Abstract
In this study, the El Nino Southern Oscillation (ENSO) phase index is used for water management over the Kotmale reservoir in Sri Lanka. Daily rainfall data of 9 stations over the Kotmale catchment during 1960–2005 June-September (JJAS) season is investigated over the Kotmale catchment. The ENSO phases are identified based on the 0.5°C sea surface temperature (SST) anomaly over Nino 3 region. The study has brought out few stations showing increasing and a few decreasing seasonal rainfall trends for JJAS season, while there is no change in the annual rainfall for the catchment. Monthly and seasonal rainfall of all the selected stations showed negative correlation with the sea surface temperature (SST) over the Nino-3 region index during JJAS season with varying magnitudes. During the warm phase of ENSO, below average rainfall is prominent for JJAS season over many stations. The rainfall especially during early September showed a significant below average rainfall during the warm ENSO phase. The seasonal rainfall during neutral and cold ENSO phases does not experience similar significant changes as seen during warm ENSO phase. Inflow of the Kotmale reservoir shows decreasing trend for the period of 1960–2005 in the observation from all stations collectively.
Highlights
Climate change and variability have considerable attention from the scientific community in the recent decades and numerous studies on this topic have led to a better understanding of various climate phenomena and their driving mechanisms
Our study revealed that all the stations experienced below average seasonal rainfall during 1982/83 El Nino Southern Oscillation (ENSO) event, except Annfield and Watawala stations; these stations showed above average seasonal rainfall during JJAS season in 1982
Kotmale catchment has a high likelihood of having below average rainfall for warm ENSO phase during JJAS season and rainfall during early September has a significant below average rainfall in the warm ENSO phase
Summary
Climate change and variability have considerable attention from the scientific community in the recent decades and numerous studies on this topic have led to a better understanding of various climate phenomena and their driving mechanisms. Prasanna and Yasunari, [9] found that, apart from the ENSO effect, Indian Ocean Dipole mode (IOD) impacts Sri Lanka and the South peninsular India during the months of October, November, and December (OND) Season, since the IOD impact is strongest in the months of September, October, and November (SON). They have shown the asymmetrical influence of positive and negative mode of IOD on Sri Lanka and South peninsular Indian monsoon during the OND season. Understanding the teleconnection of ENSO on the rainfall over the catchment area can be useful to build a new water management strategy to Kotmale reservoir
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