Principal components of monsoon rainfall in normal, flood and drought years over India

Daily precipitation data of the monsoon season (June–September) for the period 1940–1980 from 50 stations is considered in this study. The correlation of individual station rainfall with all India seasonal rainfall is carried out to identify the homogeneity associated with the nature of rainfall activity of individual stations with the rainfall character of the all India seasonal rainfall, taking into account statistical significance. Further, empirical orthogonal function (EOF) analysis is carried out on these data to find out the nature of rainfall distribution in different monsoon categories, namely normal, flood and drought years. The percentages of variance explained in these different categories for normal, flood and drought years are estimated. The technique thus serves to identity spatial and temporal pattern characteristics of possible physical significance. It has been found that during normal, flood and drought years, the first four (most dominated) principal component with ‘significantly positive’ correlated stations explains 73%, 77% and 100% of the variance, while the remainder ‘weakly correlated’ stations explains 58%, 66% and 52% of the variance with all India seasonal mean rainfall.