Social-ecological system approach for assessing impacts of sea-level rise and the benefits of natural and nature-based features

Del Angel, Diana C.
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Global sea level has increased, on average, 1.5 cm per decade since the 1900s, and according to National Climate Assessment, sea levels may rise 15–38 cm by 2050 and 30–130 cm by 2100. It is expected that sea-level rise (SLR) will have physical and geological impacts on coastal areas, including submergence and erosion, saltwater intrusion, and a decline in coastal wetlands. In the U.S. Gulf of Mexico, a significant portion of the shoreline faces moderate to high vulnerability to SLR. Further, the combined effects of SLR and storm surge can increase the risk of socio-economic consequences such as damages to buildings and public infrastructure, loss of personal property, loss of business and wages, and the need to evacuate or relocate. This dissertation contributes data and knowledge for the planning and mitigation of SLR in the Northern Gulf of Mexico. This research uses a social-ecological system framework to explore the consequences of SLR, SLR-induced coastal change, and the tools available and used for mitigating these consequences. The planning and resource management community can benefit from information and tools that communicate the potential effects of storm surge under SLR and help inform climate adaptation planning, post-disaster re-development plans, and enhance hazard mitigation. The first research chapter assessed the socio-economic consequences of storm surge under SLR. This work assessed the socio-economic impact of a 1% and 0.2% annual return storm surge under 4 SLR scenarios (0.2 m, 0.5 m, 1.2 m, and 2.0 m) for the year 2100. Assessment methods primarily used HAZUS-MH software, a GIS-based modeling tool developed by the Federal Emergency Management Agency, to estimate the physical, economic, and social impacts of natural disasters. Economic impact analysis focused on buildings, essential facilities, vehicles, roads, and crops. The study found that by the year 2100, SLR can increase flood damage by an additional $1B-$30.9B within the 1% AEP and from $0.5B-$40B within the 0.2% AEP. The additional cost of storm increases by SLR scenario and is not non-linear, showing a sharp increase in the cost-per-cm of SLR in the 0.5 m 1% AEP scenario and the 1.2 m 0.2% AEP scenario. The NGOM will likely experience increasing risk to the effects of storm surge flooding in the coming decades. Future planning and flood mitigation strategies are needed to address the projected increase in risk coupled with increasing coastal population and development. The second study in this dissertation focused on comparing technical aspects and output of three prominent SLR transition models: The Sea Level Rise Affecting Marshes Model (SLAMM), the Hydrodynamic Marsh Equilibrium Model (Hydro-MEM), and NOAA-Marsh Migration Model (NOAA-MMM). This work highlights the considerable difference between the model outputs across the sites. In addition, the results show no consistent over-estimation or underestimation of marsh habitat by a particular model, and the magnitude of variability differs across sites. Overall, differences in model output are site-specific and result from unique physical and ecological processes at each site. However, this study did not validate model results to understand which is more accurate. It is acknowledged that process-based models which integrate dynamic SLR modeling are the preferred modeling approach. However, these models are computationally and financially expensive and may not be available for many marsh locations in the U.S. The last chapter used a content analysis approach to assess the use of green infrastructure for SLR mitigation in place-based plans of the Florida Panhandle. Results found that only 42% of place-based plans in the study site incorporated SLR. Of these, water and land management plans were more likely to integrate SLR than community planning documents. The most common techniques associated with SLR mitigation are restoration and living shoreline approaches. Lastly, results presented here contribute to other studies that suggest that SLR adaptation planning and SLR management are at their early stages in Florida communities and that state programs and mandates can enhance SLR planning in the state. This study focused on the issue of SLR, consequences to coastal communities, assessment of models for decision-making, and the status of SLR planning activity. From this work, it is apparent that SLR adaptation in the NGOM is at its beginning stages. Data and scenario-driven products such as those presented in Ch II and III are essential components for adaptation. Nevertheless, adaption is a socio-political act that requires coordination and collaboration among government, non-profit, academic, and planning entities.

Adaptation, Northern Gulf of Mexico, sea level rise, Socio-economic model, Storm surge flooding, Wetland Models
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