AQA A Level Geography- Water and Carbon cycles.
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Why are models needed?
They simplify complex things so that we understand how they operate.
What is positive feedback?
Where the effects of an action are amplified by subsequent effects.
What is negative feedback?
Where the effects of an action are nullified by its subsequent knock on effects.
What is the biosphere?
Part of Earth’s systems where living things are found. Includes all life on earth.
What is the atmosphere?
Layer of gas between the Earth’s surface and space. Keeps out UV rays and has a layered structure.
What is the lithosphere?
Contains all solid rock, includes upper mantle and crust.
What is the cryosphere?
All parts of Earth that contain ice.
How much water is stored in the oceans?
97.5%
How much freshwater is in ice caps and glaciers?
68.8%
How much freshwater is in groundwater?
30.1%
What percentage of all water is accessible to humans?
0.9%
What percentage of freshwater is as liquid in the hydrosphere?
0.3%
What percentage of freshwater is water vapour in the atmosphere?
0.04%
Why is water stored unevenly globally?
Uneven spread of land to sea and permeable rock which enable aquifers to form.
What is evaporation?
Occurs when liquid water changes state into a gas, becoming water vapour. It gains energy, usually from solar radiation. Increases the amount of water in the atmosphere.
What factors affect the magnitude of evaporation?
Location , season, and long-term changes in climate- changes in solar radiation.
What is condensation?
Occurs when water vapour becomes a liquid, losing energy to its surroundings. Air containing water vapour cools to its dew point temperature
How does condensation occur typically?
Warm, moist air passes over cold surfaces. Heat is radiated into space, ground gets cooler, cooling the air in contact with it.
How does condensation occur by adiabatic cooling?
Heat is reduced by a change in air pressure, caused by volume expansion.
What happens to water droplets when they condense?
Can stay in the atmosphere or flow to other stores, e.g. can condense to form dew on leaves, decreasing the amount of water in the atmosphere.
What factors affect the magnitude of condensation?
The amount of water vapour in the atmosphere and temperature.
How are clouds formed?
Warm air cools down, causing water vapour to condense into droplets that gather as clouds. When droplets get big enough, they fall as precipitation.
What is relief rainfall?
When warm air meets mountains, it is forced up and over hills, and cools and condenses to form rainfall.
What is convectional rainfall?
Warm air rises due to heat from the sun, and condenses at higher altitudes. More localised rainfall, whereas frontal and relief rainfall are on a larger scale.
What factors affect the magnitude of cloud formation?
Water needs small particles e.g. dust to act as cloud condensation nuclei, can vary seasonally and locationally.
How does cloud formation vary seasonally?
In the UK, there is more rainfall in winter than in summer.
How does cloud formation vary locationally?
Precipitation is generally higher in the tropics than at the poles.
What are the main cryospheric procesess?
Accumulation and ablation. Balance of these vary with temperature.
How do inputs and outputs in the cryosphere vary with temperature?
Periods of global cooling mean inputs are greater than outputs, water is transferred to snow, less is lost as melting. Periods of global warming have more outputs than inputs. The magnitude of the cryosphere decreases due to melting.
When was the last glacial period maximum?
21,000 years ago.
How are there variations in cryospheric processes?
Happen over different timescales- changes in global temperatures occur over thousands of years, annual and seasonal fluctuations mean more snow falls in winter than summer.
What is an interglacial period?
Global ablation exceeds accumulation- long term changes in water stored in different spheres.
What is a drainage basin?
The area surrounding a river where the rain falling on the land flows into that river- the river’s catchment.
What is a watershed?
The area of land between two drainage basins- the boundary of a drainage basin.
What is precipitation?
Input to a drainage basin. Includes all the ways moisture leaves the atmosphere.
What is vegetation storage?
Water that is taken up by plants- all the water contained in plants at one time.
What is surface storage?
Includes water in ponds, puddles, and lakes.
What is groundwater storage?
Water stored in the ground, in soil or rocks.
What is an aquifer?
Porous rocks that hold water.
What is the zone of saturation?
The zone of soil or rock where all the pores in the soil or rock are full of water.
What is channel storage?
The water held in a river or stream channel.
What is interception?
Where some precipitation lands on vegetation or structures, before it reaches the soil.
Why is interception storage only temporary?
The water collected may evaporate quickly, or fall from the leaves as throughfall.
What is infiltration?
Water soaking into the soil. Rates are influenced by soil type, soil structure, and how much water is already in soil.
What is overland flow?
Runoff- water flowing over the land. can flow over the whole surface or in small channels. Occurs when rain is falling faster than infiltration can occur.
What is throughfall?
Water moving slowly downhill through the soil. Faster through cracks in soil or animal burrows.
What is percolation?
Water seeping down through soil into the water table.
What is groundwater flow?
Water flowing slowly below the water table through permeable rock. Moves slowly through most rocks, but can move faster through permeable rocks with many joints e.g. limestone.
What is transpiration?
Plants and trees take up water water through their roots and transport it to their leaves where it evaporates into the atmosphere.
What is evapotranspiration?
The processes of evaporation and transpiration together.
What is the Pantanal, South America?
A complex system of marshlands, floodplains, lagoons, and interconnected drainage lines. Provides a water supply, climate stabilisation and economic benefits.
What is the water balance?
The difference between the inputs and outputs in a drainage basin. Affects how much is stored in the basin.
What is a negative water balance?
Outputs are bigger than inputs.
What is discharge?
The amount of water in a river at any given point (m3/s)
What is the soil moisture budget?
The change in the amount of water stored in the soil throughout the year.
What is potential evaporation?
The amount of evapotranspiration that could occur if there was sufficient water available in the system.
What is soil moisture recharge?
The replenishment of stores of water used during warmer months when evapotranspiration has exceeded precipitation.
What is soil moisture surplus?
Precipitation is higher than evapotranspiration. All space in soil has filled, creating a surplus in groundwater. Overland flow can result in flooding.
What is soil moisture utilisation?
Increase in temperature, potential evapotranspiration exceeds precipitation. Water store is being used by plants.
What is soil moisture deficit?
Soil moisture is used up. Precipitation likely to go straight into the soil, river levels fall/dry up. Plants wilt or adapt.
Why is the discharge of a river important?
Water resource management, design of related structures, flood warning schemes, HEP production, ecological/recreational value of land, impacts of climate change.
What is a flood/storm hydrograph?
A graph of river discharge levels around the time of a storm event.
What physical factors affect the shape of a storm hydrograph?
Size and shape of a drainage basin, topography, rock and soil type, intensity of precipitation.
How do winter temperatures cause variation in runoff and the water cycle?
Temperatures may drop below 0 degrees, causing water to freeze, reducing the size of flows in drainage basins and increasing the store of ice. Flows grow when ice melts.
How do plants create seasonal variations in the water cycle?
Many plants die back in the winter, so there is less interception and precipitation is moved into channel storge more quickly.
How does ploughing affect infiltration rates?
Breaks up surface soil so more water can infiltrate, reducing the amount of runoff.
How do crops affect infiltration rates?
Increase infiltration and interception rates compared to bare ground, reducing runoff. Evapotranspiration increases, which can increase rainfall.
How do livestock affect infiltration rates?
Cattle trample and compact the ground, decreasing infiltration and increasing runoff.
How does irrigation affect infiltration rates?
Can increase runoff if some of the water cannot infiltrate. Groundwater or river levels fall if water is extracted for irrigation.
How does deforestation affect the water cycle?
Reduces the amount of water intercepted by vegetation, increasing the amount that reaches the surface. Dead material on forest floor can hold water, allowing it to infiltrate soil. When this is removed, infiltration decreases.
How does urbanisation affect the water cycle?
Concrete and infrastructure creates an impermeable layer over land, preventing infiltration. Runoff is increased, so water passes through the system more rapidly and flooding is more likely.
Why does water abstraction occur?
Water is taken from stores to meet demand in areas where population density is high. Reduces the amount of water in stores.
What issues does water abstraction in dry seasons create?
Even more water is abstracted, especially from reservoirs and groundwater, for consumption and irrigation, so stores are depleted further and cannot be restored as quickly.
What is carbon?
One of the most chemically versatile elements. Basic chemical element that is needed by all plants and animals to survive.
What is inorganic carbon?
Geological, non-living carbon, found in sedimentary rocks, gas, and fossil fuels.
What percentage of carbon is stored in the lithosphere?
Over 99.9%.
What percentage of carbon is stored in the atmosphere?
0.001%
How is carbon stored in the atmosphere?
As carbon dioxide and methane.
How is carbon stored in the biosphere?
In the tissues of living organisms. Is transferred to soil when they die and decay.
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