Based on oil fate modeling of the Deepwater Horizon spill through August 2010, during June and July 2010, ~89% of the oil surfaced, ~5% entered (by dissolving or as microdroplets) the deep plume (>900 m), and ~6% dissolved and biodegraded between 900 m and 40 m. Subsea dispersant application reduced surfacing oil by ~7% and evaporation of volatiles by ~26%. By July 2011, of the total oil, ~41% evaporated, ~15% was ashore and in nearshore (10 m (including 1.5% after August 2010). Volatile and soluble fractions that did not evaporate biodegraded by the end of August 2010, leaving residual oil to disperse and potentially settle. Model estimates were validated by comparison to field observations of floating oil and atmospheric emissions.

Recent completion of oil fate modeling and a mass budget of the Deepwater Horizon (DWH) oil spill allows for a counter-historical study using quantitative Comparative Risk Assessment (CRA) methodology. Novel application of subsea dispersant injection (SSDI) during the response reduced surfacing oil, volatile organic carbon emis-sions, and oil on shorelines. The effectiveness of that application, and potential alternatives had dispersant not been used or been used more aggressively, were evaluated by modifying and comparing the validated oil fate model under different SSDI strategies. A comparison of mass balance results, exposure metrics, and CRA scoring for Valued Ecological Components (VECs) shows the value of SSDI in achieving risk reduction and tradeoffs that were made. Actual SSDI applied during the DWH oil spill reduced exposures to varying degrees for different VECs. Exposures and relative risks across the ecosystem would have been substantially reduced with more effective SSDI.

Sandy barrier systems are highly dynamic, with the most significant natural morphological changes to these systems occurring during high-energy storm conditions. These systems provide a range of economic and ecosystem benefits and protect inland areas from flooding and storm impacts, but the persistence of many coastal barriers is threatened by storms and sea-level rise (SLR). This study employed observations and modeling to examine recent and potential future influences of storms on a sandy coastal barrier system in Nauset Beach, MA. Drone-derived imagery and digital elevation models (DEMs) of the study area collected throughout the 2023–2024 winter revealed significant alongshore variability in the geomorphic response to storms. Severe, highly localized erosion (i.e., an erosional “hotspot”) occurred immediately south of the Nauset Bay spit as the result of a group of storms in December and January. Modeling results demonstrated that the location of the hotspot was largely controlled by the location of a break in a nearshore sandbar system, which induced larger waves and stronger currents that affected the foreshore, backshore and dune. Additionally, model simulations of the December and January storms assuming 0.3 m (1 ft) of SLR showed the system to be relatively resistant to major geomorphic changes in response to an isolated storm event, but more susceptible to significant overwash and breaching in response to consecutive storms. This research suggests that both very strong isolated storm events and sequential moderate storms pose an enhanced risk of major overwash, breaching, and possibly inlet formation today and into the future, raising concern for adjacent communities and resource managers.

Beach barrier systems (BBS) act as “ecosystem engi-neers” (EE), protecting the mainland and back bays from direct wave impact and reducing storm surge and flow passing through their inlets. BBS naturally adapt to slowly evolving wave climates by regressing or transgressing. However, observations show that BBS have been destabilized during past periods of fast changes in sea level or wave climate, potentially leading to drowning of the barrier. In this respect, current predictions of large changes in future Sea Level Rise (SLR) and wave climate, combined with anthropogenic effects, are concerning as these could challenge the natural adaptability of BBS. This raises the following questions: (1) can the future protective ability of local EE be predicted? (2) can the added benefits of implementing selected Nature Based Solutions (NbS) to enhance this natural protective ability be quantified, as well as their potentially negative feedback effects? In this study, these questions are considered for the south shore of Rhode Island (RI) through numerical modeling, in part based on earlier regional storm hazard assessment (Grilli et al., 2020). Specifically, here, as part of a NOAA project (“Effects of Sea-Level Rise 2021, Coastal Resilience” program), we assess the efficiency of NbS in changing climate conditions, while integrating local concerns, observed trends, and supporting local ecosystem and people’s way of life.

Coastal communities are unquestionably threatened by sea level rise and storm intensification. Their vulnerability is primarily function of their exposure, increasing in time, resulting into cascading effects affecting the spatial and temporal risk variability along shorelines. Many coastal communities, fearing for their future, are considering interventions aimed at improving their resilience, in particular, Natural and Nature-Based Features (NNBF) to respect the functionality of the local ecosystem and minimize negative feedback effects, that are often induced by interventions. While such features are appealing, their long-term efficiency in a changing environment is not always anticipated, and sometimes misunderstood or overestimated. In the present study, which is sponsored by the United States (US) NOAA’s “Effects of Sea-Level Rise (SLR) 2021, Coastal Resilience” Program, building on over a decade of hazard and risk assessment studies along the US New England shoreline (e.g., Grilli et al., 2017, 2020; Schuh et al., 2023), we assess the efficiency of selected NNBF in changing climate conditions, while integrating local concerns, observed trends, and supporting local ecosystem and people’s way of life.