Dynamic Protective Capacity of Nature Based Solutions in Alpine Infrastructure Protection Strategies

The combined pressure of climate change and an increasing demand for settlement space poses an escalating threat to critical infrastructure, human lives, and livelihoods in alpine regions. While conventional grey engineering is commonly deployed to provide immediate safety, its static nature often fails to adapt to shifting environmental risks and requires cost-intensive maintenance. Nature-based Solutions (NbS) offer a sustainable alternative, yet their deployment is hindered by a lack of quantitative links between physical hazardous processes and the long-term performance of individual solutions. To bridge this gap, this study introduces a three-layered framework to assess the protective capacity throughout the service-life of a NbS on a functional, quantitative, and temporal level.The methodology categorizes 74 NbS types against 29 distinct natural hazards and identifies six functional clusters using Principal Component Analysis. These clusters reveal strategic trends ranging from localized bioengineering solutions (e.g., vegetated cribwalls, live fascines) to landscape-level watershed management approaches (e.g., afforestation, wetland restoration). A specialized Mitigation Score identified "hotspots," such as erosion control, where NbS are highly effective, while highlighting critical "gaps" in complex flood hazards where hybrid grey-green infrastructure may be necessary. The Mitigation Score varied significantly across hazard classes. Erosion processes (e.g., sheet, rill, and gully) achieved the highest scores (1.90), supported by a high density of effective NbS interventions (21–33 types). Conversely, fluvial and pluvial flooding yielded moderate scores (1.64–1.66), while coastal and impact floods showed the lowest mitigation potential (1.00–1.42) due to a more limited range of viable NbS options.The framework’s core innovation is the use of temporal hazard profiles to track intervention utility across four phases: reduced predisposition, trigger prevention, ongoing process mitigation, and post-event resilience. These profiles reveal distinct patterns and visualises the temporally variable effectiveness for each individual natural hazard.Unlike grey infrastructures, which reach their maximum protection capacity immediately after construction, the effectiveness of NbS is not linear and is intrinsically linked to biological maturation, which may take decades. This framework provides practitioners and policymakers with a robust, evidence-based guide for the strategic and lifecycle-aware deployment of NbS, bridging the gap between theory and engineering practice to ensure the long-term resilience of alpine infrastructures and livelihoods. Acknowledgments: Funding for this research has been provided by the European Union’s Horizon Europe Programme in the framework of the NATURE-DEMO project under Grant Agreement no. 101157448.