TYPOLOGY OF RAINFALL FIELDS TO IMPROVE RAINFALL ESTIMATION IN THE SAHEL BY THE AREA THRESHOLD METHOD

The stratification of rainfall fields to improve specific rainfall mod els is a subject that has received relatively little attention in the literature. It is shown here that objective classification techniques, based on the intensities and spatial distribution of the rainfall fie lds, can produce meaningful results in terms of the area threshold met hod (ATM) model and climatology. Four approaches for rainfall classifi cation, using rain gauge data, are proposed in order to improve the av erage areal rainfall estimation in the Sahel by the ATM model. Two of them are based on the structural behavior of the rainy area (area wher e it rains above a given threshold) function against a threshold, Base d on this function, a new parameter, called the under profile area (UP A), has been proposed for the classification of rainfall fields. The g roups obtained from the method based on this parameter are characteriz ed by different average spatial structures. A significant improvement on the ATM model is observed by considering classification based on th e UPA parameter. An average reduction of 34% of the root-mean-square e rror is observed in a validation term, This improvement is a direct co nsequence of the fact that the optimal thresholds are different from o ne group to another, which is an important point when considering the impact of classification on the ATM model.