Rainfall intensity-duration-frequency (IDF) curve development using Hazen, Weibull, and Gringorten methods for the upstream Permatang Rawa catchment

The rainfall intensity-duration-frequency curve is an essential design tool in hydrology and hydraulics for stormwater, flood, and infrastructure planning. Its accuracy depends greatly on the probability estimation method used, particularly the plotting position formula. This study aims to draw IDF curves for the upstream Permatang Rawa catchment with the following three commonly used methods, namely Weibull, Hazen, and Gringorten. The annual maximum rainfall values at the rainfall station in the upstream catchment were obtained from DID Malaysia and analysed for various storm durations and return periods for the period 2000-2024. The results indicated that there was a clear inverse relationship between the rainfall intensity and the duration of the rainstorm, which is related to the rainfall intensity. The three plotting methods varied considerably in storm-plotting position, particularly for short-duration storms and high return periods. Rainfall intensities calculated using the Weibull method were about 0.06-7.99% lower than those from the Hazen method for higher return periods, suggesting that the Weibull method may underestimate extreme rainfall events. The Gringorten method, on the other hand, produced more intense and variable intensities because of its more prominent upper tail representation of the probability distribution. In general, the Weibull method exhibited good performance with smooth and consistent IDF curves for all storm durations and return periods. Thus, it was deemed to be the most suitable approach for the upstream Permatang Rawa catchment, considering the curve behaviour and the representation of extreme rainfall events. Findings are useful to inform the design of stormwater drainage and urban flood mitigation, and support Sustainable Development Goal 11 (SDG 11) Sustainable Cities and Communities by building more resilient infrastructure and practices for flood management.