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The Living World - Hot Deserts - Coggle Diagram
The Living World - Hot Deserts
Hot Deserts
Definition: An area receiving less than 250mm of rainfall resulting in extreme aridity
Characteristics: A biome found near the Tropics of Cancer and Capricorn (20-30 degrees north and south of the equator) characterized by a dry high pressure system and less than 250mm of rainfall annually resulting in low vegetation cover and poor soils. Temperatures can reach 45C in the day and 0C at night
Plants
Due to the low rainfall, plant growth is sparse. The plants that do grow (cacti and thornbushes etc) do not need much water
Plants are usually short
Many plants have short life cycles, growing quickly after rain
Soil
Lack of leaf fall limits the soil fertility
Little rainfall means the soil dries out often
Soil is often shallow with gravelly texture
Animals
Hot deserts contain animals adapted to the harsh environment
Mammals tend to be small and nocturnal eg kangaroo rats
Most birds leave the desert during the harshest conditions but some can live there all year round
Climate
Less than 250mm rainfall per year
Rainfall patterns vary
Temperatures can reach 45C in the day and 0C at night
People
Many people living in deserts grow a few crops near natural water sources, usually in desert fringes
Indigenous people are often nomadic, they keep travelling to find food and water for their livestock
Adaptions
Plants
Plant roots are either extremely long to reach deep water supplies or they spread out very wide near the surface to absorb as much water as possible when it rains
Many plants (eg cacti) and succulents - they have large fleshy stems for storing water and thick waxy skin to reduce transpiration
Some plants have small leaves and spines to lower surface area and reduce transpiration. The spines can contain toxins to protect from predators
Animals
Nocturnal animals stay cool by sleeping when temperatures are hottest. Many desert animals also have long limbs and ears giving them a larger surface area to lose heat from
Lots of animals live in underground burrows where temperatures are less extreme
Camels:
feet are wide so they can walk on sand more easily and not sink in
Long, muscular legs allow the camels to walk long distances with large paces without having to stop
Their humps are stores of fat for energy
They also have triple eyelids, long eyelashes and the ability to close their nostrils to keep sand out.
Desertification
Causes
Climate Change
Rainfall - climate change is expected to reduce rainfall in areas that are already dry. Less rain means less water is available for plant growth so more plants die
Temperatures - global temperatures are increasing. Higher temperatures cause more water to evaporate from the land. This makes soils drier, so plants struggle to grow
Human Activities
Deforestation - Removal of fuel wood - many people in arid areas rely on wood as fuel for cooking. Removal of trees leaves the soil exposed
Overgrazing - too many cattle or sheep eat plants faster than they can re-grow. Trampling by animals also erodes the soil
Over-cultivation - if crops are planted in the same area continually, all the nutrients in the soil are used up. This means that plants can no longer be grown in those areas
Population growth - more people put more pressure on the land, leading to even more deforestation (e.g. for firewood), more overgrazing and more over-cultivation
Desertification
Desertification is the degradation of land, making it drier and less productive. A third of the world's land is at risk of desertification, particularly desert margins
Desertification occurs when vegetation dies or is removed. Exposed soil is easily removed by wind or water as there are no roots to hold it together. Nutrients in he soil are lost making it unproductive. Eventually the ground becomes sandy, dusty, stony or bare rock
Reducing Risk
Water management - growing crops that need little water (e.g. millet, sorghum or olives) can reduce water use. Using drip irrigation on crops instead of surface irrigation means that the soil isn't eroded by lots of water being added all at once
Tree planting - trees can be planted to act as windbreaks, reducing wind erosion and provide interception from precipitation which reduces water erosion. The trees roots can stabilise the sand and prevent desert from encroaching on farm land and also reduce soil erosion as the land is more secure and at a lower risk of cracking. Growing trees in amongst crops protects them and the soil by providing shade, interception of precipitation and reducing temperatures
Soil management - leaving areas of land to rest in between grazing or planting lets them recover their nutrients. Rotating crops that take diffferent nutrients from the soil prevents the same nutrients from being continually removed. Compost can be used to add extra nutrients to the soil
Appropriate technology - this involves using cheap, sustainable and easily available materials to build things that are easy for local people to maintain. For example, sand fences (barriers to trap windblown sand) or terraces can be constructed to stabilise the soil and reduce erosion. The rate of deforestation can also be reduced by using solar cookers, which use the sun's energy to heat food. They are cheap and easy to make, and don't require fuel wood to work
Desert Fringe Areas
Semi-deserts, semi-arid areas, drylands, borders of hot deserts. They support greater biodiversity and larger plants however despite higher rainfall they are still classified as fragile environments and are at constant risk of desertification
Sahara Desert
Great Green Wall
Location
The Sahel runs south of the Sahara Desert from Senogal to Eritrea which is from the west to the east of Africa. It runs through 9 countries including Mali, Chad and Sudan. The Great Green Wall runs along the north of the Sahel but the south of the Sahara Desert however the line does flucuate along the way
Concept
A 7,110 km, 15 km wide belt of trees and vegetation designed to stop the spread of the desert. The trees provide shade reducing temperatures and interception of precipitation for the soil which lies underneath
Effectiveness
Appropriate technology as locals can work it
Trees provided by charities and so are affordable
Not very sustainable because it could be deforested in the future
Bunds
Water and soil management addresses the problem of heavy rainfall washing away loose soil and causing soil erosion.
One common strategy involves constructing a series of low rock walls called bunds parallel to the contours of the land. These interrupt the flow of surface water and collect soil carried by the water creating fertile moist land which can be cultivated.
Case Study: The Western Desert
Location
The USA's Western Desert stretches across several states in the south-west, including California, Arizona and New Mexico. It comprises three separate deserts: the Sonoran Desert, the Mojave Desert and the Chihuahuan Desert
Development Opportunities
Mineral Extraction
Rich reserves of copper, uranium and coal. Copper is mined in the Sonoran Desert near Ago, Arizona. Elsewhere, developments have been limited by environmental concerns, including the possibility of mining uranium in the Grand Canyon
Energy
Energy resources include:
Solar energy being developed extensively, e.g. Sonoran Solar Project in Arizona, which will supply electricity to 100,000 homes
Oil in Arizona, owned and operated by the indigenous Navajo people
HEP generated from Lake Mead
Farming
Irrigation enables commercial farming to thrive in sunny and hot conditions, e.g. Coachella Valley (California) produces vegetables, peppers and grapes (for wine) using water abstracted from underground aquifers. Elsewhere, irrigation canals are used for large-scale industrialised farming
Tourism
Many people visit the National Parks and wilderness areas (e.g. Joshua Tree and Grand Canyon) to enjoy the landscape, peace and solitude. Lake Mead and Lake Powell are popular for waterspouts and Las Vegas is an entertainment centre attracting 37 million visitors a year
Development Challenges
Water Supply
For the Western Desert, water transfer, particularly from the Colorado River, has supplied drinking water and irrigation since the Hoover Dam was constructed in 1935. Piped water no sup-lies homes, farms and even golf courses. Water supply could be a major problem in the future as demand soars in cities such as Phoenix, Arizona. Temperatures are forecast to rise as a result of climate change
Inaccessibility
In the Western Desert, the relatively low density population has resulted in a lack of surfaced roads through the desert. Access is limited away from the main cities. Some major highways have been constructed linking the major cities, such as Route 70 through Utah, and Route 66, which connects Chicago with California through the Western Desert
Extreme Temperatures
While the average temperature is 27 degrees, summer temperatures can soar above 50 degrees. This creates many problems:
Work outside is very hard, especially for farmers who have to work during the day
High temperatures lead to high rates of evaporation and water shortages
Population Growth
Between 2000 and 2010 the population grew by 35% in Nevada, 25% in Arizona and 24% in Utah. The population growth is very hard to manage as could cause issues as the demand on resources increases
Settlements such as Las Vegas made possible by huge water projects e.g. Hoover Dam on Colorado River
Aquifer
Grand Canyon
Water security
Central Arizona project (canals taking water to cities)
Climate change and population growth
Tourism is biggest industry