Tropical Thunderstorms Increase Rainfal Totals with Climate Change

Increasing rainfall in certain parts of the tropics has long been a projection of climate change. Now, though, researchers have found the reason why the wet is getting wetter: an increase in large thunderstorms.

Thunderstorms play an important role in rainfall in the tropics. Despite organized deep convective storms only occurring 5 percent of the time in the world's equatorial region, they deliver almost 50 percent of its 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," said Jackson Tan, lead author of the new study, in a news release. "What we are seeing is more big and organized storms and fewer small and disorganized storms."

Although researchers have long known that climate change results in increased rainfall amounts, they've been unsure what mechanisms causes this. Now, researchers have answered the question whether increase in rainfall in the tropics was simply caused by a warmer atmosphere or whether the underlying circulation in the region had changed. It seems as if there have been changes to the deep convection.

"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," said Tan. "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 simply warming of the atmosphere."

The findings actually reveal why climate models may have difficulties in accurately representing the details of tropical rainfall. The small-scale processes giving rise to thunderstorm make their direct simulation in climate models impossible with current computing power.

The findings are published in the journal Nature.

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