The design storm estimation of ungauged sites using regional frequency analysis

Several hydrological analyses are based on a reliable design storm, which is the rainfall depth for a given duration and probability of occurrence. The estimation of design storms at ungauged sites is a difficult task because of the lack of data. Hence, an approach based on regional frequency analysis is proposed in this paper to estimate design storms at ungauged sites. First, cluster analysis is performed to identify hydrologically homogeneous regions for gauged sites. Second, a regional growth curve is developed in a homogeneous region. Third, ungauged sites are assigned to geographically proper regions and index floods (mean annual maxima of rainfall in this case) of ungauged sites are estimated using kriging method. Finally, design storms at ungauged sites are estimated using regional growth curves and index floods. For the assessment of the applicability of the proposed approach, design storms in case that certain gauges are treated as ungauged and those obtained by using all gauges, are compared.