Composite representation and scenarios of surface temperatura and precipitation in Southern South America by IPCC-AR4 models

CAMILLONI, INÉS

San Francisco

Workshop; WGNE Workshop on Systematic Errors in Climate and NWP Models; 2007

Program for Climate Diagnosis and Intercomparison

The objective of the present work is to evaluate the ability of a set of global climate models available for the preparation of the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) to represent monthly and annual surface temperature and precipitation fields over Southern South America. Monthly fields derived from different models were compared with the University of Delaware database available in a 0.5° x 0.5° grid for the period 1950-99. Those models with good representation of the dominant regional patterns in the area delimited by 15°S-60°S and 80°W-45°W were selected to analyze future seasonal and annual temperature and precipitation scenarios. The evaluation of present climate model simulations was done using Climate of the 20th Century (20C3M) experiments and scenarios A1B and A2 were used to prepare climate change scenarios for the period 2020-2029. GCMs skill to represent the observed temperature and precipitation fields was assessed from the linear spatial correlation coefficients between monthly mean fields derived from the observed database and from GCMs.Differences between observed and GCM anuual mean fields were also calculated to identify regions with large biases. Surface temperature linear monthly correlation coefficients are higher than 0.7 for all the analyzed GCMs with the lowest values during the summer months. Spatial representation of the annual mean temperature show that all GCMs overestimate its magnitude in about 5°C in the central region of the Andes and underestimate it in 3°C in the Patagonia. In the Plata Basin differences among GCMs are evident with some of them (i.e. MPI_ECHAM5, GFDL_CM2_1, CNRM_CM3_1 y CSIRO_Mk3_0) overestimating the annual mean temperature.Precipitation analysis shows that the lowest linear spatial correlation coefficients are observed during the austral autmn and spring months. All GCMs show some similar patterns: underestimation of annual rainfall over the Plata Basin and central Chile and overestimation over the central-western of Argentina, northern Chile, Bolivia and to the south of 40°S. Seasonal and annual surface temperature and precipitation scenarios for 2020-2029 based on 1961-90 were prepared composing those GCMs with better agreement with the present climate. The statistical significance at a 5% level was calculated showing a significant regional warming in the annual mean temperature between 0.7°C and 1.4°C. Annual precipitation scenarios show areas like the Humid Pampas and the southern region of La Plata basin with increasing rainfall between 1% and 8% and significant decreasing values in all the mountain region of Los Andes and Patagonia. Only a region of the Humid Pampas, its size depending on the SRES scenario, shows a significant positive rainfall change.