Stimulating investment in pearl farming in ... - World Fish Center

Water Temperature and Cyclone Frequency in the Pacific: Implications for Pearl Farming Final, June 2008Cyclone ActivityTropical cyclones are non-frontal low pressure systems characterised by sustained gale forcewinds in excess of 63 km/h and wind gusts greater than 90 km/h near their centre and thatpersist for at least six hours. They vary in intensity, life cycle, pattern of movement, size andimpact. Their activity and intensity also varies within seasons, between years, decades andover multi-decadal timescales. In the Australian/Southwest Pacific basin, tropical cyclonesgenerally occur between late October/early November and early May and peak in lateFebruary/early March. The total number of tropical cyclones per year varies markedly,with two events being recorded in this basin in 1981 and 16 in 1971. The annual variation incyclone numbers has been linked with local sea surface temperature before and at the startof the cyclone season and the El Niño-Southern Oscillation (ENSO) phenomenon.The frequency of tropical cyclones also varies spatially. Between 1970/1971 and 2003/2004,the South Pacific region experienced 8.6 cyclones on average per season, 4.1 of which weresevere and 1.7 intense, whereas the Australian region experienced 12.8 cyclones per season,6.3 of which were severe and 2.5 intense. The South Pacific region was also exposed totropical cyclones and severe cyclones for fewer days on average than the Australian region.The frequency of cyclones also varies across the South Pacific, with the greatest number onaverage occurring around Vanuatu, followed in turn by Fiji, the Cook Islands, FrenchPolynesia and the Solomon Islands. Cyclones rarely hit Papua New Guinea. In Australia,tropical cyclones are more frequent in the northwest, between Exmouth Gulf and Broome,and in northeast Queensland, between Port Douglas and Maryborough. In widespreadnations, such as French Polynesia, the risk of cyclones varies across the archipelagos.During El Niño years, there is a marked shift in the regional pattern of cyclone risk, withactivity being greater than on average in the vicinity of Vanuatu, Fiji, the Cook Islands andFrench Polynesia, of similar incidence in the Solomon Islands, but less frequent off the northAustralian coast. During La Niña years, cyclones are more common than on average in thevicinity of Vanuatu, New Caledonia and the South Coral Sea, but not evident beyondlongitude 150° W. Whilst cyclones are clearly less frequent in Solomon Islands than in mostpearl farming areas, it is not possible, on the basis of our current knowledge, to determinewhether pearl farming would be more advantageous in Solomon Islands than in other SouthPacific nations.The occurrence and intensity of tropical cyclones may change with global warming. InAustralia, there is expected to be a decrease in total number of tropical cyclones per year, butan increase in the proportion of the more intense categories of cyclones. Cyclones that hitthe east coast are expected to persist longer than at present. In the South Pacific, there isexpected to be little change in cyclone frequency, but an increase in their intensity andlifespan. Tropical cyclones are also expected to spread further east and track further souththan at present.The gale force winds accompanying cyclones can cause extensive property damage, turnairborne debris into missiles and generate rough seas. The heavy rainfall that occurs as thecyclone passes over can cause extensive flooding, which, in turn, can result in extensivedamage. The storm surge that accompanies some tropical cyclones is another potentiallydestructive phenomenon, particularly if it coincides with high tide.The impact of tropical cyclones on the physical environment depends on their frequency,intensity, speed of movement, longevity, size and proximity to land. The physical featuresof the landscape also influence their response to the geomorphic and hydrological processestriggered by cyclones. Low-lying coral islands, such as the atolls of Cooks Islands andFrench Polynesia, are prone to overtopping by storm surge and wave action generated byThe Ecology Lab Pty Ltd – Marine and Freshwater StudiesPage iii