The Science Of Desertification 1: The Great Australian Deserts

 

Australia is a country within Oceania, the smallest continent on Earth. It is the 6th largest country, the largest island and often considered as the largest island continent. The country consists of a mainland territory, Tasmania, and many offshore islands. Surrounding the continent are the Indian and Pacific Oceans. Australia is indeed a distinctive continent with different climatic conditions and biomes across the country. On the mainland are found the deserts of Australia (also called the Great Australian Deserts). Collectively, these deserts are the 4th largest in the world coming after Antarctic, Arctic, and Sahara deserts. In this article, we shall have a good glance at the physics underlying formation of the desert climate. We shall see how oceanic water currents, air flows and heat transfer across the globe affect the climate of the mainland country.

Due to harsh conditions, the deserts are largely void of human settlements and activities although there is evidence that aboriginals and indigenous tribes occupied the outback many thousands of years ago even to date in small settlements.

The Grillegaleat Australian Deserts (also called the outback) cover an area of 2,700,000Km². It is located mainly in the Western region and the interior lowlands of the country. It is the driest inhabited continent although most of it's interior is desolate.

Australia is made up of 8 states i.e.:

• Western Australia

• Northern Territory

• South Australia

• Queensland

• Victoria

• New South Wales

• Australia Capital Territory

• Tasmania

The deserts in Australia stretch across Western Australia, Northern Territory, Queensland, and South Australia.

Although the outback receives a significant charge of rainfall, quick evaporation of water makes the desert arid, hot, and unfavorable for life. It is therefore largely uninhabited. In the desert can be found rocky plains, heavy dunes, xerophytic shrubs, stony masses, savannahs, grasslands, and bushes. Several rivers and lakes supply the desert. These water supplies are usually dry during the summer.

Observe the rocky terrains and shrubs. Several species of xerophytes can be found here

What are the 10 deserts that make up the Australian desert?

By their landmasses, they are listed below:

• Great Victoria desert

• Great Sandy desert

• Tanami desert

• Simpson Desert

• Gibson Desert

• Little Sandy Desert

• Strzelecki desert

• Sturt Stony Desert

• Pedirka desert

Physics of the climate

Do you notice that almost all important cities including (state capitals) in the country are concentrated in the coastal areas? Most of them are in the eastern and southern parts of the country. This is where most of the Australian settlements are found. This is because of a better favorable climate. Rainfall is more abundant, the atmosphere is cooler, and even temperate conditions and rainforests can be found there. 

The average rainfall in the outback is usually less than 250mm.  Summers are hot and dry and during lengthy periods of drought, wildfires can break out. Due to the massive geographical size of Australia, climate varies across the country. A large percentage of Australia is desert, mostly hot and dry. Rainfall concentrates along coastal areas.  The size, structure, and elevation of the continent do not permit penetration of moist winds keeping rainfall scarce in the regions (Victoria and New South Wales) are temperate (cool climate with occasional snowfall!) while Northern regions (Queensland and Northern Territory are tropical with Savannahs, semi-arid areas, monsoons, and even rainforests). The average summer daytime temperature is about 32-40°C. During winter it is about 18-23°C. Nighttime can be as low as -2-3°C. The temperature in the desert can rise to as high as 50°C. 

Ocean Currents

There are 5 major currents with distribute and circulate heat around the current. The Eastern Australian current moves warm waters southwards from Queensland to the Eastern shore of Tasmania. Leeuwin current moves warm water along the coast of Western Australia.

The climate and rainfall in Australian deserts are greatly influenced by the West Australian Current, a surface current with flows in the opposite direction to the Leeuwin Current carrying cool water.  Ocean currents are very important in regulating local and global weather conditions, moving heat from the equatorial regions towards the poles and returning cooler water to the tropics. Since the West current is of polar origin and cold water does not evaporate readily, rainfall and precipitation are prevented, with a limit along the Western side. This contributes to why the Australian deserts are located especially around the west.

The Australian High

Anticyclones are high-pressure systems and carry heat. When over a geographical zone, they provoke a hot atmosphere and even drought.

This is another crucial factor that contributes to the climatic state of Australia. The Australian High (also called Australian Subtropical Ridge) is an anticyclone that drifts seasonally from the Great Australian Bight to the northern regions of the country. It is intense during summer and weaker during winter when it moves to the interior part of the continent. Its circulation brings hot weather to southern Australia during the summer. It is largely responsible for the aridity and droughts of the summer season. During winter, the cyclone migrates north allowing low-pressure systems from the bight to relocate to the southern areas bringing rainfall. When it moves interiorly during winter, it brings about droughts and dry conditions in the north and eastern areas. The high is therefore largely responsible for the atmospheric desertification of Australia

Walker cell phenomenon

Apart from the two mechanisms given above, east-west circulation across the equatorial Pacific also affects the weather and climate in Australian deserts. This is called Walker circulation and is influenced by temperature and pressure gradients. Areas of high pressure set in the eastern Pacific while low-pressure forms on the Western side. As winds from airflow across pressure gradients, trade winds move from East to West. These winds carry warm moisture from the surface of the ocean to the west. There it accumulates, forms clouds, and precipitates as rainfall. The dehydrated lighter air then cycles back to the east. This leads to less rainfall and thunderstorms in the east due to low atmospheric moisture or humidity. In addition, within the ocean, warm water from the east is pushed to the west. Water in deeper parts of the ocean rises to fill the space (this is called upwelling). When the cool water reaches the surface, it is blown westwards towards Australasia. This forces the warm water there to sink (downwelling) and is pushed to the east forming a cycle. This is the normal cycle of heat distribution. 

When trade winds weaken, (the phenomenon called El Nino), warm water from the Pacific moves towards the east disrupting the upwelling process. This therefore leads to drought, and dry climate and is a contributing factor to the Australian desert climate.

Uluru Kata Tjuta located in the Simpsons desert is one of the prime cultural heritage of indigenous Australians and is a very important national landmark.

Located in the central Australian desert is the Uluru also known as the Ayers Rock. It is a 348m tall sandstone, reddish due to iron oxides. It is sacred and of great cultural significance to the Aboriginal people of Australia and is listed as a UNESCO World Heritage Site. Located specifically in the the Simpson Desert (Northern Territory) It is one of the most spectacular landmarks in Australia and a popular tourist site. It appears to change color at different times of the day.