Comparative Assessment of Different Methods in Generating Design Storm Hyetographs for the Philippines

Abstract

Design storm hyetographs are synthetic temporal rainfall patterns used as input for flood modeling studies, drainage design and hydrodynamic modeling. In practice, the Philippines adopts the alternating block (AB) method to derive hyetographs using PAGASA-synthesized rainfall intensity-duration-frequency (RIDF) curves. In this study, six other methods- AB from actual RIDF curve, actual normalized 24-hour storms and four different patterns derived by Huff (1967)- were tested using the tipping-bucket raingauge records of a local weather station. Nonparametric statistical tests were employed to determine the significant difference between and among distributions. Moreover, Chi-squared goodness-of-fit test was used to compare the hyetographs with data from actual storms. The PAGASA AB hyetographs, while accurate in some instances, do not always represent actual storms well. Furthermore, other methods may have better fits for other storms. This study recommends further research in establishing design hyetographs in the Philippines.