Cluster Analysis of Hourly Rainfalls Using Storm Indices in Peninsular Malaysia

Abstract

Storm-event analysis (SEA) is a method of extracting information from rainfall data by defining rainfall events as storm events. A profile-based model in SEA defines storm events using the interevent time definition (IETD), which is the minimum value between consecutive storms. Based on statistical hypothesis tests done on the difference of the average annual total frequency of storm events obtained when the value of IETD increases, it is found that 6 h is suitable as an IETD value for storms in peninsular Malaysia. In this study, two storm indices, storm intensity (SI) and storm concentration index (SCI), are used to summarize the relationship between storm duration and storm amount as well as to cluster storms. The Ward method is used for cluster analysis, and four distinct regions are found. By categorizing storm events in the four regions, it is shown that the differences are greatly influenced by the monsoon and intermonsoon seasons in peninsular Malaysia. From the result in this study, further analysis can be reduced by performing regionalized frequency analysis instead of at-site frequency analysis.