Hot desert environments
Physical characteristics
Sahara (9 million km2) has 2 million people
On borders = semi-arid areas (drylands or desert fringe areas). Sahel is strip of semi-arid drylands
along south of Sahara (Sudan, Chad, Burkina Faso, Niger).
Water obtained from aquifers or rivers (e.g. Nile), which transport water from wetter regions.
Hot desert climates
Found 20-30° N and S of Equator- Tropics pass through these regions
Hot and dry sinking air- arid conditions
Annual precipitation low and unreliable
Hot desert regions receive 100-200mm rainfall/year.
Range of temperatures throughout the day
Cloudless skies- high levels of insolation in daytime, rapid heat loss at night with drastic fall
in temperatures (occasionally sub-zero)
Diurnal temperature range may exceed 35°C
Hot desert soils
Soil-forming processes limited by lack of water and vegetation
Little organic content due to shortage of vegetation
Sandy, rocky soils are 1m deep- in some places wind action = dunes, increasing depth of soil
Sand dunes are not classified as soil unless they have organic matter
Some desert soils are very fertile because nutrients for plant growth (e.g. calcium) have not
been leached- so after irrigation they are productive for agriculture
Hot desert ecosystems and biodiversity issues
How have plants adapted to life in hot desert environments?
Desert biodiversity = low
Dry conditions- xerophytes (plants that survive dry conditions).
o Range of adaptations: thick, waxy cuticle, shedding of leaves (reduces
transpiration) to minimise water loss
High temperatures- plants have most biomass below ground surface where temperatures
are cooler
Short periods of rainfall- deserts bloom suddenly after rainfall to complete their lifecycle
quickly (important issue when looking at biodiversity)
Drought-tolerant Acacia trees- short, fat trunks act as reservoirs for excess water. They are
trees also fire-resistant. Roots can penetrate 50m into ground and reach sideways
to find water
Cacti They are ‘succulents’: store water in their tissues. USA Saguaro cactus can
grow 15m high, and spikes deter consumers. Small, waxy leaves minimise
transpiration loss
Flowering plants Desert flower seeds germinate only after heavy rain- can lay dormant for
, years between rains. They are ‘ephemerals’- complete lifecycle in under one
month. They can immediately produce bright coloured flowers to attract
insects.
Lichen Flaky crust on ground, rocks and tree trunks. Do not need soil- ‘pioneer
species’- can grow in bare rock surface in high temperatures. They break
down rock surface using organic acids, extracting nutrients needed
How have animals adapted to life in hot desert environments?
Few animals have adapted except scorpions and small reptiles.
More water supply = more biodiversity (tough grasses, shrubs, cacti, hardy trees)
These form larger food webs with mammals (foxes, coyotes) and raptors (buzzards, hawks)
Coyote and hawk are top predators in Mojave Desert in the US- hottest and driest hot desert region
in North America
Adaptations of consumer species:
Kangaroo rats: do not need to drink water; they get it from food. Live in burrows to avoid
extreme heat during the day. Do not perspire + have efficient kidneys that produce little
urine
Desert foxes: thick fur on soles of feet- protection from hot ground. Light-coloured fur on
bodies reflects sunlight, keeps them cool
Interdependence in hot desert environments
Biotic and abiotic components are interdependent- biotic creatures play an important role in
maintaining healthy environment (abiotic parts), and vice versa. Abiotic examples: soil, underlying
rocks, water supplies. Interdependency shown by:
- Links between parts of food web (animals eating plants that have gained nutrients from the
soil)
- Role that plant roots play in stabilising sandy soils in semi-arid areas at edges of desert.
Plants stop soil being blown away- sometimes causes desertification
- Exchange of nutrients between soil and plants, and vice versa. Plants take nutrients for
growth, release them when they die- health of soil and plants are dependent on each other
Development opportunities in the USA’s Western Desert
Western Desert = Mojave, part of Sonoran and part of Chihuahuan - covers 200 000 km2
How has migration changed the Western Desert?
Western Desert includes California, Nevada, Utah, Arizona and New Mexico
Half of population live in big cities (Phoenix and Tuscan in Arizona, and Las Vegas and
Henderson in Nevada), or coast where it is cooler. Recently, retirement migration.
Western Desert development opportunities
Las Vegas: 2 million people, Phoenix: 4.8 million people
Residents work in retail + service industries. Money earnt from:
Farming
o High temperatures and sunlight= favourable conditions, but water needed for
irrigation. Sources of water:
Physical characteristics
Sahara (9 million km2) has 2 million people
On borders = semi-arid areas (drylands or desert fringe areas). Sahel is strip of semi-arid drylands
along south of Sahara (Sudan, Chad, Burkina Faso, Niger).
Water obtained from aquifers or rivers (e.g. Nile), which transport water from wetter regions.
Hot desert climates
Found 20-30° N and S of Equator- Tropics pass through these regions
Hot and dry sinking air- arid conditions
Annual precipitation low and unreliable
Hot desert regions receive 100-200mm rainfall/year.
Range of temperatures throughout the day
Cloudless skies- high levels of insolation in daytime, rapid heat loss at night with drastic fall
in temperatures (occasionally sub-zero)
Diurnal temperature range may exceed 35°C
Hot desert soils
Soil-forming processes limited by lack of water and vegetation
Little organic content due to shortage of vegetation
Sandy, rocky soils are 1m deep- in some places wind action = dunes, increasing depth of soil
Sand dunes are not classified as soil unless they have organic matter
Some desert soils are very fertile because nutrients for plant growth (e.g. calcium) have not
been leached- so after irrigation they are productive for agriculture
Hot desert ecosystems and biodiversity issues
How have plants adapted to life in hot desert environments?
Desert biodiversity = low
Dry conditions- xerophytes (plants that survive dry conditions).
o Range of adaptations: thick, waxy cuticle, shedding of leaves (reduces
transpiration) to minimise water loss
High temperatures- plants have most biomass below ground surface where temperatures
are cooler
Short periods of rainfall- deserts bloom suddenly after rainfall to complete their lifecycle
quickly (important issue when looking at biodiversity)
Drought-tolerant Acacia trees- short, fat trunks act as reservoirs for excess water. They are
trees also fire-resistant. Roots can penetrate 50m into ground and reach sideways
to find water
Cacti They are ‘succulents’: store water in their tissues. USA Saguaro cactus can
grow 15m high, and spikes deter consumers. Small, waxy leaves minimise
transpiration loss
Flowering plants Desert flower seeds germinate only after heavy rain- can lay dormant for
, years between rains. They are ‘ephemerals’- complete lifecycle in under one
month. They can immediately produce bright coloured flowers to attract
insects.
Lichen Flaky crust on ground, rocks and tree trunks. Do not need soil- ‘pioneer
species’- can grow in bare rock surface in high temperatures. They break
down rock surface using organic acids, extracting nutrients needed
How have animals adapted to life in hot desert environments?
Few animals have adapted except scorpions and small reptiles.
More water supply = more biodiversity (tough grasses, shrubs, cacti, hardy trees)
These form larger food webs with mammals (foxes, coyotes) and raptors (buzzards, hawks)
Coyote and hawk are top predators in Mojave Desert in the US- hottest and driest hot desert region
in North America
Adaptations of consumer species:
Kangaroo rats: do not need to drink water; they get it from food. Live in burrows to avoid
extreme heat during the day. Do not perspire + have efficient kidneys that produce little
urine
Desert foxes: thick fur on soles of feet- protection from hot ground. Light-coloured fur on
bodies reflects sunlight, keeps them cool
Interdependence in hot desert environments
Biotic and abiotic components are interdependent- biotic creatures play an important role in
maintaining healthy environment (abiotic parts), and vice versa. Abiotic examples: soil, underlying
rocks, water supplies. Interdependency shown by:
- Links between parts of food web (animals eating plants that have gained nutrients from the
soil)
- Role that plant roots play in stabilising sandy soils in semi-arid areas at edges of desert.
Plants stop soil being blown away- sometimes causes desertification
- Exchange of nutrients between soil and plants, and vice versa. Plants take nutrients for
growth, release them when they die- health of soil and plants are dependent on each other
Development opportunities in the USA’s Western Desert
Western Desert = Mojave, part of Sonoran and part of Chihuahuan - covers 200 000 km2
How has migration changed the Western Desert?
Western Desert includes California, Nevada, Utah, Arizona and New Mexico
Half of population live in big cities (Phoenix and Tuscan in Arizona, and Las Vegas and
Henderson in Nevada), or coast where it is cooler. Recently, retirement migration.
Western Desert development opportunities
Las Vegas: 2 million people, Phoenix: 4.8 million people
Residents work in retail + service industries. Money earnt from:
Farming
o High temperatures and sunlight= favourable conditions, but water needed for
irrigation. Sources of water:
