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Hot deserts

001DesertAir

Key idea Specification content
Hot desert ecosystems have a range of distinctive characteristics.

 

The physical characteristics of a hot desert.

The interdependence of climate, water, soils, plants, animals and people.

How plants and animals adapt to the physical conditions.

Issues related to biodiversity.

Development of hot desert environments creates opportunities and challenges.

 

A case study of a hot desert to illustrate: • development opportunities in hot desert environments: mineral extraction, energy, farming, tourism • challenges of developing hot desert environments: extreme temperatures, water supply, inaccessibility.
Areas on the fringe of hot deserts are at risk of desertification.

 

Causes of desertification – climate change, population growth, removal of fuel wood, overgrazing, over-cultivation and soil erosion.

Strategies used to reduce the risk of desertification – water and soil management, tree planting and use of appropriate technology

Work through the PowerPoint (below) it deals with all the main concept for this unit of work.

Ecosystems – Deserts

Location 
Deserts

Climate

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Soil

Pedocal – it is a class of soil which forms in semi-arid and arid regions. Has low soil organic matter with only a thin topsoil (A horizon).

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Biodiversity – plant adaptation

GeoActive – Hot deserts – characteristics and plant adaptations

How have plants adapted to the harsh environment?

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Biodiversity – animal adaptation

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Interdependence that exists in the hot desert environment

Links between the different parts of the food web – biotic and abiotic.

The role of vegetation in stabilising sandy soils – plants stop the soils from being blown away by the wind (desertification).

Increasing unsustainable use in the deserts – threatens the interdependence.

Fragility of deserts affects the biodiversity. A sensitive area, such as the Aral Sea (below), used in an unsustainable manner has dire consequences for both the environment and societies that inhabit the area.

The Aral Sea is situated in Central Asia, between the Southern part of Kazakhstan and Northern Uzbekistan. Up until the third quarter of the 20th century it was the world?s fourth largest saline lake, and contained 10grams of salt per liter. The two rivers that feed it are the Amu Darya and Syr Darya rivers, respectively reaching the Sea through the South and the North. The Soviet government decided in the 1960s to divert those rivers so that they could irrigate the desert region surrounding the Sea in order to favour agriculture rather than supply the Aral Sea basin. 

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Aral Sea

We must remember at all times that society is responsible for the crisis that has unfolded in and around the Aral, the point we want to make is that most of the actual changes that have afflicted the Sea since the 1960s are the result of our environment’s reaction to the stresses society has imposed on it. (http://www.columbia.edu/~tmt2120/introduction.htm)

Development opportunities in the Western Desert
Location

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Western Desert’s development opportunities:

Farming, Mineral extraction, Energy & Tourism

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Les Vagus – Las Vegas – built in the desert – attracts 37 million tourists a year – sustainable?

Development challenges in the Western Desert

Adapting to the hot desert environment has been a challenge to settlers this is due to the high temperatures (50C) in the Mojave Desert’s Death Valley – this is the the survival limit of the plants an the absence of people reflects the low carrying capacity of the land.

Accessibility – this area lacks surfaced roads due to the low population densities 1 person per square km. The extreme temperatures make this a dangerous place to travel. However – improvements have been make:

(a) Railway moved in(1900s) – the choice of sites for situation has influenced the growth of future key settlements.

(b) Better roads were laid in the 1900s.

(c) Major cities can now be reached by air.

How have people adapted to the climate – before air conditioning and improved water supplies houses needed: flat roofs, small to reduce sunlight keeps temps down, whitewashed walls.

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The Western Desert water crisis

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The Colorado River is located in South-West USA and North-West Mexico. It is over 2,300km and has its source in the Rocky Mountains and its mouth in the Gulf of California. Its drainage basin covers an area of 640,000km2. The Colorado River and its tributaries pass through the US states of; Wyoming, Nevada, Utah, California, Arizona, Colorado and New Mexico. The climate across the river basin is very varied, in the Rockies temperatures can fall to -50 degrees Celsius an experience precipitation in excess of 1000mm, whereas some areas in the Mojave Desert can experience temperatures of nearly 50 degrees Celsius and precipitation as low as 15mm. About 12.7 million people live within the drainage basin of the Colorado River, although some people outside the drainage basin (especially in California) use water from the Colorado River. In total it is estimated that about 40 million rely on the river for domestic, agricultural, industrial and energy needs.

To cope with the massive demand, the Colorado River has become one of the most managed river’s in the world. The river has over 29 major dams built along its and hundreds of miles of artificial canals. The Hoover Dam was one of the first major dams built along the river (and certainly the most famous), it was completed in 1936 and created Lake Mead – this is still the US’s largest artificial lake.

Colorado River Aqueduct (CRA): This is 389km of tunnels, pipes and canals taking water from the Colorado River to California. The water is taken from the Parker Dam and is pumped up over the Rockies ending up at Los Angeles. Work on the project began in 1933 and water was first pumped in 1939. On average 1.5km3 of water is pumped through the aqueduct each year.

Central Arizona Project (CAP): This is 541km diversion canal. The canal was designed to provide water for irrigation of 405,000 hectares (1.85 trillion litres a year) and for domestic use in cities like Phoenix and Tuscon. Construction of the project began in 1973 and it was completed in 1993. The canal starts at Lake Havasu and eventually finishes at Tucson. The scheme cost about $4 billion to build.

California State Water Project (SWP): The project aimed to provide water for 23 million people and 6.6 million MWh of electricity to people living in Southern California. The project began in the 1950’s.

Environmental & management strategies

It is impossible to manage a river so much and not create some environmental problems. Problems include:

The Colorado River used to carry about 90 million tonnes of sediment (alluvium) a year down to its mouth. However, the majority of this now gets trapped behind dams, damaging the delta and wetland ecosystem at the river’s mouth.

Salinity in the lower Colorado has increased changing the ecosystem.

The number of fish shrimps and sea mammals have all reduced around the mouth of the river.

Evaporation rates have increased behind the river’s many dams. About 15% of water is evaporated.

The deep water in the reservoirs behind the dams has reduced the temperature of the river in many areas.

In an attempt to reduce environmental damage while allowing continued economic and population growth, a number of management strategies have been implemented and/or suggested, including:

Reduced leakage: It is estimated that 25% of all water is currently lost through leaking pipes and canals.
Recycling Water: Using more grey water in domestic homes.
Sewage Treatment: Recycling industrial and domestic waste more efficiently.
Domestic Conservation: Improving education and introducing things like half flush toilets.
Drip Irrigation: Use more efficient irrigation techniques.
Changing Crops: Growing crops or varieties that need less water.
Metering and Pricing: Increasing the price of water and metering its use.
Cloud seeding: Using chemicals to create artificial rain has been talked about.
Desalination: With the Pacific Ocean on California’s door step the technology of desalination could be improved.
Groundwater: Increase extraction of groundwater supplies.

Crisis along the Colorado River – drought

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Before and after – The Colorado River

 

Desert fringes and desertification:

Desertification is –  (a) the processes by which an area becomes a desert & (b) the rapid depletion of plant life and the loss of topsoil at boundaries and in semiarid regions, usually caused by a combination of drought and the overexploitation of grasses and other vegetation by people.

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What are the causes:

Overcultivation: the land is continually used for crops and does not have time to recover eventually al the nutrients are depleted (taken out) and the ground eventually turns to dust.

Overgrazing: In some areas animals have eaten all the vegetation leaving bare soil.

Deforestation: Cutting down trees leaves soil open to erosion by wind and rain.

Climate Change: Decrease in rainfall and rise in temperatures causes vegetation to die.

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The Sahel region of Africa has been suffering from drought on a regular basis since the early 1980s. The area naturally experiences alternating wet and dry seasons. If the rains fail it can cause drought.

In addition to natural factors, the land is marginal. Human activities such as overgrazing, overcultivation and the collection of firewood can lead to desertification, particularly when combined with drought conditions.

The result is crop failure, soil erosion, famine and hunger: people are then less able to work when their need is greatest. It becomes a vicious circle and can result in many deaths, especially among infants and the elderly.

What is needed is development aid, which involves educating the local community in farming practices.

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Human causes

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Physical causes

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The YouTube clips below provide a good overview to what is happening in the Sahel region.

Great Green Wall to stop Sahel desertification

The wall envisioned by 11 African countries on the southern border of the Sahara, and their international partners, is aimed at limiting the desertification of the Sahel zone.

Imagine a green wall – 15km wide, and up to 8,000km long – a living green wall of trees and bushes, full of birds and other animals. Imagine it just south of the Sahara, from Djibouti in the Horn of Africa in the east, all the way across the continent to Dakar, Senegal, in the west.

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The building of this pan-African Great Green Wall (GGW) was approved by an international summit this week in the former German capital Bonn, a side event of the joint conference of the committees on science and technology and for the review of the implementation of the UN Convention to Combat Desertification(UNCCD).

Read the following articles which deal with desert environments:

Desert ecosystems

Hot deserts – characteristics and plant adaptations

Processes and landforms in hot deserts

 

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