hot deserts Flashcards
what is mineral extraction
the removal of solid mineral resources from the earth. these resources include ores, fuels such as coal or oil and precious stones
desert definition
an area receiving less than 250mm of rainfall resulting in extreme aridity
desertification definition
the process by which land becomes drier and degraded, as a result of climate change or human activities or both
biodiversity definition
the variety of life in the world or a particular habitat
overgrazing definition
grazing too many livestock for too long on the land, so it is unable to recover its vegetation
over-cultivation definition
exhausting the soil by over-cropping the land
appropriate technology definition
technology suited to the needs of the local people that combines cheap materials and is environmentally friendly
soil erosion definition
removal of topsoil faster than it can be replaced, due to natural (water and wind action), animal, and human activity. topsoil is the top layer of the soil and is the most fertile because it contains the most organic, nutrient-rich materials.
aridity definition
the state or quality of being extremely dry
irrigated definition
artificial watering of the land
xerophytes definition
plants that can survive in very dry conditions
carrying capacity definition
the maximum number of people an area of land can support before environmental damage occurs
physical characteristics of a hot desert
- dry
- arid
- sandy
- lack of biodiversity
- baron
- isolated
how much rainfall is there per year in deserts
less than 250mm per year
consistency of rainfall in deserts
rainfall patterns may vary - it might rain once every few years
why are temperatures extreme
due to the lack of cloud covers
- it can reach 45 degrees celsius in the day, then drop to below 0 degrees at night
where are deserts typically found
between 15 degrees and 35 degrees north and south of the equator
what lines pass through most of the worlds hot desert regions
Tropic of Cancer and Tropic of Capricorn
what continent has NO deserts
europe
why is desert soil not fertile
due to lack of organic matter + lack of leaf fall
what is desert soil typically like
typically sandy or stony and dry
what does little rainfall mean for the soil
it dries out often
why is most hot desert soil dry and not very fertile
due to lack of rainfall and sparse vegetation, there is little decomposing matter to enrich the soil. the nutrients that are present decay rapidly due to the high temperatures. only a limited number of plants, such as the drought-resistant cactus, can survive the harsh desert conditions
what is the effect of having low cloud cover
there is high diurnal temperature range because lack of cloud means that temperatures during the day are very hot. at night temperatures fall to very cold as there is nothing to keep the heat in (lack of clouds)
why do deserts occur where they are
most deserts are at 30 degrees north and south of the equator - air is sinking (high pressure) - as it isn’t rising - few clouds forming and little rain. lack of cloud means hot during the day and very cold at night
plants in hot deserts:
- due to the low rainfall, plant growth is sparse - the plants that do grow, such as cacti or thornbushes, don’t need much water
- plants are usually short (eg. low shrubs or short woody trees) though cacti can grow fairly tall
- many plants have short life cycles, growing quickly after rain
animals in hot deserts:
- 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 birds, like roadrunners, can live there all year round
people in hot deserts:
- many people living in deserts grow a few crops near natural water sources, usually in the desert fringes
- indigenous people are often nomadic - they keep travelling to find food and water for their livestock
biotic meaning
living
abiotic meaning
non-living
what is biotic and abiotic organisms relying on each other called
interdependence
how are plants and animals interdependent
plants take up nutrients from the soil and provide nutrients and water to the animals that eat them. in turn, animals spread seeds through their dung, helping the plants to reproduce
how are plants and soil interdependent
- plants help soil retain more water, by providing shade from the searing sun
- roots of plants help to bind the soil together and prevent gulley erosion
- plants prevent soil erosion and excessive leaching of nutrients in wetter periods
- soils rely on plants to provide extra nutrients through dead vegetation and fixing chemicals from the air into soil
- in turn, plants rely on soil for their nutrients
why do plants struggle to grow in hot deserts
soils are salty due to high evaporation rates, and relatively low in nutrients because there is little decomposition of dead plant material by fungi and bacteria
how can humans positively impact the interdependence of soil/water/plants/animals in hot deserts
- sustainable land management practices
- wilding
- afforestation
- using underground or surface water at a sustainable rate
how can humans negatively impact the interdependence of soil/water/plants/animals in hot deserts
- urbanisation putting pressure on scarce resources
- deforesting/removal of vegetation
- footpath erosion in busy places like the Grand Canyon, making soil vulnerable to blowing away
what are plants that can survive in very dry conditions called
xerophytes
what do xerophytes use to minimise water loss
a range of adaptations, including thick, waxy cuticles and the shedding of leaves to reduce transpiration
what do some plants do to combat high temperatures
have the bulk of their biomass below the ground surface where temperatures are cooler
what happens to deserts after rainfall
deserts bloom suddenly so complete their life cycle quickly
what areas of deserts have the highest levels of biodiversity
small areas around ephemeral (temporary) ponds and rivers or along the desert margins have the highest levels of biodiversity, and contain a high proportion of species that are endemic (unique) to the desert
what areas of deserts have the highest human population
areas with water
how can people threaten biodiversity
by increasing desertification and over-using or contaminating water supplies
what does development around the desert margins mean
means that habitats are being divided up by roads. this is threatening animals that migrate over large distances to find food and water
what is global warming doing to hot deserts and what effect will it have on species living there
making them hotter and drier
this is forcing some species to move to cooler areas. however, some species are already at the limits of their environment and don’t have anywhere else to go, so art at risk of decline or extinction
what does low biodiversity and pressure from development and climate change mean for deserts
means that deserts contain many biodiversity hotspots - places where there are a high proportion of endemic species that are threatened with extinction
how are the leaves of plants adapted to live in deserts
- most plants will have small, linear leaves or needles in order to reduce loss of water through evapotranspiration
- leaves often also have a waxy resin to reduce evapotranspiration
- these help the plant adapt to dry conditions and high nutrients
how are the roots of plants adapted to be able to live in deserts
- plant roots are either extremely long to reach deep water supplies (eg. mesquite roots can grow 50m long)
- or they can spread out very wide near the surface to absorb as much water as possible when it rains
- this helps them to adapt to dry conditions and competition for nutrients
example of a xerophyte
Saguaro Cactus
adaptations of the Saguaro Cactus:
- grows very slowly in order to conserve energy
- can store up to 9 tonnes of water
- body is made of vertical pleated that expand to allow greater water storage
- can lose 82% of its water before dying of dehydration
- these adaptations help it combat dry conditions and competition for nutrients
adaptations of succulents (eg. cacti) in deserts
- have large, fleshy stems for storing water
- have a thick, waxy skin to reduce transpiration
how do some plants adapt to the lack of rainfall in desert
some plants (eg. brittlebush) only germinate after it rains - if its too dry the seeds stay dormant (inactive)
however, when they do grow, they grow quickly to make the most of wet conditions
how are kangaroo rats adapted to live in deserts
- don’t sweat/have oily skin (reduce water loss)
- produce little urine
- live in burrows during day
- don’t need to drink - get water from food
adaptations of adder to live in desert
move side ways - means less than 50% of body is in contact with hot sand
how are fennec fox’s adapted to live in hot deserts
- their large ears, which are usually 6 inches long, help dissipate excess body heat on hot days in the desert
- the fennec fox seems to be the only carnivore living in the Sahara desert able to survive without free water
-> their kidneys are adapted to restrict water loss
-> their extensive burrowing may cause the formation of dew, which can then be consumed, and they will receive moisture from the food they eat - their thick fur helps insulate them from the cold desert nights
- their sandy fur helps to reflect heat, and also provides excelled camouflage
- they have thick hair on the soles of their feet, which insulates against the hot sand of the desert -> this extra fur also affords them excellent traction in the loose sand
how are camels adapted to live in hot deserts
- they can go a week or more without water, and can last several months without food
-> they can drink up to 46 litres of water at one drinking session - camels store fat in the hump, that can be metabolised for energy
- unlike most mammals, a healthy camels body temp fluctuates throughout the day -> this allows the camel to conserve water by not sweating as the environmental temp rises
- camels feet are wide so they can walk on sand more easily -> their huge feet stop them sinking into the sand when walking
- they have thick lips so they can eat the prickly desert plants without feeling pain
- their ears are covered with hair, even on the inside, to keep out sand or dust that might blow in their ears
economic and social opportunities in hot deserts
- tourism
- mineral extraction
- farming
- solar energy
what is the case study for hot deserts
the Western Desert, USA
what three smaller deserts is the western desert made up of
- mojave desert
- sonora desert
- chihuahua desert
what states does the western desert cover
- new mexico
- arizona
- california
- nevada
opportunities of development in the western desert
- high temperatures and sunlight are favourable for agriculture
- rich in minerals - including copper, uranium, lead, zinc and coal
- the strong insulation provides a fantastic opportunity for solar power -> the entire western desert is predicted to benefit from the construction of new solar power plants
- hydroelectric power plants also supply the western desert communities with some of their electricity
- fossil fuels
where can water be found for farming in the western desert
aquifers:
- large stores of water lie beneath some hot desert regions
- sometimes, a layer of permeable rock lies on top of an impermeable rock
- rainwater and groundwater seep into the permeable layer and become trapped
- this water can be brought to the surface by digging a well
- aquifer-based farming produces lush crops of vegetables, lemons, peppers and grapes (and in turn a wine industry)
what are the challenges of development in the western desert
- the uranium found there can’t be used as uranium is used in nuclear power plants so they were concerned about the risk to wildlife and endangered species and the contamination of water supplies
- lack of water discourages large scale farming
what is the western deserts most important source of income
tourism
how many visitors per year does Las Vegas attract
37 million
how many visitors per year does Lake Mead and Lake Powell attract
2 million
tourism in the western desert:
- national parks offer visitors a chance to experience a wilderness area -> important areas include the Grand Canyon and California’s Joshua Tree National Park
- the heritage and culture of Native americans is celebrated at the Colorado Museum
- the entire enconomy of vegas is built around entertainment, attracting 37 million visitors per year
- two major lakes have been created as part of water management projects: Lake Mead and Lake Powell -> they attract 2 million visitors per year and offer sailing, power boating, water-skiing and fishing
how many homes will the Sonoran Solar Project produce energy for
100,000
at the peak of its construction (in the 1930s), how many people did the Hoover Dam provide jobs for
5000
since what year have people been drilling for oil in arizona
since 1905
how many active oil production sites are there
25
farming in the western desert:
- irrigation enables commercial farming to thrive in sunny and hot conditions
-> coachella valley (california) produces vegetables, peppers and grapes (for wine) using water abstracted from underground aquifers
potential challenges of tourism in the western desert
- jobs encourage population growth in an already fragile environment
- tourists demand water - showers, swimming pools, food requires huge amounts of water
potential challenges of mineral extraction or energy generation in western desert
- conflicts with other land uses (like tourism and farming)
- contamination of water
- hoover dam increases evaporation
challenges faced by desert areas
- climate
- water supply
- transport and accessibility
- climate change
climate challenges in deserts:
- high temps lead to high rates of evaporation and water loss
- work outside is very hard, especially for farmers who have to work during the day
- summer temps can get to about 50 degrees celsius
water supply challenges in deserts:
- water supply could be a huge problem in the future as demand soars
- temps are forecasted to rise due to climate change
- piper water supplies homes, farms and golf courses
- water transfer, from the colorado river has supplied drinking water + irrigation since the hoover dam was constructed
transport and accessibility challenges in deserts:
- access is limited when away from major cities
- the relatively low population density resulted in a lack of surfaced roads through the desert
climate change challenges in desert:
temperatures are forecasted to rise due to climate change -> means more water will be demanded
what is desertification
the process of land becoming drier and degrading in quality due to both human activities and natural processes
what fraction of the worlds land is at risk of desertification
1/3, particularly desert margins
when does desertification occur
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 the soil are lost, making it unproductive. eventually the group becomes sandy, dusty, stony or bare rock
what are the main causes of desertification
climate change and human activities and population growth
why is climate change a cause of desertification
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 temps cause more water to evaporate from the land
- this makes soils drier, so plants struggle to grow
why are human activities a cause of desertification
removal of fuel wood:
- many people in arid (dry) 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 regrow
- 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 (eg. for firewood), more overgrazing and more over-cultivation
what is an example of a fringe desert area
the Sahel
where is the Sahel
south of sahara desert
how many people live in the sahel region
over 50 million
what are the causes of population pressure in fringe desert regions
- reasons linked with poverty, such as lack of education
- migration
- drought and desertification displace people to other areas
- conflict in the sahel region
why is population growth a main cause of desertification
- high fertility among local people + migration
- leads to higher demand of water
different strategies to reduce the risk of desertification
- water management
- tree planting
- soil management
- appropriate technology
how can water management reduce the risk of desertification
- growing crops that need little water (eg. 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 at once
how can tree planting reduce the risk of desertification
- trees can be planted to act as windbreaks, reducing wind erosion
- trees can also stabilise the sand and prevent desert from encroaching on farm land
- growing trees in amongst crops protects them and the soil by providing shade, reducing temperature and evaporation rates
how can soil management reduce the risk of desertification
- leaving areas of land to rest in between grazing or planting lets them recover their nutrients
- rotating crops that take different nutrients from the soil prevents the same nutrients from being continually removed
- compost can be used to add extra nutrients to the soil
how can appropriate technology reduce the risk of desertification
- 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
common strategy of water and soil management
- used in parts of the sahel
- involves constructing a series of low rock walls called bunds
- these are deliberately constructed to follow the contours of the land, interrupting the downslope flow of the surface water
- and soil carried by the water is deposited on the upslope side of the walls, creating a reasonable thickness of soil that can be cultivated
common strategy of appropriate technology
- low walls (bunds) to manage water -> makes use of local materials, basic tools and transport and it based on a simple idea. is community led, it makes use of the local people who work together for a common aim
