Millions of Americans just woke up in a flood zone that had never before been listed on U.S. government maps. The first-ever public evaluation of flood risk for every property in the 48 contiguous states has found that federal maps underestimate the number of homes and businesses in significant danger by 67%. The new flood-risk data, released Monday by the research and technology nonprofit First Street Foundation, is a virtually unprecedented disclosure of how much damage climate change can be expected to inflict at the level of individual homes.