Mountainous regions cover about 24% of the global land area and are a living space for about 10 % of the world's population. They also play an important economic role (e.g. tourism). Mountainous regions are susceptible to natural hazard processes and are severely affected by climate change impacts. This poses major challenges for mountain areas when it comes to securing these areas as a sustainable living space. Detailed knowledge and assessment of natural hazard processes is therefore key when it comes to sustaining livelihoods in mountain regions, This PhD thesis addresses four research objectives and aims to overcome existing challenges in natural hazard research in complex mountain environments. With a comprehensive compilation of process chains from all over the world a basis for characterization and classification was established. A methodology based on fuzzy logic was developed to assess the climate sensitivity of natural hazard processes. The actual state and the further development of permafrost degradation is simulated, using a numerical model. Finally, the potential of system dynamics is being examined to get a better understanding of complex system behavior of natural hazard processes.