Regional Rainfall Frequency Analysis for the Luanhe Basin – by Using L-moments and Cluster Techniques

Abstract

Flood frequency analysis is essentially a problem of information scarcity in arid and semi-arid regions. Practically in these regions, the length of records is usually too short to insure reliable quantile estimates. The density of rainfall station network of LuanHe basin is not enough for rainfall estimation at ungauged regions. Therefore, rainfall regionalization should be used to extend rainfall data to regions where rainfall data are not available. The aim of this study is to use cluster analysis and L-moment methods together to quantify regional rainfall patterns of LuanHe basin using annual rainfall of 17 stations for the period of 1932-1970. The cluster analysis follows “Ward's method” and shows seven regions of rainfall in Luanhe basin. The homogeneity test of L-moments shows that some of these regions are homogeneous. Using the goodness-of-fit test, ZDist, the regional frequency distribution functions for each group are then selected. In this study, five three parameter distributions generalized logistic (GLO), generalized extreme-value (GEV), generalized normal (GNO), Pearson type-3 (PE III) and generalized pareto distributions (GPA) were fitted to the four homogeneous regions. However, because of different rainfall generating mechanisms in the basin such as elevation, sea neighborhood and large atmospheric circulation systems, no parent distribution could be found for the entire basin.