1. Assessing Climate Change Risks Under Uncertain Conditions

Climate and environmental change is expected to affect hydrometeorological hazard and ecosystem functioning, with possible threats to human societies due to increased probability of extreme events and loss of ecosystem services. In mountain regions, the environmental response could be even larger. For this reason, it is important to obtain estimates of the expected modifications in natural hazards associated with climate and environmental change, to develop appropriate adaptation and risk mitigation strategies. This goal, however, is made difficult by the scale mismatch between climate model projections and land surface response, which requires the use of appropriate climate downscaling procedures. To complicate the picture, one should also cope with the chain of uncertainties which affect climate and risk projections, from the wide range of global climate model estimates for the water cycle variables, to the uncertainties in regional climate response, to the uncertainties in the hydrological and/or ecosystem models themselves. Precipitation data used to validate the models, on the other hand, are also affected by severe uncertainties, especially in mountain regions. This leads to the general problem of assessing natural hazards for different climate and environmental change scenarios under uncertain conditions.