Two 25 year time-slice experiments were conducted using a 20 km mesh global atmospheric model, one for the present (1979–2003) and the other for the future (2075–2099). To assess the uncertainty of climate change projections, we performed ensemble simulations with the 60 km mesh model combining 4 different sea surface temperatures and 3 atmospheric initial conditions. Horizontal resolution of these global models is higher than or comparable to that of regional climate models applied to South American climate change projections. Both the 20 km mesh model and 60 km mesh model reproduce sufficiently well the observed seasonal precipitation patterns. These models project an increase in wet-season precipitation and a decrease in dry-season precipitation over most of South America. In the future, almost all over South America, precipitation intensity will increase. In particular, precipitation intensity is largest over the southeast South America in the present-day simulation, where future change is also large, implying an increasing risk of flooding in this region including the Parana River. At the same time a large increase of consecutive dry days is projected over the western part of the Amazon, where the amplitude of the seasonal hydrograph is projected to increase in the Amazon River, implying more floods in wet season and droughts in dry season.