Assessment of the Intensity-Duration-Frequency (IDF) Curves for Storms in Peninsular Malaysia Based on the Generalized Extreme Value Distribution

Rainfall characteristics can be analyzed by using storm events with storms representing actual rainfall events instead of rainfall amounts in fixed time frames. One of the most commonly used methods in rainfall analysis is the construction of intensity-duration-frequency (IDF) curves. IDF curves help in designing hydraulic structures by providing a mathematical relationship between storm intensity, duration and return period. In Peninsular Malaysia, these curves are often built using the generalized extreme value (GEV) distribution to represent annual maximum storm intensity. The mathematical formula for the curves is usually taken from either known empirical equations or from quantile functions of probability distributions. However, there is no research which compares and analyzes the differences between the curves obtained for storms in Peninsular Malaysia based on the empirical and quantile functions. Thus, the aim of this study is to build IDF curves for storms in Peninsular Malaysia using typical empirical equations and the quantile function of the GEV distribution. Then, the analysis of differences is performed on the curves obtained from both approaches. The analysis consists of the coefficient of variation of root mean square error mean percentage difference and the coefficient of determination, R-2. The analysis shows small differences between the curves based on the empirical equations and those obtained using the quantile function of GEV distribution. According to these results, it can be concluded that the simple empirical equations are sufficient in constructing IDF curves based on GEV distribution for storms in Peninsular Malaysia.