Simulation, observations show how extreme precipitation is affected by climate

Extreme precipitation has been increasing throughout the mainland United States due to climate change, and that is not going to stop any time soon. We have a general idea that it should continue to increase by about seven percent for each degree Celsius the climate warms.

Such an increase should lead to much greater danger of flash floods throughout the US. However, it’s difficult to use that to make specific predictions, because the figure—seven percent—is not accurate across the board. It changes with the particular region, moisture level, elevation, and other factors. These variables make it difficult to use current precipitation models, or even past observations, to extrapolate into the future and make exact, local predictions. And, vice versa, it’s also difficult to extract any meaningful information about the global climate from such local data.

In a new study, researchers address this problem by constructing a novel, high-resolution computer simulation of precipitation throughout the contiguous United States and observing how precipitation changes in local areas. The study, published in Nature Climate Change, also compares the modeled results to observations of real precipitation throughout the country.

By examining this data, the researchers developed a more detailed understanding of what’s going on right now in terms of the local distribution of extreme weather events: in moist environments, the precipitation is increasing with temperature. In dry environments, however, the opposite occurs: extreme precipitation abruptly drops off.

As for what's ahead, the researchers wanted to use their model to understand the environment's “breaking point”—the temperature above which the precipitation rate stops increasing and starts to decline. The concept was not well understood before, but the researchers wanted to know whether global warming may shift this breaking point.

According to their model—which assumes that future weather patterns look more or less like current and past weather patterns—extreme precipitation events in the future “are projected to significantly increase in almost all North American land regions,” the authors write in their paper. That’s because climate change creates warmer and moister environments, which in turn produce more extreme precipitation events—shifting the “breaking point.”

Thus, the model developed by the researchers can be used both to explain past events and to make future predictions. “This novel framework explains the large variability in the observed and modeled scaling rates,” the authors write in their paper. (The scaling rate is the rate of extreme precipitation per degree of temperature). The model could also help researchers relate local data to the large-scale situation.

In future studies, their model could be used to investigate potential changes in the rate of extreme precipitation per degree. They also hope to use it to investigate the effect of these local changes upon the larger global environment.

Their results still produce a general rate of roughly seven percent per degree Celsius, in line with other studies done elsewhere in the world. So, unfortunately, their results do not mark a contradiction of the aforementioned worrisome rate.

The researchers warn that these extreme precipitation events cause a hazard to society, one we should take seriously. “The increase in the intensity and frequency of extreme precipitation would cause major challenges for existing infrastructure systems, as well as demand fundamental reassessments of planning approaches to intense precipitation, local flooding, landslides, and debris flows,” they write.