Deserts Flashcards
Where are hot deserts found?
In the subtropics between 20 degrees and 30 degrees north and south of the equator.
Describe and explain the aridity of hot deserts
Total annual rainfall below 250mm caused by the high pressure conditions. As air sinks, it prevents the formation of cloud and rain, resulting in dry conditions.
Stat for the heat and low rainfall of hot deserts
Summer temps rise above 40 oc.
Total annual rainfall below 250mm
Describe and explain the climate of hot deserts
Sub-tropic high pressure zone either side of the equator causes air to sink, resulting in cloudless skies. Cloudless skies allow for high insolation during the day but rapid heat loss at night hence why hot during day and cold at night.
Describe water in hot deserts
Less than 250mm rainfall per year.
Water is in short supply. Rainfall occurs as short torrential downfalls, causing flash flooding.
High temps and low humidity results in rapid evaporation.
Describe soils in hot deserts
Typically sandy or stony and contain very little organic matter due to sparse growth of vegetation, making them not very fertile. 1m deep.
High evaporation draws water to surface, leaving behind salt deposits on the surface (salinisation).
Some desert foils may be very fertile because important nutrients for plant growth, such as calcium, haven’t been leached away over time. Once irrigated, desert soils can be used for agriculture.
Is the biodiversity low or high in the desert?
Very low
Describe the adaptations of plants in the hot desert using specific examples
Desert Yellow Daisy - small, linear, waxy leaves to reduce loss of water by evapotranspiration. Desert flowers also have seeds that only germinate after heavy rainfall and can complete lifecycles in less than a month.
Saguaro Cactus - Xerophyte. Can store up to 9 tonnes of water. Grows slowly to conserve energy. Have needles to reduce water loss via transpiration. Has vertical pleats that expand to allow greater water storage
Acacia trees - Short, fat trunks act as reservoirs for excess water. Roots can penetrate 50m to find water.
Describe the adaptations of animals in the hot desert using specific examples
Kangaroo rat - Don’t sweat to reduce water loss. Highly efficient kidneys produces little urine. Obtain water from food. Live in burrows during the day to avoid extreme heat.
Camel - Hump stores fat which can be metabolised for energy. Wide feet to walk on sand easily. Long eyelashes to keep sand out of eyes. Can go a week without water. 46 litres at one drinking session.
Fennec fox - Kidneys adapted to reduce water loss. Thick fur insulates them from cold desert nights. Large ears dissipates excess body heat. Nocturnal, hunt during cool nights.
Interdependence between soil and plants
Soils rely on plants to provide extra nutrients through dead vegetation. Plants help soil to retain more water, by providing shade from the searing desert sunlight. Plants tie soil together preventing soil erosion from wind and leaching of nutrients during wetter periods.
Describe people in hot deserts
Tribes such as Bedouin in Jordan live in large open tents, keeping them cool day, warm night. Food is cooked within warm sandy soils. Head scarves are worn by men provide protection from the Sun.
Case study for hot desert?
Western Desert, USA
Describe mineral extraction as a development opportunity in the Western Desert
Rich reserves of copper, uranium and coal. Copper is mined in the Sonoran Desert near Ajo, Arizona. Developments for uranium mining near the Grand Canon were limited due to environmental concerns from Havasupai people.
Describe energy as a development opportunity in the Western Desert
Solar - Strong insolation in deserts is opportunity for solar power. Sonoran Solar Project in Arizona will supply electricity to 100,000 homes.
Oil - 25 active oil sites in Arizona all owned by Navajo people. Over 100 indigenous employee produce oil worth $50 million.
HEP - Powered by Lake Mead.
Describe farming as a development opportunity in the Western Desert
Irrigation enables commercial farming to thrive in high temps and sunny conditions.
Aquifer-based (water abstracted from wells) farming in California’s Coachella Valley produces vegetables, lemons, peppers.
Canals are used for large-scale industrialised agriculture.
Describe tourism as a development opportunity in the Western Desert
Western’s desert most important source of income. Visits to National Parks and wilderness areas such as Joshua Tree and Grand Canyon. Lake Mead and Lake Powell, created as water management projects, attract 2 million visitors a year, offering sailing, water-skiing, fishing.
Las Vegas attracts 37 million visitors a year.
Describe the challenge of water supply in developing hot deserts
Water transfer from Colorado River has supplied drinking water and irrigation since Hoover Dam’s construction in 1935. 30 million people depend on water from the Colorado. Phoenix’s population is predicted to double by 2050, increasing water demand which may be larger than water supply. Water security is also threatened by climate change as annual temps may be 5 degrees higher in 2100 compared to 1970.
Describe the challenge of inaccessibility in developing hot deserts
Low population density has resulted in a lack of surfaced roads through the desert. Away from main cities, access is limited. This because when Native Americans first settled, they chose places where the temp was most tolerable away from high temps in Death Valley. Some major highways such as Route 66, links Chicago with California through the Western Desert. In 2015 an elderly tourist died of dehydration after becoming lost after attempting to drive off-road.
Describe the challenge of extreme temperatures in developing hot deserts
Summer temps can soar above 50oC.
Work outside is hard, especially for farmers who have to work outside. High temps lead to high rates of evaporation and water shortages. Traditional houses in Western Desert have whitewashed walls to reflect sunlight.
Describe desert fringes
Border of a hot desert. They support greater biodiversity and larger plants. Rain falls in a fairly predictable manner, making settled agriculture possible. They are classified as fragile environments as they face risk of desertification
Describe how climate change is a cause for desertification
Since the 1970s, the Sahel region of West Africa has experienced signifcant reductions in annual rainfall. Scientists believe that climate change may be disrupting normal rainfall patterns, causing more droughts and the spread of sand dunes across valuable crop land.
Describe how population growth is a cause for desertification
By 2050, population of Sahel is predicted to reach 1 billion. This growth is caused by many children being born and people living longer than they used to do.
People have migrated to desert fringe areas due to conflict in the Sahel region or else drought in other regions.
As population grows along the desert fringe, demand for food increases putting land under pressure, leading to vegetation destruction, soil erosion and desertification.
Describe how overgrazing is a cause for desertification
Overgrazing by goats and cattle results in vegetation being stripped from an area, leaving the soil bare and vulnerable to erosion. Overgrazing occurs when available pasture land is reduced either by natural causes (drought) or human causes such as political conflicts, restrictions on the movements of nomadic herders and population pressure.
Describe how overcultivation is a cause for desertification
Land is exhausted of its nutrients as more crops are grown. Soils in semi-desert are not fertile anyway and contain little organic mater. When soils are over-cultivated (caused by population pressure of restrictions in available land) the soil becomes dry and infertile, leaving it vulnerable to soil erosion.
Describe how soil erosion is a cause for desertification
When vegetation is stripped or killed, soil is left bare to be baked by the sun. When rainfall occurs, it washes over the hard surface, eroding rills and gullies and washing away the topsoil. The infertile sub-soil that is left behind cannot be used for anything. Soil can take thousands of years to form but can be eroded very quickly.
Describe how removal of firewood is a cause for desertification
Millions of people living in semi-arid regions depend upon wood as their primary source of fuel. When the land is stripped of its trees, it can be vulnerable to erosion by wind and rain and can quickly turn to desert. Also occurs with population growth as wood is used for building houses.
Describe how water and soil management can be used to reduce the risk of desertification
Used in Burkina Faso area of Sahel. Involves constructing a series of low rock walls called bunds which follow the contours of the land, interrupting the flow of surface water downslope. Any soil carried by water is deposited on the upslope side of walls, collecting soil that can be cultivated. This addresses the problem of intense rainfall washing away loose soil, causing soil erosion.
Describe how tree planting can be used to reduce the risk of desertification
Trees are very effective in preventing soil erosion and desertification as they prevent soil from direct force of torrential rain. Roots also help to bind the soil together preventing it from being washed away.
2007 African Union launched a project called the ‘Great Green Wall’ a plan to plant trees across southern edge of Sahara Desert to reduce desertification. 15 million hectares have already been restored in Ethiopia. 21 African countries involved.
Describe how use of appropriate technology/intermediate technology has been used to reduce desertification
Bunds in Burkina Faso. Makes use of local materials, basic tools and trucks for transport .
Fuel-efficient stoves in Senegal reduces reliance on fuelwood. These fuel-efficient stoves require 55% less firewood, reducing fuel costs, amount of vegetation needed and therefore reducing deforestation on the desert-fringe. Often supplied by charities such as Practical Action.
