researchers and policy-makers continue to assume that migration will reduce the future damages of climate change. For example, recent estimates of the damage from climate-driven coastal flooding, to which hurricanes contribute, suggest that changes in investment and migration will reduce damage by as much as 98% over the next 150 years.<sup>33</sup> If, however, individuals choose not to migrate, other – potentially more costly – forms of adaptation (for example, sea barriers that protect low-lying coastline) might instead be implemented. Understanding the extent to which migration patterns have responded to storm events in the past is thus critical for understanding the likely scope for future migration as adaptation.

In this paper, we define adaptive migration as follows: migration away from counties that are frequently impacted by storms and towards counties that are less impacted. Migration need not reduce the risk of future storms to zero in order to be adaptive. But at a minimum, it must reduce risk relative to the expected future risk of the sending location. This implies that at a population level, if adaptive migration is occurring, average exposure weighted by population should be declining over time. It suggests, though does not require, that net migration (inmigration minus out-migration) to storm impacted places should also be negative in the longrun.

We examine two specific empirical questions: (1) do more individuals migrate out of counties in the years following the experience of a hurricane than in non-hurricane years? and (2) after a hurricane, do migrants move to counties that are less at risk than the counties migrants move to in non-hurricane years? As a corollary and weaker condition to the second point, we also ask whether people move to counties that are less at risk than the county they are moving from. Changes in short-term migration rates after an individual storm are not by themselves evidence of adaptive migration, nor is it a requirement for adaptive migration to be occurring in general. General long-run trends in migration may be adaptive, even if the immediate response to a particular storm shows no evidence of adaptation. As a result, we also examine how population-level exposure has changed over the full 25-year period in our panel.

To perform our analyses, we assemble data from the IRS Statistics of Income (SOI) on aggregate county-to-county migration in the United States and data on the paths of every Atlantic basin hurricane from 1992 to 2017. These data allow us to examine how migration patterns change in counties that are impacted by hurricanes following a storm, relative to the normal patterns of migration from those counties. They also have the advantage of capturing only individuals who file taxes in their new county and so do not include temporary migrants who might relocate only for the length of time it takes to rebuild their home before returning. We use multiple definitions of exposure to hurricanes based on the incidence of flood warnings, wind speeds, and Federal Emergency Management Agency (FEMA) disaster damage determinations. Our results are broadly consistent across all of these definitions. We also collect data on county-level 4