Big storms increase tropical rainfall

http://www.sciencedaily.com/releases/2015/03/150325151857.htm

Joint research from the Monash branch of the Australian Research Council Centre of Excellence for Climate System Science (ARCCSS) and NASA published in Nature found even though other types of rainfall has decreased in frequency and the total number of thunderstorms remained the same, the increase in big storms had elevated total rainfall.

Thunderstorms play an important role in rainfall in the tropics. Despite organised deep convective storms only occurring 5% of the time in the world's equatorial regions, they deliver almost 50% of all its rainfall.

The research has also contributed to answering the important question whether the increase in rainfall observed in the tropics was simply caused by the fact of a warmer atmosphere or whether the underlying circulation in that region had changed.

The changes to the deep convection discovered in the study suggested a dynamic change in the climate system was responsible for the change in rainfall.

The revelation that large thunderstorms appear to be the source of increased precipitation in the tropics explains why climate models may have difficulties in accurately representing the details of tropical rainfall.

The small-scale processes giving rise to thunderstorms make their direct simulation in climate models impossible given current computing power.

"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 light rain," said another author from Monash University, Prof Christian Jakob.

"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 changes in the future."