Arid and Semi Arid Environments

Question 1

What does arid mean?

Answer 1

Arid refers to areas with a permenant water deficit and less than 250mm of rainfall per annum.

Question 2

What does semi-arid mean?

Answer 2

Area with less than 500 mm of rainfall per annum

Question 3

What is aridity?

Answer 3

Is the lack of moisture and insufficient rainfall to support flora.

Question 4

Where are arid areas located?

Answer 4

Mostly in the tropics asscociated with high pressult belt. However some alongside cold coean currents e.g. Namib and Atacama. And lee of mountain ranges e.g. Gobi

Question 5

What is the equation for index of moisture availability? Evaluate the equation.

Answer 5

lm= (100S-60D)/PE

S= Moisture surplus
D=Moisture Deficit
PE= Potential evapotranspiration

Question 6

What is the index of moisture availability for semi-arid areas?

Answer 6

between -20 and -40

Question 7

What is the index of moisture availability for Arid areas?

Answer 7

-40 and -56

Question 8

What is the index of moisture availability for Extremely arid areas?

Answer 8

Less than -56

Question 9

What influences the effects of precipitation and evapotranspiration on hot arid and semi arid env?

Answer 9

Rate of Evaporation
Seasonality
Rainfall Intensity
Soil Type

Question 10

Causes of aridity?

Answer 10

Continentality
Cold off shore currents
Rainshadow effects

Question 11

How does the Global atmospheric circulation cause aridity?

Answer 11

Most deserts lie in the subtropical high pressure zone, where the air is subsiding in the descending limb of the Hadley cell causing dry stable air.

Question 12

How does the Cold Ocean Currents cause aridity?

Answer 12

Upwelling of cold water due to the circulation of wind currents. The cold water on the surface decreases the temperature of the overlying air mass and reduces how saturated it can be with water. Which makes the air above the land dry. E.G. Atacama and Namib

Question 13

How does continentality cause aridity?

Answer 13

If the air mass moves over a continent it will lose moisture due to rainfall. It will not pick up much moisture due to low evaporation rates and so areas which are located in the centre of continents will have very little rainfall.

Question 14

What are the charecteristics of desert climates?

Answer 14

High diurnal temperature range
Less than 500mm of rainfall per year
Extreme rainfall events
High evaporatranspiration rates

Question 15

What are the natural sources of water in hot arid and semi arid env?

Answer 15

Aquifers- Due to permeable rock containg fractures

Coastal mist and fog- Sinking air above moist air formed over a sea

Dew- Water in the form of droplets

Question 16

What are the processes of erosion in Hot Arid and Semi Arid environments? Explain them individually.

Answer 16

Deflation - wind removes/carries away loose and fine regolith forming stony desert surfaces

Abrasion by wind- Particles in the wind are driven against the rocks and erode surfaces like sandpaper. Rate depends on velocity of wind.

Abrasion by water- Sediment in water grind and wears away bank and bed of channel

Sheet runoff- After a heavy rainfall event high discharge in channel causes fluvial erosion to occur.

Question 17

What are the processes of wind transportation? Explain them individually.

Answer 17

Suspension- Particles less than 0.15mm carried in the air.

Saltation- Small pebbles and stones are bounced along river bed.

Surface creep- Where particles that are greater than 0.25mm are rolled or pushed along the ground.

Question 18

Types of water transportation?

Answer 18

Suspension- Where fine particles of clay and silt are dislodged and carried by the turbulence in the river.

Solution- Where soluble material is dissolved in the running water and removed in solution due to the acid in the river.

Traction- Large boulder erode sea bed

Saltation- Is where pebbles and gravels are temporarily lifted by the current and bounced along the bed.