Development of regional design hyetographs

A method is proposed to establish regional design hyetographs for facilitating the determination of design hyetographs at ungauged sites. The method is applied to the central area of Taiwan. First, the single-station design hyetographs at all rain gauges are analysed using principal components analysis and cluster analysis. The principal components analysis shows that there are six dominant factors, and the cluster analysis indicates that the time to peak rainfall has the largest influence on the classification of hyetographs. It also shows that the single-station hyetographs in the study area can be classified into three clusters. Finally, the homogeneous regions for these three clusters are delineated and the corresponding regional design hyetographs are proposed. Once the homogeneous regions and the regional hyetographs are available, the design hyetograph at the point of interest can be easily determined. The proposed method is expected to be useful for providing the design hyetographs at ungauged sites.