More Big Thunderstorms Boost Tropical Rainfall

As the global climate continues to change and extreme weather becomes the new norm, annual rainfall is expected to increase in certain parts of the tropics. Now new observations have shown that more big thunderstorms are behind this boost in total tropical rainfall.

That's at least according to a recent study published in the journal Nature, in which researchers say that even though other types of rainfall has decreased in frequency and the total number of thunderstorms remained the same, the increase in large storms has elevated total rainfall.

"The observations showed the increase in rainfall is directly caused by the change in the character of thunderstorms in the tropics rather than a change in the total number of thunderstorms," lead author Dr. Jackson Tan, from the Australian Research Council Centre of Excellence for Climate System Science (ARCCSS), said in a press release. "What we are seeing is more big and organized storms and fewer small and disorganized storms."

While they may be wet and miserable, thunderstorms actually play an important role in rainfall in the tropics. Even though organized deep convective storms only occur 5 percent of the time in the world's equatorial regions, they deliver almost 50 percent of its annual rainfall.

However, until now the question remained as to whether the increase in rainfall seen in the tropics was simply due to our warmer atmosphere or the changed underlying circulation in those regions. The new findings suggest that a dynamic shift in the climate system was responsible for the change in rainfall.

"If this rainfall change was caused simply by a warmer atmosphere holding more moisture, we would have expected an increase in the average rainfall when each system, organized or disorganized, occurs," Tan explained. "Instead, the number of organized storms, which is largely controlled by the dynamics of the atmosphere, have increased in frequency, suggesting that the increase in rainfall is related to more than a simple warming of the atmosphere."

Climate model results have long suggested that we would see increased precipitation in the tropics as a result of climate change. However, the exact nature of this change remained unclear. Now that large thunderstorms appear to be the drivers of increased tropical rainfall, scientists can work to make climate models more accurate.

"Given how important these large storms are to rainfall in the tropics," added Christian Jakob, one of the researchers, "it is vital that there is a renewed effort to represent convective organization in global climate models if we are to fully understand precipitation changes in the future."

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