California’s sandy beaches are iconic, highly valued spaces that provide many co-benefits to our communities, economies, and coastal ecosystems. In recent years, the impacts of El Niño events 1-6 and winter storms on beaches across the state have amplified concerns about how to manage the impacts of ongoing climatic variability events superimposed on more insidious, longer-term sea-level rise (SLR). The state recognizes the need for viable adaptation strategies, including nature-based solutions (NbS), in many policies (see below). Coastal dune systems, both extant and restored, have the potential to buffer and enhance the resilience of adjoined beaches to climate forcing. The goal of this project is to enhance understanding of, and provide actionable information for, the use of coastal dune systems as a NbS for enhancing the resilience of sandy beaches in California to climate change impacts including flooding, erosion, and loss of specialized habitats and related biodiversity. Specifically, we will help identify sites, methods, and actions to accelerate implementation and effectiveness of beach-dune restoration or emplacement as a viable, scientifically informed, accessible adaptation strategy for California’s coast. Coastal dunes in California are highly dynamic systems that vary in shape, size, and composition. Their ecogeomorphology is highly dependent on local biology, coastal processes (waves, winds, tides), and exposure to extreme events/hazards. These factors, and site-specific land use constraints, recreational use, stakeholder interests, and dune management practices, make it difficult to achieve dune resilience through a uniform design. Planning and design must instead represent the most effective approach given site conditions for improving the ability of the dune ecosystem to withstand climate stressors (e.g., waves, high waters) and maintain itself over time, including naturally rebuilding after being disturbed. In recent years, dozens of coastal dune restoration projects have been implemented statewide 7-14 , varying in extent, design, and purpose; yet many are not fully informed by pilot studies or current science on beach-dune geomorphology, restoration ecology, coastal hazards, or future forecasts. This proposal leverages results from existing pilot sites and significant expertise from a team of scientists, practitioners, and land managers with substantial experience in dune geomorphology, ecology, and restoration projects that span the California coast. To improve understanding, facilitation, and success of dunes as a NbS for enhancing coastal resilience, our activities will focus on 3 main research objectives: 1) Create a state-wide inventory and vulnerability assessment of coastal dunes in California to establish a baseline of past and present attributes (e.g., dune types, extent, morphometrics, plant communities, critical habitats) and other ecosystem services. The vulnerability assessment will identify the status of resilience to erosion and SLR of sites based on a cumulative assessment of changes in shoreline positions, habitat distributions, beach-dune sediment budgets, plant cover, land use, and other interventions (e.g., sand nourishment, restoration, armouring) 16-19 . Future SLR impact scenarios for the risk assessment will be modeled using 2023 updates for relative sea-level (RSL) trends and the USGS Coastal Storm Modelling System (CoSMoS 20-23 ). Empirical data gathered from this project will also help refine future development of CoSMoS to better simulate responses of coupled beach-dune systems. 2) Assess current responses of restored coastal dunes using observations and results from a network of pilot sites that California agencies have invested in with our research team and collaborating partners. Sites span the geographic range of California’s coast, a variety of land tenures, human pressures, management settings, and restoration approaches (Table 2). Results and data will be shared with a broad network of >200 end users engaged in the Coastal Dune Science Network 1 (CDSN) to advance understanding of how dunes can provide NbS to improve coastal resilience via lessons learned and knowledge on effective design, monitoring methods, and adaptive management approaches3) Synthesize findings from Obj. 1 & 2 to develop site suitability, restoration, and performance assessment frameworks for restoration projects in collaboration with state and local management entities. These frameworks will help identify priority sites and methods for implementing, replicating, scaling, and monitoring dune restoration projects to improve coastal resilience and capacity building for underserved communities. This information will help inform eventual development of state-wide guidance and best-practice guidelines for improving coastal resilience using dunes as a NbS.