Rising Rainfall: US Cities Face Overwhelming Flood Risk

New calculations by the First Street Foundation suggest that one in nine residents of the lower 48 states in the US is at significant risk of downpours that deliver at least 50% more rain per hour than local pipes, channels, and culverts might be designed to drain. The calculations indicate that 12.6 million properties nationwide face significant flood risks despite not being required by the federal government to buy flood insurance. The National Oceanic and Atmospheric Administration's estimates of expected rainfall are only intermittently updated, and the agency's estimates assume that the intensity and frequency of extreme rain hasn't increased in recent decades, despite ample evidence to the contrary.