Geography - Drylands Flashcards
Diversity of drylands…
Rocky mountains, lake beds, river valleys or desert plains…
How many inhabit drylands?
2 billion.
Properties of dry lands?
Precipitation is weak and erratic annually, with arid areas.
Potential Evapotranspiration
The amonut of transpiration that would occur if there was a sufficient water source
When is there deficient moisutre?
When PET exceeds p
Types of arid envrionment…
Hyper-arid
Arid
Semi-arid
Dry-subhumid
Hyper-arid
True deserts with a P/PET value of less than 0.05
Examples of hyper-arid deserts?
Central sahara, Arabian peninsula and Namib deserts.
Arid
Classified as between 0.05 and 0.2, with 200mm annual rainfall
Semi-arid
Between 0.2 and 0.5, with 500mm rainfall in winter and 800m rainfall in the summer.
What does varying precptiation effect?
Agriucltural practices, huamn welfare, drougth susceptibiltiy
Dry-subhumid
Areas between 0.5 to 0.65
What causes aridity?
Subtropical regions
Intercontinentiality
Mountain Shadow Effect
Western Coastlines
Mountain Rain Shadow Effect
A patch of land that desertifies due to mountain rnage blocking plant growing, rainy weather.
Example of cause of aridity?
Sahara is subtropical, intercontinental and affected by the Tibesti Massif mountains
Why are Central Asia and North America Arid in places?
Continentality so weather systems cannot penetrate these area
Example of currents affecting aridity…
Namib and Atacama deserts affected by Antartic cold ocean currents, bringing colder cliamtes to these regions supressing sea surface evaporation and rainfall.
Example of seasonal variations of aridity…
Closer to the ITCZ then more susceptible to its movements and rainfall varaitions.
What are the types of soil?
Aridisoil
Alfsol
Entisoil
Mollisoil
Vertisol
What causes soil crusting?
High evaporation with icnreased mineral concentraiton that dry and form hard layers
How do biological crusts form?
Algae and Cyanobacteria with silica and calcium carbonate.
Hydrophytes
Wetland plants tolerating permenently saturated soils, foudn in very few drylands.
Mesophytes
Tolerate 10-20% soil moisture, measured between its fiedl capaicity and wilting point
Xerophytes
Can tolerate extreeme moisture deficieny with little as 5% moisture
How plants adapt to arid areas?
Regulate dormancy and limitation of growth and reproduction to the wet seasons.
What plants are found in deserts?
Rarely 10% cover, contain shrubs and grasses
What geographical sturctures influence drylands?
Tectonic activity and morphology like mountainous areas or flatlands.
Rock weathering in drylands..
High ET means higher mineral/salt concentration as well as the bare rock surfaces
Most common forms of weathering in arid areas?
Insolation and thermal weathering
Granular Disaggregation
The detachment of minerals due to stress of intercrystalline bonds being weaker than the intracrystalline bonds.
Salt Weathering
This is where high precipitaiton causes high salt concentration in tnadem with limited leeching
Why is salt crystallization favoured with higher temperatures?
Moisture induces increased salt volume and thermal expansion of increasing heat.
Infilitration Excess Overland Flow
A for of runoff where the surface is bare rock, and can promote surface sealin/crusting inunconsolidated sediments.
How does sedimentation occur in drylands despite low precipitation?
High convection and thunderstorms
Why do drylands ONLY exhbit low channel formation?
Low catchment and infilitration through the bed.
Aeloian Processes
Refers to wind activity and its erosion, tranportation and sediment deposition.
Example of aeloian processes?
Sand dunes
Types of dune?
Barchan, seif, star dunes and transverse dunes
Barchan and Seif dunes
Crescent shaped and Elongated respectively
Star dunes
Pyramidal sand mounds with slip faces on three or more arms that radiate from the high centre of the mound.
Transver Dunes
Are symmetrical, elongated dunes lying at right angles to the prevailing wind direction
