Regional partial duration series modelling of hydrological droughts in Zimbabwean rivers using a two-component exponential distribution

A regional analysis of hydrological droughts is conducted using the partial duration series model with the two-component exponential (TCE) distribution as exceedence distribution. The index-flood method is applied in order to obtain more efficient estimates of the T-year events. Only one of the three parameters of the TCE distribution contributes significantly to the uncertainty of the T-year events and, therefore, only this parameter is regionalized. In total 25 gauging stations covering most of Zimbabwe were used to identify sufficiently homogeneous regions for use with the index-flood method. Separation of the stations according to mean annual precipitation indicated the existence of three or possibly more homogeneous regions, though the limited number of available stations did not allow for any rigorous conclusions.