Predictability of daily streamflow for the great rivers of South America based on a simple metric

In this work, the role of the initial conditions (ICs) and boundary conditions (BCs) on the predictability of natural flows of large basins rivers (>1000km²) in South America from the MGB-SA (South American Large Basins Model) was investigated. We proposed an analysis based on a simple metric: predictability was estimated by the number of days the streamflow forecasts had a performance greater than a threshold. The role of ICs was assessed through null precipitation experiments and the role of BCs trough climatological rainfall. For the experiments with the Kling-Gupta efficiency metric and threshold of 0.95, the study shows that streamflow predictability from the ICs is relatively high (up to 40 days) in the main river reaches of flat relief basins. The increase in predictability due to climatology-based BCs mostly occur in areas with high predictability based on ICs. Basins with fast response present low streamflow predictability (up to three days).