Collaborative Research: Floodplain Management in the United States: Where, Why, and How Policies Have Shaped Flood Exposure Outcomes

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Nearly 41 million Americans are at risk of flooding, and new homes continue to be built in flood-prone areas across the country. Federal, state, and local governments can use a range of policies and programs to limit or reduce construction in floodplains and promote development in safer areas. This award supports research to explore why some communities have been able to use these tools to grow without building in floodplains and why others have not. The researchers develop an index to identify communities who have successfully limited flood-prone development, and use case studies to explore the contexts, actions, and policies that enable towns to successfully limit flood exposure. As climate change leads to more intense storms and higher sea levels, effectively managing development in floodplains is increasingly critical to the health, prosperity, and well-being of communities across the United States. The research will enhance efforts by researchers, policymakers, and the public to build vibrant communities while limiting damage from climate extremes. The project supports collaboration and learning across flood management contexts, as well as the training of a diverse, inclusive next generation of climate adaptation researchers and practitioners.This project has three components. The first step is to measure floodplain development in municipalities across the United States, filling a critical data gap. Using real estate datasets, property buyout locations, and remotely sensed land use information, the net change in housing units and the increase in impervious surface from 2001 to 2016 are tabulated in relation to the regulatory 100-year floodplain. Raw measurements are then converted into development indices by scaling based on the municipality’s exposure to flood risk and total development. By creating standardized measures of floodplain development, this step enables strategic case selection and investigation of communities across a range of floodplain development outcomes, which is not currently possible. Second, patterns in floodplain development outcomes are analyzed using geographic, social, and economic factors. Third, the project will explain why communities differ in floodplain development outcomes using comparative case studies. Specifically, this component examines how the adoption, purpose, and implementation of legal and regulatory tools to avoid or retreat from floodplains shape floodplain development outcomes. Municipalities are selected in pairs: those that have limited floodplain development, and those that have not. Interviews and document analysis are used to assess what legal and regulatory tools were adopted, for what purpose, and how they were implemented, considering both tool design and enforcement. By first creating a way to measure development outcomes, this project provides a unique level of insight into both patterns in floodplain development and how and why legal and regulatory policies influence these outcomes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.