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Effect of Indian Ocean Dipole (IOD) Events on the Second Inter-monsoonal Rainfall in the Wet Zone of Sri Lanka

Authors:

A. B. Abeysekera ,

Department of Agriculture, Peradeniya, LK
About A. B.
Natural Resources Management Centre
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B. V. R. Punyawardena,

Department of Agriculture, Peradeniya, LK
About B. V. R.
Natural Resources Management Centre
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B. Marambe,

University of Peradeniya, LK
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Department of Crop Science, Faculty of Agriculture
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I. M. S. P. Jayawardena,

Department of Meteorology, Colombo, LK
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T. Sivananthawerl,

University of Peradeniya, LK
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Department of Crop Science, Faculty of Agriculture
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V. N. M. Wickramasinghe

Department of Agriculture, Peradeniya, LK
About V. N. M.
Natural Resources Management Centre
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Abstract

The climatic variations in the Indian Ocean have a strong relationship with the rainfall anomaly of Sri Lanka. Indian Ocean Dipole (IOD) is an ocean-atmospheric coupled phenomenon associated with an east-west gradient in the tropical Indian Ocean Sea Surface Temperature (SST) anomalies. Identifying the impact of IOD phenomenon on the spatial and temporal variation of the rainfall pattern is a useful tool for seasonal climate forecasting. The present study examined the influence of IOD on the Second Inter-monsoon (SIM) rains of the Wet zone (WZ) of Sri Lanka. Considering 16 rain-gauge locations scattered in the WZ of Sri Lanka covering nine Agro-ecological Regions (AERs), daily rainfall time series for 44-years (1976-2019) were collected. The IOD-positive and IOD-negative years were extracted based on the Dipole Mode Index (DMI) over the neutral years. Five rainfall indices, namely, cumulative rainfall, the maximum rainfall received within a day, number of wet days, heavy rainfall events and the maximum consecutive dry days were statistically analysed. The results revealed a significant positive anomaly of mean cumulative rainfall in the SIM season during the IOD-positive years while in IOD-negative years this anomaly was negative (p<0.05). An apparent increase or decrease of number of wet days and heavy rainfall events was observed during IOD-positive or IOD-negative years, respectively. However, the mean maximum consecutive dry days showed a distinct negative anomaly with the positive IOD events and positive anomaly with the negative IOD events. Further investigations are suggested to elucidate the El Niño Southern Oscillation (ENSO)-induced anomalous variation over IOD impacts.
How to Cite: Abeysekera, A.B., Punyawardena, B.V.R., Marambe, B., Jayawardena, I.M.S.P., Sivananthawerl, T. and Wickramasinghe, V.N.M., 2021. Effect of Indian Ocean Dipole (IOD) Events on the Second Inter-monsoonal Rainfall in the Wet Zone of Sri Lanka. Tropical Agricultural Research, 32(3), pp.287–297. DOI: http://doi.org/10.4038/tar.v32i3.8492
Published on 30 Jul 2021.
Peer Reviewed

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