44% of the flash flood in Klang Valley occurred coincidentally during the typhoon period: A review on 2015

Abstract

This paper reviewed the occurrences of all the flood events that happened in the Klang Valley of Malaysia in 2015. The aim is to identify the sources of the heavy and extreme rainfall that triggered the flood; either it was attributed to the seasonal monsoon flows or other plausible factors. The major concern of flash floods is that many of them had frequently occurred regardless of the seasonal monsoon period; as it seems to be influenced by other factors. Therefore, besides the three monsoonal seasons with common heavy and extreme rainfall in Klang Valley which includes the Northeast Monsoon (Nov. – Feb.), Inter-monsoon 1 (Mar.-Apr.), and Inter-monsoon 2 (Oct.), this study also takes into account the typhoon season which occurred from April to December. There are 43 flash flood cases and most of them occurred during the wet period of the Northeast monsoon (Nov. – Feb.). 44% of the flash flood events did occur during the typhoon season (Apr. – Dec.) with its distribution varied via different monsoon seasons. The majority of the flash flood during the dry season (Southwest Monsoon) and wet season (Northeast Monsoon) happened during the same period of strong typhoons. Severe flash flood cases that occurred coincidentally with strong typhoons (category 4 and above) during the Northeast Monsoon had impacted larger spatial coverage, increased rainfall intensity and longer duration. The hypothetical explanation offered is that the occurrence of strong typhoons (category 4 and 5) with trajectory near the Philippines in the South China Sea could affect the regional weather of Peninsular Malaysia; in which resulting in stronger wind flows and accelerating the transportation of moist air parcels from regional ocean or seas to land areas. Such information is required for adaptation, mitigation and preventive actions including early warning systems.