Read here. The Climategate scientists of the IPCC predicted that modern global warming would cause an increase of severe floods, as did the IPCC climate models. But when the science is objectively analyzed and the empirical evidence crunched, this prediction fails as so many before it.
Researchers Hirsch and Ryberg examine the U.S. evidence from a period of 85 to 127 years and conclude there is no significant relationship between the growth of atmospheric CO2 levels (that causes modern AGW) and annual floods.
"...shows that flooding has not increased in the United States over records of 85 to 127 years. This adds to a pile of research that shows similar results around the world. This result is of course consistent with our work that shows that increasing damage related to weather extremes can be entirely explained by societal changes, such as more property in harm's way. In fact, in the US flood damage has decreased dramatically as a fraction of GDP, which is exactly whet you get if GDP goes up and flooding does not." [R. M. Hirsch, K. R. Ryberg 2011: Hydrological Sciences Journal]