General Circulation Models (GCMs)are the main tools to explore the climate system at global scales to study past climate and estimate future projections. In this thesis, we use GCMs at a regional scale in order to evaluate climate variability and changes in extreme events. The Alpine and the Andean region located in two different continents, Europe and South America respectively, both with different climatic characteristics and biodiversity. These are identified among the most vulnerable regions. Studies have shown that there is great variability in the climate change impacts over these regions, due to their complex topography. Hence the evaluation of temperature and rainfall simulations seasonal and annual time scales are studied using global climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5).