Extreme rainfall events are interconnected around the globe

With extreme precipitation set to become more frequent in many locations, it has become critical to understand what drives these events. They can bring hazards such as floods and landslides, which cause untold devastation to individuals and communities, and make the exploration of these rainfall patterns, on a global scale, an issue of great societal importance.

Researchers in Germany have developed a system that uses a complex-network-based clustering workflow to search for synchronized structures of extreme rainfall events within the context of atmospheric chaos. Using this approach, they were able to reconstruct a functional climate network to characterize underlying interactions within the climate system. 

Clusters on the network revealed regions of similar climatological behaviors and allowed the scientists to identify the climatic interdependence of extreme-rainfall events around the globe. Their findings are published by the American Institute of Physics in the journal Chaos . 

The researchers identified that extreme rainfall events in different locations around the globe are not independent of each other, but tend to occur in clusters with a certain degree of similarity. For example, monsoons describe seasonal changes in atmospheric circulation and, while they are distributed on different continents, monsoons are usually accompanied by extremes in precipitation.

“Although global-scale atmospheric circulation within the tropics and subtropics forms connections between different monsoons, they are essentially driven, synchronized, and coordinated by the annual cycle of solar radiation,” said Zhen Su at Potsdam Institute for Climate Impact Research and Humboldt Universität zu Berlin. “Synchronization can also occur between extreme rainfalls, even when they are not occurring within monsoon regions.”

The way in which extreme rainfall is synchronized, globally, has two main patterns that differ with time and spatial distribution. “One occurs mainly from early June to mid-July,” said Su. “The other happens primarily from mid-July to late August.”

Between these periods there is a northward shift in the rain belt and, therefore, a spatial change in the distribution of monsoons. The researchers noticed both of the spatial distributions cover monsoon regions and also oceanic and inland areas.

“The synchronization structure of extreme rainfall tells us how the climate system is interconnected on a global scale,” said Su. “It also provides insights for improving corresponding interaction processes in general circulation models, which are mostly used for estimating the state of our future climate.”

“However, it still remains unclear what the global-scale synchronization pattern of extreme rainfall will look like, for example, during the summer season of the Northern Hemisphere,” Su said. “We aim to find the answer from observational precipitation data.”

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By Alison Bosman, Earth.com Staff Writer