Pante Macassar

Savu Sea Suai

Timor Sea

Current and future climate of -Leste

> Timor-Leste National Directorate of Meteorology and Geophysics > Australian Bureau of Meteorology > Commonwealth Scientific and Industrial Research Organisation (CSIRO) Timor-Leste’s current climate

In Dili the temperatures in the warmest months are about 2.5ºC warmer than a natural climate pattern that occurs those in July, the coldest month. Temperature is strongly tied to changes in across the tropical Pacific Ocean and the surrounding ocean temperature. Dili has a very marked wet season from affects weather around the world. December to May and a dry season from June to November. For most of the There are two extreme phases of the wet season average monthly rainfall is above 100 mm per month while for most El Niño–Southern Oscillation: El Niño of the dry season it is less than 30 mm per month. and La Niña. There is also a neutral phase. El Niño events generally bring Timor-Leste’s climate is affected by the very dry to very wet conditions. The drier conditions to Dili, and often lead West Pacific Monsoon, which is driven normal south-easterly trade winds in to a late onset and early finish to the by large differences in temperature Dili are replaced by westerly winds wet season. During La Niña events, between the land and the ocean. It from the monsoon onset until the dry season rainfall tends to be above moves north to mainland Asia during end of the monsoon season. normal, and the wet season often starts the Southern Hemisphere winter and earlier and finishes later. The Indian Year to year variations in Timor-Leste’s south to Australia in the Southern Ocean Dipole is a climate pattern that climate are due to the El Niño–Southern Hemisphere summer. Its seasonal affects weather around the Indian Oscillation and the Indian Ocean Dipole. arrival usually brings a switch from Ocean basin. During a positive phase The El Niño–Southern Oscillation is of the Indian Ocean Dipole dry season rainfall in Dili is lower than normal. Sea surface temperature 35 200 Dili, Timor-Leste, 125.57ºE, 8.57ºS Floods and droughts 30 150 During La Niña years above- normal rainfall leads to increased flooding and landslides in Timor- Leste, while El Niño years are 25 100 associated with droughts. The

Temperature (ºC) most significant impact on the

Monthly rainfall (mm) population during El Niño years is

0 reduced ground water availability. 20 05 15 Jan Apr Jul Oct Figure 1: Seasonal rainfall and temperature at Dili. Timor-Leste National Directorate National Directorate Timor-Leste and Geophysics of Meteorology

Flooding in Dili during 2010/11 La Niña.

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 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 0 180 11 12 0 13 0 14 0 15 0 16 0 17 0 17 0 16 0 15 0 14 0 Figure 2: The average positions of the major climate features in 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.

2.5 Tropical Tropical cyclones 11-yr moving average 2 cyclones Tropical cyclones can 1.5 affect Timor-Leste between 1 November and April, however their effect tends to be weak. 0.5 In the 41-year period between 1969 and 2010, 31 tropical No. of tropical cyclones 0 cyclones passed within 400 km of Dili, an average

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 of less than one cyclone Figure 3: Number of tropical cyclones passing within 400 km of Dili. per season (Figure 3). Eleven-year moving average in purple.

3 Timor-Leste’s changing climate

Temperatures and Sea level has risen Ocean acidification rainfall are changing As ocean water warms it expands has been increasing causing the sea level to rise. The Air temperature data for Dili are About one quarter of the carbon dioxide melting of glaciers and ice sheets only available from 2003 which emitted from human activities each year also contributes to sea-level rise. makes it impossible to establish is absorbed by the oceans. As the extra temperature trends. However, sea Instruments mounted on satellites and carbon dioxide reacts with sea water surface temperature in the Timor- tide gauges are used to measure sea it causes the ocean to become slightly Leste region has increased by level. Satellite data indicate the sea level more acidic. This impacts the growth 0.15–0.2°C per decade over the has risen near Timor-Leste by about of corals and organisms that construct period 1950–2009. It is likely that 9 mm per year since 1993. This is larger their skeletons from carbonate minerals. air temperature has increased by a than the global average of 2.8–3.6 mm These species are critical to the balance similar amount over the same period. per year. This higher rate of rise may of tropical reef ecosystems. Data show be partly related to natural fluctuations that since the 18th century the level Annual and dry season rainfall data that take place year to year or decade of ocean acidification has been slowly show a trend of decreasing rainfall from to decade caused by phenomena such increasing in Timor-Leste’s waters. 1952–2009 (Figure 4). However, as ten as the El Niño-Southern Oscillation. years of data are missing and annual This variation in sea level can be seen rainfall ranges from less than 200 mm in Figure 6 which includes data since to over 1400 mm, the confidence 1984 from Timor-Leste’s closest in this long-term trend is low. tide gauge (at Wyndham in Western Australia) and satellite data since 1993.

1600 El Niño La Niña 1400

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0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year

Figure 4: Annual rainfall for Dili Airport. Light blue bars indicate El Niño years, dark blue bars indicate La Niña years and the grey bars indicate Fishing off Dili coast. neutral years.

4 Timor-Leste’s future climate

Climate impacts almost all aspects of life in Timor-Leste. Understanding the possible future climate of Timor-Leste 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

rapid introduction of new and more t r climate slightly differently. Scientists from 1990 500 efficient technologies. Greenhouse e n the Pacific Climate Change Science 400

gas and aerosol emissions scenarios on c Program (PCCSP) have evaluated 24 300 C

are used in climate modelling to 2

models from around the world and found O provide projections that represent that 18 best represent the climate of the C a range of possible futures. western tropical Pacific region. These Figure 5: Carbon dioxide (CO2) 18 models have been used to develop The climate projections for concentrations (parts per million, ppm) climate projections for Timor-Leste. Timor-Leste are based on three associated with three IPCC emissions IPCC emissions scenarios: low (B1), scenarios: low emissions (B1 – blue), The future climate will be determined medium (A1B) and high (A2), for time medium emissions (A1B – green) and by a combination of natural and human periods around 2030, 2055 and 2090 high emissions (A2 – purple). The factors. As we do not know what the (Figure 5). 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. 2030, 2055 and 2090 (shaded). or scenarios, in climate models. The

Coastline, Dili district. Flooding, Dili 2011.

5 Timor-Leste’s future climate

This is a summary of climate projections for Timor-Leste. For further information refer to Volume 2 of Climate Change in the Pacific: Scientific Assessment and New Research, and the web-based climate projections tool – Pacific Climate Futures (available at www.pacificclimatefutures.net).

Temperatures will Changing rainfall Less frequent continue to increase patterns tropical cyclones Projections for all emissions scenarios There is uncertainty around rainfall On a global scale, the projections indicate that the annual average projections as model results are not indicate there is likely to be a decrease air temperature and sea surface consistent. However, projections in the number of tropical cyclones by temperature will increase in the future generally suggest a decrease in dry the end of the 21st century. But there is in Timor-Leste (Table 1). By 2030, season rainfall and an increase in likely to be an increase in the average under a high emissions scenario, this wet season rainfall over the course maximum wind speed of cyclones increase in temperature is projected of the 21st century. Wet season by between 2% and 11% and an to be in the range of 0.4-1.0°C. increases are consistent with the increase in rainfall rates of about 20% expected strengthening of the West within 100 km of the cyclone centre. More very hot days Pacific Monsoon. Little change is projected in the frequency of In the Timor-Leste region, projections Increases in average temperatures droughts throughout this century. tend to show a decrease in the will also result in a rise in the number frequency of tropical cyclones by the of hot days and warm nights, and late 21st century. a decline in cooler weather. More extreme rainfall days Table 1: Projected annual average air temperature changes for Timor-Leste Model projections show extreme rainfall for three emissions scenarios and days are likely to occur more often. three time periods. Values represent 90% of the range of the models and changes are relative to the average of the period 1980-1999.

2030 2055 2090 (°C) (°C) (°C) Low 0.3–1.1 0.5–1.7 0.8–2.2 emissions scenario Medium 0.4–1.2 0.9–2.1 1.4–3.2 emissions scenario High 0.4–1.0 1.0–1.8 2.1–3.5 emissions scenario Taking temperature observations, National Directorate of Meteorology and Geophysics.

Monsoon season conditions, Dili.

6 Sea level will Table 2: Sea-level rise projections Ocean acidification for Timor-Leste for three emissions continue to rise scenarios and three time periods. will continue Values represent 90% of the range of Sea level is expected to continue Under all three emissions scenarios the models and changes are relative to to rise in Timor-Leste (Table 2 and (low, medium and high) the acidity the average of the period 1980-1999. Figure 6). By 2030, under a high level of sea waters in the Timor-Leste emissions scenario, this rise in sea 2030 2055 2090 region will continue to increase over the level is projected to be in the range of (cm) (cm) (cm) 21st century, with the greatest change 6-15 cm. The sea-level rise combined under the high emissions scenario. Low 6–15 10–27 17–47 with natural year-to-year changes The impact of increased acidification emissions will accentuate the impact of storm scenario on the health of reef ecosystems is surges and coastal flooding. As there likely to be compounded by other is still much to learn, particularly how Medium 6–15 12–30 21–59 stressors including coral bleaching, emissions large ice sheets such as Antarctica storm damage and fishing pressure. scenario and Greenland contribute to sea-level rise, scientists warn larger rises than High 6–15 12–29 22–62 currently predicted could be possible. emissions scenario

90 Figure 6: Observed and projected Reconstruction relative sea-level change near Timor- 80 Leste. The observed sea-level records Satellite altimeter are indicated in dark blue (relative tide- 70 Tide gauge gauge observations from Wyndham Projections 60 in Western Australia) and light blue (the satellite record since 1993). 50 Reconstructed estimates of sea level near Timor-Leste (since 1950) are 40 shown in purple. The projections for 30 the A1B (medium) emissions scenario (representing 90% of the range of 20 models) are shown by the shaded 10 green region from 1990 to 2100. Sea level relative to 1990 (cm) The dashed lines are an estimate of 0 90% of the range of natural year- to-year variability in sea level. −10

−20

−30 1950 2000 2050 2100 Year

7 Changes in Timor-Leste’s climate

> Temperatures have > Rainfall data for Dili > By the end of this > Sea level near Timor- > Ocean acidification warmed and will Airport show a clear century projections Leste has risen has been increasing continue to warm decreasing trend in suggest decreasing and will continue in Timor-Leste’s with more very hot annual and dry season numbers of tropical to rise throughout waters. It will days in the future. rainfall since 1952, cyclones. this century. continue to increase however, there are data and threaten coral gaps. Rainfall patterns reef ecosystems. are projected to change over this century with more extreme rainfall days but little change in drought frequency.

The content of this brochure is the result of a collaborative effort between the Timor- Contact the Timor-Leste Leste National Directorate of Meteorology and Geophysics and the Pacific Climate National Directorate of Change Science Program – a component of the Australian Government’s International Meteorology and Geophysics: Climate Change Adaptation Initiative. This information and research conducted by the web: www.dnmg.gov.tl Pacific Climate Change Science Program builds on the findings of the 2007 IPCC Fourth Assessment Report. For more detailed information on the climate of Timor-Leste and the email: [email protected] Pacific region see: Climate Change in the Pacific: Scientific Assessment and New Research. phone: +670 3331092 Volume 1: Regional Overview. Volume 2: Country Reports. Available from November 2011. © Pacific Climate Change Science www.pacificclimatechangescience.org Program partners 2011.