Abstract
Daily gridded rainfall data over Peninsular Malaysia are delineated using an objective clustering algorithm, with the objective of classifying rainfall grids into groups of homogeneous regions based on the similarity of the rainfall annual cycles. It has been demonstrated that Peninsular Malaysia can be statistically delineated into eight distinct rainfall regions. This delineation is closely associated with the topographic and geographic characteristics. The variation of rainfall over the Peninsula is generally characterized by bimodal variations with two peaks, i.e., a primary peak occurring during the autumn transitional period and a secondary peak during the spring transitional period. The east coast zones, however, showed a single peak during the northeast monsoon (NEM). The influence of NEM is stronger compared to the southwest monsoon (SWM). Significantly increasing rainfall trends at 95% confidence level are not observed in all regions during the NEM, with exception of northwest zone (R1) and coastal band of west coast interior region (R3). During SWM, most areas have become drier over the last three decades. The study identifies higher variation of mean monthly rainfall over the east coast regions, but spatially, the rainfall is uniformly distributed. For the southwestern coast and west coast regions, a larger range of coefficients of variation is mostly obtained during the NEM, and to a smaller extent during the SWM. The inland region received least rainfall in February, but showed the largest spatial variation. The relationship between rainfall and the El Niño Southern Oscillation (ENSO) was examined based on the Multivariate ENSO Index (MEI). Although the concurrent relationships between rainfall in the different regions and ENSO are generally weak with negative correlations, the rainfall shows stronger positive correlation with preceding ENSO signals with a time lag of four to eight months.
Highlights
Delineating climatic zones facilitates the investigation of the general climate characteristics of the region, and helps improve understanding of climate variability across a range of spatial and temporal scales
The classification patterns are generally consistent with Lim [5] that classified subjectively the Peninsular Malaysia rainfall into five different zones based on pentad data
The general similarity appears to be the existence of the northwest zone and the central interior rainfall zone over the appears to be the existence of the northwest zone and the central interior rainfall zone over the central central mountainous valley areas of Peninsular Malaysia
Summary
Delineating climatic zones facilitates the investigation of the general climate characteristics of the region, and helps improve understanding of climate variability across a range of spatial and temporal scales. It plays an important role in gaining knowledge of water balance dynamics on various scales for water resources planning and management [1,2,3]. Climatic boundaries are often plotted according to mean monthly rainfall, varying gradually except where the gradients steepen on mountain slopes or along seacoasts [4]. The climatic regions are grouped according to the same category of isohyet range, the climatic zones boundaries are not clear and are always subjectively determined [4]. An objective quantitative climatic classification is essential for discovering definite and distinctive climate zones boundaries using the climatic data
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