booklet 1a Flashcards
what are deserts?
- dry areas with an annual precipitation of less than 250mm
- barren land w/ little vegetation cover (due to little / no precipitation → difficult for plants to grow + soil becomes infertile)
- take up almost ⅓ of the earth’s total landmass
- evaporates water faster than it is received
where are the largest deserts generally in the world
in the polar regions
2 types of desert
- tropical desert
near the tropic of cancer / tropic of capricorn (23.5N // S)
hot all year
eg. sahara / somali / arabian desert - temperate desert
at higher latitudes
winters are cold
eg. mojave / great basin / namib desert
characteristics of deserts
- scarce and unreliable rainfall
annual rainfall is scarce in deserts, and is irregular and unpredictable
there may not be rain for months at a time, or even for several years
when rain comes, it falls very heavily over a short time
for inland deserts: distance from sea → less exposure to onshore winds, leading to insufficient
moisture → high evaporation rate
for deserts near mountain ranges: little to no rainfall is received in inland areas (deserts) as the water vapour brought by onshore winds is blocked by mountains - high evaporation rate
evaporation rate is high because there is little cloud cover → high concentration of insolation
rainwater may evaporate shortly in the air and never reach the ground - large daily range of temperature
clouds are rare in deserts → increased concentration of insolation
land absorbs heat quickly / directly during daytime → very hot during the daytime
land releases heat quickly / directly during nighttime → very cold during nighttime
the ocean can act as a moderating effect (as it absorbs / loses heat slower than the land)
climatic factors
- latitude / angle of the sun
- distance from the sea (coastal / inland –> maritime / continental climate)
- altitude
- relief (onshore winds –> rain shadow effect)
where does convectional rain form and where is it common?
convectional rain forms on heated (ground) surfaces and is the most common type of rain that falls in tropical deserts / rainforests
formation of convection rain
- intensely heated earth’s surface
- air expands and rises
- air temperature falls
- relative humidity increases
- water is saturated in the air at dew point
- condensation occurs and water vapour condenses into clouds
- condensation releases heat and air continues to rise
- strong convection currents are created
- cooler air sinks to replace the rising air
- the water vapour in the clouds fall as convection rain with a short duration
characteristics of convection rain
commonly occurs in continental regions + tropical regions during summer
usually occurs in the late afternoon (as it is hotter then) when the convection current is the strongest
short duration
often accompanied by thunderstorms
how is soil like in deserts
soil in most deserts is dry, thin, sandy and salty with a lack of organic matter (hence cannot support dense vegetation)
3 types of surfaces deserts can be made up of
- rocky desert (have barren rock surfaces and is made up of large rocks)
- stony desert (covered w/ broken pieces of stone)
- sandy desert (covered with sand, made up of sand dunes and large areas of sand)
deserts are usually made up of more than 1 type of material
why is there little vegetation in deserts
air in deserts is often quite dry bc the humidity of the air is usually very low → insufficient rainfall for vegetation, dryness results in a low vegetation cover
how are desert landscapes like and why are there little plants
desert landscapes are often barren lands w/ a small amount of vegetation
very few plants can grow bc they need more water
short rough shrubs / low trees are found here as they don’t need as much water
cactus characteristics and functions
- spines → less water is lost through transpiration because there is less surface area for water to evaporate from + protects against predators
- waxy skin → reduce water lost through transpiration
- large and thick fleshy stem → helps with water storage
acacia tree characteristics and functions
wide root network → absorb more water from the surface of the soil
small leaves → reduce surface area for water loss
rose of jericho characteristics and function
dormant seeds → can wait till correct conditions are met to propagate
can dry to retain only 3% of its mass → helps maintain itself in low rainfall and moisture conditions
