A Level Geography- The Water Cycle and Systems

What is a system?

A set of interrelated components (flows and stores) working towards a process. Within this there are: stores/components, attributes, flows.

What is an input?

The addition of matter or energy into a system.

What is an output?

The loss of matter or energy out of a system.

What is a flow?

The movement of matter and energy from one store to another in a system

What are the 3 types of system classification?

Isolated, Closed, Open.

What is an isolated system?

No interactions with anything outside the system boundary. They are rare in nature.

What is a closed system?

Energy is transferred in and out of the system but no matter can transfer out. E.g. The global water and carbon cycles.

What is an open system?

Matter and energy can be transferred from the system into the surrounding environment. E.g. a drainage basin.

What is feedback?

The relationship/balance between the inputs and outputs of a system.

What is dynamic equilibrium?

When the inputs equal the outputs so the stores stay the same.

What is positive feedback?

When the effects of an action are amplified by changes to the inputs/outputs/processes.

Example: Global warming which causes sea ice to melt which causes sea levels to rise.

What is negative feedback?

When the effects of an action are nullified by changes to the inputs/outputs/processes.

Example: In the water cycle increased sea surface temperature causes more evaporation which leads to more condensation and more cloud cover which reduces surface temperatures.

What are cascading systems?

Where open systems form a chain and the outputs of one system are the inputs of another system.

What are the 5 sub-systems on Earth?

Atmosphere (air)

Lithosphere (geology)

Hydrosphere (water)

Biosphere (organic life)

Cryosphere (ice)

What is the hydrosphere divided into?

Oceanic water

Cryosphereic water

Atmospheric water

Terrestrial water

What percentage of the earths water supply is found in the oceans and seas?

96.5%

What percentage of the earths freshwater is stored as groundwater?

30.1%

What percentage of earths surface water is stored in lakes?

20.1%

What percentage of earths surface water is stored in snow and ice?

73.1%

What percentage of the earths freshwater is surface water?

1.3%

What is an aquifer?

A body of water stored underground.

Where is the largest aquifer found?

The High Plains aquifer in Central America covers 174,000 square miles.

What factors affect water storage in an aquifer?

Rainwater

Surface water

Human use

Temperature

Hydraulic conductivity

What rocks types store water in aquifers?

Porous and permeable rocks with air pockets such as chalk and sandstone.

What is surface storage?

The water held on the earth's surface including lakes, ponds and puddles.

What is precipitation?

Water that falls on the earth in any form: rain, sleet, hail, snow.

What is evaporation?

Moisture lost into the atmosphere by the sun's heat and wind.

What is transpiration?

A biological process where water is lost through minute pores in plants.

What is condensation?

Transfer of water from a gaseous state to a liquid state.

What is interception?

Raindrops fall on vegetation, preventing it from reaching the soil and river.

What is stemflow and throughfall?

Water reaches the ground by flowing down trunks or stems or by dropping off leaves.

What is infiltration?

The passage of water into the soil. This takes place quickly at the beginning of a storm, but ad the soil becomes saturated, infiltration falls rapidly.

Sand- high infiltration.

Clay- low infiltration.

What is groundwater flow?

Water moves laterally at a very slow rate to the river and provides the main input of water into the river during a dry season. It can take thousands of years to reach the river. Often called base flow.

What is percolation?

Water reaches underlying rock and its progress slows. This vertical movement is called percolation and it depends on the nature of the rock.

What is throughflow?

Water flows laterally through the soil into the channel.

What is surface runoff?

Movement of water above the soil. Occurs during heavy rainfall or when the ground is saturated. Very rare expect in urban areas.

What is channel fall?

Precipitation directly entering the river channel.

What is soil storage?

Water stored in the soil above the water table?

What is the water table?

The boundary between saturated and unsaturated soils.

What is groundwater storage?

Water stored below the water table in saturated soil or rock.

What is the watershed?

Boundary between 2 basins.

What is a tributary?

Where a smaller river joins a main river.

What is a confluence?

Where two rivers meet.

What is resident time?

The average time for water to pass through a subsystem of the hydrological cycle e.g. a rover.

It is important as it dictates the renewability of water.

Residence time (Tr)= Storage (S)/ Flow rate (Q)

What is evapotranspiration?

The process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants.

What affects evapotranspiration?

Amount of solar energy.

Amount of wind.

Availability of water.

Air temperature.

Humidity.

What factors affect infiltration and surface runoff?

vegetation cover

soil texture

soil porosity and permeability

soil structure and compaction

frost

length of rainfall

urban areas

intensity of rainfall

slope/ topography

How are clouds formed?

1.) They form when the air is saturated and cannot hold anymore water vapour. The warmer the air the more water vapour it can hold. As the air rises it cools and loses its ability to hold water vapour so condensation occurs.

2.) There is water all around us in the form of tiny gas particles known as water vapour. There are also tiny particles floating around in the air called aerosols with a diameter of a hundredth of a millimetre.

3.) The water vapour and the aerosols are constantly bumping into each other and some of the water vapour sticks to the aerosols-condensation.

4.) Eventually bigger water droplets form around the aerosol particles and these water droplets start sticking together which form clouds.

5.) As the tiny water droplets group together they grow very heavy and gravity pulls them down as raindrops.

6.) Clouds are either made up of ice or water droplets depending on the height of the cloud and the temperature of the atmosphere. Due to water droplets being so small they can remain as a liquid at temperatures as low as -30 degrees Celsius.

Why does cloud formation vary over spatial and temporal scales?

Due to global atmospheric circulation. Solar energy is more concentrated at the equator than the poles, the high temperatures result in evaporation and the air rises. As the moist air rises, it cools and condenses to firm clouds in the ITCZ due to low pressure. Depending on the season it moves north/south.

What is convectional rainfall?

This occurs when the sun heats the ground and a shallow layer of air close to the ground. It becomes warm and rises into the atmosphere where it is cooler so it condenses and forms clouds and eventually it rains.

This occurs in small areas and can be anywhere as they can be blown around.

What is frontal rainfall?

This is when cool air meets warm air in a weather front. The warm air rises above the cold air and cools and condenses in the atmosphere which forms water vapour and so it rains.

It brings grey, overcast skies and persistent rainfall that lasts for a long period of time.

What is Orographic rainfall?

Rain that is produced from the lifting of moist air over a mountain. Orographic precipitation is produced when moist air is lifted as it moves over a mountain range.

What is collision theory?

In clouds where temperatures are above 0°c there are no ice particles so ice droplets collide with each other and grow by coalescence. Larger droplets fall with greater speeds thought he smaller droplets with which they collide and join.

What is the Bergeron-Findeisen theory?

Requires the coexistence in a cloud of super cooled droplets and ice particles and a temperature below 0°c. Water vapour is deposited on the ice particles to form ice crystals. The air becomes unsaturated with water and the ice crystals will fall when large enough. They melt as they fall into warmer temperatures to become rain.

What is accumulation?

The increase in volume of an ice mass.

What is ablation?

The loss of volume of an ice mass.

What factors effect the hill slope water cycle?

deforestation

storms

farming

seasonal changes

urbanisation

How does deforestation impact local water stores?

Reduces interception and stemflow which reduces infiltration. water accumulates on the soil surface increasing surface storage and reducing potential storage in soil and underground.

How do storms impact local water stores?

Intense rainfall is greater than potential infiltration rates and soils quickly becomes saturated. Water accumulates on the soil surface. Reduces groundwater storage.

How does farming impact local water stores?

Ditches encourage water flow quickly into rivers and irrigation increases amount of water in the soil. Agricultural machinery compresses the soil. Less infiltration more surface run off into rivers.

How do seasonal changes impact local water stores?

Snow and ice interrupt water transfers so stores don't gain any water until melting where they are rapidly saturated.

How does urbanisation impact local water stores?

Impermeable surfaces reduce infiltration and lack of trees means not interception. Water doesn't infiltrate the ground. Pipes rapidly carry water into rivers.

What is the soil water budget?

runoff= precipitation - evapotranspiration +/- changes in storage

What does a hydrograph show?

It shows the change in a rivers discharge over a short period of time and the amount of precipitation.

What factors does a hydrograph show?

base flow

storm flow

lag-time

peak rainfall

peak discharge

rising limb

falling limb

What factors impact a hydrograph?

basin size

drainage density

rock type

land use

relief

soil water

rainfall intensity

What has happened to global water consumption over time?

Due to a growth in population the demand for water has increased and so we are using much more water (Asia using the most). Industries such as fast fashion has grown dramatically which uses large amounts of water to produce clothing- another reason water consumption has increased.

Why might climate change lead to intensification of the water cycle?

increase in temperature= increase of evaporation for land and sea into the atmosphere

warmer air= increased capacity to hold water leads to intense rainstorms

rainstorms= increased flood risk and increased runoff into rivers which decreases infiltration

this decrease in moisture and increase in temperature increases drought risk.

Define the water cycle

How water is cycled around the earth through rivers, oceans, atmosphere.

Define the carbon cycle

How carbon as an element is cycled around the Earth through plants, animals, atmosphere.

Precipitation

Any form of water that falls from clouds and reaches Earth's surface.

Formation of precipitation

1) Cooling of air to dew point temperature.

2) Cloud condensation nuclei (CCN) provides surface area for droplet formation.

3) Water vapour attracted to CCN surface.

4) Condensation on nuclei to form cloud droplets around CCN.

5) Growth of droplets or crystals into rain drops or snowflakes.

6) Importation of water to maintain this process.

Soil water budget

Runoff= precipitation - evapotranspiration +/- changes in storage

Water Balance

Precipitation= total runoff + evapotranspiration +/- storage

Base flow

Amount of water in the river channel derived from groundwater sources.

Storm flow

Discharge resulting from storm precipitation involving both overland flow, throughflow and groundwater flow

Lagtime

Time between mid point of precipitation event and peak discharge

'Flashy Hydrograph'

short lag time

high peak

'Subdued Hydrograph'

low

flat

long lag time

gentle rising limb

low peak

Soil moisture utilisation

When evapotranspiration exceeds precipitation

Factors affecting flashy hydrograph

Deforestation

Saturated/frozen soil

Impermeable bedrock

Steep relief

Small, round drainage basin

Agricultural land

Urban areas

Factors affecting subdued hydrograph

Afforestation

Unsaturated soil

Flat relief

Permeable rock

Large, elongated drainage basin

Uncultivated land

Rural areas

Human Influence on water cycle

Deforestation

Short Term Impact of Deforestation on water cycle

Less water evaporated from land surface to be returned to atmosphere- more water runs off land, streamflow increased.

Large effect if over 50% deforested

Long term impact of deforestation on water cycle

After initial rise in discharge, river levels will fall to new lows- once water has left system via river, with less vegetation there will be less evapotranspiration- less atmospheric moisture- less rainfall- lower river levels.

Reduced atmospheric moisture will be passed throughout entire region via localised atmospheric circulation.

Human Influence- Urbanisation

Decreasing water quality and increased pollution-when water comes into contact with urban areas it becomes contaminated.

Increased flooding- impermeable surfaces, reduces infiltration, increases SR.

Decreased Soil moisture- impermeable surfaces prevent infiltration and percolation, causing low soil moisture. irrigation required for plant growth.

London aquifer

London basin dominated by Cretaceous Chalk. this is the major aquifer, 60m below central London.

Kept in place by London clay formation. Also fluvial mud and fine sands between clay and chalk.

Aquifer recharged where chalk sticks out at surface, such as the Chiltens in the North. Allows water to percolate rapidly though aquifer to accumulate in large volumes beneath central London

Soil Drainage- human impact

Water carried through a network of perforated clay tubes 60-120 cm below the surface (tiles). Although expensive it's essential for areas with poorly drained soils.

Increases productivity of field.

For every $1 spent on drainage, grower gets $1.20-$1.90 in extra corn or soybean harvest.

Natural factors impacts water cycle

Seasonal changes

Ground type

Precipitation

Temperature

Vegetation

Extreme weather events

Rock type

Impacts of Storms

Increased precipitation

Increased infiltration

Increased surface runoff

Increased store levels

Decreased evaporation

Impacts of drought

Decreased precipitation

Decreased infiltration

Decreased surface runoff

Decreased level in stores

Increased evaporation

Define salinity

A measure of the amount of dissolved salts in a given amount of liquid

What influences the rate of evaporation from ocean surface?

Sea surface temperature

Air temperature

Surface winds

Climate change leading to intensification of water cycle

Increased temperature= increased evaporation from land and sea into atmosphere

Warmer air temperature= increased capacity to hold water= intense rain storm= increased flood risk

Floodwater runoff into rivers/lakes= decrease infiltration= decrease moisture + increased temps= drought (positive feedback)