Water cycle theory Flashcards
What is the ‘Goldilocks Zone’?
The zone in which Earth lies, which is the perfect distance form the Sun for water to appear everywhere on Earth in a liquid state
What % of the Earth’s surface is ocean?
71%
How does water moderate temperatures on Earth?
- absorbing heat via oceans
- clouds - reflect around 1/3 of solar radiation
- water vapour (greenhouse gas) absorbs long-wave radiation from Earth helping to maintain temperatures by 15 dgrs C higher than they would be otherwise
What are the uses of water in flora?
- photosynthesis - combining CO2, sunlight + water to make glucose + starches
- respiration of plants = glucose to energy, releasing CO2 + water in process
- plant cells require water to remain rigid (plant cells must be turgid to prevent wilting)
- water transports mineral nutrients from soil to plant
- transpiration for water from leaf surfaces cool plants by evaporation
What kind of system does water flow in at a global scale?
water flows in a closed system between the atmosphere, biosphere, oceans and land
What are the three main stores of water at a global scale?
atmosphere, oceans and land
what kind of system are smaller scale drainage basins?
at a smaller scale, eg drainage basin water cycle, these systems are open w inputs + outputs
What % of global water do oceans store?
97%
What % of global water does the atmosphere store and why is it such a small %?
0.001% - paradox can be explained by the rapid flux of water into + out of the atmosphere
What are the inputs of water to the atmosphere?
inputs of water to the atmosphere include water vapour evaporated from oceans, soils, lakes + rivers, + vapour transpired through leaves of plants. together known as evapotranspiration
how does moisture leave the atmosphere?
moisture leaves the atmosphere as precipitation + condensation
how do ice sheets, glaciers + snowfields release water?
ice sheets, glaciers + snowfields release water by ablation
how do precipitation + meltwater drain from the land surface and where does the water go?
precipitation + meltwater drain from land surface as surface runoff into rivers
a large part of water falling as precipitation on the land reaches rivers only after…
infiltrating + flowing through soil
what happens to water under gravity after infiltrating the soil
after infiltrating soil, water under gravity may percolate into permeable rocks or aquifers
what is an aquifer?
A layer of rock that is sufficiently porous to store water, and permeable enough to allow water to flow through it. for example, sandstone and limestone
what is groundwater?
Water stored within permeable rock underground, entering either through gaps between the grains (porous sandstone) or down joints and cracks in the rock (pervious limestone)
what happens to groundwater in the water cycle?
groundwater eventually reaches the surface as springs pr seepages + contributes to total surface runoff
what are the water flows?
precipitation, transpiration + condensation
how does precipitation occur?
forms when water vapour in the atmos. cools to dew point + condenses into water droplets or ice particles to form clouds. eventually, droplets/ice particles aggregate, reach a ‘critical size’ + leave the cloud as precipitation
what does aggregate mean?
a whole formed by combining several separate elements
what is the dew point
the atmospheric temperature at which water droplets begin to condense + dew forms
what is transpiration
the diffusion of water vapour to the atmosphere through leaf pores
what % of moisture in the atmosphere is transpiration responsible for
transpiration is responsible for 10% of moisture in the atmosphere
what is latent heat
the heat required to convert a solid into a liquid or vapour, or a liquid into a vapour, without change of temperature
why is heat needed for evaporation
heat is needed for evaporation to occur in order to break the molecular bonds in liquid water. this is absorbed as latent heat - no temp change
interception
when vegetation absorbs a proportion of precipitation, storing it temporarily on branches, leaves or stems. this moisture is evaporated (interception loss)
what factors affect interception loss
- interception storage capacity - as vegetation becomes saturated, stemflow + throughfall will increase
- wind speed - evaporation rates increase w higher wind, leading to greater interception loss
- vegetation type
- tree species - evergreens have greater interception loss than deciduous as they have leaves all year round
what is throughfall
rainwater that is briefly intercepted before dripping to the ground
what is stemflow
the flow of intercepted rainwater to the ground along branches + stems
what is percolation
slow movement of water through the pores in soil or permeable rock
what is infiltration
the process by which water on the ground surface enters the soil
what is overland flow
transfers water through the basin either as sheetwash, across the surface, or in tiny channels called rills
what are the cryospheric processes
ablation - when glacial ice melts
meltwater - water released by the melting of snow or ice
what is sublimation
process of changing directly from a solid to a gas
how does urbanisation affect the water cycle
- artificial surfaces (concrete) = impermeable, no infiltration can occur + no groundwater storage, meaning large surface runoff
- also, urban development on floodplains reduce water storage capacity in drainage basins, increasing river flow + flood risk
what human factors affect the water cycle
- forest management
- urbanisation
- farming
how does farming affect the water cycle
- cropland intercepts significantly less precipitation, meaning less evaporation + transpiration form leaf surfaces
- surface run-off increases where heavy machinery compacts soils. thus peak flows on streams draining farmland are generally higher than in natural ecosystems
how does forestry affect the water cycle
- high rates of rainfall interception in plantations of natural forestry
- large proportion of intercepted rainfall is stored on leaf surfaces + is evaporated
- compared to farmland, transpiration rates are increased
- reduced run-off + stream discharge - high interception + evapotranspiration rates + absorption of water through roots, run-off is reduced
what is clear felling
a forestry practise in which most or all trees in an area are uniformly cut down
how does clear felling affect the local water cycle
- clear felling increases surface run-off, reducing evapotranspiration + increasing stream discharge
- however if clear felling is carried out sustainably, the changes to the water cycle should only be temporary as a proportionate biomass of forest will grow before next clear felling
what has happened to the Artesian Aquifer in London
- groundwater in the chalk aquifer is is trapped between two types of impermeable clay
- rainwater enters the aquifer on the edge of the basin
- groundwater flows through the chalk towards the centre of the basin
- groundwater from the chalk is an important water for London
- overexploitation in 19th + first half of 20th century caused a drastic fall in the water table
- in recent years, the demand for water has fallen w the decline in industry + the water table has begun to rise to such an extent that in 1992, Thames Water has been abstracting water to prevent flooding
what is a drainage basin
A river basin or drainage basin is an area of land drained by a river and its tributaries
how has climate change affected the global water cycle?
- global warming has increased evaporation, thus the amount of water vapour in atmos. has increased
- water vapour is greenhouse gas, so more wv means further raising of global temperatures (positive feedback loop) as well as increased evaporation + precipitation
- increased precipitation = higher runoff, raising flood risks
- also accelerating melting of glaciers, ice sheets + permafrost, thus water storage in cryosphere shrinks as water is transferred to oceans + atmosphere - sea level rise
what are the three reasons drainage basin planning might take place
- to reduce runoff
- to improve water storage
- to maintain groundwater/aquifer levels
rapid runoff, such as that caused by urbanisation and farming, is controlled by…
reforestation programmes in upland catchments, reducing artificial drainage + extending permeable surfaces in urban areas
surface water storage is improved by…
conserving and restoring wetlands
groundwater levels are maintained by…
limiting abstraction + by artificial recharge, where water is injected into aquifers
how much water withdrawals and water consumption does agriculture account for globally?
agriculture is by far the biggest consumer of water, accounting for 70% of water withdrawals + 90% of water consumption
what is waterlogging?
land saturated with water
