The Water Cycle and Water Insecurity Flashcards
Flux
the rate of flow between stores
Systems approach
Studying hydrological phenomena by looking at the balance of inputs and outputs, and how water is moved between stores by flows
Cryosphere
Areas of the Earth where water is frozen into snow and ice
Open system
- have transfers of energy and matter beyond and into the boundaries
Closed system
- have transfers of energy beyond the boundaries but not matter
dynamic equilibrium
when there is a balance between the inputs and outputs of a system, so matter stored in the system is constant
The global hydrological cycle
- closed system
- driven by solar energy (input) and gravitational potential energy
- the amount of water is constant on Earth and in the atmosphere
- proportions of different forms of water can change over time (solid, liquid and gas)
What flows/processes are there inside a hydrological system
- surface runoff
- groundwater flows
- channel flows
- precipitation
- evapotranspiration
- interception
- percolation
What stores are there inside a hydrological cycle
- atmosphere
- hydrosphere
- cryosphere
- biosphere
- lithosphere
Where is the Earth’s water stored?
- 96.5% stored in ocean
- 2.5% of the world’s water is surface and groundwater freshwater
- very little of this freshwater is accessible, with the majority of it stored as ice-caps
drainage basin system
- an area of land drained by a river and its tributaries
- is an open system so the amount of water in the drainage basin system varies over time
structures within a drainage basin
- main river
- tributaries
- watershed ( high land around the edge of the basin)
- catchment area (whole basin)
- source (start)
- mouth (end)
- confluence (two rivers join)
Blue water
water stored in rivers, streams or lakes and groundwater in liquid form (the visible part of the hydrological cycle)
Green water
Water stored in the soil and vegetation (the invisible part of the hydrological cycle)
Precipitation and the conditions required for it
- the movement of water in any form from the atmosphere to the ground
- air cooled to saturation point with a relative humidity of 100%
- condensation nuclei, such as dust particles, to facilitate the growth of droplets in clouds
- a temperature below dew point
Evaporation
the change of state of water from a liquid to a gas
Transpiration
the diffusion of water from vegetation into the atmosphere involving a change from a liquid to a gas
surface storage
the storage of water on the ground’s surface
soil storage
the storage of water in the soil
groundwater storage
the storage of water underground that has percolated through porous rocks
channel storage
the storage of water in streams or rivers
interception
water that is retained by vegetation surfaces from precipitation
infiltration
the movement of water from the ground to the soil
percolation
the transfer of water from the surface soil into the bedrock beneath
surface runoff
the movement of water that is unconfined by a channel across the surface of the ground
infiltration capacity
the maximum rate at which a soil is capable of absorbing water in a given condition
what factors determine infiltration capacity
- duration and intensity of rainfall
- surface gradient
- antecedent rainfall
- soil porosity
- compaction of the soil
- vegetation type and cover
subsurface throughflow
the lateral transfer of water downslope through the soil via natural pipes and percolines
potential evapotranspiration
the water loss that would occur is there was an unlimited supply of water (in the soil for use by vegetation) Distance between actual evapotranspiration rates and potential evapotranspiration is larger in arid areas
Interception capacity
the ability of the vegetation to store water in a given conditions
factors that determine interception capacity
- vegetation type and cover
- season
- duration and intensity of rainfall
- land use (natural, agricultural, urban)
Convectional rainfall
- common in tropical areas or in the summer in the UK
- often associated with intense thunderstorms
- the sun heats the land, making the air above it become warmer
- the air rises and expands
- as it rises, the air cools and its ability to hold water vapour decreases, creating convection currents
- condensation occurs and clouds develop
- if air continues to rise, rain will fall
Orographic rainfall and rain shadows
- warm, moist air from the oceans rises up over mountains
- when it rises it cools and condenses to form clouds, bringing rain
- once the air has passed over the mountain it descends and warms
- this creates drier conditions at the leeward end of the mountain known as a rain shadow
Cyclonic/frontal rainfall
- when a warm front meets a cold front
- the heavier cold air sinks to the ground so the warm air is forced to rise above it
- when the warm air rises, it cools and its ability to hold water vapour decreases
- condensation occurs, forming clouds which bring heavy rain
Physical factors that influence the drainage basin cycle
- climate
- soils
- geology
- relief
- vegetation
How does climate influence the drainage basin cycle
Has a role in influencing the type and amount of precipitation overall and the amount of evapotranspiration
Has an indirect impact on the vegetation type
How does soil influence the drainage basin cycle
Determines the amount of filtration and throughflow (dependent on porosity and compactness)
Indirectly influences the type of vegetation
How does geology influence the drainage basin cycle
can impact of subsurface processes such as percolation and groundwater flow, so also impacts aquifers
Indirectly alters soil formation
How can relief influence the drainage basin cycle
Altitude can impact on precipitation totals
Slopes can affect the amount of runoff
How can vegetation influence the drainage basin cycle
The presence or absence of vegetation impacts on the amount of interception , infiltration and occurrence of overland flow as well as transpiration rates
Human impact on precipitation
- pollution can provide condensation nuclei
- cloud seeding = the introduction of silver iodide pellets or ammonium nitrate to act as condensation nuclei to attract water droplets and increase rainfall in drought-stricken rainfall. It has variable results
Human impact of evapotranspiration
- changes in global land use especially through deforestation
- increased potential evaporation resulting from artificial reservoirs behind mega dams
- channelisation of rivers in urban areas into conduits cuts down surface storage and therefore evaporation
Human impact on interception
- deforestation and afforestation
- deforestation leads to a reduction in evapotranspiration and an increase in surface runoff, increasing flooding potential and decreases lag time (speeds up the cycle)
- after the planting of young trees there is a period of time where there is an increase in runoff due to earth compaction by planting equipment
Human impact on infiltration and soil water
- conversion of forest to grassland/farmland decreases infiltration
- farmland and grazing animals also increase soil compaction which increases overland flow
Human impact on groundwater
- human use of irrigation for extensive cereal farming has led to declining water table in areas such as the Aral Sea
- recent reductions in groundwater abstraction in British cities have led to flooding of basements and cellars, surface water flooding and leaking into tunnels such as the London Underground as groundwater rises. The water supplies are also more likely to become more polluted
Replacement of vegetated soils with impermeable surfaces (urbanisation)
- increases runoff as the ground is impermeable. Infiltration and percolation decreases
- high density of buildings means that rain falls on to roofs and then is swiftly dispatched into drains by gutters and pipes, reducing storage capacity and lag time
- piles of dumped soil from building activity increases sediment in soils
- interception decreases as there is less vegetation
Encroachment on the river channel (urbanisation)
- urban rivers tend to be channelised with embankments
- reclamation and riverside roads also decrease the width of the river channel
- floods can be more devastating because of the restricted river
- bridges can restrain discharge and act as dams, increasing water levels upstream
Pollution control problems (urbanisation)
- storm water washing off roads and roofs can contain heavy metals, volatile solids and organic chemicals
Water resource problems in urban areas
- sewers do not allow for percolation so groundwater that has been extracted cannot be replaced