Water cycle

Inputs

How the water enters the system

Precipitation

Includes all of the ways that moisture comes out of the atmosphere, mainly rain but can also be snow, hail and sleet

Channel fall

Precipitation falling directly into the river

Stores

Water stored in the system

Interception storage

Rainwater that lands on vegetation and other structures before reaching the soil, creating a temporary but significant store of water in wooded areas

Vegetation storage

Water that has been taken up by plants

Surface storage

Water in puddles, ponds and lakes

Soil storage

Moisture in the pores of the soil (unsaturated)

Groundwater storage

Water stored in the ground, either in the saturated soil beneath the water table or in bedrock.

Aquifers

Porous rocks beneath the water table that store water

Channel storage

Water held in the river or stream

Flows

Water flowing from one place to another

Infiltration

Vertical movement of water from the surface into unsaturated soil

What affects rates of infiltration

Soil type, structure and saturation

Overland flow

Water flows over the surface

Causes of overland flow

Saturated soil that cannot soak up more rain or rain is falling faster than it can be infiltrated

Through fall

Water dripping from a leaf

Stemflow

Water running down a plant stem or tree trunk

Throughflow

Water moving slowly downhill through unsaturated soil

Percolation

Vertical movement from unsaturated soil to saturated soil (across the water table)

Groundwater flow

Water flowing very slowly downhill through saturated soil and permeable bedrock

Baseflow

Groundwater flow that flows into rivers

Channel flow

Water flowing in the river, known as discharge

Outputs

Water leaving the system

Evaporation

Water turning into water vapour

Transpiration

Evaporation from the stomata at found of the underside of a leaf, helps to regulate water storage in a plant

Evapotranspiration

The process of evaporation and transpiration together

River discharge / flow

Water flowing into the sea

Input

Matter or energy added to a system

Output

Matter or energy leaves a system

Transfer

Matter or energy moves from one store to another

Open system

Both energy and matter can enter and leave the system

Closed system

Energy can but matter cannot enter or leave a system

Equilibrium

Inputs and outputs of a system are balanced

Dynamic equilibrium

When there are minor changes to the inputs and outputs of a system buy they do little to nothing to change the overall balance of the system

Positive feedback

A change to an input that amplifies the output of a system

Negative feedback

Changes to an input that nullifies the output of a system

Biosphere

The subsystem where organisms are found

Cryosphere

The subsystem that is frozen - ice

Hydrosphere

The subsystem that contains all of the water

Atmosphere

The subsystem that makes up the layer of gas between the Earth’s surface and space

How to work out the water balance

The changes to the inputs and outputs

Soil moisture surplus

When there is an excess of water in the soil – inputs greatly exceed outputs.

Soil moisture utilisation

When soil moisture is being used up – due to increases in outputs of evapotranspiration

Soil moisture deficit

The point when all soil moisture has been used up

Soil moisture recharge

When soil moisture increases following utilisation in the summer.

Field capacity

The point at which the soil becomes fully saturated in autumn

Flood hydrograph

A graph that shows how a river reacts to rainfall

Discharge

The amount of water that passes a point in a river in one second

Bankfull

The point when a river will overflow

Raising Limb

Shows how a quickly a river responds to a storm

Falling Limb

Shows how quickly a river recedes after a storm

Baseflow (rivers)

The amount of water that would be in the river without the water from the storm

Lag Time

Time between peak rainfall and peak discharge

Atmospheric water

12900km³ of water stored as ice, water and mainly vapour which absorbs, reflects and scatters incoming radiation

Oceanic water

1.32-1.37 billion km³ of water covering 72% of the Earth’s surface

Cryospheric water

The major store of water as a solid (ice)

Terrestrial water

The major store of water on Earth’s surface which has 4 main categories

Sea ice

Frozen seawater which, when thawed, doesn’t cause sea levels to rise

Ice sheet

Masses of glacial ice that are larger than 50000km²

Ice cap

Masses of glacial ice that are smaller than 50000km²

Alpine glacier

Thick masses of ice found in deep valleys that are fed by ice caps

Permafrost

Ground that is frozen for at least 2 years at depths of up to 15000 m

Surface water

Water stored on the surface, including rivers and lakes - a major terrestrial store

Groundwater

Water held underground in the soil or in pores in the rock

Soil water

Water that is naturally found in the soil

Urbanisation

Replacement of vegetation with impermaible concrete and tarmac

Impermiable

Does not allow water to soak in

Aquifer

Freshwater stored in rocks forming underground reservoirs

Deforestation

Cutting down trees leading to increased soil erosion and reduced soil water stores

ITCZ

The intertropical convergence zone is an area of low pressure found in equatorial regions

Irrigation

Artificial watering of crops

Water abstraction

Taking water from rivers and groundwater aquifers

Percentage of the Earth’s water in the ocean

97%

Percentage of Earth’s water that is freshwater

3%

Percentage of freshwater that is in the cryosphere

79%

Percentage of freshwater that is groundwater

20%

Percentage of surface water that is in lakes

52%

Percentage of surface water that is in soil

38%

Percentage of surface water that is in the atmosphere

8%

Percentage of surface water that is in biomass and rivers

2% - 1% each

Latent heat

The energy that is absorbed during evaporation and released during condensation

Dew point

The temperature when condensation of vapour occurs

Frontal rain

Rainfall formation where warm and cold air meet along a front, causing the warm air to rise, condensing.

Relief rain

Warm air meets mountains, forcing it to rise, cool and condense.

Conventional rain

Sun heats up the ground, causing a column of warm air to rise and the cools and condenses to make rain.

The Water Balance

The balance of inputs and outputs in the water cycle

Equation for the water balance

Precipitation = Total Runoff + Evpotranspiration ± Storage

Green section

Soil moisture recharge

Blue section

Soil moisture surplus

Orange section

Soil moisture utilisation

Red section

Soil moisture deficit

Point A

The point of maximum evaporation, with the highest risk of drought

Natural factors which cause change to the water cycle

Storms and precipitation, seasonal changes, movement in the ITCZ in equatorial zones and glacial / interglacial cycles

Human factors which cause change in the water cycle

Farming practices, land use changes and water abstraction

How storms and precipitation cause change to the water cycle

Larger input of water increases the size of stores - some flows may not be able to occur quick enough to withstand - increased surface runoff and a higher flood risk.

How seasonal changes cause change to the water cycle

Size of the flows and stores change with the seasons - flows decrease in winter - cryosphere increases - flows increase in summer due to an increase in seasonal vegetation.

How the ITCZ cause change to the water cycle

The band of low pressure moves with the seasons, causing heavy rainfall in summer months.

How glacial and interglacial cycles chase change to the water cycle

Glacial periods - 100000 years - cryosphere increases - more water is frozen - interglacial periods - hydrosphere and atmosphere increase - more ice thaws and evaporation rates increase.

How ploughing causes change to the water cycle

Breaks up the soil surface - higher infiltration rates