This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Extreme precipitation events are among the most damaging natural disasters and a major concern in our changing climate. In the U.S., since 1980, the most destructive events alone have caused more than 2,800 deaths and $700 billion in damages.
But what is the total area of the country affected by these events each year? And how have these patterns changed over the past several decades? In a recent study in Geophysical Research Letters, led by researchers at Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School, the authors discovered some unexpected trends.
Extreme rainfall events that cover large areas, including hurricanes, atmospheric rivers and thunderstorm complexes, are a growing threat, but many studies on extreme precipitation focus on the statistics of rainfall recorded at individual locations, like weather stations. This new study takes a slightly different approach, looking at not only when heavy rainfall events occur but also how much nearby area was affected by the same event on the same day. For example, a small-area extreme rainfall event may result in a localized flash flood in just a few towns, but large-area extreme events like Hurricane Ida in 2021 can easily cause destruction across entire states at once.
Looking at the statistics of extreme precipitation events across both space and time has yielded some surprising results. For example, the average weather station in the eastern half of the U.S. has recorded a growing number of days with extreme rainfall since 1980. At the same time, extreme rainfall events might be decreasing in frequency.
How can both findings be true? By looking at the spatial footprints of storms over time, this study provides insight into these seemingly contradictory trends. Across the U.S., it used to be more likely to have many small-area extreme rain events throughout the year, all happening on different days.
Now, the entire country is tending toward fewer small-area extreme rain events. In the western U.S., the story seems to more or less end there, but in the eastern U.S., large-area extreme rainfall events appear to be growing more common as well. Combining these two effects means that the average station in the eastern U.S. is experiencing more extreme rainfall events, but with a greater tendency toward large-scale events that affect large swaths of the country at once, instead of smaller-scale storms on different days of the year.
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