A northeaster — a common type of storm on the East Coast — is causing severe flooding in Virginia.
The occurrence of extreme precipitation has increased in the mainland United States due to climate change, and it won’t stop anytime soon. We have a general idea that it should continue to rise at about seven percent for every degree Celsius that the climate warms.
Such an increase should lead to a much greater flash flood hazard in the US. It’s hard to use that fact to make specific predictions, though, because the figure — seven percent — isn’t accurate across the board. It changes with the specific region, moisture content, altitude and other factors. These variables make it difficult to use current precipitation models, or even past observations, to extrapolate into the future and make precise, local predictions. And conversely, it is also difficult to extract meaningful information about the global climate from such local data.
In a new study, researchers tackle this problem by building a new high-resolution computer simulation of precipitation in the contiguous United States and observing how precipitation changes in local areas. The study, published in nature climate change, also compares the modeled results with observations of real precipitation across 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 humid environments, precipitation increases with temperature. In dry environments, however, the opposite happens: extreme precipitation falls away abruptly.
Looking to the future, the researchers wanted to use their model to understand the environment’s “breaking point” — the temperature above which the rate of precipitation stops increasing and begins to decrease. The concept was previously not well understood, but the researchers wanted to know if global warming could shift this breaking point.
According to their model – which assumes future weather patterns to be more or less similar to current and past weather patterns – extreme precipitation events are expected to increase significantly in nearly all North American land regions in the future.,‘ write the authors in their paper. That’s because climate change is making for warmer and more humid environments, which in turn are driving more extreme precipitation events, shifting the “breaking point.”
The model developed by the researchers can therefore be used both to explain past events and to make future predictions. “This new 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 can also help researchers relate local data to the large-scale situation.
In future studies, their model could be used to investigate possible changes in the rate of extreme precipitation per degree. They also hope to use it to investigate the effect of these local changes on the larger global environment.
Their results still yield an overall rate of about seven percent per degree Celsius, in line with other studies done elsewhere in the world. So unfortunately their results don’t contradict the worrying percentage mentioned above.
The researchers warn that these extreme precipitation events pose a threat to society that we should take seriously. “The increase in the intensity and frequency of extreme precipitation would pose major challenges to existing infrastructure systems, as well as requiring fundamental reassessments of planning approaches to intense precipitation, localized flooding, landslides and debris flows,” they write.
Nature climate change2016. DOI: doi:10.1038/NCLIMATE3168 (About DOIs)