CLASSIFICATION OF SUMMER MONSOON RAINFALL PATTERNS OVER INDIA

Seasonal (June through September) percentage departure from normal rainfall patterns over India have been classified by objective methods utilizing data for a 120-year period (1871 1990). The methods used are the map-to-map correlation method and the k-means clustering method. Empirical orthogonal functions (EOFs) are also presented. It is seen that 75 per cent of the charts can be classified into six distinct types by the map-to-map method. Six distinct types also are obtained by the k-means method. The first four dominant EOFs explain 52 per cent of the variance. Intercorrelations and contingency tables among the types obtained by these methods and visual examination suggests that the dominant patterns are similar, irrespective of the method used. It is also seen that the monsoon rainfall for the country as a whole and the spatial patterns may have no relationship. Even during normal monsoon years, the spatial patterns may be different. The advantages and disadvantages of the methods used are discussed.