The ongoing Midwest floods are a horrible disaster. The United States however has seen a long-term trend of decreasing flood losses as a fraction of GDP, as shown in the following graph.

Flood Damage 1929-2003.jpg

Sources

Flood damage data: Here (Note no data 1980-82)

GDP data: Here

For further reading:

Pielke, Jr., R.A., M. Downton, J. Z. B. Miller, S. A. Changnon, K. E. Kunkel, and K. Andsager, 2000: Understanding Damaging Floods in Iowa: Climate and Societal Interactions in the Skunk and Raccoon River Basins, Environmental and Societal Impacts Group, National Center for Atmospheric Research, Boulder, CO, August. (PDF)

Pielke, Jr., R. A. and M.W. Downton, 2000. Precipitation and Damaging Floods: Trends in the United States, 1932-97. Journal of Climate, 13(20), 3625-3637. (PDF)

Downton, M. and R. A. Pielke, Jr., 2005. How Accurate are Disaster Loss Data? The Case of U.S. Flood Damage, Natural Hazards, Vol. 35, No. 2, pp. 211-228. (PDF)