The hydrological cycle in southern South America in three general circulation models: CNRM-CM3, ECHAM5/MPI-OM and GFDL2.0

SAURRAL, R.; BARROS, V.

Melbourne

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

American Meteorological Society

Climate change represents a great challenge for water management for the upcoming decades. According to the general circulation models (GCM) used for the last IPCC report, temperature will increase during the next decades nearly over the whole world, so regional differences in hydrological variables such as evapotranspiration and runoff will be mainly controlled by precipitation. In this research, the skill of two GCM (CNRM-CM3 and ECHAM5/MPI-OM) in representing ‘present climate’ precipitation and surface temperature variability over southern South America is analyzed. The study is centered over the Plata basin (the fifth largest river basin worldwide), the main water reservoir for millions of people across Brazil, Bolivia, Paraguay, Uruguay and Argentina. Annual mean precipitation and surface temperature from the GCM are contrasted against the NCEP reanalysis data and regional misrepresentations are analyzed. Atmospheric circulation (dynamics) and temperature-moisture fluxes (thermodynamics) are also compared to explain the observed differences.Furthermore, a distributed hydrology model (VIC) is used with GCM daily minimum and maximum temperature and precipitation across the entire Plata basin to determine the skill of the models in capturing the hydrologic cycle of the Plata River. A deeper analysis is also performed by dividing the basin into four sub-basins, covering the main tributaries of the Plata River. One of the characteristics is that both models are warmer across the basin (with the ECHAM5/MPI-OM being the warmest, especially in summer). In precipitation, both models have problems in representing the annual behavior of rainfall in the area, although ECHAM5 seems to be more reliable. The causes for these misrepresentations are analyzed in detail in the present paper.