Climate of Australia

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The climate of Australia varies widely, but by far the largest part of Australia is desert or semi-arid – 40% of the landmass is covered by sand dunes. Only the south-east and south-west corners have a temperate climate and moderately fertile soil. The northern part of the country has a tropical climate: part is tropical rainforests, part grasslands, and part desert.

Rainfall is highly variable, with frequent droughts lasting several seasons thought to be caused in part by the El Niño-Southern Oscillation. Occasionally a duststorm will blanket a region or even several states and there are reports of the occasional large tornado. Rising levels of salinity and desertification in some areas is ravaging the landscape.

Australia's tropical/subtropical location and cold waters off the western coast make most of western Australia a hot desert with aridity, a marked feature of greater part of the continent. These cold waters produce precious little moisture needed on the mainland. A 2005 study by Australian and American researchers ^[1] investigated the desertification of the interior, and suggested that one explanation was related to human settlers who arrived about 50,000 years ago. Regular burning by these settlers could have prevented monsoons from reaching interior Australia.

Contents 1 Elements of Australia's climate 1.1 Air temperature 1.2 Atmospheric pressure 1.3 Precipitation 1.3.1 Snow 2 Regions 2.1 South-eastern temperate region 2.2 Central arid region 3 Natural hazards and disasters 3.1 Bushfires 3.2 Global warming 3.3 Drought 3.4 Cyclones 3.5 Blizzards 4 See also 5 References 6 External links

[edit] Elements of Australia's climate

[edit] Air temperature

Australia's hottest temperatures may reach 50°C, while minimums can reach sub-zero temperatures. The continent does not have very high mountain ranges and is surrounded by mostly warm oceans. The result is that extremely cold temperatures are uncommon. ^[2]

The average surface air temperature of Australia has increased by 0.7 °C over the past century. ^[3]

[edit] Atmospheric pressure

In Australia, the unit for measuring atmospheric pressure is the hectopascal. Because of Australia's mid latitude position, its climate is generally dominated by high pressure systems. This correlates with increasingly often high levels recorded in the Southern Oscillation Index, and the increasing amounts of El Niño years in Australia. High pressure systems are generally associated with stable atmospheric conditions; clear skies, gentle winds and little rain.

[edit] Precipitation

see: Drought in Australia

The rainfall patterns across Australia are highly seasonal. Compared to the Earth's other continental landmasses Australia is very dry. More than 80 percent of the continent has an annual rainfall of less than 600 millimetres, only Antarctica receives less rainfall than Australia. There are four main factors that contribute to the dryness of the Australian landmass:

• Cold ocean currents off the west coast
• Low elevation of landforms
• Dominance of high-pressure systems
• Shape of the landmass

Low rate of evaporation from this very cool body of water result in little evaporation occurring. As a result, rain clouds are sparsely formed and very rarely do they form long enough for a continuous period of rain to be recorded. Australia's arid/semi-arid zone extends to this region. The absence of any significant mountain range or area of substantial height above sea level, results in very little rainfall caused by orographic uplift. This is when air rushes up the mountain side and follows it to its summit, where it cools, condenses and forms rain on the opposite side of the mountain. In the east the Great Dividing Range limits rain moving into inland Australia. Australia has a compact shape and no significant bodies of water penetrate very far inland. This is important because it means that moist winds are prevented from penetrating to inland Australia, keeping rainfall low.

[edit] Snow

In Australia, snow can fall in the mountains of Victoria, Australian Capital Territory, New South Wales and Tasmania. There is a regular snow season in several areas which have seasonal ski tourism industries. Sometimes snow has even been reported in the mountains of South Australia, Western Australia and Queensland though this is very rare.

The occasional cold snap, caused by cold air drifting north from Antarctica, can cause significant snowfall in rural areas, as well as major cities such as Hobart, Melbourne's outer mountain suburbs and Canberra. Such occasions are rare, but have occurred in 1951, 1986 and 2005.^[4]

[edit] Regions

[edit] South-eastern temperate region

The south-eastern temperate zone spans from Ceduna in South Australia along the coast to the town of Forster in New South Wales, the climate in this region is also referred to as an oceanic climate. The region's climate is typified by warm summers and mild winters, with temperatures averaging close to 20°C. Statistically the warmest month is January and the coldest month is July, though it is rare that either will provide extreme temperatures on either end of the spectrum, however this is not the case further inland. Rainfall is evenly spread between summer and winter though is generally heavier in the first half of the year. Although the region does not suffer from natural phenomena such as cyclones, it is affected by the El Niño Southern Oscillation with drought and bushfires during El Niño^[5] and storms and flooding in periods of La Niña.^[6] The region’s climate has also been affected by global warming in recent times, with January of 2006 becoming the hottest month on record and the tenth consecutive month above median temperature.^[7] Below is a climate table for Sydney, typical of the New South Wales coastal region.

Climate Table

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Mean daily maximum temperature (°C)	25.8	25.7	24.7	22.4	19.3	16.9	16.2	17.7	19.9	22.0	23.6	25.1	21.6
Mean daily minimum temperature (°C)	18.6	18.7	17.5	14.7	11.5	9.2	8.0	8.9	11.0	13.5	15.5	17.5	13.7
Mean total rainfall (mm)	103.3	117.4	131.2	127.2	123.3	128.1	98.1	81.5	68.7	76.9	83.1	78.1	1217.0
Mean number of rain days	12.1	12.3	13.3	12.0	12.0	11.4	10.3	9.9	10.3	11.5	11.4	11.5	138.0
Source: Bureau of Meteorology

[edit] Central arid region

Main article: Deserts of Australia

Deserts of Australia cover a large portion of the land in Australia. Most of the deserts lie in the central and north-western part of the country. The largest part of Australia is desert or semi-arid. The size of the deserts in Australia combined is 2.3 million square km^{[citation needed]} (1.3 million square miles), and occupies 44% of the continent. The average annual rainfall is low, ranging from 200 to 250 mm (8 to 10 in) per year. Thunderstorms are relatively common in the region, with an average of 15 - 20 thunderstorms per annum. Summer daytime temperatures range from 32 to 40 °C (90 to 104 °F). In winter, this falls to 18 to 23 °C (64 to 75 °F). Snow never falls in any Australian desert.

[edit] Natural hazards and disasters

[edit] Bushfires

Main article: Bushfire

Climatic factors contribute to Australia's high incidence of bushfires, particularly during the summer months. Low relative humidity, wind and lack of rain can cause a small fire, either man-made or caused naturally by lightning strikes, to spread rapidly over large distances. Low humidity, the heat of the sun and lack of water cause vegetation to dry out becoming a perfect fuel for the fire. High winds fan the flames, increasing their intensity and the speed and distance at which they can travel.^[8]

Many of the worst bushfires in eastern Australia, such as the 1983 Ash Wednesday fires, accompany El Niño-Southern Oscillation events which tend to cause a warm, dry and windy climate.^[9]

[edit] Global warming

Main articles: Effects of global warming on Australia and Climate change in Australia

Global warming is causing climate change which is predicted by the CSIRO^[10] to have significant effects on the climate of and extreme weather events in Australia. It is predicted that the Great Barrier Reef and reefs surrounding Lord Howe Island could be killed as a result of the rise in water temperature forecast by the IPCC Fourth Assessment Report. The Murray River, Darling River Coorong and Macquarie Marshes are all at risk from decreased rainfall from climate change.^{[citation needed]}

Coastal communities face risks from sea level rise, albeit over a long period of time based on current estimates of the IPCC Fourth Assessment Report. The Gold Coast, being built on sand and with many canal developments, could be considered particularly at risk. Suburbs of Sydney like Drummoyne and Concord on rivers like the Parramatta River face risks of inundation of low lying areas such as parks (such as Timbrell Park and Majors Bay Reserve) reclaimed from mudflats at the heads of bays, or massive expenses in rebuilding seawalls to higher levels.

Currently, there are several environmental movements and campaigners advocating for action on climate change. One such campaign is "The Big Switch", Australia's largest community climate change campaign.^[11]

New projections for Australia's changing climate includes: ^[12]

• droughts are likely to become more frequent, particularly in the south-west
• evaporation rates are likely to increase, particularly in the north and east
• high-fire-danger weather is likely to increase in the south-east
• sea levels will continue to rise

[edit] Drought

Main article: Drought in Australia

Drought in Australia is defined by rainfall over a three month period being in the lowest ten percent of amounts having been recorded for that region in the past.^[13] This definition takes into account that low rainfall is a relative term and rainfall deficiencies need to be compared to typical rainfall patterns including seasonal variations. Specifically drought in Australia is defined in relation to a rainfall deficiency of pastoral leases and is determined by decile analysis applied to a certain area.^[14]

Historical climatic records are now sufficiently reliable to profile climate variability taking into account expectations for regions.^[15] State Governments are responsible for declaring a region drought affected and the declaration will take into account factors other than rainfall.^[13]

[edit] Cyclones

Australia is affected by tropical cyclones which primarily occur between December and April. A few cyclones are known to impact the coast in November and May as well.^[16] The region between Broome and Exmouth are most prone to cyclones.^[17] Tropical cyclones are known to bring destructive winds, heavy rain with flooding creating storm surges along the coast, causing inundation in low, lying areas. The strongest cyclones can have wind gusts reaching 280 km/h. Cyclones can also move inland, decaying to a rain depression, dumping heavy rain in these areas and causing flooding.^[18]

The worst cyclones of Australia have caused billions of dollars of damage and many deaths. Cyclone Tracy crossed directly over Darwin in 1974 which killed 71 people and caused nearly $5 billion (2005 AUD) in damage. Cyclone Mahina in 1899 brought a storm surge to Far North Queensland reaching 13 metres high, and causing 400 deaths.

[edit] Blizzards

Blizzards are not a common thing in Australia's Mainland though Blizzards have occurred in the Snowy Mountains in New South Wales and Victoria. When blizzards do occur they are most likely to effect the Tasmanian Highlands and particularly Mount Wellington which towers over the Tasmanian capital Hobart. Blizzards do not effect any towns or cities because no populated areas are located in the mountains except skiing resorts.

[edit] See also

• Indigenous Australian seasons
• List of wettest known tropical cyclones in Australia

[edit] References

[edit] External links

• Australian Bureau of Meteorology - Climate Information
• The Big Switch, Australia's largest community climate change campaign