This paper investigates the capability of a regional climate model (RegCM3) to simulate the Southern Brazil rainfall during three periods: the El Ni？o (1982), the neutral intermediary phase (1985), and the La Ni？a (1988). Each integration has used three of different boundary conditions available: NCEP-NCAR Reanalysis (I and II) and ECMWF Reanalysis—ERA-40. The simulations were performed covering a South America domain and some descriptive statistics analyses have been applied, like arithmetic mean, median, standard deviation and Pearson’s correlation; and frequencies histogram over Southern Brazil. The main results show that the model satisfactorily reproduces the rainfall in this region during the El Ni？o, neutral, and La Ni？a events, indicating that the boundary conditions which were tested adequately describe this simulations type. 1. Introduction In Southern Brazil, the Rio Grande do Sul (RS) state has uniform precipitation during the year, with accumulated values around 1800？mm/year [1]. The climate in this region is affected by many meteorological phenomena, for example, cold fronts [2, 3], mesoscale convective systems [4], or El Ni？o phenomenon [5, 6]. The regional climate model—version 3 (RegCM3) model (see more details in [7])—has been used to solve high-resolution local circulation by dynamic downscaling. The information is consistent with the large-scale circulation supplied by the driving GCMs or by reanalysis data at the boundaries [8]. Regional climate models (RCMs) have been used for a wide variety of studies of the present-day climate and possible future climates over a number of regions throughout the world. In the CLARIS-LPB project, the capability of a set of 7 coordinated regional climate models in reproducing the mean climate conditions over the South American continent was evaluated. Results show that the RCMs ensemble adequately reproduces these features, with biases mostly within ±2°C and ±20% for temperature and precipitation, respectively. However, some systematic biases were detected over the La Plata Basin region, such as underestimation of rainfall during winter months and overestimation of temperature during summer months [9]. The dry bias during winter in the Southeast of South America has also been observed in [10]. A RegCM3 was able to simulate the dramatically different large-scale circulations during La Ni？a and El Ni？o events in Amazon basin. The regional model showed reduction of rainfall in the western Amazon when compared to the observed estimates. This precipitation is associated to weak low-level moisture
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