Sources of uncertainty in the NRCS CN model: Recognition and solutions

The Natural Resources Conservation Service Curve Number model is one of the most recognizable procedures in the field of rainfall–run-off estimation. It has been widely applied for different purposes in hydrological models. In spite of its widespread use, some uncertainties have not even clarified and must be examined for its proper application. Particularly, choosing the most representative rainfall–run-off events, and the coefficient λ that relates the parameters of the model (curve number CN and initial abstraction I_a). In this research, an advanced analysis is developed to evaluate the influence of λ for a set of representative watersheds of the Agricultural Research Service of the United Stated Department of Agriculture. They are characterized by different soil properties, land uses, and climatic conditions. Finally, 2 novel methodologies for the selection of the most representative rainfall–run-off events and for the adaptation of coefficient λ are included, based on the pattern of rainfall distribution.