A study of the Northeast Monsoon Rainfall of Tamilnadu

Abstract

A mainly statistical study of the northeast monsoon (October to December) rainfall of Tamilnadu has been made utilising the rainfall data for the 80 years, 1870 to 1949. A grouping of the districts on the basis of average rainfall has been indicated. The distribution of the rainfall has been studied and the probability of occurrence of rainfall within certain specified limits has been given. The normality of distribution of the district rainfalls has been tested. The occurrence of abnormalities has been discussed with reference to the incidence depressions and cyclonic storms in the south Bay of Bengal. It is found that large excesses of rainfall occur when depressions and cyclonic storms strike or come very near to the Coromandel coast and large defects occur when such depressions and storms do not strike the coast although they may occur in the south Bay of Bengal.

An examination has also been made as to how far the influence of "World Factors " on the northeast monsoon rainfall of Tamilnadu shown by Doraiswamy Iyer could account for the abnormalities, The secular variation in the seasonal rainfall in the Tamilnadu districts has, been examined but no significant changes during the past 80 years could be found. The inter-district correlation co-efficients for the northeast monsoon rainfall have been calculated and it is found that all the correlation co-efficients are positive and except for a few all are significant by indicating that the whole of Tamilnad is a fairly homogeneous region as far as northeast monsoon rainfall is concerned.