Resumen
This work focuses on evaluating the ability of the MM5 regional model to represent the basic features of present climate over South America. The spatial distribution of seasonal means and its interannual variability as well as annual cycles for precipitation and near-surface temperature have been evaluated. The internal variability has also been investigated. The analysis has two objectives, one of them is to quantify the dynamic downscaling ability to represent the current climate and the other identify the critical aspects of the regional climate model in South America in order to interpret future projections for the end of XXI century in the SRES A2 scenario with a degree reliability.In general, the MM5 model is able to adequately reproduce the main general features, the seasonal cycle and the year-to-year variability of surface variables over South America. The spatial distribution of temperature is well represented, but it can be found some systematic errors such as an overestimation in central and northern Argentina and an underestimation in the mountainous regions throughout the year. The general structure of precipitation is also well captured by the regional model, although it overestimates the precipitation in the Andean region (specifically in the central and southern Chile) in all seasons and underestimates the rainfall in tropical latitudes. The annual cycle of precipitation is adequately represented in the subregions analyzed, but its representation is better at La Plata Basin (LPB), Cuyo (CU) and Sureste Pampas (SEP). The annual cycle of mean temperature is well represented, too. The model systematically overestimates the interannual variability of temperature and underestimates the interannual variability of precipitation. From the analyses of interannual, internal variability and biases, it can be conclude that regardless the season, the MM5 regional model precipitation is reliable at subtropical latitudes, Uruguay, southern Brazil and centre east of Argentina but it is unreliable over areas of elevated topography. For temperature the regional model is reliable on subtropical latitudes, Uruguay and south of Brazil only during winter, but it less reliable is or even it is in the limit of reliability over centre and south of Chile along the year.Therefore, it is concluded that the MM5 model is a useful tool in the generation of regional climate change scenarios of high resolution over southern South America and is an interesting starting point to perform others evaluations on climate change studies that are discussed in a companion paper.