and the western Pacific Ocean, where storms are usually accompanied by heavy rain. 

A TRS system normally weakens with time because the water cools off, thanks to the strong winds prevalent. However, in conditions when a TRS blows over an area where a large amount of fresh water is flowing into the ocean (often about 50 meters below the surface) from rivers or due to rain, the fresh water forms a 'barrier layer' that insulates the surface layer from the denser (and colder) water below. As a result, the cooling effect is reduced by as much as 36 percent, effectively making the ocean pump up to 7 percent more heat into the cyclone. The end result: A TRS that may be 50 percent more deadly. 

Researchers say that climate change is having an effect on the 'ocean water cycle'-water movement between the oceans and the atmosphere- and studies will have to be conducted again as climate patterns change in a warmer world. They point out that climate change is making the phenomena accelerate, as melting glaciers and the amount of rain falling over oceans has a direct effect on the salinity of water- and, indirectly, on 'barrier layers.'

In the present study, scientists studied 587 TRS systems over two decades in the Atlantic, Pacific and the Indian Oceans before coming to a conclusion. They are now hoping that the new findings will help predict TRS systems better. "We can predict the paths cyclones take, but we need to predict their intensity better to protect people susceptible to their destructive power,” said Balaguru.

 “A 50% increase in intensity can result in a much larger amount of destruction and death."


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