Statistical Properties of Partial Duration Series and Its Implication on Regional Frequency Analysis

The use of partial duration series (PDS) in hydrological application includes the difficulty in determining the exceedance threshold or the number of average peaks per year (λ) used to define extreme events from observation. The difficulty is exacerbated when the PDS is used in the context of regional frequency analysis; however, there are only limited studies to address this difficulty. This study aims to investigate the determination of an optimum regional value of λ for the North Island of New Zealand by examining the performance of the PDS when used in a regional frequency analysis (RFA). The suitability of a number of frequency distributions to be used in the regional frequency is examined. The results confirmed that the generalized Pareto (GP) best described the PDS in the study area. The results also show that the best PDS/GP performance is obtained when the value of λ is equal to 5.