B:Hot and Semi-Arid Environments Flashcards
(16 cards)
What are the causes of aridity
- Atmospheric Circulation
- Continentality
- Rainshadow Effect
- Cold Ocean Currents
- Drought Periodicity
Explain how the global atmospheric circulation causes aridity
- Dry descending air associated with the sub-tropical high-pressure belt is the main cause of aridity around 20-30 degrees North
- The stable adiabatically warmed subsiding body of air prevents rising air from reaching any great height
- Convection currents are rarely able to reach sufficient height for condensation and precipitation.
what does adiabatically warmed mean
atmospheric pressure changes associated with changing altitudes. Increasing pressure adiabatically heats air masses,
Explain how the rain shadow effect causes aridity
Produced by tall mountain ranges known as orographic belts. The windward slopes of these barriers are wetter than the leeward side. This is because as the air rises on the windward slopes of the mountains, pressure decreases and it cools resulting in condensation, cloud formation and rain. As air descends on the leeward side, pressure increases and the air is warmed preventing condensation.
How does Drought periodicity cause aridity
- Widespread rains are almost unknown over large parts of the arid areas, most of the precipitation comes in violent convectional showers that do not cover extensive areas. Because of the violence of these rains and the sparseness of the vegetation cover runoff is excessive, and consequently the less of the total rainfall becomes effective for vegetation
explain how continentality causes aridity
As an air mass moves over a continent it will lose moisture as precipitation. Equally the air will take up very little due to the low evaporation rates over land surfaces. Therefore, arid areas tend to occur in the centre of continents such as in Australia
State the characteristics of typical desert climates
- High diurnal temperature range
- Low rainfall totals
- High levels of evapotranspiration
5 factors which influence temperature
- Latitude
- Altitude
- Continentality
- Proximity to cold ocean currents
- Albedo
Why do deserts have high diurnal ranges
- Due to there being little cloud cover
- This means in the day incoming solar radiation is not impeded by cloud cover, and temperatures rise rapidly
- Then at night high-pressure clear skies mean terrestrial radiation is allowed to escape from the ground surface consequently the temperatures fall quickly
Why are evapotranspiration rates high
In arid areas, evapotranspiration rates are very high due to high levels on insolation and lack of cloud cover.
Characteristics of the hydrological cycle in arid regions
- Infrequent, short-lived rainfall events of high intensity
- Low interception rates
- rapid rates of evaporation and transpiration
- Little infiltration
- A greater proportion of overland flow than through flow
What are the 3 natural sources of water in arid environments
- Aquifers
- Coastal mist and fog
- Dew
What is an aquifer
the underground areas of water storage occur at different depths. Aquifers closer to the surface are often easy to exploit, and many have been over-used. Examples in the Atlas Mountains in North Africa. In other areas, deep fossil aquifers can hold vast amounts of water dating back thousands of years. underground layers of water bearing permeable rock. Can be located at ground surface or deep underground. Aquifers can have high permeability, so water can flow easily in this layer. Always an impermeable barrier under.
What is a Ephemeral River
These are rivers that flow seasonally or sometimes after rainstorms
What is an exogenous river
What that originates from outside the desert area
How can coastal mist and fog be harnessed
Chile has installed large nylon nets which cause water to condense on the mesh and it is transported away in pipes
