Causes
High pressure belts → descending air warms and expands → warm air has lower humidity, same amount of water vapour relative to parcel of air
Rain Shadow → air is forced up mountains → cools and condenses → rain falls on windward side → leeward side is high pressure and dry
Continentality → air that travels over large land masses becomes dry
Cold Ocean Currents → no precipitation from evaporation, e.g. Humbolt, Benguela, California
Flash Floods
Common in arid areas as ground is baked to be impermeable
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Causes
High pressure belts → descending air warms and expands → warm air has lower humidity, same amount of water vapour relative to parcel of air
Rain Shadow → air is forced up mountains → cools and condenses → rain falls on windward side → leeward side is high pressure and dry
Continentality → air that travels over large land masses becomes dry
Cold Ocean Currents → no precipitation from evaporation, e.g. Humbolt, Benguela, California
Flash Floods
Common in arid areas as ground is baked to be impermeable
High Pressure Belts
Tri-Cellular Model: Hadley, Ferrel, Polar
Hadley Cell: Low pressure at equator, high pressure at 30° north and south(subtropical high)
Human Challenges
Heat:
Resource Development:
Desertification
results from large-scale, longterm land degradation, land becoming desert
1/3 of land is at risk today
Land/Soil Degradation
Process whereby soil becomes less productive as a result of physical factors(e.g. drought) or human factors(e.g. overgrazing, bad land management)
Natural Causes of Desertification
Drought
Human Causes of Desertification
Changing Distribution: Sahar & Kalahari
Changing Distribution: Fertile Crescent
Why is it no longer fertile?
Deserts
Climatic region that receives less than 250mm a year of rain, 1/3 of the world is arid, <25mm is extremely arid
Challenges of Agriculture in Arid Areas(8)
Benefits of Agriculture in Arid Areas
Saline Soil
contains an excessive amount of soluble salts
Sodic Soil
contains high amount of absorbed sodium ions that damage structure
SAS
Soil-affected soil, 8.7% of land(833 million hectares)