150 Years ― QLD Weather Events See allDrought/Heat Wave

Recently the world's top climate scientists have warned that the heat waves that have killed thousands of people during recent summers are to become more common and more deadly. Droughts and heat waves are dangerous aspects of severe weather trends.

We have accessed this overview from BOM's Climate Education website.

Drought. The word evokes images of barren fields, dying stock, and water holes and reservoirs drying to cracked mud. Shrivelled hopes, failed crops, and often economic ruin are its trademarks.

Drought is also part and parcel of life in Australia, particularly in the marginal areas away from the better-watered coasts and ranges. Of all the climatic phenomena to afflict Australia, drought is probably the most economically costly: major droughts such as that of 1982/83 can have a major impact on the national economy. Moreover, apart from crop failure and stock losses, droughts set the scene for other disastrous phenomena, such as fires, dust-storms, and general land degradation.

Why is Australia drought prone?

Australia is prone to drought because of its geography. Our continent sits more or less astride the latitudes of the subtropical high pressure belt, an area of sinking, dry, stable air and usually clear skies. The far north and south of the country come under the influence of reasonably regular rain-bearing disturbances for at least part of the year, and the east coast is watered reasonably well by moisture from the Tasman and Coral Seas. However over most of the country rainfall is not only low, but highly erratic.

Many, but by no means all, droughts over eastern and northern Australia accompany the El Niño-Southern Oscillation phenomenon, which typically lasts about a year, as in 1982/83. Droughts in the western areas and over much of the interior normally have different causes. Nevertheless, on some occasions (such as 1914 and 1994) El Niño-related droughts may extend across virtually the entire country. On such occasions, the economic and livestock losses are exacerbated

Long-term droughts

Over much of the country, droughts can extend over several years, relieved only by brief, transitory rains. Indeed, probably the most damaging type of drought is when one or two very dry years follow several years of generally below-average rainfall. The "Federation drought" of the late 1890s through 1902 is an example, as is the more recent 1991-95 drought in Queensland, northern New South Wales and parts of central Australia. Over still longer time-scales, Australia's rainfall history features several periods of a decade or longer that seem to have been distinctly "drought prone". For instance, the mid to late 1920s and the 1930s were a period of generally low rainfall over most of the country, continuing through most of the 1940s over the eastern states. A similar dry spell occurred in the 1960s over central and eastern Australia. During these low rainfall periods, not every year is dry; it is just that rainfall in most years is below the long-term average, and there are often runs of years with recurrent drought. Thus in the late 1930s-40s major droughts occurred over eastern Australia in 1937-38, 1940-41, and 1943-45.
The 1990s saw formal Government acknowledgement that drought is part of the natural variability of the Australian climate, with drought relief for farmers and agricultural communities being restricted to times of so-called "exceptional circumstances". In other words, the agricultural sector was expected to cope with the occasional drought, and relief would be available only for droughts of unusual length or severity.

Heat and cold

Australia is not only a dry country, but is also subject to fierce heat. As the sun tracks into the southern hemisphere in early spring, it begins to strongly heat northern and interior parts of the country. By November, average maximum temperatures have already climbed to the high 30s over wide areas of northern and central Australia - and into the low 40s in parts of northwestern Australia and western Queensland. The heat does not relent until the following autumn.

Heat waves

On occasions when the synoptic situation is favourable, the hot air extends south over the southern States. In South Australia and the southeast, this occurs when high pressure systems lie to the east, and a cold front is advancing from the west - a combination that directs a hot northerly airstream across these states. In southwestern Australia, the hottest conditions are normally associated with low pressure troughs that direct east to northeasterly winds from the hot interior. In both cases, eastward movement of the front or trough introduces cooler air from the oceans or higher latitudes - the so-called, and often eagerly awaited, "cool change".

These "hot weather" patterns occasionally become slow-moving, and the trough or front bringing the cool change may stall, or even dissipate. On such occasions, very high temperatures - high 30s or even 40s - can persist for days, and in inland areas, for weeks on end. These are the "heatwaves" of the southern States. Such heatwaves can lead to heat exhaustion, and even death, particularly among the very young or old. Heatwaves have, in fact, accounted for more deaths in Australia than any other natural hazard: according to Emergency Management Australia the January 1939 heatwave in South Australia, Victoria and NSW killed 438 people. 

 

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