Teleconnection between Cold ENSO Phases and Seasonal Rainfall Over Sri Lanka: Case Study in Kotmale Catchment

Cold ENSO phase or La-Nina is the least considered atmospheric oscillation in the hydro-meteorological sector in Sri Lanka. Therefore, this study focused on understanding teleconnection between cold ENSO phases and the seasonal rainfall over Kotmale catchment. Daily rainfall data of 9meteorological stations were used to investigate behaviour of annual rainfall climatologies of the catchment. Daily mean inflow data of Kotmale reservoir for the duration of 1984 - 2012 was analysed to understand the trends of the reservoir inflow. Sea surface temperature values were extracted from the Japan Meteorological Agency to determine cold ENSO phase. Rainfall trend for each station and inflow trend of the reservoir both declined throughout the selected time duration. However the rate of decreasing trend changes with each station. Seasonal rainfall of all the stations showed negative correlation with mean sea surface temperature over Nino 3 region for December to September. Cold ENSO phases encounter prominent above-average seasonal rainfall during and the onset of South-West monsoon. Further, onset and during of North-East monsoon rainfall over the catchment was weakened due to the impact of cold ENSO phase over Nino 3 region. However, further studies are suggested to identify hidden opposite phenomenon observed during cold ENSO phases on 1964 and 1967 in Kotmale catchment, where all the stations experienced worst below-average seasonal rainfall.