extreme weather
TRANSCRIPT
Extreme weatherAustralia vs. US
Australia• 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 dust storm 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 a greater part of the continent. These cold waters produce precious little moisture needed on the mainland. A 2005 study by Australian and American researchers 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.
• 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 millimeters; only Antarctica receives less rainfall than Australia. From one extreme to another, parts of the far North Queensland coast annually average over 4000 mm, with the Australian annual record being 12461 mm, set at the summit of Mount Bellenden Ker in 2000. 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. 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.
• 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.
• Snow at sea level has been recorded on mainland Australia but has happened more times in Tasmania, some of the snow at sea level has fallen in the off season like summer. Snow has fallen nearly everywhere in Tasmania, though it is rare to fall in the north coast at sea level.
• 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, Canberra and Sydney. Such occasions are rare, but have occurred in 1951, 1986 and 2005.
Central arid region• 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. Just under three quarters of Australia lies within a desert or semi-arid zone. The size of the deserts in Australia combined is 2.3 million square km (1.3 million square miles), and occupies 44% of the continent. The average annual rainfall is low, ranging from 200 to 250 mm (7.9 to 9.8 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 73 °F).
States and Territories
Australian Capital Territory• Because of its elevation (650 m) and distance from the coast, the Australian Capital Territory
experiences four distinct seasons, unlike many other Australian cities whose climates are moderated by the sea. Canberra is notorious for hot, dry summers, and cold winters with occasional fog and frequent frosts. Many of the higher mountains in the territory’s south-west are snow-covered for at least part of the winter. Thunderstorms can occur between October and March, and annual rainfall is 623 millimeters (24.5 in), with rainfall highest in spring and summer and lowest in winter.
New South Wales• The highest maximum temperature recorded was 50.0 °C (122.0 °F) at Wilcannia in the state's
west on 11 January 1939. The lowest minimum temperature was −23 °C (−9 °F) at Charlotte Pass on 29 June 1994 in the Snowy Mountains. This is also the lowest temperature recorded in whole of Australia excluding Australian Antarctic Territory.
Northern Territory• Monsoonal squall nears Darwin The Northern Territory has two distinctive climate zones. The
northern end, including Darwin, has a tropical savanna climate (Köppen Aw) with high humidity and two seasons, the wet (November to April) and dry season (May to October). During the dry season nearly every day is warm and sunny, and afternoon humidity averages around 30%. There is very little rainfall between May and September. In the coolest months of June and July, the daily minimum temperature may dip as low as 14 °C (57 °F), but very rarely lower, and frost has never been recorded. The wet season is associated with tropical cyclones and monsoon rains. The majority of rainfall occurs between December and March (the southern hemisphere summer), when thunderstorms are common and afternoon relative humidity averages over 70% during the wettest months. On average more than 1,570 mm (62 in) of rain falls in the north.
Queensland• Because of its size, there is significant variation in climate across the state. Low rainfall and
hot summers are typical for the inland west, a monsoonal 'wet' season in the far north, and warm temperate conditions along the coastal strip. Inland and in southern ranges low minimum temperatures are experienced. The climate of the coastal strip is influenced by warm ocean waters, keeping the region free from extremes of temperature and providing moisture for rainfall.
• There are five predominate climatic zones in Queensland, based on temperature and humidity:• hot humid summer (far north and coastal)• warm humid summer (coastal elevated hinterlands and coastal south-east)• hot dry summer, mild winter (central west)• hot dry summer, cold winter (southern west)• temperate - warm summer, cold winter (inland south-east, e.g. Granite Belt)
South Australia• South Australia's mean temperature range is 29 °C
(84 °F) in January and 15 °C (59 °F) in July. Daily temperatures in parts of the state in January and February can be up to 48 °C (118 °F).
• The highest maximum temperature was recorded as 50.7 °C (123.3 °F) at Oodnadatta on 2 January 1960, which is the highest official temperature recorded in Australia. The lowest minimum temperature was −8 °C (17.6 °F) at Yongala on 20 July 1976
Tasmania• Tasmania has a cool temperate climate with four
distinct seasons. Summer lasts from December to February when the average maximum sea temperature is 21 °C (70 °F) and inland areas around Launceston reach 24 °C (75 °F). Other inland areas are much cooler with Liawenee, located on the Central Plateau, one of the coldest places in Australia with temperatures in February ranging between 4 °C (39 °F) to 17 °C (63 °F). Autumn lasts between March and May and experiences changeable weather, where summer weather patterns gradually take on the shape of winter patterns.
Victoria• Victoria has a varied climate despite its small size. It
ranges from semi-arid and hot in the north-west, to temperate and cool along the coast. Victoria's main land feature, the Great Dividing Range, produces a cooler, mountain climate in the centre of the state.
• Western Australia• The southwest coastal area is relatively temperate
and was originally heavily forested, including large stands of the karri, one of the tallest trees in the world. This agricultural region of Western Australia is in the top nine terrestrial habitats for terrestrial biodiversity, with a higher proportion of endemic species than most other equivalent regions. Thanks to the offshore Leeuwin Current the area numbers in the top six regions for marine biodiversity, containing the most southerly coral reefs in the world.
Natural hazards and disasters
Bushfires• 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.
• 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. The worst bushfires in Australian history occurred on Black Saturday in February 2009. The human death toll of the disaster exceeded 200, and over 2000 homes were lost.
Global warming• Global warming is causing climate change which is predicted by the CSIRO 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.
• 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.
• New projections for Australia's changing climate includes: – 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
Drought• Drought-affected paddock in the New South Wales farming region of the Riverina• 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. 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.
• Historical climatic records are now sufficiently reliable to profile climate variability taking into account expectations for regions. State Governments are responsible for declaring a region drought affected and the declaration will take into account factors other than rainfall.
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. The region between Broome and Exmouth are most prone to cyclones. 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 Australian region cyclone was Cyclone Monica in 2006 which had wind gusts in excess of 350 km/h. Cyclones can also move inland, decaying to a rain depression, dumping heavy rain in these areas and causing flooding.
• The worst cyclones of Australia have caused billions of dollars of damage and many deaths. Cyclone Tracy crossed directly over Darwin in 1974, 71 people were killed and caused nearly $5 billion (2005 AUD) in damage. Cyclone Mahina in 1899 brought a storm surge to Far North Queensland reaching 13 meters high, and causing 400 deaths.
Blizzards• Blizzards are not a common thing in Australia's mainland though blizzards have occurred in
mountainous areas, including the Snowy Mountains in New South Wales and Victoria. When blizzards do occur they are most likely to affect the Tasmanian Highlands and particularly Mount Wellington, which towers over the Tasmanian capital Hobart. Blizzards do not affect any towns or cities, because no populated areas are located in the mountains except skiing resorts.
• Dust storms• A dust storm or sandstorm is a meteorological phenomenon common in arid and semi-arid regions
and arises when a gust front passes or when the wind force exceeds the threshold value where loose sand and dust are removed from the dry surface. Particles are transported by saltation and suspension, causing soil erosion from one place and deposition in another.
• The term sandstorm is used most often in the context of desert sandstorms, especially in the Sahara, when, in addition to fine particles obscuring visibility, a considerable amount of larger sand particles are blown closer to the surface. The term dust storm is more likely to be used when finer particles are blown long distances, especially when the dust storm affects urban areas.
Us• The United States includes a wide variety of climate types due to its large size,
range of geographic features, and noncontiguous arrangement. In the contiguous United States to the east of the 100th meridian, the climate ranges from humid continental in the north to humid subtropical in the south. The southern tip of Florida is tropical. The Great Plains west of the 100th meridian are semi-arid. Much of the Rocky Mountains, the Sierra Nevada, and the Cascade Range are alpine. The climate is arid in the Great Basin, desert in the Southwest, Mediterranean in coastal California, and oceanic in coastal Oregon and Washington. The state of Alaska—on the northwestern corner of the North American continent—is largely subarctic, with an oceanic climate in its southern edge and a polar climate in the north. The archipelago state of Hawaii, in the middle of the Pacific Ocean, is tropical.
• Extreme weather is not uncommon—the states bordering the Gulf of Mexico are prone to hurricanes, and tornadoes regularly occur in the area of the Midwest referred to as Tornado Alley. The United States has more tornadoes than the rest of the world combined.
• The main influence on weather in the United States is the polar jet stream, which brings in large low pressure systems from the northern Pacific Ocean. Once a Pacific cyclone moves over the Great Plains, uninterrupted flat land allows it to reorganize and can lead to major clashes of air masses. Sometimes during late winter and spring these storms can combine with another low pressure system as they move up the East Coast and into the Atlantic Ocean, where they intensify rapidly. These storms are known as Nor'easters and often bring widespread, heavy snowfall to the Mid-Atlantic and New England. The uninterrupted flat grasslands of the Great Plains also leads to some of the most extreme climate swings in the world. Temperatures can rise or drop rapidly; winds can be extreme; and the flow of heat waves or Arctic air masses often advance uninterrupted through the plains.
• The Great Basin and Columbia Plateau (the Intermountain Plateaus) are arid or semiarid regions that lie in the rain shadow of the Cascades and Sierra Nevada. Precipitation averages less than 15 inches (38 cm). The Southwest is a hot desert, with temperatures exceeding 100°F (38°C) for several weeks at a time in summer. The Southwest and the Great Basin are also affected by the monsoon from the Gulf of California from July-September, which brings localized but often severe thunderstorms to the region.
Precipitation• The characteristics of rainfall across the United States differ significantly across the United States and its possessions. Late summer and fall extra tropical cyclones bring a majority of the precipitation which falls across western, southern, and southeast Alaska annually. During the fall, winter, and spring, Pacific storm systems bring most of Hawaii and the western United States much of their precipitation. Nor'easters moving up the East coast bring cold season precipitation to the Mid-Atlantic and New England states. Lake-effect snows add to precipitation potential downwind of the Great Lakes, as well as Great Salt Lake and the Finger Lakes during the cold season. The snow to liquid ratio across the contiguous United States is 13:1, meaning 13 inches (330 mm) of snow melts down to 1 inch (25 mm) of water. The El Niño-Southern Oscillation affects the precipitation distribution, by altering rainfall patterns across the West, Midwest, the Southeast, and throughout the tropics.
• During the summer, the Southwest monsoon combined with Gulf of California and Gulf of Mexico moisture moving around the subtropical ridge in the Atlantic ocean bring the promise of afternoon and evening thunderstorms to the southern tier of the country as well as the Great Plains. Equator ward of the subtropical ridge, tropical cyclones enhance precipitation across southern and eastern sections of the country, as well as Puerto Rico, the United States Virgin Islands, the Northern Mariana Islands, Guam, and American Samoa. Over the top of the ridge, the jet stream brings a summer precipitation maximum to the Great Lakes. Large thunderstorm areas known as mesoscale convective complexes move through the Plains, Midwest, and Great Lakes during the warm season, contributing up to 10% of the annual precipitation to the region.
• In northern Alaska, tundra and arctic conditions predominate, and the temperature has fallen as low as −80 °F (−62.2 °C). On the other end of the spectrum, Death Valley, California once reached 134 °F (57 °C), the second-highest temperature ever recorded on Earth.
• On average, the mountains of the western states receive the highest levels of snowfall on Earth. The greatest annual snowfall level is at Mount Rainier in Washington, at 692 inches (1,760 cm); the record there was 1,122 inches (2,850 cm) in the winter of 1971–72. This record was broken by the Mt. Baker Ski Area in northwestern Washington which reported 1,140 inches (2,900 cm) of snowfall for the 1998-99 snowfall season. Other places with significant snowfall outside the Cascade Range are the Wasatch Mountains, near the Great Salt Lake and the Sierra Nevada, near Lake Tahoe.
• Along the coastal mountain ranges in the Pacific Northwest, rainfall is greater than anywhere else in the continental U.S., with Quinault Ranger in Washington having an average of 137 inches (3,500 mm). Hawaii receives even more, with 460 inches (12,000 mm) measured annually, on average, on Mount Waialeale, in Kauai. The Mojave Desert in the southwest is home to the driest locale in the U.S. Yuma, Arizona, has an average of 2.63 inches (67 mm) of precipitation each year.
Natural disasters• The United States is affected by a large variety of weather related natural disasters. Deadly and
destructive hurricanes occur almost every year along the Atlantic seaboard and the Gulf of Mexico. Hurricanes can also strike Hawaii in the Pacific Ocean. Particularly at risk are the central and southern Texas coasts, the area from southeastern Louisiana east to the Florida Panhandle, the east coast of Florida, and the Outer Banks of North Carolina. Hurricane season runs from June 1 to November 30, with a peak from mid-August through early October. Some of the more devastating hurricanes have included the Galveston Hurricane of 1900, Hurricane Andrew in 1992, and Hurricane Katrina in 2005. The remnants of tropical cyclones from the Eastern Pacific also occasionally impact the southwestern United States, bringing sometimes heavy rainfall.
• The Great Plains and Midwest, because of the contrasting air masses, have frequent severe thunderstorms and tornado outbreaks during spring and summer. In central portions of the U.S., tornadoes are more common than anywhere else on Earth and touch down most commonly in the spring and summer. The strip of land from north Texas north to Kansas and east into Tennessee is known as Tornado Alley, where many houses have tornado shelters and many towns have tornado sirens.
• The Appalachian region and the Midwest experience the worst floods. Widespread severe flooding is rare. Some exceptions include the Great Mississippi Flood of 1927, the Great Flood of 1993, and widespread flooding and mudslides caused by the 1982-1983 El Niño event in the western United States. Localized flooding can, however, occur anywhere, and mudslides from heavy rain can cause problems in any mountainous area, particularly the Southwest. The narrow canyons of many mountain areas in the west and severe thunderstorm activity during the monsoon season in summer leads to sometimes devastating flash floods as well, while Nor'easter snowstorms can bring activity to a halt throughout the Northeast (although heavy snowstorms can occur almost anywhere).
• The Southwest has the worst droughts; one is thought to have lasted over 500 years and to have decimated the Anasazi people. Large stretches of desert shrub in the west can fuel the spread of wildfires. Although severe drought is rare, it has occasionally caused major problems, such as during the Dust Bowl (1931-1942), which coincided with the Great Depression. Farmland failed throughout the Plains, entire regions were virtually depopulated, and dust storms ravaged the land. More recently, the western U.S. experienced widespread drought from 1999-2004, and signs of a major, long-term drought across the Great Plains have developed. In the past year, drought has spread from the Southern Plains westward through the Southwest and east along the Gulf Coast to Florida.
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