Across the continental United States, the most destructive rainfall events can occur three times more often and become 20% more destructive by 2079. This conclusion was made by scientists from the University of California at Los Angeles.
In an article published in the journal Earth’s Future of the American Geophysical Union, scientists concluded that global warming strongly affects both the intensity and frequency of extreme precipitation and flooding – what climatologists in the United States call “centennial.”
The term “100-year flood” is a statistical term for an unlikely event. Statistically, the likelihood of a “centennial flood” occurring in any 100-year period is about 63%, not 100%. However, climatologists said that the term itself will soon become obsolete, because extreme precipitation will happen much more often and more likely to lead to catastrophic consequences.
An example of “centennial flooding” is the Great California Flood in 1862, along the Mississippi and Missouri rivers in 1993, in Houston due to Hurricane Harvey in 2017.
Climate change consequences
The study predicts a sharp increase in precipitation for the entire continental United States. However, in some areas the situation will be worse than in others. For example, on the West Coast and the southeast of the country.
Floods will become more frequent, and the number of human casualties will also increase. Scientists came to such conclusions using climate models, water physics and demographic data in their work. For example, climate change coupled with population growth will increase the number of people at risk of “centennial floods” – by about 50 million in the continental United States.
And even in the absence of climate change, population growth will expose an additional 34 million people to such floods. A combination of factors will exacerbate the situation in regions that were still outside the floodplains and were sparsely populated.
Previously, extreme rainfall forecasts were based on limited historical data that is only 100 years old. In the new study, scientists used a simulation technique to create a variety of likely future events.
It is important to note, the authors write, that the risk of flooding in the United States will increase significantly over the next 30 years, even with moderate warming, that is, a 1.5-2.5 degree Celsius increase in temperature worldwide. Over the next 30 years, they predict, more than 20 million people will be affected by the “centenary flood”.