Abstract
ABSTRACT The planning and the efficiency of water resources are subject to the uncertainties of the input data of climate and hydrological models. Prediction of water inflow to reservoirs that would help decision making for the various water uses, contain uncertainties fundamentally the initial conditions assumed in the modeled processes. This paper evaluates the coupling of a regional atmospheric model with a hydrological model to make streamflow forecast for seasonal operation of Orós reservoir, Ceará State, Brazil. RAMS model, version 6.0, was forced by the ECHAM 4.5 atmospheric general circulation model over Alto Jaguaribe basin to obtain the rainfall data. To remove biases in the simulated precipitation fields was applied the probability density function (PDF) correction on them. Then the corrected precipitation data were inserted in the hydrologic Soil Moisture Account (SMA) model from the Hydrologic Modeling System (HEC-HMS). For SMA calibration, it was used the Nash-Sutcliffe objective function. Finally, decisions to water release from the Orós were evaluated using the Heidke Skill Score (HSS). The SMA model showed a satisfactory performance with Nash-Sutcliffe values of 0.92 (0.87) in the calibration (validation) phase, indicating that it is a rainfall runoff model alternative. For decisions in releasing water from the Orós reservoir, using climate predictions, obtained HSS = 0.43. The results show that the simulated rainfall coupled with a hydrological model is able to represent the hydrological operation of Brazilian semiarid reservoir.
Highlights
Semiarid regions, such as the Northeast of Brazil (NEB), are vulnerable to climate fluctuations and their impact on water supply shortage
The following parameters were more sensitive on the river discharges: maximum soil infiltration (2.5 mm/h), storage in the soil (45 mm), storage in tension zone (30 mm), impermeable area (15%), soil percolation (1.5 mm/h) and storage in the surface layer (2.0 mm)
The values of the parameters calibrated with the observed data for the January–June period of 1979 to 1995 feature NS values equal to 0.92
Summary
Semiarid regions, such as the Northeast of Brazil (NEB), are vulnerable to climate fluctuations and their impact on water supply shortage. Forecast models of rivers discharges for a few months or a year’s horizon time are an interesting research topic from the viewpoint of achieving more efficient operation of water supplies and water allocation among competing uses and users (SOUZA FILHO; LALL, 2004). Issues such as the prevention and flood control, reservoir operation, and the planning of water use are directly associated with the prediction of rivers discharges, which present uncertainties arising essentially from the modeling process and the assumptions of the model initial conditions (GEORGAKAKOS et al, 2005; DOBLAS-REYES et al, 2005). It has become increasingly important to seek better water management practices, including better reservoir inflow forecasts and improved reservoir operations
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