Modelagem regional hidroclimática da bacia do Rio São Francisco.

Abstract

The São Francisco River basin (BHSF) is the main basin of the Brazilian Northeast water system due to its capillarity in the water systems of this region, contributing to ensure the water availability of several states in the Northeast. Simulating the rainfall and runoff patterns of this basin along its four physiographic regions, spatial division along the main river, is substantially strategic for the management of water resources in the States that benefit from the use of water in this basin. Thus, the objective of this study was to analyze the hydroclimatology of the São Francisco River basin using regional climate modeling. In this sense, the RegCM climate model was used to simulate precipitation, temperature, potential evapotranspiration and runoff in the São Francisco River basin for a period of ten years (2000 to 2010). The model was integrated using ERA-interim reanalysis data as initial and lateral boundary conditions. Sensitivity tests of the cumulus parameterization in the ocean and on the continent were carried out due to the close relationship between precipitation and runoff, and the uncertainty in choosing this parameterization in the simulations. In these tests, the most adequate parameterization in the representation of precipitation patterns in the basin was evaluated. This evaluation was conducted from an objective analysis using functions that quantify the dexterity of the simulated rain in relation to the observed rain from three different sources. The uncertainty in the definition of the grid domain used in the simulations motivated the performance of a sensitivity test to evaluate this aspect, configured as follows: the first test, with a larger domain, and the second with a smaller domain, whose limits have a configuration significantly away from and close to the basin, respectively. In general, among the evaluated parameterizations, Emanuel's, both in the ocean and on the continent, was the one that best represented the precipitation in the basin, and with the use of a greater grid domain. As for hydroclimatic modeling, the model satisfactorily simulated seasonal and annual rainfall patterns, evapotranspiration and basin runoff. The Submédio and Alto São Francisco sub-basins presented the best results in the simulation of rainfall and potential evapotranspiration. However, although the simulations represent the hydroclimatic patterns of the basin, rainfall and potential evapotranspiration were underestimated, which implied an overestimation of runoff in the basin. The continuity of hydroclimatic modeling studies with RegCM at BHSF requires an analysis and probable improvements in the surface modulus of the model in order to adjust the simulated evapotranspiration, and therefore, adjust the precipitation and runoff in the basin.