Coastal risk assessment: Nature-based solutions’ ecosystem services to drive transformative adaptation

The escalating climate change impacts and increasingly frequent extreme events pose severe threats to coastal ecosystems. As emphasized by the IPCC, these threats demand a strategic transition from incremental to transformative adaptation. Nature-Based Solutions (NBSs) are increasingly embedded in policies for climate adaptation, due to their capacity to mitigate risks and buffer against shocks. However, empirical evidence regarding NBS performance under the long-term influence of climate change and large-scale interventions is limited. Consequently, transformative risk modelling approaches that integrate response and adaptation measures provide a structured pipeline for evaluating both the risks posed by accelerating climate change and the effectiveness of transformative pathways at the landscape scale.

The Horizon 2020 REST-COAST project was designed to demonstrate how upscaled coastal restoration can identify climate adaptation pathways. This study utilizes a Bayesian Decision Network (BDN) capable of simulating NBSs and supporting decision-making to evaluate the performance of large-scale restoration in the Venice Lagoon (Italy). Specifically, it examines wetlands’ ability to enhance ecosystem services and reduce risks under current and future climate conditions. The model consists of nodes representing key variables - including total water level, significant wave height, suspended sediment concentration, saltmarsh vegetation, and elevation - and arcs allowing for the explicit modelling of how climate conditions and restoration could affect ecosystem services, i.e., wave attenuation, sedimentation, carbon accumulation and nutrient uptake.

The developed BDN incorporates historical observations, earth observations and modelling data from 2020 to 2024 to establish the initial conditions of the network. The pilot site in-situ monitoring data, not used for the initialization of the BDN, provides a calibration and validation dataset to evaluate the model predictions and confidence in the model’s ability to support risk-informed adaptation decisions. By comparing the model's predictions with the observed data, the probabilities associated with different states and transitions can be adjusted to better reflect reality. Once validated, the model serves as a tool to evaluate restoration upscaling - the replication of small-scale restoration interventions to the increased lagoon-scale to achieve increased adaptation benefits. These restoration scenarios, co-designed with local stakeholders to reflect their local knowledge, values, and vision for the future of the Venice lagoon, are simulated alongside climate conditions for the current, mid- and long-term RCP4.5 and 8.5 projections.

By modelling the impact of these what-if adaptation strategies, the BDN simulates the effectiveness of upscaled restoration in providing regulating ecosystem services under shifting climate conditions. By moving from localized restoration effects to lagoon-scale system responses, the framework supports the evaluation of transformative adaptation pathways rather than incremental interventions. This risk assessment framework brings together the local stakeholders and decision-makers to better understand, estimate and evaluate the effect of NBS interventions. Further developments will expand upon the REST-COAST findings by investigating the land-sea interface through the EU-funded COAST-SCAPES project, that will assess cross-sectoral interactions, synergies-tradeoffs, up- and outscaling of climate-resilient adaptation through an integrated, landscape-scale approach.