Links between the Southern Oscillation Index and Hydrological Hazards on a Tropical Pacific Island

Abstract

River floods and hydrological droughts (low stream water resources) are a recurrent problem in different parts of Fiji, causing disruption and hardship for many rural communities. These extremes in fluvial behavior are associated with large seasonal variability in rainfall, generated by intense tropical storms in the wet season and prolonged rain failure in the dry season. Such conditions are linked to the influence of El Nino/Southern Oscillation (ENSO) in the Southwest Pacific. The Southern Oscillation Index (SOl) is the climatic measure of the strength of ENSO activities and shows good correspondence with (1) tropical cyclone flood magnitude and (2) critically low stream discharges after a 2-month time lag, in two of Fiji's main river systems. IfENSO conditions become more frequent or sustained in the future as some climate models suggest, then the SOl will be a useful tool for projecting in advance the severity of hydrological hazards, which can assist in disaster mitigation and management. ON THE INTERANNUAL timescale, the El Nino/Southern Oscillation (ENSO) is our planet's most powerful climatic phenomenon (Hilton 1998). At intervals of about 5-7 yr, there is a disturbance in the Walker atmospheric circulation over the Pacific Ocean and a weakening of the southeast trade winds. This causes a large pool of warm ocean water usually centered around New Guinea to surge eastward across the equatorial Pacific (Congbin Fu et al. 1986). This disturbance to the Pacific Ocean and atmospheric system, called El Nino, lasts for more than a year and brings droughts, prolonged wet conditions, 1 Financial support provided by the University of the South Pacific and the Natural Sciences and Engineering Research Council of Canada. Manuscript accepted 13