Regional Drought Rainfall for Selangor River Basin in Malaysia Estimated Using L-Moments

Abstract

Water from the Selangor river basin is the main source of supply for the federal capital of Kuala Lumpur and the various districts of Selangor State located in the centre of Peninsular Malaysia since 2000. As this region is the most populated area in the country, its rapid economic development and population growth have caused concern over the adequacy of the quantity and quality of water abstracted from the Selangor basin, both at present and in the future. A recent prolonged drought has caused a one-month water rationing in the Kuala Lumpur and adjacent areas which basically has seriously affected the everyday life of the people and the industrial and agricultural sectors. A rainfall drought analysis is therefore required for assessing the severity of the drought events in the study area. In this study, L-moments have been used to compute the rainfall quantile values for 9 probabilities, 6 durations, 12 starting months for the 2 regions across the Selangor basin. The choice of the Pearson Type III and Wakeby distributions for fitting the Selangor rainfall data is presented. Quantile values are expressed as a percentage of mean rainfall of the particular duration and presented as drought indication maps. Rainfall of specific return period can be calculated easily using these maps and the mean rainfall for the particular station. The return period (severity) of a historical rainfall event from the station can be known when the magnitude of the historical event is compared with that of the rainfall event of a particular return period. This helps in monitoring and management of droughts.