Authors: D. McNamara, M. Smith, Z. Williams, S. Gopalakrishnan and C. Landry.

Abstract: Despite increasing risks from sea-level rise (SLR) and storms, US coastal communities continue to attract relatively high-income residents, and coastal property values continue to rise. To understand this seeming paradox and explore policy responses, we develop the Coastal Home Ownership Model (C-HOM) and analyze the long-term evolution of coastal real estate markets. C-HOM incorporates changing physical attributes of the coast, economic values of these attributes, and dynamic risks associated with storms and flooding. Resident owners, renters, and non-resident investors jointly determine coastal property values and the policy choices that influence the physical evolution of the coast. In the coupled system, we find that subsidies for coastal management, such as beach nourishment, tax advantages for high-income property owners, and stable or increasing property values outside the coastal zone all dampen the effects of SLR on coastal property values. The effects, however, are temporary and only delay precipitous declines as total inundation approaches. By removing subsidies, prices would more accurately reflect risks from SLR but also trigger more coastal gentrification, as relatively high-income owners enter the market and self-finance nourishment. Our results suggest a policy tradeoff between slowing demographic transitions in coastal communities and allowing property markets to adjust smoothly to risks from climate change.

Authors: S. Radfar, S. Mahmoudi, H. Moftakhari, T. Meckley, M. Bilskie, R. Collini, K. Alizad, J. Cherry and H. Moradkhani.

Abstract: As coastal regions face escalating risks from flooding in a changing climate, Nature-based Solutions (NbS) have garnered attention as promising adaptation measures to mitigate the destructive impacts of coastal flooding. However, the challenge of compound flooding, which involves the combined effects of multiple flood drivers, demands a deeper understanding of the efficacy of NbS against this complex phenomenon. This manuscript reviews the literature on process-based modeling of NbS for mitigating compound coastal flooding and identifies knowledge gaps to enhance future research efforts. We used an automated search strategy within the SCOPUS database, followed by a screening process that ultimately resulted in 141 publications assessing the functionality of NbS against coastal flooding. Our review identified a dearth of research (9 %) investigating the performance of NbS against compound flooding scenarios. We examined the challenges and complexities involved in modeling such scenarios, including hydrologic, hydrodynamic, and ecological feedback processes by exploring the studies that used a process-based modeling framework. Key research gaps were identified, such as navigating the complex environment, managing computational costs, and addressing the shortages of experts and data. We outlined potential modeling pathways to improve NbS characterization in the compound flooding framework. Additionally, uncertainties associated with numerical modeling and steps to bridge the research-to-operation gaps were briefly discussed, highlighting the bottlenecks in operational implementation.

Authors: C.B. Woodson et. al.

Abstract: Climate change poses an urgent threat to biodiversity that demands societal responses. The magnitude of this challenge is reflected in recent international commitments to protect 30% of the planet by 2030 while adapting to climate change. However, because climate change is global, interventions must transcend political boundaries. Here, using the California Bight as a case study, we provide 21 biophysical guidelines for designing climate-smart transboundary marine protected area (MPA) networks and conduct analyses to inform their application. We found that future climates and marine heatwaves could decrease ecological connectivity by 50% and hinder the recovery of vulnerable species in MPAs. To buffer the impacts of climate change, MPA coverage should be expanded, focusing on protecting critical nodes for the network and climate refugia, where impacts might be less severe. For shared ecoregions, these actions require international coordination. Our work provides the first comprehensive framework for integrating climate resilience for MPAs in transboundary ecoregions, which will support other nations’ aspirations.

Authors: B. Suedel, A. Tritinger, S.K. McKay, J. Calabria, M. Bilskie, J. Byers, C.B. Woodson, K. Broich, E. Dolatowski and E. Hair.

Abstract: As shorelines change and infrastructure ages, communities may be faced with how to strengthen their shoreline or protect against flooding. Using an example of a failing bulkhead that is slated for repair, landscape architecture can play a meaningful role in each step of the process for implementing nature-based infrastructure: scoping, decision-making, implementation, and operations.

When assembling a project team, nature-based infrastructure expertise should be identified and included to help define the nature and scope of the bulkhead repair. In planning, drawings and renderings of various bulkhead designs are developed by landscape architects and designers to help facilitate a transparent evolution of the alternative being considered, inform the analysis and identify the highest priority alternatives.

When communities are faced with decision-making, effective communication can be promoted by landscape architecture drawings and renderings. These graphics serve as communication tools to visualize the final alternative bulkhead design and its inherent benefits. These inherent benefits can be better understood after implementation. In the design of bulkhead alternatives, landscape architects and designers promote biodiversity while considering other project objectives such as local hydrodynamic conditions and recreational benefits.Design features that are convertible or modifiable based on lessons learned or in response to changing environmental conditions can also be communicated by landscape architecture graphics.

In addition to design, landscape architecture renderings can be used to create outreach material for the general public and design professionals, supporting education and training efforts as well as the development of technical reports. Lessons learned from the design process and long-term maintenance of the alternative design can inform webinars or workshops and further the development of Engineering With Nature (EWN) practices. The following handout explores aspects of EWN and landscape architecture that promote biodiversity on coastal infrastructure. This series of graphics has been used in several deliverables: a journal article, a technical series and an ArcGIS storymap.

Authors: D. Passeri, R. Jenkins, A. Poisson, M. Bilskie and P. Bacopoulos.

Abstract: The effects of large-scale interior headland restoration on tidal hydrodynamics and salinity transport in an open coast, marine dominant estuary (Grand Bay, Alabama, U.S.A) are investigated using a two-dimensional model, the Discontinuous-Galerkin Shallow Water Equations Model (DG-SWEM). Three restoration alternatives are simulated for present-day conditions, as well as under 0.5 m of sea level rise (SLR). Model results show that the restoration alternatives have no impact on tidal range within the estuary but change maximum tidal velocities by ±5 cm/s in the present-day scenarios and by ±7 cm/s in the scenarios with 0.5 m of SLR. Differences in average salinity concentrations for simulated tropical and frontal seasons show increases and decreases on the order of 2 pss in the embayments surrounding the restoration alternatives; differences were larger (on the order of ±4 pss) for the scenarios with 0.5 m of SLR. There were minimal changes in average salinity outside of the estuary and no changes offshore. The size and position of the alternatives played a role in the salinity response as a result of changing the estuarine shoreline geometry and affecting the fetch within the bay. SLR was more impactful in increasing exposure to low salinity values (i.e., less than 5 pss) than the presence of the restoration alternatives. Overall, the modeled results indicate that these large-scale restoration actions have limited and localized impacts on the hydrodynamics and salinity patterns in this open coast estuary. The results also demonstrate the nonlinear response of salinity to SLR, with increases and decreases in the maximum, mean and minimum daily salinity concentrations from present-day conditions. This nonlinear response was a result of changes in the directions of the residual currents, which affected salinity transport.