Experiments Using New Initial Soil Moisture Conditions and Soil Map in the Eta Model Over La Plata Basin

MOIRA E. DOYLE; JAVIER TOMASELLA

Foz do Iguasu

Congreso; Meeting of the Americas; 2010

American Geophysical Union

Strong interactions between soil moisture and the atmospheric processes take place in all spatial and temporal scales. The effects of soil moisture on rainfall can be associated with dynamical modifications of atmospheric systems as well as the generation of mesoscale circulations through the formation of spatial sensible heat flux gradients. A new effort towards a more realistic representation of soil moisture and its impact on the modeling of weather systems is presented. The Eta model is chosen to perform numerical simulations over South America testing the sensitivity of precipitation to soil and soil moisture changes. In this sense, the meteorological situation analyzed is a cold front crossing southeastern South America which is followed by the development of a mesoscale convective complex over northern Argentina in October 2006. The ETA model was configured to run on a 40km grid resolution and 38 vertical levels on a domain which includes all of South America north of 40°S. Initial conditions used to force the Eta Model experiments are taken from the CPTEC global model (Bonatti 1996), as well as the lateral boundary conditions which are updated every 6 hours. The control run (CTRL) uses the NOAH land surface model, with a 4 layer soil model and 9 different types of soil. Three other experiments were performed in order to test the sensibility to modifications of a) initial soil moisture conditions (MOIST), b) a new soil map (MAP) and c) both initial soil mositure conditions and new soil map (M&M). Modified initial soil moisture conditions for the ETA simulations were obtained from a hydrological balance model developed and running operational at CPTEC. The model uses integrated daily precipitation obtained from TRMM product 3B42 version 6  on a 0.25° x 0.25° grid, and rain gauge observed precipitation collected by different institutions in Brazil and by the National Weather Services of Argentina, Uruguay and Paraguay. A new soil map was elaborated using the available soil profile information in the CPTEC/INPE soil data base. It includes information on soil profiles for Brazil, Paraguay, Uruguay and Argentina. Each profile includes basic information such as soil types, texture classes, horizon depths, amount of organic carbon, etc. The different hydrological parameters defining each soil were obtained applying pedotransfer functions. The new soil map includes 16 different soil types. Results indicate that modifying inicial soil moisture conditions and incorporating a new soil map with hydraulic parameters, more representative of South American soils, improves rainfall forecasting both through a better spatial representation of precipitation and a daily total precipitation values. Although both CTRL and M&M overestimate the total precipitation of the MCC, M&M maximum precipitation is located closer to Presidente Roque Saenz Peña where the most intense precipitation was registered and the difference with the observed value is smaller.