Assessing climate change risks under uncertain conditions Antonello Provenzale, Elisa Palazzi (1) 1 ISAC-CNR, Torino Climate and environmental change is expected to affect hydrometeorological haz- ard and ecosystem functioning, with possible threats to human societies due to in- creased probability of extreme events and loss of ecosystem services. In mountain regions, the environmental response could be even larger. For this reason, it is im- portant to obtain estimates of the expected modifications in natural hazards asso- ciated 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 re- quires 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 un- certainties in the hydrological and/or ecosystem models themselves. Precipitation data used to validate the models, on the other hand, are also affected by severe un- certainties, especially in mountain regions. This leads to the general problem of assessing natural hazards for different climate and environmental change scenarios under uncertain conditions. Keywords: Climate Change, Risk, Uncertainty assessment 1. Introduction Global warming should not be intended as a slow, continuous and homogene- ous temperature rise. Temporally, the warming of the last eighty years has mani- fested itself in a sequence of steps, alternating periods of rapid change with times of slowly changing temperatures (as in the last ten years). Spatially, the tempera- ture increase is widely varying, with geographical areas where the warming has been up to three times the global mean (as in the Arctic and in several mountain chains such as the Alps), and other regions where warming has been more modest (IPCC 2013). Even more importantly, the effect of global warming is not solely a temperature increase. The largest energy of the atmospheric motions and the potentially larger amount of moisture in the atmosphere can lead to an intensification of the hydro- logical cycle, with more intense precipitation events and more prolonged dry peri-