26 March 2015

Africa: Stronger Thunderstorms Driving Rise in Tropical Rainfall - Study

London — An increase in strong thunderstorms could be responsible for greater rainfall in the tropics as a result of climate change, new research says.

The joint research, which was conducted by the Australian Research Council Centre of Excellence for Climate System Science (ARCCSS) and NASA, research found that even though other types of rainfall have decreased in frequency and the total number of thunderstorms has remained the same, the increase in big storms has elevated total rainfall.

Thunderstorms play a key role in keeping the tropics wet, with large thunderstorms delivering almost 50 percent of its total rainfall despite only occurring 5 percent of the time in equatorial regions.

The study, which was published in the journal Nature on Wednesday, was based on satellite observations and showed that the frequency of big and powerful thunderstorms increased in the tropics between 1998 and 2009 and was strongly correlated with rainfall changes.

"What we are seeing is more big and organised storms and fewer small and disorganised storms," said Jackson Tan, lead author of the study from ARCCSS, in a press release.

The trend suggests a "dynamic change in the climate system" that is believed to be responsible for the change in rainfall.

"The number of organised storms, which is largely controlled by the dynamics of the atmosphere, has increased in frequency, suggesting that the increase in rainfall is related to more than simple warming of the atmosphere," Tan said.

Climate models have predicted that global warming would lead to more precipitation, especially in the tropics region.

But the research could explain why climate models have difficulties representing the details of tropical rainfall. Current computing power makes it "impossible" to simulate the small-scale processes that give rise to thunderstorms.

"This limitation, which is a well-known issue in global climate models, might well be a contributing factor to the precipitation errors and the bias towards (predictions of) light rain," said co-author Christian Jakob of Monash University, in the release.

"Given how important these large storms are to rainfall in the tropics, it is vital that there is a renewed effort to represent convective organisation in global climate models if we are to fully understand precipitation change in the future," he said.

- Reporting by Kyle Plantz; editing by Laurie Goering

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