Deserts As Natual Systems

Question 1

Explain the concept of systems in hot deserts?

Answer 1

Deserts are open systems because they transfer both energy and matter in and outer of the system.

For example: input of energy from the sun -> transfer/flows : erosional processes -> store/components: erosional landforms and landscapes -> flows/transfers -> wind and water transport -> output: water and wind remove sediment

Question 2

Explain the concept of open systems in the context of hot deserts?

Question 3

Explain the concept of closed systems in context of hot deserts?

Question 4

Explain the concept of dynamic equilibrium in the context of hot deserts?

Question 5

Explain the concept of positive feedback systems in the context of hot deserts?

Answer 5

Recreated agricultural and livestock yields -> local populations increase livestock numbers and extend and intensify cultivation -> deforestation and overgrazing occur -> soil quality is degraded and reduced vegetation leaves soil exposed to erosion by water and wind -> desertification -> ……..

Question 6

Explain the concept of negative feedback systems in the context of hot deserts?

Answer 6

Intense weathering of slopes -> build of an apron of scree -> the apron extends up the mountains -> lower slopes are protected from weathering

Question 7

Explain the concept of the water balance in the context of hot deserts?

Question 8

Explain the concept of landforms and landscapes?

Answer 8

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Landforms combine to produce the characteristics of a hot desert and landscapes are constantly changing elements of the geomorphological systems of which they are a point.

Question 9

How do related landforms combine to form characteristic landscapes?

Question 10

Describe and explain the global distribution of hot deserts?

Answer 10

1. Deserts cover over 1/5th of the surface of the earth
2. Generally run in parallel belts north and south of the equator in arid and semi arid mid and low latitude locations
3. Almost all hot deserts landscapes in the northern hemisphere are located towards the west of continents
   - the Sahara in North Africa
   - the Mojave deserts in North America
4. In the Southern Hemisphere hot deserts include
   - Atacama in South America’s
   - the Namibian in Southern Africa
   - Great Sandy (western) in Australia

Question 11

What is the aridity index and how is it used to classify deserts ?

Answer 11

1. The aridity index (AI) provides a numerical value to indicate the relative dryness of deserts
2. (Aridity Index = the ratio between precipitation (P) and potential evaporation (PET))
3. Semi arid deserts and arid deserts can therefore be separated into categories.
   - arid = climate of an area that receives less than 250mm of precipitation per year
   - semi arid = the climate of an area that receives between 250 and 500mm of precipitation per year
4. Can be used to indicate the native vegetation which can possibly inhabit a given area.
5. Also useful for crop cultivation. As high than avg precipitation and lower than average temps are best to limit stress to crops
6. Changing measurements can be tracked to indicate the process of desertification, particularly longitudinal studies

Question 12

Explain the 4 causes of aridity and regional variations in their importance?

Answer 12

Global
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(Atmospheric conditions)
Atmospheric circulation causes air to sink 20-30 c north and south of the equator. This prevents cloud formation, creating an arid desert environment. In the terms of scale, atmospheric conditions occurs on a very global scale, affecting all hot desert environments. However, on its own atmospheric circulation isn’t responsible for the formation of most arid environments.
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(Continentality)
Continentality can be a factor in forming an arid environment, however on its own its affect is limited. In simple terms, Continentality is when further from the coast you are, the less cloud forms, and the warmer the area because land heats up quicker than water due to its lower specific heat capacity. This affects quite a lot of the world, affecting large continents like Africa, with central Sahara being more arid than areas closer to the coast.
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(Relief Rainfall)
A cause of reasonably arid environments is the rain shadow effect. Where moist air is forced up a mountain rage and cools, condenses and forms clouds. There’s relief rainfall on the windward side of the mountain, creating a dry environment on the leeward side, as the airs lost its moisture. This effect contributes to arid environments such as the Colorado Desert. It’s effect however is quite local, although it effects more of the worlds deserts than cold ocean currents.
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(Cold ocean currents)
In order to create very arid environments a main cause is cold ocean currents. This can be seen in south western America, in the Atacama desert. This desert is hyper arid, and a large factor in this effect is cold ocean currents. These currents prevent moist air from rising, therefore preventing cloud formation, instead providing a low mist which is burnt away by large amounts of insolation. Despite forming a very arid environment, its scale is local. Looking at the amount of deserts where cold ocean currents are a cause there are very few. Only the Atacama, as well as in the very North and South of Africa.
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Local

Question 13

Describe and explain the climatic differences between hot desert environments?

Answer 13

Although hot deserts are warm throughout the year with very hot summer temperatures, they have climates characterised by extremes:

1. Temperatures vary widely (between the hottest and coldest months) and diurnally (between day and night temperatures)
   - cloudless skies explain the high diurnal range as temps drop very rapidly at night, with hot deserts losing twice as much heat at night as the more humid latitudes ( in some places diurnal range can be over 30 c)
2. As distance from the tropics increase so does the annual temperature range in hot deserts due to the increased seasonality of climate. This means that desert margins have huge variations in temperature, with those on the poleward side of arid areas being significantly colder than those on the equatorial side.
   - With very low humidity levels in hot deserts, especially those in subtropical latitudes, cloud levels are extremely low. Clear skies allow significant amounts of insolation to reach the surface, almost twice that at more humid latitudes close to the equator.

Question 14

Describe and explain the relationships between the climate and the soils in the hot desert environment?

Answer 14

• 17% earths surface has desert soils
  When soils do develop i deserts they are often infertile with a thin soil profile and tend to be alkaline and quite saltine. Rates of soil development are extremely slow in hot deserts due to
  
  • the skies are clear and combine with the high angle of incidence of sun’s rays which causes insulation levels to be extremely high. This means that evaporation rates are high and leave topsoil very little moisture to absorb. Thus arid climate as resulted in loose, alkaline and quite infertile topsoil that supports sparse, highly adapted vegetation. The poor soils result in low productivity soil.

Question 15

Describe and explain the relationships between the climate ad the vegetation in the hot desert environments?

Answer 15

Due to the lack of precipitation and extremely high temperatures, plants have to make adaptions to survive.
Eg plants that can adapt their features to suit arid environments are called xerophytic

Adaptations
1. Thick and waxy cuticles that reduce transpiration, meaning they lose less water, and they crop their leaves to prevent water loss.
2. Desert trees, such as the acacia tree, have wide trunks so they can store water in them to use in periods of no rainfall. Their bark is also thick which makes the fire-resistant to extreme heat.
3. Due to extreme heat, some plants store their biomass under th surface of the soil, where temps are cooler, reducing risk of dying.
4. Many plants such as cacti, are succulents, meaning they store water in their tissue. Cacti also have spikes which stop animals from eating them and reduce water loss
5. Some plants also have horizontal root systems that spread out to get as much water as possible when it does rain, whilst others have long tap roots that reach 7- 10 metres below the surface to get groundwater.
6. Plants can also be ephemeral, which mean they change their behaviour to suit the conditions. Some desert flowers lie dormant for years and germinate quickly after a period of rain. This helps them complete their lifecycle in a few weeks, including creating flowers to attract insects