Abstract
Development patterns and climate change are contributing to increasing flood risk across the United States. Limiting development in floodplains mitigates risk by reducing the assets and population exposed to flooding. Here, we develop two indexes measuring floodplain development for 18,548 communities across the continental United States. We combine land use, impervious surface, and housing data with regulatory flood maps to determine what proportion of new development has taken place in the floodplain. Nationwide from 2001 to 2019, 2.1 million acres of floodplain land were developed, and 844,000 residential properties were built in the floodplain. However, contrary to conventional perceptions of rampant floodplain development, just 26% of communities nationwide have developed in floodplains more than would be expected given the hazard they face. The indexes and the analyses they enable can help guide targeted interventions to improve flood risk management, to explore underlying drivers of flood exposure, and to inform how local-to-federal policy choices can be leveraged to limit hazardous development.