Repeated Hurricanes Reveal Risks and Opportunities for Social-Ecological Resilience to Flooding and Water Quality Problems

Abstract:

Hurricanes that damage lives and property can also impact pollutant sources and trigger poor water quality. North Carolina has experienced 3 devastating 500-yr storms within 2 years; wastewater treatment plants and sanitary sewer overflows occurred up to 300 km inland, as well as coal ash spills, breaches of confined animal feeding operation (CAFO) waste lagoons, and numerous fish kills. Many in-situ sensors went offline and hazardous conditions precluded field sampling during and after these events. Publicly available satellite data enables delineation of flooding over broad areas, which can aid in quantifying the extent of flood exposure and potential water quality impacts. We developed an operational remote sensing-based hurricane flood extent mapping method, examined potential water quality implications of two “500-year” hurricanes in 2016 and 2018, and identified options to increase social-ecological resilience in North Carolina. Flooding detected with synthetic aperture radar (>91% accuracy) extended beyond state-mapped hazard zones. Furthermore, the legal floodplain underestimated impacts for communities with higher proportions of older adults, disabilities, unemployment, and mobile homes, as well as for headwater streams with restricted elevation gradients. Pollution sources were repeatedly affected, including ∼55% of wastewater treatment plant capacity and swine operations that generate ∼500 million tons of manure per year. We identified ∼4.8 million square kilometers for possible forest and wetland conservation and ∼1.7 million square kilometers for restoration or altered management opportunities. The results suggest that current hazard mapping is inadequate for resilience planning; increased storm frequency and intensity necessitate modification of design standards, land-use policies, and infrastructure operation. Implementation of interventions can be guided by a greater understanding of social-ecological vulnerabilities within hazard and exposure areas.