WATER CYCLES CONTENT

Hydrological cycle

Continuous transfer of water between the land, atmosphere and oceans

Carbon cycle

Continuous movement of carbon between living organisms and the environment through processes like photosynthesis, respiration, decomposition, and combustion

Infiltration

Movement of water from ground into soil

Throughflow

Movement of water through soil

Percolation

Movement of water from soil into rock

Evapotranspiration

Evaporation of water from plants

Flows/transfer

Movement of matter/energy

Closed system

Has a transfer of energy both into and beyond the system boundary but not a transfer of matter

Open system

Matter and energy can be transferred from the system across the boundary intro the surrounding environment

Dynamic equilibrium

Whee inputs and outputs of a system are balanced (affected by timescale)

Positive feedback

Where the effects of an action are amplified or multiplied by subsequent knock-on effects

Negative feedback

Where the effect of an action are nullified by its subsequent knock-on effects

Where is water stored?

The lithosphere, hydrosphere, cryosphere, atmosphere

Water storage The lithosphere

Solid outer crust and upper mantle. In oceanic crust it is stored within the rock structure which it is composed of and in continental it is also found in rocks, minerals, and also in clay and as groundwater

Water storage in the hydrosphere

Water on the surface of the planet. Includes oceans, lakes, rivers, ponds, and streams

Water storage in the cryosphere

Frozen areas on the planet. Includes glaciers and ice sheets as well as frozen sections of oceans, such as around the Antarctic.

Water storage in the atmosphere

Layer of gases surrounding the planet. Storage of water in clouds, and all layers of the atmosphere including in clear air, are microscopic particles of water vapour are carried

Transfers that change the size of the stores of water

Evaporation, condensation, cloud formation, precipitation

Evaporation

Process whereby liquid water changes into a gas when it absorbs heat energy. Approx. 90% of the atmospheric water store is from evaporation from the oceans and seas.

Condensation

Process whereby gaseous water vapour changes back into liquid water within the atmospheric water store. Occurs as temperature falls and humidity increases.

Cloud formation

Clouds form when water molecules aggregate. Frequently noticed at the altitude where air temperature has fallen to a point where condensation of invisible water vapour occurs

Aquifer

Body of permeable rock which can contain or transit groundwater

Seasonal changes in the cryosphere

Occur through ablation and accumulation

Accumulation: addition of material to the store of ice through snowfall

Ablation: loss of material through melting, evaporation, and sublimation

Long term changes in the cryosphere

• during glacial periods, more water stored in ice

• Due to expanding of ice stores, sea levels approx 120m lower than at present and many terrestrial areas experienced a much drier climate

Inter-tropical convergence zone

• in between two hadley cells

• Moves throughout the year

• Reaches furthest south in January and furthest north in July

• Moves areas of low pressure and rainfall with it

How does deforestation affect the hill slope cycle

• reduces interception nd infiltration

• Overland flow increases

How do storms affect the hill slope cycle

• increased amount of rainfall reaching the ground

• Increases magnitude of stores

How do seasonal changes affect the hillslope cycle

Winter snowfall and frozen ground interrupt the water transfers and affect magnitude of stores

How does urbanisation affect the water cycle

• more impermeable surfaces eg tarmac which reduce infiltration

• Deforestation occurs

• Water flows quickly through pipes to nearby river channels

How does farming affect the hillslope cycle

• ditches drain the land and encourage water to flow quickly to rivers

• Irrigation increases the amount of water on he ground

Water cycle in drier seasons

• evapotranspiration exceeds precipitation = groundwater depletion

• Some lows into the river channel but is not replaced by precipitation

What is surface runoff ?

When the ground becomes saturated with rainwater, it can’t take any more in. Any extra rain flows over ground

Factors affecting surface runoff

• antecedent rainfall (rain that has already occurred)

• How permeable the soil is (permeable soils eg sandy soils and impermeable soils eg clay)

• How heavy the rain falls

How does urbanisation affect surface runoff?

• more impermeable surfaces and significant reduction in infliltration

• 10% surface runoff and 40% evapotranspiration with fields and forests, 55% runoff and 30% evapotranspiration with urbanisation

How does deforestation affect surface runoff

• reduces interception and infiltration

• Less obstacles eg trees to stop surface runoff

What does a storm hydrograph tell you

How fast a river floods after rainfall

Basin lag time

Difference between peak of rainstorm and peak discharge. Short lag time = faster the flooding occurred

Rising limb (hydrograph)

Rising water level

Recession / falling limb (hydrograph)

Falling flood water

Peak flow (hydrographs)

Max. Discharge in the river

How do drainage basin characteristics affect lag time?

Steep slopes = fast lag time and steep rising limb

Higher number of streams = shorter lag time

How does antecedent moisture affect lag time?

More antecedent moisture = steeper rising limb and shorter lag time

How does rock type affect lag time?

Impermeable rock = steeper rising limb and shorter lag time

How does soil type affect lag time?

Saturated soil = shorter lag time

How does deforestation / afforestation affect lag time?

More deforestation = shorter lag time and steeper rising limb because of less interception

How does urbanisation affect lag time?

Urban areas = more impermeable surfaces and deforestation = steep rising limb and short lag time

Factors affecting the water cycle: weather phenomenons (el Nino)

PHYSICAL factor: every roughly 6 years, warmer water replaces cooler water in the eastern pacific off the coast of South America.

• had direct consequences for the local weather patterns and global weather conditions

• Changing rainfall patterns in South America: usually high rainfall = more rainfall, and usually low rainfall = even less

• Changes evaporation rates depending on usual conditions

Factors affecting the water cycle: Land drainage

HUMAN factor:

• removes excess water from the soil profile

• More interception = less surface runoff

• Example; the area of Somerset levels were once submerged by water. Deep drains and a network of ditches were created to move water quickly through the system so the land can now be used for farmland

Factors affecting the water cycle: water abstraction

HUMAN factor: abstraction of water from the ground water or rivers for irrigation, industry and domestic purposes.

• reduces volume of water in surface stores eg lakes

• Increase in dry seasons - eg more water needed for irrigation

• Aquifers abstraction to meet water demands offer greater than inputs to aquifer - leading to decline in long term stores. (Eg Middle East - aquifers are recharging at a slower rate to consumption)

Factors affecting the water cycle: farming practices

HUMAN factor: ploughing can break up the soil surface. Crops have a more positive impact on the water cycle than livestock. Irrigation can cause there to be and excess of water on the land.

• pastoral farming: livestock trampling ground can reduce infiltration

• Arable farming: ploughing reduces infiltration by creating a looser soil however digging drainage ditches increases surface runoff and stream flow

• Irrigation: can lead to groundwater depletion, and more saturated soil leads to more surface runoff

Factors affecting the water cycle: drought

PHYSICAL factor: lack of rainfall over a long period of time. Fires are often common due to the lack of water available. Soil becomes dried out due to heat and a lack of water

• rivers and lake storage reduced

• Vegetation destroyed by fires = transpiration and interception reduced

• Groundwater flow becomes more important as it i a deep long term storage of water that is unaffected by drought.

• Heat and dry air can cause higher rates of evapotranspiration until soil water dries up