hot arid and semi arid environments definitions Flashcards
semi-arid
having rainfall of less than 500mm per annum
Aridity
is a permanent water deficit: less than 125mm of rainfall per annum
subtropical high-pressure belt
a zone of dry, descending air (high pressure) at the poleward side of the Hadley cell, leading to arid conditions
subtropical high-pressure belt
a zone of dry, descending air (high pressure) at the poleward side of the Hadley cell, leading to arid conditions
continentality
a climate that is charecteristic of a continental area having very hot summers, very cold winters and low rainfall
Rain shadow effects
the drier conditions on the leeward side of the mountains compared with the windward side
desertification
the spread of desert-like conditions, causing land degradation in humid and semi-arid areas - involves the loss of biological and economic productivity and it occurs where climatic variability (especially rainfall) coincides with unsustainable human activities
diurnal
difference between night and day
salt crystal growth
type of mechanical weathering in areas where temperatures fluctuate around 26-28 degrees - leads to the expansion of crystals by 300% such as sodium sulphate and carbonate
thermal fracturing
form of mechanical weathering caused by repeated cycles of heating and cooling over long periods of time
disintergration
type of weathering found in hot desert areas where there is a large diurnal temperature change
block disintergration
form of mechanical weathering whereby rocks are split into blocks, caused by repeated cycles of heating and cooling over long periods of time
granular disintegration
form of mechanical weathering whereby different minerals are broken down, caused by repeated cycles of heating and cooling over long periods of time
hydration
a form of chemical and mechanical weathering whereby rocks take in water, expand and contract and over time are broken down
deflation
lowering of the surface
suspension
describes sediment that are carried aloft (in the air) without touching the ground
pluvial
a period of increased rainfall in deserts
Gours
mushroom pinnacles where the base has been undercut, and bands of hard and soft rock have been differentially sand blasted
Zeugens
wind-eroded rocks in which different different rock strata lie horizontally
Yardangs
wind-eroded rocks where hard and soft rock lie side by side. the softer rocks are worn down to form troughs while harder rocks stand up as wind-worn ridges
barchan dunes
crescent-shaped and found in areas where sand is limited but there is a constant wind supply
parabolic dunes
crescent-shaped dunes that point downwind
linear dunes
found in areas where there is a seasonal change in wind direction
hydrological regime
describes annual and seasonal variations in the flow of water in a river
flash floods
sudden floods caused by heavy downpours or storms
sheet floods
fllods in which the river is not confined in an identifiable river channel, but floods over a large surface
exogenous rivers
flow in arid regions but have their origin in humid areas
endoreic rivers
flow into inland lakes
ephemeral rivers
flow only after rainstorms
wadis
generally steep-sided, flat-bottomed river valleys that vary in size from a few metres in length to over a 100km long
Alluvial fan
a cone of sediment occuring between a mountain and a lowland plain
piedmont zone
is a lowland area/plain generally located at the base of the mountain
bajada
is formed by a number of alluvial fans merging
pediments
gently sloping areas (<7 degrees) of bare rock where there is a distinct break with the mountain region
playas
comprised of a thick crust of salt which has formed after water has flowed into a depression and then evaporated, leaving behind a crust
mesas
plateau-like features with steep sides at their edges
buttes
smaller versions of mesas. they are thinner landforms that have very steep sides and a flat top
inselbergs
any isolated hills that stand prominently over a level surface
biomass productivity
the amount of new organic matter produced each year by the existing biomass
biodiversity
the range of habitat, species and population variety
physical drought
describes water shortages over a long period of time
physiological drought
describes water shortages experienced by plants despite there being sufficient soil moisture available - mainly caused by high evapotranspiration rates
succulents
plants that have well developed storage tissues
Aridisols
desert soils with a low organic content
Solonchaks
soils with a saline horizon of NaCl (sodium chloride) - also known as white alkali soils
Solonetz
soils with a horizon of Na2CO3 (sodium carbonate) - also known as black alkali soils
salination
the concentration of saline salts, usually in the upper horizon of the soil. It can be toxic to plants
overgrazing
when pastoralists allow too many animals to graze on a fixed area of land
overcultivation
where growing of crops exhausts soil nutrients
soil degradation
the decline in quantity and quality of soil
