Probable maximum precipitation for 24 h duration over southeast Asian monsoon region—Selangor, Malaysia

Abstract The probable maximum precipitation (PMP) for stations in Malaysia using Hershfield formula is routinely estimated as mean plus 15 standard deviations processed from yearly maximum rainfall values. The value of 15 as frequency factor is too high for a humid region such as Malaysia. In this paper, yearly maximum 1-day rainfall data of about 30–60 years for 33 stations in the region of Selangor, Malaysia, were analysed in an attempt to estimate PMP for 1-day duration based on an appropriate frequency factor for the first time. Based on the actual rainfall data of the stations, the highest value of this frequency factor was found to be 8.7. The frequency factor of 8.7 was subsequently used to estimate 24-h PMP values for the 33 stations. Using these PMP estimates, a generalised map was prepared showing the spatial distribution of 24-h PMP. It was found that 24-h PMP over Selangor, Malaysia, varied from 375 to 500 mm and the average ratio of the 24-h PMP to the highest observed 1-day rainfall was found to be about 2.0. The PMP map is considered as important to determine reliable and consistent PMP estimate for any location in Selangor, Malaysia, for designing costly and large hydraulic structures.