GESS is a user friendly model for the forecasting of inflows and the generation of synthetic streamflow scenarios. These scenarios can be used as input information for simulation / optimization tools, such as SDDP (hydrothermal operation planning) or ParSul (river basin simulation).

GESS uses the information of macroclimatic variables such as the sea surface temperature, which are associated to the El Niño / La Niña events. GESS has a feature called the telescopic effect: it allows the user may produce daily synthetic streamflow scenarios for the immediate future, say the next 7 days, weekly scenarios for the intermediate future, say from week 2 to week 4, and monthly scenarios for the remote future, for example, from month 2 to month 24. Naturally, this feature can only be used when input data files exist for daily, weekly and monthly inflows.

GESS offers a wide group of alternatives for experimenting in the area of stochastic hydrology, such as the determination of the parameters while considering sample variability.

The results produced by GESS can be formatted files, Excel worksheets or SDDP hydrological files. Additionally, there are built in macros for the preparation of reports with the statistics of the historical inflows and the comparison of the inflow forecast of GESS and the historic inflows, like: minimum, mean and maximum values, variances, skewness coefficient, space (cross) and serial correlations.