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RESEARCH PRODUCT

The orthogonal structure of Monsoon rainfall variation over Sri Lanka

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The spatial organization of Monsoon rainfall over Sri Lanka is examined using Orthogonal Factor Analysis (OFA) on long-term mean monthly rainfall data. Three types of orthogonal structure of Monsoon regime in Sri Lanka have been identified. Interpretation of orthogonal factor scores revealed that a large amount of rainfall occurs from March to October in the southwestern parts of Sri Lanka, from December to February in the eastern parts, and in November in the northern and mid-western parts which are all represented by high positive factor scores. Orthogonal factor scores for the first three factors account for 93.6% of the total variance of mean monthly rainfall and clearly indicate that the southeast and northwest parts of the country with lowest rainfall, resulting from lack of Monsoons, are represented by negative factor scores. The three orthogonal factors identified different rainfall maxima in different time periods and, additionally, significant spatial differences between regions. Seasonal changes in the Monsoon wind system, ITCZ weather phenomena, and topography were the main factors which influence the spatial structure of Monsoon rainfall over Sri Lanka.