hot deserts as a natural system

hot deserts as an open system

inputs- sun energy,wind,precipitation

erosional processes

components-erosional landforms and landscapes

wind and water transport

components-depositional landforms and landscapes

water and wind transport

output-water and wind remove sediment from desert,clear skies allow large amounts of energy to reradiate back to space

how is desertification an example of a positive feedback system

desertification

decreased agriculture and livestock yields

local populations increase livestock numbers and extend and intensify cultivation

deforestation and overgrazing occur

soil quality is degraded and reduced vegetation leaves soil exposed to erosion by water and wind

what is the term for influence that change to one element can have on other elements

feedback

what does dynamic equilibrium mean

when there is a changing balance between inputs and outputs in an open system overtime

dynamic means the equilibrium changes due to distruption which cause feedback cycles

positive feedback

change in the state of a system that enhances the measured effect of the initial alteration

negative feedback system

the diminution or counteraction of an effect by its own influence on the process giving rise to it

global distribution

hot desert environments and their margins generally run in parallel belts north and south of the equator in arid and semi arid mid and low latitude location

extremem arid environments cover 4%of the total world land surface concentrated in central sahara in north africa ,southern africa and southern parts of arabian desert

semi arid and arid environments distributed over a wider area covering 30% of the total world land surface

characteristics of extreme arid environments

low levels of mean annual less than 500mm/yr and some areas receiving less than 100m/yr in the arabian sahara

arid

the climate of an area that recieves less than 250mm of precipitation per year

aridity index

the ratio between precipitation and potential evapotranspiration

climate

temperatures vary wildly annually between the hottest and coldest months and diurnally between daytime and nighttime

low humidity levels ,cloud cover extremely low - increased insolation

the cloudless skies explain the high diurnal range as temperatures drop very rapidly at night with hot deserts losing twice as much heat at night as the more humid latitudes

soil

often infertile with thin soil profile and alkaline and saline

often characterised by a thick accumulation of basic minerals salts at or near the surface this is due to capillary movement where any moisture in the soil or bussoil moves upwards through the tiny spaces between soil particles - this capillary action is the most effective when evaporation exceeds precipitation hence its prevalence in arid environments

examine the relationship between the climate and soils of hot desert environments

low rainfall limits plants growth and decomposition so no 0 horizon and little organic material in a horizon

low rainfall limits leaching so a horizon thin

high temperatures cause high potential evaporation causing high rates of capillary action in soil this causes salts to accumulate in b horizon

why is rates of soil development slow in deserts

lack of moisture

extremely high temperatures and high rates of evaporation

sparse vegetation and limited organic material

aridisols

order of soils including infertile alkaline saline soils of desert areas characterised by accumulation of mineral salts at or near the surface

two main categories of aridisols

sierozems(in semi arid areas)

raw mineral soils ( in arid environments)

raw mineral soils

• Texture: Coarse, rocky, and gravelly due to physical weathering.

• Chemical Weathering: Occurs where water is present in the subsoil. Capillary action brings calcium and sodium salts to the surface.

• Limited Leaching: Due to low moisture, minerals remain near the surface rather than washing away.

• Alkaline & Unproductive: Nutrients are available, but extreme temperatures and water scarcity limit plant growth.

• Salt Crusts: High salt concentrations can form hard crusts on the surface

siorezms

• Location: Found in arid to semi-arid regions with ~250 mm rainfall.

• Organic Content: Darker colour due to some organic material, often beneath desert shrub vegetation.

• Cultivation: Can be used for farming with irrigation.

• Calcium Accumulation: Calcium carbonate or gypsum builds up in the B horizon, creating a lighter colour beneath the thin A horizon

vegetation

plants are usually ground hugging shrubs or short woody trees however even in the least hospitable arid envrionments vegetation cover remains sparse and depending on the temperature and rainfall net primary productivity values can range from near 0 to 120 g/m2/year

physical and behaviroural adaptations of plants in deserts

maximise use of and limit loss of moisture

store moisture in their stem and leaves

procure water with extensive and or keep root system

respond rapidly to sporadic rainfall followed by rapid life cycles

succulence(xerophytes)

suculence planst or xerophytes contain compounds or cells in flsehy leaves stems or roots where they can store water for example all cacti and non cacti like aloes and have drought and salt tolerance

for example saguro cactus

pherophytes

very deep root systems reaching water deep underground

ephemerals

dormant and drops leaves during drought

for example the salt bush

halophytes

salt tolerant plant that grows in waters of high salinity

for example the resurrection plant

salt bush

its an ephemeral

blooms in spring and summer to coincide with seasonal rains

salt bladders on leaves to remove deposit excess salt

resurrection plant

very shallow roots so it can move on wind in search of standing water

ephemeral so dormant for long periods

doesnt require water during prolonged dry periods

saguaro cactus

xerophytes, fleshy leavs and stems or roots

this epidermis which prevents water loss and reduce transpiration

very tall

one tap root and shallow lateral root system

access ground water and moisture from rainstorm

adapted to take moisture from salt rich b shallow roots in this a horizon which on occasion is saturated with rain water

this is a water storage sztretegy as apposed to shutting down functions to cope without water

spines have replaces leaves this seocndary adaptation also supports the primary adaptation by protecting the water stores from animals and furhtwe reduce rate of evapotranspiration to conserve water

procuring water after brief rainstorms

water does not penetrate deep into the soil or remain wet for very long so succulents have the ability to rapidly absorb huge amounts of water as plants roots can only take up water when the soil is more moist than the interior of the roots

succulents havel shallow and very wise extensive root systems

conserving water

thick waxy cuticles and close stomates making the lead surface waterproof small spiky or waxy leaves to reduce the surface area to limit transpiration

protection from thristy animals

being spiny bitter or toxic

living in inaccessible locations

drought tolerance

some plants are phreatophytes with very deep root systems reaching water deep undergorund

many plants are ephemerals with adaptation including becoming dormant or lising their leaves during dorughts appereing dead or domrant for months or even years

drought avoidance

extemely short life cycles

they come into boom rapidly after rainfall

they channel all their life energy into producing seeds

ther seeds lay dormant until a future rainfall event

salt tolerance

due to high rates of evaporation desert plants such as saltbush need to be halophytes with cells that have adapted to deal with high levels of elements such as sodium and chlorine

plant tissue adapts to survive in a saline environment

causes of aridity in hot deserts

pattern of atmospheric circulation

oceansdistance from ocenas or continentiality

relief

cold ocean currents

wind

global atmospheric circulation

• Equator (ITCZ): Intense solar radiation heats the surface, warming the air. This causes it to rise, cool, and condense, forming clouds and heavy rainfall (low pressure). This creates the humid, tropical climate found at the equator.

• Air Movement: The rising air moves polewards, cooling as it travels.

• Subtropics (20-30° N/S) – Desert Formation: As the cool air reaches the subtropics, it descends, becoming denser. This compression causes warming, leading to dry, stable conditions with little cloud formation. As a result, regions like the Sahara and Arabian Deserts experience arid climates due to persistent high pressure and lack of rainfall.

• Hadley Cells: This circulation system between the equator and subtropics explains why tropical rainforests form at the equator and deserts form at 20-30° N/S

continentality

• Water has a higher specific heat capacity than land, meaning it heats up and cools down more slowly.

• Land heats quickly in summer and cools rapidly in winter, leading to more extreme temperature variations in inland areas.

• Temperature Moderation in Coastal Areas

  • Coastal locations experience a maritime influence, where the sea regulates temperature, creating a milder climate with less variation.

  • In summer, the sea absorbs heat, keeping coastal areas cooler. In winter, the sea slowly releases heat, keeping coastal areas warmer.

• Impact on Rainfall

  • Oceans provide a constant source of moisture, leading to higher humidity and more cloud formation near coasts.

  • Inland areas, far from the sea, lack this moisture source, making them drier and more prone to arid conditions.

• Extreme Conditions in Continental Interiors

  • As distance from the sea increases, climates become more extreme, with hot summers, cold winters, and low rainfall.

  • Example: Siberia experiences freezing winters, while desert interiors like the Gobi are dry due to lack of moisture.

relief

• Moist Air is Forced to Rise

  • Prevailing winds push moist air inland towards a mountain range.

  • As the air meets the windward side, it is forced to rise, leading to adiabatic cooling.

• Cooling, Condensation & Rainfall

  • As the air rises, it cools and reaches its dew point, causing condensation and cloud formation.

  • This results in heavy rainfall on the windward side of the mountain.

• Leeward Side – Dry Conditions

  • Once over the summit, the air descends on the leeward (rain shadow) side.

  • Sinking air warms, reducing relative humidity, leading to clear skies and dry conditions.

• Impact on Climate

  • Wet windward side supports lush vegetation (e.g., western UK).

  • Dry leeward side can become arid (e.g., Atacama Desert behind the Andes)

cold ocean currents

• Cooling of Air Over Cold Ocean Currents

  • Cold ocean currents cool the air above them, reducing its ability to hold moisture.

  • These cool, dense air masses move toward coastal areas, displacing warmer air over the land.

• Formation of Coastal Fog

  • As the cool air reaches land, it heats up, causing evaporation of any moisture present.

  • This leads to the formation of coastal fog, which provides some moisture but not significant rainfall.

• Inland Air Becomes Dry & Warm

  • As the air moves further inland, it continues to warm, reducing relative humidity and preventing rainfall, leading to arid conditions.

• Impact on Desert Formation

  • Cold ocean currents contribute to arid coastal deserts like the Namib, Atacama, and Sonoran Deserts, where moisture is suppressed, limiting rainfall