Investigating the Teleconnection between Warm ENSO Phases and Seasonal Rainfall over Kotmale Catchment in Sri Lanka

Seasonal rainfall over Kotmale reservoir is changing at an alarming rate due to atmospheric oscillations taking place over Sri Lanka. Therefore, this study focused on the teleconnection between warm El-Nino Southern Oscillation (ENSO) phases and rainfall over the Kotmale catchment. Daily rainfall data obtained from 11 meteorological stations were used to identify the behaviour of the annual rainfall climatologies of the catchment. Inflow data of the Kotmale reservoir obtained for the period 1984 to 2012 were analysed to understand reservoir inflow trends. Sea surface temperatures were obtained from Japan Meteorological Agency to determine the warm El-Nino Southern Oscillation phase. The rainfall at the stations and the inflow to the reservoir have declined over the period selected. However, the rate of decrease has varied from station to station. Seasonal rainfall at all the stations considered between December and September showed a negative correlation with the mean sea surface temperature of the Nino 3 region. Warm El-Nino Southern Oscillation caused below average seasonal rainfall over the catchment between December and September. The northeast and southwest monsoon rainfall over the catchment has weakened because of warm El-Nino Southern Oscillation phase in the Nino 3 region. However, the effect has got reduced with the onset of monsoons.