Hot Deserts

Desert

A large barren area with minimal precipitation and high temperatures. 1/5 of earth’s surface, often running in parallel belts either side of the equator in mid-low latitudes, mostly in the northern hemisphere to the west of continents

Aridity Index

Ratio between precipitation and evapotranspiration

Hyper-arid

Arid

An area 100-250mm of rain, with a 0.05-0.20 aridity index 

Semi-arid

250-500mm precipitation, 0.20-0.50 aridity index 

Water balance

Precipitation = evaporation +/- soil water storage + runoff

Continentality

The way a large land mass affects weather and climate, with air masses losing moisture as it travels inland, leading to less precipitation and vegetation

Relief

Air descends on the leeward side of a slope, causing it to become warmer and drier

Global oceanic circulation 

The large-scale movement of water, with warm water carried towards the poles, cooling and sinking, and eventually returning to the surface, carried back to the tropics 

Inter-tropical convergence zone (ITCZ) 

A band of low pressure around the Earth which generally lies near to the equator

Atmospheric processes

Air is heated at the equator, rising, cooling, condensing and eventually sinking, producing a high pressure air mass which warms due to compression as it descends This produces a stable air mass, creating an anticyclone

Hadley Cell 

0-30° Beginning at the equator, where solar radiation warms the air causing it to rise through convection. This rising air causes low pressure at the surface

Ferrell Cell 

30-60° latitude, with cold air sinking at 30 and rising at 60 

Diurnal temperature range 

The difference between the hottest and coldest point over a 24-hour period: high due to little cloud cover

Potential evapotranspiration (PET) 

The amount of water that would be evaporated if sufficient water is available 

Humidity

How much water vapour is in an air particle 

Soil profile

Vertical cross-section of the soil 

Capillary movement

Water moving upwards through soil pores 

Aridisols

Reddish-yellow to grey-brown in colour, thin

Raw mineral soils

Coarse texture, rocky due to physical weathering. Calcium/sodium salts accumulate near the surface due to water existing, little leaching causes little variation between horizons. Slightly alkaline, unproductive

Sierozem

Grey desert soils, developing below vegetation, calcium-rich horizons can develop below, with rich accumulations of calcium carbonate lightening the soil. Often used for cultivation

Leaching

Removal of nutrients by water

Xerophyte

Plants that have adapted to live in desert environments with thick, waxy cuticles, and small/spiky/no leaves reducing water loss

Phreatophyte 

Plants with long roots to tap into the ground water 

Halophyte

Plants adapted to saline soils

Ephermals

Plants with short life cycles, appearing after storms and becoming dormant during dry spells

Angle of incidence

The angle formed by a ray or wave on a surface and a line perpendicular to the surface at the point of incidence

Insolation

The amount of short-wave radiation reaching the earth’s surface, some radiated back due to little cloud cover

Rain shadow 

An area forced to become a desert due to mountain ranges blocking rain 

Sediment

Small material usually consisting of sand  

Sediment cell

The movement of sediment

Sediment budget

Relative amount of sediment in each part of the system 

Weathering

The breakdown or decay of rocks as a result of the weather 

Thermal fracture

Weathering due to expansion and contraction of the outer surface of rocks due to intense temperatures 

Exfoliation

The peeling/flaking of the outer skin of the rocks due to intense hot and cold temperatures

Chemical weathering

Absorption of carbon dioxide in the atmosphere, breaking down rocks

Mass movement

The movement of a large amount of material downwards due to gravity 

Erosion

The wearing away of material

Denudation

Wearing away of the surface by weathering and erosion

Rill erosion

Sheet wash forming a path

Sheet erosion

Water flowing as a sheet, washing away particles

Gully erosion

Rills becoming wider and deeper

Splash erosion

The force of rainwater displacing soil particles

Bank erosion

Fast water wearing away the sides of streams

Hydraulic action

The force of water into cracks of rock

Abrasion

Transported material hits exposed surfaces, carving and sculpting it, affected by the particle size/nature, the lithology of the ground and the directon/frequency/velocity of the wind

Corrosion

Fragments of rock carried by water

Solution

The dissolving of soluble rocks

Wind

Driven by atmospheric circulation, seasonal or trade winds. Caused by: air is heated, rises and cooler air moves to replace, high angle of incidence, limited cloud cover and vegetation

Traction

The rolling of sediment over the surface

Saltation

Sand-sized particles bounce along the surface

Suspension

Fine particles held in the air

Deposition

When waves run out of energy to carry and transport sediment

Hydration

The process of absorbing water

Hydrolysis

The chemical breakdown due to a reaction with water

Oxidation

The addition of oxygen

Crust

Thin layer of material on top of soil 

Duricrust or hardpan 

A mineral crust formed on the surface of soil due to evaporation of groundwater

Desert varnish

A dark coating found on rocks exposed to the sun

Block/granular disintegration

The breaking down of rocks made of grains into sand grains 

Loess

A wind deposit of silty material, usually yellow to brown in colour 

Deflation

Wind erosion involving the removal of loose material from the desert floor, exposing underlying bedrock 

Surface creep

Accounts for 25% of movement: particles hit larger ones, causing them to slide/roll along the surface, in conjunction with saltation

Exogenous rivers

Originating outside the desert

Endoreic rivers

Rivers that never reach the sea, draining into an inland sea instead

Ephemeral rivers

Rivers that only flow seasonally, after a heavy rainfall event

Distributaries

River channels branching away from the main river channel 

Episodic flash floods

Infrequent rainfall events, causing intense surface runoff

Sheet flooding

Flooding after a storm where water flows in sheets across a landscape rather than going into gullies and valleys 

Channel flash flooding

Flooding that happens after a storm where water makes it way into channels

Deflation hollows

A depression caused by wind eroding loose material from the surface 

Reg/desert pavement

A stony desert area where rock fragments are scattered over a large plain 

Venifacts

Sharply angled rock found on a desert pavement formed by abrasion 

Yardang

A streamlined rock structure formed where horizontally laid rocks form elongated ridges, separated by deep grooves cut into the surface. Weaker rock is eroded by abrasion to form deep troughs, with tougher rock left upstanding

Zeugen

Ridge formed by abrasion of vertical bands of resistant rock

Barchan

Crescent-shaped sand dunes formed at right angles to the prevailing winds 

Sief dunes

Linear sand dune formed parallel to prevailing winds 

Wadis

Dry river channel formed by periodic water erosion 

Pediments

Gently sloping, usually concave rocks surface at the foot of a mountain front

Alluvial fan - Lucy Gray Fan

Washed out sediment is deposited, displaying stratification with finer sediment washed out onto the desert plain

Bajada

Extensive alluvial fans can coalesce to form a continuous apron of sediment

Playa - soda lake

Water carried onto the desert floor percolates through loose sediment, transferring as throughflow to collect in large hollows/depressions

Inselbergs

Develop from rocks which eroding at a slower rate than surrounding rocks, consisting of erosion-resistant rock protecting the softer rock

Scree

Small loose stones forming over a slope 

Mesa

Table-like relic landform formed in horizontally bedded rocks 

Butte

Smaller pinnacles of rock surrounded by flat desert plains 

Badlands

Clay-rich soil, extensively eroded  

Plateaux

A flat, elevated landform rising sharply above the surrounding area on one side 

Gullies

A trench in land due to eroded water, created an accelerated stream

Interglacial

A warm period between glacial eras

Oasis

An area made fertile due to freshwater in an otherwise dry area

Desertification

Turning marginal land into desert by destroying the biodiversity potential

Ecosystems

A geographic area where a range of organisms depend on each other for life 

Human Development Index (HDI) 

A mix of indices that show life expectancy, knowledge (adult literacy and education) and standard of living (GDP per capita) measuring development 

Grassroots 

Using the people in a given area as the basis for a larger political or economic movement 

Regionalisation 

Dividing an area into smaller segments, adapting to fit a smaller area 

Globalisation 

The increased connections between places and people over the world 

Landsat 

A satellite studying and photographing the earth's surface using remote-sensing techniques

Mitigate 

Reduce or prevent the effects of something 

Sustainable Solutions 

Allowing something to continue without harming the future generation’s resources