- Fifty years from now, floods in the eastern half of the United States will last longer as climate change creates warmer and wetter weather patterns, a new study suggests.
- Floods will last longest in the winter, the analysis predicts, marking a shift in damaging flood seasons.
- The trends underscore a need to renovate levees and dams, flood channels, and other infrastructure to protect residents and cities, researchers say.
A “once-in-a-century” flood washed through much of the eastern and southeastern United States in spring 2019 as the Mississippi River overflowed for 145 days straight, breaking the river’s 1927 record for its longest flood. But in 50 years’ time, this disaster might not be nearly as rare.
According to a new analysis of the impacts of climate change, flood waters in this wet part of the U.S. won’t just run deeper; they’ll wreak havoc for more days at a time.
Moved by the tragedy of 2019’s historic Mississippi River and Missouri River floods, civil engineers Hanbeen Kim and Gabriele Villarini at Princeton University in New Jersey decided to predict how long floods will last toward the end of the century.
“We looked at duration to understand how long floods might keep people out of their homes—if they have to find long-term alternatives, or even rebuild their houses,” Villarini said.
In an initial paper published in Nature Communications in January, the researchers projected that floods throughout the U.S. will become more extreme. Rising amounts of rainfall will create floods with more water surging through affected areas at any one time, they concluded.
However, the pair also wanted to explore the impacts on people and residences by predicting whether those floods will become more persistent, too. Their latest results, published in npj Natural Hazards in August, showed that as precipitation levels and carbon emissions increase, floods will likely last longer several decades from now.
Kim and Villarini studied flood duration by combining historical climate records with projections for the future. Using U.S. Geological Survey data for 378 sites across 23 states from Maine to Louisiana, the team determined how previous flood durations shifted depending on each site’s monthly average temperature and total rainfall. Then, based on predictions for future precipitation and temperature patterns as the world’s carbon emissions increase, they applied the same trends to calculate how flood durations might change from 2071 to 2100.
The final model depicts a future of longer-lasting floods. What’s more, the peak flood season shifts from spring to winter in the team’s projections.
“With climate change, temperatures will increase and snowmelt will occur earlier, affecting the main flood seasons,” Kim said. Not only does a warmer climate cause snow to thaw earlier and pool into rivers, but it also leads to an earlier transition from snowfall to rain, Villarini explained.
This forecast isn’t necessarily the final word, said Xubin Zeng, a hydrology and atmospheric scientist at the University of Arizona in Tucson. Incorporating more factors into the analysis would lead to stronger projections, noted Zeng, who was not involved in the research.
However, the team’s results may still warrant renovations for at-risk infrastructure in eastern and southeastern states, especially levees and dams, he said. “The average age of these structures is somewhere around 60 or 70 years old,” Zeng said. “We are in trouble if we don’t repair and strengthen them.”
The challenge is a costly one: In the 2021 Report Card for America’s Infrastructure from the American Society of Civil Engineers, dams, levees, and stormwater systems received straight Ds. The report noted an $8 billion gap between federal funding and what it will take to meet current regulations.
Preparing for future floods will require national policies that prioritize this infrastructure, Zeng said. Such measures might include raising the heights of existing structures or adding another set of levees further away from rivers to provide extra space for flood water to collect. “The question is whether politicians follow through” in response to science-based projections, Zeng observed.
Villarini aims to continue studying flood risks in finer detail. But even this glimpse of a waterlogged future is compelling enough to begin the renovation process, he urged: “The idea of this information is that we should always think of designing for the future, not the past.”
Citations:
- Kim, H., Villarini, G. Floods across the eastern United States are projected to last longer. npj Natural Hazards1, 23 (2024). doi:10.1038/s44304-024-00021-y
- Kim, H., Villarini, G. Higher emissions scenarios lead to more extreme flooding in the United States. Nature Communications15, 237 (2024). doi:10.1038/s41467-023-44415-4
Jenna Ahart is a graduate student in the Science Communication M.S. Program at the University of California, Santa Cruz. Other Mongabay stories produced by UCSC students can be found here.
