Savai’i South Pacific Ocean Apolima APIA Upolu ApolimaManono Strait South Pacific Ocean Namu’a Nu’utele Nu’ulua Current and future climate of Samoa > Samoa Meteorology Division, Ministry of Natural Resources and Environment > Australian Bureau of Meteorology > Commonwealth Scientific and Industrial Research Organisation (CSIRO) Samoa’s current climate Temperatures in Samoa are generally consistent throughout the year, with only very small seasonal differences (Figure 1). Average temperatures are coolest Floods and in July, when the cool, dry south-east trade winds are strongest. The warmest month is March. The country has two distinct seasons – a wet season from droughts November to April and a dry season from May to October. On average 75% Droughts and flooding of Samoa’s total annual rainfall occurs in the wet season. associated with the El Niño- Southern Oscillation have Samoa’s rainfall is greatly influenced by Samoa’s climate varies considerably impacted the socio-economic the position and strength of the South from year to year due to the El Niño- livelihoods of the Samoan people Pacific Convergence Zone. This band of Southern Oscillation. This is a natural on many occasions in the past. heavy rainfall is caused by air rising over climate pattern that occurs across warm water where winds converge, the tropical Pacific Ocean and affects Flooding associated with resulting in thunderstorm activity. It weather around the world. There are tropical cyclones and strong extends across the South Pacific Ocean two extreme phases of the El Niño- La Niña events has caused from the Solomon Islands to the Cook Southern Oscillation: El Niño and widespread damage in Samoa Islands and lies between Samoa and La Niña. There is also a neutral in the past, particularly in Fiji during the wet season (Figure 2). phase. In Samoa, El Niño events Apia. In early 2008 and 2011, tend to bring wet seasons that are for example, transportation Samoa’s mountains have a significant drier than normal, while La Niña infrastructure and water supplies effect on rainfall distribution. Wetter events usually bring wetter and were severely damaged. areas are located in the south-east and cooler than normal conditions. relatively sheltered, drier areas in the Drought impacts are most north-west. notable in the north-west regions of the main islands and at times Maximum temperature Average temperature are associated with forest fires. Minimum temperature Sea surface temperature In Asau, there were major forest 35 Apia, Samoa,171.78ºW, 13.80ºS 500 fires during the dry seasons of 1982-83, 1997-98, 2001-02 and 2002-03. 400 30 300 25 Temperature (ºC) 200 Monthly rainfall (mm) 20 Sunny Seuseu, Meteorology Division, Ministry Environment and Resources Natural of 100 2008 flood, Apia. 0 15 Jan Apr Jul Oct Figure 1: Seasonal rainfall and temperature at Apia. 2 N H o N 20 o Federated States of Micronesia Palau Marshall Islands o n e I n t e r t r o p i c a l C o n v e r g e n c e Z Kiribati 10 o W a Nauru 0 r m p Tra de W inds o o l S o Papua New Guinea u M o t h Tu valu n Solomon Islands S s o P o East Timor o n a c i f i c C o n v e Samoa r g Vanuatu Fiji e n Niue c e S 10 Z o o To nga Cook Islands n e S 20 H o 0 500 1,000 1,500 2,000 30 Kilometres o E E E E E E E W W W W o o o o o o o o o o o 0 0 0 0 0 0 0 0 0 0 0 180 11 12 13 14 15 16 17 17 16 15 14 Figure 2: The average positions of the major climate features from November to April. The arrows show near surface winds, the blue shading represents the bands of rainfall convergence zones, the dashed oval shows the West Pacific Warm Pool and H represents typical positions of moving high pressure systems. 6 Tropical Tropical cyclones 11-yr moving average 5 cyclones 4 Tropical cyclones affect Samoa 3 between November and April. In the 41-year period between 2 1969 and 2010, 52 tropical 1 cyclones passed within 400 km No. of tropical cyclones of Apia, an average of one 0 cyclone per season (Figure 3). The number of cyclones varies 1969/701971/72 1973/74 1975/76 1977/78 1979/80 1981/82 1983/84 1985/86 1987/88 1989/90 1991/92 1993/94 1995/96 1997/98 1999/00 2001/02 2003/04 2005/06 2007/08 2009/10 greatly from year to year, with Figure 3: Number of tropical cyclones passing within 400 km of Apia. none in some seasons but up Eleven-year moving average in purple. to five in others. Over the period 1969–2010, cyclones occurred more frequently in El Niño years. 3 Samoa’s changing climate Temperatures Sea level has risen Ocean acidification have increased As ocean water warms it expands has been increasing causing the sea level to rise. The Annual maximum and minimum About one quarter of the carbon dioxide melting of glaciers and ice sheets temperatures have increased in emitted from human activities each year also contributes to sea-level rise. Samoa since 1950 (Figure 4). In Apia, is absorbed by the oceans. As the extra maximum temperatures have increased Instruments mounted on satellites and carbon dioxide reacts with sea water at a rate of 0.22°C per decade. These tide gauges are used to measure sea it causes the ocean to become slightly temperature increases are consistent level. Satellite data indicate the sea level more acidic. This impacts the growth with the global pattern of warming. has risen near Samoa by about 4 mm of corals and organisms that construct per year since 1993. This is slightly larger their skeletons from carbonate minerals. Apia’s rainfall than the global average of 2.8–3.6 mm These species are critical to the balance unchanged per year. This higher rate of rise may of tropical reef ecosystems. Data be partly related to natural fluctuations show that since the 18th century the Data since 1950 for Apia show no that take place year to year or decade to level of ocean acidification has been clear trends in annual or seasonal decade caused by phenomena such slowly increasing in Samoa’s waters. rainfall (Figure 5) but, over this period as the El Niño-Southern Oscillation. there has been substantial variation This variation in sea level can be seen in rainfall from year to year. in Figure 7 which includes the tide gauge record since 1950 and the satellite data since 1993. 27.5 El Niño La Niña 27 26.5 emperature (ºC) 26 T 25.5 Average 25 1950 1955 1960 1965 1970 1975 Year1980 1985 1990 1995 2000 2005 Figure 4: Annual average temperature for Apia. Light blue bars indicate El Niño years, dark blue bars indicate La Niña years and grey bars indicate neutral years. Taking temperature observations, 4500 El Niño La Niña Samoa Meteorology Division. 4000 3500 3000 2500 2000 Rainfall (mm) 1500 1000 500 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year Figure 5: Annual rainfall for Apia. Light blue bars indicate El Niño years, dark blue bars indicate La Niña years and the grey bars indicate neutral years. 4 Samoa’s future climate Climate impacts almost all aspects of life in Samoa. Understanding the possible future climate of Samoa is important so people and the government can plan for changes. How do scientists develop climate projections? Global climate models are the best tools Intergovernmental Panel on Climate for understanding future climate change. Change (IPCC) developed a series of Climate models are mathematical plausible scenarios based on a set of representations of the climate system assumptions about future population that require very powerful computers. changes, economic development and They are based on the laws of physics technological advances. For example, 2090 and include information about the the A1B (or medium) emissions scenario 800 atmosphere, ocean, land and ice. envisages global population peaking mid-century and declining thereafter, 2055 700 There are many different global climate 600 very rapid economic growth, and 2030 tion (ppm) models and they all represent the a r rapid introduction of new and more t climate slightly differently. Scientists from 1990 500 n efficient technologies. Greenhouse e the Pacific Climate Change Science 400 c gas and aerosol emissions scenarios on Program (PCCSP) have evaluated 24 C 300 are used in climate modelling to 2 models from around the world and O provide projections that represent found that 18 best represent the climate C a range of possible futures. of the western tropical Pacific region. Figure 6: Carbon dioxide (CO2) These 18 models have been used to The climate projections for Samoa concentrations (parts per million, ppm) develop climate projections for Samoa. are based on three IPCC emissions associated with three IPCC emissions scenarios: low (B1), medium (A1B) scenarios: low emissions (B1 – blue), The future climate will be determined and high (A2), for time periods medium emissions (A1B – green) and by a combination of natural and human around 2030, 2055 and 2090 high emissions (A2 – purple). The factors. As we do not know what the (Figure 6). Since individual models PCCSP has analysed climate model future holds, we need to consider a give different results, the projections results for periods centred on 1990, range of possible future conditions, are presented as a range of values.