Review and Derivation of Areal Reduction Factor in Malaysia with Response to Changing Climate

This study presents the reviews and derivations of ARF for storm design applications in Malaysia. Considering that present rainfall characteristics may change due to climate change, rainfall time series data of the selected rainfall interval of nine rainfall stations in Kuala Lumpur were examined by several homogeneity tests and trend test to determine the existence of trends. Average-Point rainfall tracking method was adopted to compute the Maximum Areal Average Rainfall (MAAR). Increasing trends were observed both in the point rainfalls and areal rainfalls especially for short rainfall interval which cause increment of ARF derived in this study. However, the increasing trend diminished as the rainfall interval increased. The increment also implies that ARF is a non-stationary factor. Thus the ARF derived several decades ago is not appropriate for present storm design applications. Spatial autocorrelation results indicated that the study area is characterized with localized rainfall pattern with threshold radius of about 11km which corresponding to circular area of 400 km2. The reviewed ARF complies with the localized rainfall pattern and comparison revealed that ARF is not a universal factor. In conclusion, the ARF estimations has been improved for storm design applications of local concerns with response to changing climate.