Abstract

Human populations and infrastructure in high mountain regions are exposed to a wide range of natural hazards, the frequency, magnitude, and location of which are extremely sensitive to climate change. In cases where several hazards can occur simultaneously or where the occurrence of one event will change the disposition of another, assessments need to account for complex process chains. While process chains are widely recognized as a major threat, no systematic analysis has been undertaken. We therefore assemble a broad set of process chain events from across the globe to establish new understanding on the factors that directly trigger or alter the disposition for subsequent events in the chain. Based on this new understanding, we derive a novel classification scheme and parameters to aid natural hazard assessment. Most process chains in high mountains are commonly associated with glacier retreat or permafrost degradation. Regional differences exist in the nature and rate of sequencing---some process chains are almost instantaneous, while other linkages are delayed. Process chains involving rapid sequences are difficult to predict or mitigate, and impacts are often devastating. We demonstrate that process chains are initialized most frequently as threshold failures, being the result of gradual landscape weakening and not due to the occurrence of a distinct trigger. The co-occurrence of fluvial processes or activation of sediment deposition areas increases the reach of process chains. Climate change is therefore expected to increase the reach of events in the future, as glacial environments transform into sediment-rich paraglacial and fluvial landscapes.