Eton Beach, West Efate Chapter 16 Vanuatu The contributions of Salesa Kaniaha and Philip Malsale from the Vanuatu Meteorology and Geo-hazard Department are gratefully acknowledged 243 Introduction This chapter provides a brief (e.g. the El Niño-Southern Oscillation) These projections are presented description of Vanuatu, its past and are analysed and discussed. Observed along with confidence levels based on present climate as well as projections trends and analysis of air temperature, expert judgement by Pacific Climate for the future. The climate observation rainfall, extreme events (including Change Science Program (PCCSP) network and the availability of tropical cyclones), sea-surface scientists. The chapter concludes atmospheric and oceanic data records temperature, ocean acidification, mean with a summary table of projections are outlined. The annual mean climate, and extreme sea levels are presented. (Table 16.4). Important background seasonal cycles and the influences of Projections for air and sea-surface information including an explanation large-scale climate features such as temperature, rainfall, sea level, ocean of methods and models is provided the South Pacific Convergence Zone acidification and extreme events in Chapter 1. For definitions of other and patterns of climate variability for the 21st century are provided. terms refer to the Glossary. 16.1 Climate Summary 16.1.1 Current Climate • The sea-level rise near Vanuatu • Little change is projected in annual measured by satellite altimeters mean rainfall (low confidence). • Temperatures in the since 1993 is about 6 mm per year. • The intensity and frequency of days warmest months in Vanuatu • Annual and seasonal rainfall trends of extreme heat are projected to (January-February) are about 4ºC for Port Vila and Aneityum for increase (very high confidence). higher than those in the coolest the period 1950–2009 are not months (July-August). • The intensity and frequency of days statistically significant. of extreme rainfall are projected to • Vanuatu has a marked wet season • On average Port Vila experiences increase (high confidence). from November to April. 23 tropical cyclones per decade, • Little change is projected • Vanuatu’s rainfall is strongly with most occurring in January in the incidence of drought influenced by the position and and February. The high interannual (low confidence). strength of the South Pacific variability in tropical cyclone • Tropical cyclone numbers are Convergence Zone. During summer numbers makes it difficult to identify projected to decline in the the South Pacific Convergence any long-term trends in frequency. Zone intensifies and moves further south-west Pacific Ocean south, bringing the higher rainfall of basin (0–40ºS, 130ºE –170ºE) the wet season. 16.1.2 Future Climate (moderate confidence). • Rainfall in Vanuatu varies Over the course of the 21st century: • Ocean acidification is projected to continue (very high confidence). greatly from year-to-year due • Surface air temperature and mainly to the influence of the sea-surface temperature are • Mean sea-level rise is projected to El Niño-Southern Oscillation. projected to continue to increase continue (very high confidence). • Warming trends are evident in (very high confidence). both annual and seasonal mean • Wet season rainfall is projected to air temperatures for Bauerfield increase (moderate confidence). Airport (Port Vila) for the period • Dry season rainfall is projected to 1950–2009. decrease (moderate confidence). 244 Climate Change in the Pacific: Scientific Assessment and New Research Volume| 2: Country Reports 16.2 Country Description The island archipelago of Vanuatu are characterised by rugged volcanic Most of Vanuatu’s population relies lies between 13°S-21°S and peaks and tropical rainforests. The on subsistence agriculture. Cocoa, 166°E–171°E and includes over highest peak, Mount Tabwemasana on copra and coffee exports contribute 80 islands. The largest island is Espiritu Santo, is 1877 m above mean to Vanuatu’s economy alongside Espiritu Santo while the island of sea level. tourism, logging and fishing. Efate is home to the capital, Port Vila Revenue from mineral extraction is Vanuatu’s population in 2009 was and the Vanuatu Government. relatively new to the economy and estimated at 234 023 of which Vanuatu has an Economic Exclusion may provide significant revenue in around 80% live in rural areas Zone of 710 000 km2 which the future (Vanuatu Country Profile, (Vanuatu Country Profile, SOPAC, encompasses Vanuatu’s total land SOPAC, 2000). 2000; Vanuatu National Statistics area of 12 190 km2. Larger islands Office, 2010). Figure 16.1: Vanuatu Chapter 16: Vanuatu 245 16.3 Data Availability There are currently 47 operational Records used include a composite years. Both satellite (from 1993) and in meteorological stations in Vanuatu. Iririki-Vila rainfall record, composite situ sea-level data (1950–2009; termed Multiple observations within a 24-hour air temperature Iririki-Vila-Bauerfield reconstructed sea level; Volume 1, period are taken at Sola, Pekoa, record and single site record from Section 2.2.2.2) are available on a Saratamata, Lamap, Bauerfield, Aneityum (southern Vanuatu) global 1° x 1° grid. Whitegrass and Analguahat. At three for the period 1950–2009. Long-term locally-monitored sea- climate stations, Lambubu, Lamap The Iririki-Vila-Bauerfield and Aneityum surface temperature data are and Aneityum, and at 39 rainfall records are homogeneous and more unavailable for Vanuatu, so large-scale stations across the country a single than 95% complete. gridded sea-surface temperature observation is taken daily at 9.00 am Oceanographic records do not datasets have been used (HadISST, local time. The primary climate cover such a long time period. HadSST2, ERSST and Kaplan stations are located at Port Vila and Monthly-averaged sea-level data are Extended SST V2; Volume 1, Bauerfield Airport on the island of available from Port Vila (1993–present). Table 2.3). Efate (Figure 16.1). Several stations, A global positioning system instrument including Iririki (Port Vila), have rainfall to estimate vertical land motion was data from the early 1900s. Iririki deployed at Port Vila in 2002 and also has the earliest air temperature will provide valuable direct estimates observations which began in the of local vertical land motion in future late 1940s. Climate data management training, Vanuatu Meteorology and Geo-hazard Department 246 Climate Change in the Pacific: Scientific Assessment and New Research Volume| 2: Country Reports 16.4 Seasonal Cycles The seasonal variations in rainfall and match those of air temperatures (SPCZ), which lies north of the country air temperature at both Port Vila (in and have a strong influence on the during the winter. During summer the the central region of Vanuatu) and air temperatures on the islands SPCZ intensifies and moves further Aneityum (in the south) are very similar of Vanuatu. south, bringing the higher rainfall (Figure 16.2). Being further south, of the wet season. Low pressure Both sites have a marked wet season mean monthly Aneityum temperatures systems embedded in the SPCZ often from November to April, with highest are about 2ºC cooler than those in become tropical cyclones during the rainfall from January to March, and Port Vila. Both sites have highest cyclone season. Topography also a dry season from May to October. temperatures in January-February, plays a role in the variations in rainfall The difference between seasons is with the coolest months (July-August) across some islands. During the wet slightly more marked in Port Vila as about 4ºC cooler than the warmest season, rainfall is particularly high Aneityum receives more rainfall from months. The cooler winter air on the windward (south-east) side extra-tropical influences such as temperatures are due to weaker solar of the mountain ranges of the bigger cold fronts during the dry season. radiation and the influence of high islands, and scarce during the dry Vanuatu’s rainfall is strongly influenced pressure cells bringing cold winds from season, especially on the leeward by the position and strength of the higher latitudes. Seasonal variations (north-west) sides. South Pacific Convergence Zone in sea-surface temperatures closely Figure 16.2: Mean annual cycle of rainfall (grey bars) and daily maximum, minimum and mean air temperatures at Port Vila (left) and Aneityum (right), and local sea-surface temperatures derived from the HadISST dataset (Volume 1, Table 2.3). Chapter 16: Vanuatu 247 16.5 Climate Variability Large variations in rainfall are Table 16.1: Correlation coefficients between indices of key large-scale patterns of observed in Vanuatu from year-to-year climate variability and minimum and maximum temperatures (Tmin and Tmax) and (Figure 16.4). The wettest years rainfall at Port Vila. Only correlation coefficients that are statistically significant at the receive up to three times more than 95% level are shown. the driest years. Much of this variability is linked to the El Niño-Southern Dry season Wet season Oscillation (ENSO). There are Climate feature/index (May-October) (November-April) significant correlations between Tmin Tmax Rain Tmin Tmax Rain ENSO indices and both rainfall and air ENSO Niño3.4 -0.41 -0.41 -0.45 -0.49 temperature in Vanuatu (Tables 16.1 Southern Oscillation Index 0.36 0.41 0.36 0.51 and 16.2). The impact of ENSO on Interdecadal Pacific Oscillation Index -0.28 climate in Port Vila and Aneityum Southern Annular Mode Index are similar: El Niño events tend to ENSO Modoki Index -0.40 -0.36 -0.26 -0.28 -0.45 bring a late start to the wet season Number of years of data 62 62 98 62 63 100 and lower rainfall in both the wet and dry seasons, as well as cooler conditions in the dry season. Opposite Table 16.2: Correlation coefficients between indices of key large-scale patterns of impacts are usually observed during climate variability and minimum and maximum temperatures (Tmin and Tmax) and La Niña events.