Convective rainfall characteristics in Ampang, Selangor

Abstract

This is so especially for convective storm which has been associated with the occurrences of major flash floods in many urban areas. Short interval rainfall data recorded at Ampang, Selangor between year 2000 and 2004 was analysed in order to characterize the convective storms. The diurnal and monthly distributions of rainfall in 2004 show that 75% or 2049mm of the rain fell between 13:00 and 19:00 and about 244mm or 12.5% between 19:00 and 22:00. A threshold intensity of 35 mm/hr was used to separate convective from non-convective storms. Convective storm occurred most frequently during inter-monsoon periods (43% of the events), followed by northeast monsoon (30%) and southeast monsoon (27%). The convective storm characteristics for the highest 5-minutes intensity (Is) for ten convective events mostly occurred in the afternoon and the duration of these events range from 15 to 215 minutes. A variety of storm shape is evident and the patterns show that most of the convective events occurred over short durations. The convective storms were further classified into slightly convective, moderately convective and strongly convective. It seems that 35 mm/hr threshold intensity is appropriate for separating convection from non convective storms for local conditions.