By definition, inland flooding doesn't occur at the coast, yet hazard specialists consider it with coastal flooding because it often occurs in connection with landfalling tropical and extratropical cyclones. Inland floods can result when moderate precipitation falls for several days, when intense precipitation falls over a short period, when snowpack melts quickly, or when a dam or levee fails. Whenever the volume of water on land overcomes the capacity of the natural and built drainage systems to carry it away, flooding can result.
The Third National Climate Assessment found that the risk of inland flooding has increased as heavy downpours have increased across the nation over the last three to five decades.1 Additionally, the heaviest rainfall events have become heavier and more frequent, and since 1991, the amount of rain falling in very heavy precipitation events has been significantly above average.1
After a landfalling storm wreaks havoc on the coast, it can still produce widespread, torrential rains as it moves over land, sometimes resulting in deadly and destructive inland flooding. As demonstrated by the widespread impacts of Hurricane Agnes (1972), Tropical Storm Dennis/Hurricane Floyd combo (1999), and Tropical Storm Allison (2001), inland flooding is a major threat that tropical and extratropical cyclones pose for people and property inland from the coast. The combination of inland flooding and storm surge can worsen inland impacts. Tropical Storm Dennis dropped a lot of rain in eastern North Carolina in 1999. Right after that, Hurricane Floyd hit the same area. Floyd’s storm surge together with already swollen rivers from Dennis led to epic (500-year) flooding in places like the Tar/Pamlico River basin.
Inland floods cause more damage annually than any other severe weather event—averaging $6.9 billion per year for the period 1976–2006. More than 60 percent of U.S. hurricane-caused deaths from 1970 to 1999 occurred in inland counties, with more than half of those deaths related to freshwater flooding.2
- 1. a. b. Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, P. Thorne, R. Vose, M. Wehner, J. Willis, D. Anderson, S. Doney, R. Feely, P. Hennon, V. Kharin, T. Knutson, F. Landerer, T. Lenton, J. Kennedy, and R. Somerville, 2014: Ch. 2: Our Changing Climate. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 19-67. doi:10.7930/J0KW5CXT.
- 2. Moser, S.C., M. A. Davidson, P. Kirshen, P. Mulvaney, J. F. Murley, J. E. Neumann, L. Petes, and D. Reed, 2014: Ch. 25: Coastal Zone Development and Ecosystems. Climate Change Impacts in the United States: The Third National Climate Assessment. J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 579-618. doi:10.7930/J0MS3QNW.