Marine Atlas: Maximizing Benefits for Tonga

STORMY TIMES: CYCLONES Tropical cyclones pose direct threats to Tonga, its people and its marine life. Marine and coastal habitats including mangroves, seagrasses and coral reefs play an important role in offering effective protection and therefore need to be sustainably managed and conserved.

While it has a lower number of cyclones than some of its neighbouring countries to the west, Tonga is still heavily affected by tropical cyclones. One of the most recent of these, Tropical Cyclone Gita, was the most intense cyclone to hit Tonga since records began. It caused extensive damage on the islands of Tongatapu and ‘Eua, including in the capital Nuku’alofa, where many homes were either damaged or destroyed. Cyclones are monitored by the Regional Special- ized Meteorological Centre of the Fiji Meteorolog- ical Service, located in Nadi. In Tonga, the Tongan Meteorological and Coastal Radio Service provide warnings about tropical cyclones. Tropical cy- clones are categorized according to the Australian

ceives 1.6–1.9 cyclones per season. El Niño brings a heightened risk of cyclones.

Very vulnerable Tonga Not only is the Kingdom of Tonga situated within the Ring of Fire in the Pacific Ocean, but most of its atoll islands, including Tongatapu, are flat, with an average elevation of 2–5 metres. Thus, the country is very vulnerable to storm surges that accompany tropical cyclones, tsunami inundation and flooding from heavy rainfall. A joint Commonwealth Secretariat and World Bank study conducted in 1999, which examined the vulnerability of 111 countries to the effects of natural disasters, ranked Tonga as being “very vulnerable”. In the 25 years prior to 1999, Tonga was the second-most affected country (in terms of percentage of population) by natural disasters of all the countries in the study. Since the 1960s, four cyclones (in statistical terms, approximately and South Pacific Category System from category 1 (90 km/h gusts) to category 5 (280 km/h gusts). The cyclone season is considered to run from the beginning of November to the end of April, but de- structive cyclones can occur outside this period. The formation of cyclones in the region is strongly influenced by the ENSO (see also chapters “Go with the flow” and “Hotter and higher”). During El Niño years, cyclones are more likely to form

between 6°S and 18°S and 170°E and 170°W. Dur- ing La Niña years, slightly fewer tropical cyclones form and the origin moves to the south of Tonga (Chand and Walsh 2009). Therefore, although there is not a great deal of difference between El Niño and La Niña years, the northern Tongan islands have a lower incidence of cyclone strike during La Niña conditions than the southern Tongan islands (Chand and Walsh, 2009). On average, Tonga re- one per decade) have very severely affected Ton- ga, causing extensive damage to crops and food supply, buildings (residential and commercial), tourist resorts and infrastructure (electricity sup- ply and roads), and disrupting essential services. Tropical Cyclones Isaac (1982) and Waka (2001) resulted in seven fatalities. Estimates of damage caused range from approximately US$20 million (1982) to US$48 million (2001), representing in excess of 20 per cent of GDP in those two years. The recent Tropical Cyclone Gita in 2018 (above) was reported to be the strongest of all tropical cyclones ever to hit Tonga, with winds reaching 233 kilometres per hour, causing severe dam- age to crops, houses, infrastructure and much more worth several million US dollars.

In the past decade, there has been increasing at- tention on the relationship between climate change and the frequency and intensity of cyclones in the region. Diamond et al. (2013) found a statistically significant increase in the number and intensity of cyclones in the period 1991–2010 compared with the period 1970–1990. Rising SSTs are fuelling cyclones (see also chapters “Hotter and higher”) that are resulting in increasing damage, including to Tonga’s valuable coastal habitats. At the same time, conserving coastal habitats, such as coral reefs and mangroves, offers a very effective form of protection against storms. In this way, Tonga can strengthen its defences against cyclones like Gita.

MAXIMIZING BENEFITS FOR TONGA

CLIMATE CHANGE THREATS

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