The 9 Deadliest Floods In American History

Two flood stories are in the news this week — one because of the sheer scale of the catastrophe. Over 900 people have died in flooding in Nepal, and more than 4,000 remain missing. The national government estimates the disaster will cost over $5 billion, and it has placed the blame on climate change. Greenhouse gas emissions have raised temperatures in the region, and part of a melting glacier broke off, triggering a chain of events that caused both mudslides and flooding. Maheshwar Dhakal, climate change chief at the Ministry of Agriculture, Forest and Environment, told The New York Times that he was “100 percent” certain climate change had played a role.

Yesterday, a flash flood in the Grand Canyon killed at least one person, with another ten missing. This story is likely making front pages not because of its scale, but because it happened in America. A large storm dumped heavy rain on the region, and it’s too early to say why the flooding developed so rapidly. The area has suffered months of drought, and heavy rain often can’t be absorbed quickly by dry soil — a factor that may have contributed here as well.

One of the deadliest floods in American history was similarly worsened by heavy rain falling on parched ground. The Guadalupe River flash flood in Texas Hill Country struck on July 4, 2025, killing 139 people. Yale Climate Connections issued a report quoting Jennifer Francis, senior scientist at the Woodwell Climate Research Center, who said, “To people who are still skeptical that the climate crisis is real, there’s such a clear signal and fingerprint of climate change in this type of event.”

The Grand Canyon and Guadalupe River floods show that deadly flash floods aren’t relics of 19th- and early 20th-century weather catastrophes. Many of the underlying causes have remained the same across more than a century.

Many of the deadliest floods in U.S. history were caused by hurricanes — Hurricane Katrina tops that list. We’ve excluded storms of that scale, which can span hundreds of miles and travel thousands more, to focus instead on the deadliest “local” floods.

How many of these floods were caused by climate change? In most cases, it’s impossible to say for certain. All were caused by heavy rainfall; in one case, that rainfall was heavy enough to cause a dam to fail — the Johnstown Flood of 1889, which killed approximately 2,200 people.

Our primary sources were Yale Climate Connections, PreventionWeb, the Weather Channel, and lists from other media outlets. We have also provided individual references for each disaster.

Rank	Event	Year	Cause	Deaths
1	Johnstown Flood, Pennsylvania	1889	Dam failure (South Fork Dam)	~2,209
2	Heppner, Oregon, flash flood	1903	Extreme rainfall/flash flood	247–251
3	Black Hills flash flood, Rapid City, SD	1972	Extreme rainfall	236–238
4	Big Thompson Canyon flash flood, Colorado	1976	Extreme rainfall in narrow canyon	144
5	Guadalupe River flash flood, Texas Hill Country	2025	Stalled thunderstorms	139
6	Buffalo Creek dam-failure flood, West Virginia	1972	Coal-slurry dam collapse	126
7	Lehigh River Valley flood, Pennsylvania	1862	Extreme rainfall/river flood	~150
8	Ohio River flood (multi-state)	1937	Extreme rainfall	~385 (some sources cite lower confirmed figures; widely disputed)
9	St. Francis Dam failure, California	1928	Dam failure	~431