Chapter 6. Kiribati
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Jill Key Chapter 6 Kiribati 113 6.1 Climate Summary 6.1.1 Current Climate • Wind-waves in Kiribati are strongly • Average rainfall is projected to influenced by both north-easterly increase (high confidence), along • Warming trends are evident in and south-easterly trade winds with more extreme rain events (high both annual and half-year mean air seasonally, and the location of the confidence); temperatures at Tarawa from 1950. South Pacific Convergence Zone • Droughts are projected to decline in • At Kiritmati, in eastern Kiribati, (SPCZ), with some effect of the El frequency (medium confidence); there has been an increase in Niño–Southern Oscillation (ENSO) • Ocean acidification is expected to November–April rainfall since 1946. interannually. There is little variation continue (very high confidence); This implies either a shift in the in wave climate across the country. mean location of the Inter-Tropical Available data are not suitable • The risk of coral bleaching Convergence Zone (ITCZ) towards for assessing long-term trends will increase in the future (very Kiritimati and/or a change in the (see Section 1.3). high confidence); intensity of rainfall associated with • Sea level will continue to rise (very the ITCZ. The remaining annual and 6.1.2 Climate high confidence); and seasonal rainfall trends for Kiritimati • Wave height is projected to and Tarawa and the extreme Projections decrease in December–March (low rainfall trends for Tarawa show For the period to 2100, the latest confidence), waves may be more little change. global climate model (GCM) directed from the south in October • At Kiritmati, in eastern Kiribati, projections and climate science (low confidence). there has been an increase in findings indicate: November–April rainfall since 1946. • El Niño and La Niña events will This implies either a shift in the continue to occur in the future (very mean location of the ITCZ towards high confidence), but there is little Kiritimati and/or a change in the consensus on whether these events intensity of rainfall associated with will change in intensity or frequency; the ITCZ. The remaining annual and seasonal rainfall trends for Kiritimati • Annual mean temperatures and and Tarawa and the extreme extremely high daily temperatures rainfall trends for Tarawa show will continue to rise (very little change. high confidence); 114 Climate Variability, Extremes and Change in the Western Tropical Pacific: New Science and Updated Country Reports 6.2 Data Availability There are currently five operational 1909 but closed in 1993. Tarawa, Beru Pacific Climate Change Data Portal meteorological stations in Kiribati. and Kanton (also known as Canton) www.bom.gov.au/climate/pccsp/. Tarawa, the primary station, is located have temperature records from 1947. Wind-wave data from buoys are on the southern side of Tarawa Some temperature data are available particularly sparse in the Pacific region, Atoll at Betio in the Gilbert Islands. for Kiritimati but these records are with very short records. Model and Kiritimati, the primary station in the insufficient for analysis. reanalysis data are therefore required Line Islands, is situated on the north- Tarawa rainfall from 1947, air to detail the wind-wave climate of west side of the Kiritimati Atoll. All temperature from 1950, and Kiritimati the region. Reanalysis surface wind five operational stations, including monthly rainfall from 1946, have been data have been used to drive a wave Banaba and Tabuaeran, have rainfall used in this report. These records are model over the period 1979–2009 to records which begin between 1909 homogeneous. Additional information generate a hindcast of the historical and 1945. Banaba has the earliest on historical climate trends in the wind-wave climate. temperature record which began in Kiribati region can be found in the 6.3 Seasonal Cycles Information on temperature and rainfall Waves in the Gilbert Islands are season, December–March, waves at seasonal cycles can be found in strongly characterised by trade Tarawa have a slightly larger height Australian Bureau of Meteorology and winds, with waves coming from the and longer period than in other months CSIRO (2011). north-east to east in December–March (mean height around 1.8 m and and the east and south-east during period around 8.7 s) (Figure 6.1 and June–September. Table 6.1). In the southern trade wind 6.3.1 Wind-driven season, June–September, waves have Phoenix Islands similarly experience Waves a slightly shorter period (mean around waves characterised by trade winds, 8.3 s) and lower height (mean around Surface wind-wave driven processes but with northerly swell in December– 1.4 m) than December–March (Table can impact on many aspects of Pacific March from north Pacific-generated 6.1). These waves consist of locally Island coastal environments, including: storm waves, and south-east swell in generated trade wind waves from the coastal flooding during storm wave June–September. east and north-east in December– events; coastal erosion, both during Waves in the Line Islands are similar, March and from the east and south- episodic storm events and due to being from the north-east to east in east during June–September, as well long-term changes in integrated December–March and slightly south of as trade wind induced swell, and wave climate; characterisation of east in June–September due to trade some swell propagating from extra- reef morphology and marine habitat/ winds, with swell from the north-west tropical storms in the North Pacific and species distribution; flushing and to north-east in December–March Southern Ocean. Waves larger than circulation of lagoons; and potential resulting from north Pacific storms, 2.5 m (99th percentile) occur usually shipping and renewable wave energy and south to south-easterly swell in from the east-northeast, in any month, solutions. The surface offshore June–September. with some large west and north- wind-wave climate can be described westerly waves due to extra-tropical by characteristic wave heights, lengths In the west, e.g. off the south-east storms in the north Pacific in northern or periods, and directions. coast of Tarawa, waves are winter months. The height of a 1-in-50 characterised by variability of the The wind-wave climate of Kiribati year wave event at the south-east trade winds, both north and south, shows only a little spatial variability coast of Tarawa is calculated to with some swell from extra-tropical across the region despite its be 3.6 m. storms. During the northern trade wind large extent. Chapter 6: Kiribati 115 In the east, e.g. off the north-west There is no significant variation in power at Tarawa is around 35% coast of Kiritimati, waves are wave period. Waves larger than 2.6 m greater than during El Niño years in characterised by trade winds (99th percentile) at Kiritimati occur June–September but slightly less seasonally. Waves come from the predominantly during December– in December–March, with waves north-east during the northern trade March and have periods of between more strongly directed from the east, wind season, December–March, with 9 and 17s, usually directed from the associated with increased trade wind some small south-easterly waves, north due to North Pacific storms, speeds. To the north-west of Kiritimati, and both north-east and north-west with some large waves directed from wave power is slightly greater during swell from trade winds and extra- the south observed during other La Niña years in June–September tropical storms. Most south-east trade months (February, April-June) and from than in El Niño years, but is ~20% less wind waves in June–September are the west in February and October. in December–March than in El Niño blocked by the island, with some small The height of a 1-in-50 year wave years. Due to increased trade winds, locally generated trade wind waves, event is calculated to be 3.9 m. waves are directed more from the east and southerly swell from Southern in La Niña years. Location of the SPCZ No suitable dataset is available to Ocean storms observed (Figure 6.2). over a region may suppress locally assess long-term historical trends in Wave heights also vary seasonally, generated waves. When the Southern the Kiribati wave climate. However, reaching a maximum height in Annular Mode (SAM) index is negative, interannual variability may be assessed December–March (mean wave waves at Kiritimati are directed more in the hindcast data. The wind-wave height 1.8 m), with smaller average from the west in December–March climate displays interannual variability waves in June–September (seasonal due to propagation of swell from at both Tarawa and Kiritimati, varying mean wave height 1.4 m) (Table 6.1). increased mid-latitude storms in the with the El Niño–Southern Oscillation Southern Ocean. (ENSO). During La Niña years, wave Table 6.1: Mean wave height, period and direction from which the waves are travelling around Kiribati in December–March and June– September. Observation (hindcast) and climate model simulation mean values are given for Kiribati with the 5–95th percentile range (in brackets). Historical model simulation values are given for comparison with projections (see Section 6.5.6 – Wind-driven waves, and Tables 6.8, 6.9 and 6.10). A compass relating number of degrees to cardinal points (direction) is shown. Hindcast Climate Model Climate Model Hindcast Climate Model Reference Simulations Simulations Reference Data Simulations Data (1979 (1986–2005) – (1986–2005) – (1979–2009), (1986–2005) – 2009),Tarawa