A drought is a prolonged, abnormally dry period when there is not enough water for users' normal needs. Drought is not simply low rainfall; if it was, much of inland Australia would be in almost perpetual drought. Because people use water in so many different ways, there is no universal definition of drought. Drought occurs because rains are unreliable and in some years the ITCZ (Inner Tropical Convergence Zone = area of rainfall) may not move so far north. Thus hot, dry tropical continental air dominates for the whole year. Drought in Australia
Australia is prone to drought because of its geographic location. Much of Australia lies in a latitude belt that is under the influence of an atmospheric phenomenon known as the subtropical high. Just outside of the tropics in each hemisphere lies a swath of the globe where air frequently sinks toward the Earth’s surface from higher in the atmosphere. The air warms and dries as it sinks, creating semi-permanent zones of high air pressure at the surface. These subtropical highs are areas of stable, warm, and dry air that favour clear skies and little rainfall Where: most common in the middle of Australia (the lower you go, the drier it gets) When: Drier than average conditions tend to occur over Australia during periods of El Nino. This is due to increased amounts of sinking air in that area which acts to suppress rainfall. (El Niño translates from Spanish as 'the boy-child'. Peruvian anchovy fishermen traditionally used the term - a reference to the Christ child - to describe the appearance, around Christmas, of a warm ocean current off the South American coast, adjacent to Ecuador and extending into Peruvian waters.)
* Variable rainfall
* Depends on the spatial elements of the area
* Lack of rain causes
* absolute drought (a period of at least 15 consecutive days with less than 0.2 mm of rainfall)
* partial drought (a period of at least 29 days with the average day rainfall not exceeding 0.2 mm of rainfall) Frequency:
* Dry areas and arid condition
* subtropical high pressure area (around 20 – 30 N)
* Distance from sea (continentality) limits the amount of water carried across by winds * cold offshore currents limits the amount of condensation into the overlying air example: Atacama and Namib deserts * human activities affect the frequency of droughts –> desertification Duration:
* About 15 days – 3 years
* Even decades
Speed of onset:
* This depends on the climate and spatial elements
* usually long and slow drought one takes more than month
Why did the hazard event occur?
Australia has one of the most variable rainfall climates in the world. The strongest one is called the Southern Oscillation.
It is a major air pressure shift between the Asian and East Pacific regions. El Niño is the name of the most extreme phenomenon which makes drought a regular event in Australia which can last about 1 year. The reason for Australia being highly affected of drought simply is its geography. Due to the fact that the country is situated more or less in the subtropical hight pressure belt unregular weather events such as rain deficiency occur very often.
They can’t be avoided or prevented so that the Australian population has to be concious about the fact that there will always be droughts in Australia which might not happen regularly, but definetely will take place.
What geo-physical processes are responsible for the hazard event/disaster?
Droughts depend on water vapor in the air and the upward forcing of it. If these two factores are inbalanced the result is a drought. The high pressure conditions in the Tropic of Capricorn prevent the forming of rain and storms. When winds that carry rather continental than oceanic airmasses (containing less moisture) and high pressure areas meet, the result are behaviours which prevent precipitation or...