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Cascading impacts of combined climate extreme events: A case study to evaluate the altered protective function of forests against gravitational natural hazards
Combined climate extreme events are expected to occur more frequently under climate change. Impacts of such events can propagate through natural and socio-economic systems and further interact with other non-climatological risks (e.g. infrastructure failure, earth quakes, conflicts). Resulting process cascades may have unprecedented physical, ecological and societal impacts. Adaptation to future climate requires estimations of the likelihood and possible impacts triggered and enhanced by combined climate extreme events. Most available methods only simulate individual elements of possible process chains. It is therefore necessary to couple several processes for a given scenario.
Mountain forests are a key element in impact cascades caused and/or amplified by climate change. The protection against gravitational hazards including avalanches, rockfall and landslides is an important ecosystem service provided by such forests in populated mountain regions. Climate change, by altering tree species composition and distribution, will most likely affect the protection function of mountain forests. Furthermore, climate extreme events make mountain forests more susceptible to forest disturbances such as windthrow events, forest fires or bark beetle outbreaks. Interactions between different disturbances are likely. Forest disturbances may strongly affect the protection function against natural hazards. However, recent studies and long-term data suggest that the protective effect of deadwood against rockfall and avalanches has often been underestimated.
Based on a case study for the Dischma valley near Davos, we aim at assessing how combined climate extreme events alter the protective function of forests against gravitational hazards. We will apply the mass movement model RAMMS to simulate rockfall trajectories and avalanche deposition zones for different forest scenarios obtained from previous work. The goal is to couple climate extreme scenarios, ecological models and avalanche/rockfall impact models to ultimately allow for an enhanced process understanding and a 'translation' into practice. Here, we present first results and report on the progress and challenges of extending existing approaches to evaluate cascading impacts of combined climate extreme events.
Keywords: Combined climate extremes, Ecosystem services, Avalanches, Rockfall, Protection forests