Abstract
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.
Highlights
In Sri Lanka, spatial and temporal availability of rainfall is an important hydrological parameter because of the effect it has on many sectors such as agriculture, fisheries, hydropower generation, industries, drinking water supply, environment, tourism etc
5.1 Northeast Monsoon Rainfall at each station and inflow to the Kotmale reservoir decreased during the selected time period
Northeast monsoon (NEM) season in Sri Lanka occurs during the period between December and January
Summary
In Sri Lanka, spatial and temporal availability of rainfall is an important hydrological parameter because of the effect it has on many sectors such as agriculture, fisheries, hydropower generation, industries, drinking water supply, environment, tourism etc. It is essential to get an understanding about the availability of rainfall and the management of the existing water resources in Sri Lanka. El-Nino Southern Oscillation (ENSO) phenomenon is one of the primary modes of seasonal climatic variability, in the tropics [1]. Many studies have shown ENSO as influencing the rainfall over Sri Lanka [1], [2], [3], [4], [5], [6], [7], [8], [9], [10],. There is a strong link between seasonal rainfall anomalies in Sri Lanka and ENSO events [4].
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