South America’s present and future climate as simulated by Rossby Centre Regional Atmospheric Model

SÖRENSSON A.A., R. RUSCICA, C.G. MENÉNDEZ, P. ALEXANDER, U. HANSSON, P. SAMUELSSON, U. WILLEN

Melbourne, Australia

Conferencia; 9th International Conference on Southern Hemisphere Meteorology and Oceanography.; 2009

American Meteorological Society

The Rossby Centre regional atmospheric model, RCA3-E, is employed to downscale a transient global climate change projection over South America for two time slices of 20 years each. The radiative forcing of the system for the periods 1980-99 and 2080-99 are based on 20C3M, a scenario with historical GHG concentrations, and on the IPCC SRES A1B scenario respectively. A continental scale domain is nested in the global model ECHAM5/MPI-OM and, for validation of the system performance, RCA3-E is also nested in ERA-40 reanalysis for the period 1980-99. Both long term seasonal means and daily extremes for precipitation and near-surface temperature are analyzed. The shape of the temperature daily distributions changes; the cold tail gets shorter and the warm tail gets longer in the future climate. During SON, the season of the South American monsoon onset, the mean precipitation response is negative over the Southern and Western Amazon regions, while during the mature monsoon (DJF), the model simulates a positive response over most of South America. The response in SON (DJF) is a consequence of an increase (decrease) of dry days and an increase (decrease) of days with moderate to heavy rainfall. Southern Amazonia as well as in the Southern Andes shows a dryer climate throughout the year. In austral winter in the Southern Andes, as well as in Patagonia, the number of frost days decreases to a third of its value in present climate.