Mapping sea level rise impacts to identify climate change adaptation opportunities in the Chesapeake and Delaware Bays, USA

Salt marshes are at risk globally if they cannot keep pace with sea level rise. Along the United States Mid-Atlantic coast, high marsh has already declined, and is particularly vulnerable to future loss due to greater regional rates of relative sea level rise and limited capacity for both vertical accretion and landward migration. To support climate adaptation efforts in the region, we conducted a spatial overlay analysis to (1) assess interior ponding in the high tidal marsh zone caused by waterlogging, and (2) identify restoration opportunities where poor drainage is limiting natural recovery. Surface inundation has increased across over 14,000 ha of high marsh in the region, mostly along the eastern Chesapeake Bay and New Jersey coast. Within this waterlogged area, we identified 239 potential restoration sites (275 ha). Validation data indicate our analysis had relatively high accuracy in identifying potential restoration sites, with a true positive rate of 76% and a true negative rate of 96%. Widespread waterlogging emphasizes the need for climate adaptation efforts to restore and protect high marsh in the face of future change. Our recommended restoration strategy of connecting waterlogged sites to tidal creeks aligns with best practices by enabling drainage of high marsh to halt or even reverse ponding, improve recovery from future flooding events, and ultimately facilitate marsh migration with sea level rise.