The energy crisis that recently affected Brazil, where 95% is hydropower, pointed out the need of an increased integration of weather and climate forecast with potential hydrological impacts. To achieve this goal, there is a clear need of a greater integration between hydrological and atmospheric models.

In this paper, we present the physical basis of a simple hydrological model, based on the water balance equation, under development at CPTEC. The model is formulated on a spatial scale compatible to atmospheric models.

Model's parameters are estimated using available information from soil surveys, cartographic and vegetation maps, avoiding, a priori, the need of calibration using historical hydrological records or new field measurements. The model is being checked (not calibrated) comparing its results with available hydrological records of macroscale hydrological basins of Brazil.

Preliminary results of the validation for macro-scale basins in Brazil are presented.