AS 2016 DESERTS

Hot desert environments and their margins

• Location and characteristics of hot deserts and their margins (arid and semi-arid) – climate, soils and vegetation.

• Causes of aridity – atmospheric processes relating to pressure, winds, continentality, relief and cold ocean currents.

• Arid geomorphological processes: mechanical weathering.

• The effect of wind – erosion: deflation and abrasion; transportation; suspension, saltation, surface creep; deposition.

• The effect of water – sources: exogenous, endoreic and ephemeral. The role of flooding.

• Landforms resulting from – wind action: Yardangs, zeugen and sand dunes – water action: pediments, inselbergs, mesas and buttes, salt lakes, alluvial fans, Wadis and Badlands.

• Desertification: distribution of areas at risk, physical and human causes impact on land, ecosystem and populations.

• Case study of desertification in the Sahel – the struggle for survival to include the energy/fuel wood crisis, water supply, the impact on food supply/ farming and livelihoods and coping/management strategies including external aid.

• Managing hot desert environments and their margins – to consider and evaluate the strategies adopted with regard to land use and agriculture in areas such as the Sahel and contrast with the development of areas such as south-western USA or southern Spain. Implications and potential for sustainability.

Location and characteristics of hot deserts and their margins (arid and semi-arid) – climate, soils and vegetation

What is a hot desert?

• Deserts cover 25-30% of the earth’s land surface

• The characteristic of a hot desert is its dryness (aridity)

• Another main characteristic of hot deserts is that they have a very high rate of potential evaporation, which often exceeds precipitation. This means there is little water for plants and animals. Thus organisms living in deserts and semi deserts have adapted to cope with life in such an extreme environment

• ARID desert will have less than 250mm of rainfall a year

• SEMI-arid deserts have an annual rainfall of 250-500mm

Location of the world’s hot deserts?

• Many of the worlds deserts are found close to the Tropic of Cancer and Capricorn (30 degrees North and South of the equator)

• Other deserts are found in continental interior (eg: Gobi in Asia)

• Adjacent to mountain ranges on the leeward side (due to the rain shadow)

• On the west side of continents due to the trade winds

• Near cold ocean currents: Wind is cooled as it travels over the cold water and its ability to hold moisture reduces. Moisture that is stored in the atmosphere is released as precipitation over the ocean before reaching land. So when the wind reaches the land there is very little moisture left so there is very little rain.

   

Desert Climate

• They have high sunshine value due to the absence of clouds. This is largely because deserts are located in zones with high atmospheric pressure.

• The lack of cloud cover also leads to large diurnal (daily)m temperature variations

• Strong desert winds and sandstorms can occur

• Thunderstorms can be triggered by intense convective activity

• Some coastal deserts (eg: the Atacama in South America) can be plagued by fog rolling in off the…