Climate Change, Extreme Precipitation, and Flooding: The Latest Science

The document examines how a warming atmosphere increases the frequency and intensity of extreme precipitation, contributing to higher inland flood risks in parts of the United States, particularly the Midwest and Northeast. It highlights that while climate change is a driver, land-use changes—such as development in floodplains and the removal of wetlands—significantly exacerbate flood risk. The report argues that current FEMA flood maps are inadequate because they rely on historical data rather than future projections. To mitigate these risks, the authors recommend reforming the National Flood Insurance Program, increasing funding for river gauge networks and flood mapping, and implementing nature-based infrastructure and stricter zoning regulations to discourage floodplain development.

• Inland flood frequency has increased over the last century in the Mississippi River valley and the Midwest, and over the last 50 years in the Northeast, specifically in New York, New Jersey, and eastern Pennsylvania. Conversely, flood frequency has decreased in the Southeast, Southwest, Rocky Mountains, and Pacific Northwest.
• Extreme precipitation events have become more frequent and intense in many U.S. regions since the early to mid-1900s. The eastern half of the country has seen frequency increases of 50 percent or more, while the western half has seen smaller increases or decreases.
• Global warming increases the atmosphere's capacity to hold moisture, with a potential moisture content increase of approximately 7 percent for every 1°C (1.8°F) rise in temperature. This mechanism contributes to more intense rainfall events.
• Human-induced climate change has been linked to specific extreme events; for example, it made the record-breaking rainfall of Hurricane Harvey in 2017 15 percent more intense and three times more likely to occur.
• Land-use changes significantly increase flood risk by reducing the land's ability to absorb water. In the Mississippi River, engineering and agricultural expansion are estimated to be responsible for up to 75 percent of increased flood risk.
• Investment in riverine flood risk reduction is highly cost-effective, with the potential to save seven dollars in future disaster costs for every one dollar invested.

APA

Union of Concerned Scientists (2018). Climate Change, Extreme Precipitation, and Flooding: The Latest Science. https://www.ucs.org/sites/default/files/attach/2018/07/gw-fact-sheet-epif.pdf

Chicago

Union of Concerned Scientists. Climate Change, Extreme Precipitation, and Flooding: The Latest Science. 2018. https://www.ucs.org/sites/default/files/attach/2018/07/gw-fact-sheet-epif.pdf.

Wikipedia

{{cite report |author=Union of Concerned Scientists |title=Climate Change, Extreme Precipitation, and Flooding: The Latest Science |date=June 2018 |url=https://www.ucs.org/sites/default/files/attach/2018/07/gw-fact-sheet-epif.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{unionofconcernedscientists2018climate, author = {{Union of Concerned Scientists}}, title = {{Climate Change, Extreme Precipitation, and Flooding: The Latest Science}}, institution = {Union of Concerned Scientists}, year = {2018}, month = jun, url = {https://www.ucs.org/sites/default/files/attach/2018/07/gw-fact-sheet-epif.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }