The Relationship Between Eastern Equatorial Pacific Sea Surface Temperatures and Rainfall over India and Sri Lanka

Monsoon season (June–September) precipitation data from 31 Indian subdivisions and mean monthly precipitation data from 35 Indian and Sri Lanka stations, spanning the period 1875–79, were analyzed to determine the relationship between equatorial Pacific warm episodes (El Niño events) and interannual fluctuations in precipitation over India and Sri Lanka. The data reveal a strong tendency for a below normal summer monsoon during the 25 moderate/strong warm episodes which occurred during the period. For example, area-averaged June–September rainfall over India was below the median value in 21 of the 25 warm episode years. These years include the five largest, and nine of the eleven largest, negative monsoon season anomalies. Considerably smaller average departures occurred during the monsoon seasons of the year preceding and the year following the warm episode, and during the remaining months of the warm episode year. The anomaly pattern over Sri Lanka and extreme southern India is quite different, the major feature being a period of above normal precipitation during autumn of the warm episode year. During a typical warm episode, positive sea surface temperature anomalies appear along the Ecuador–Peru coast early in the year, and thus precede the summer monster by several months. The forecasting implications of this relationship are discussed.