Water cycle

• stores of water


  - 69% is frozen in the cryosphere

  - 30% groundwater (stored underground in lithosphere)

  - 0.3% liquid freshwater on the Earth's surface in lakes and rivers

  0.04% is water vapour in the atmosphere
• driving change in condensation

  - when water vapour changes to become liquid - losing energy to the surroundings

  
  

  - water droplets stay in the atmosphere - water can condense and form dew on leaves (this decreases water that is stored in atmosphere)

  
  

  - the magnitude of condensation flow depends on amount of water vapour in the atmosphere and temperature.
• driving change in evaporation

  - Evaporation occurs when water changes into a gas to become water vapour - it gains energy from solar radiation. Evaporation increases the amount of water stored in the atmosphere

  
  

  - the magnitude of evaporation varies by location and season. If there is lots of solar radiation, a large supply of water and warm, dry air causing evaporation to be high

  
  

  - if there isn't much solar radiation, little bit of liquid and cool air, it is unable to absorb any water vapour (evaporation will be low)
• driving change in cryospheric processes

  - accumulation and ablation change the amount of water that is stored as ice in the cryosphere - balance of accumulation and ablation varies with temperature.

  
  

  - variations in cryospheric processes happen over a long time. variations can also occur in shorter timescales - annual temperature fluctuations mean that more snow falls in the winter than summer

  
  

  - The earth is still emerging from a glacial period 21,000 years ago. There are extensive stores of ice on land in Antarctica and Greenland, and many alpine glaciers - there's a large volume of sea ice in the Artic/Antarctic

  
  

  - During period of winter, inputs into the cryosphere are greater than outputs. During warmer periods the global temperature of the cryosphere store reduces as loss is made due to melting being higher than the input of snow.
• inputs of drainage basin

  precipitation - mainly rain but can be hail, snow, frost

  
• storage of drainage basin

  interception - it is only temporary because the collected water (by vegetation, buildings and tarmac) may evaporate quickly

  
  

  surface - water in puddles, ponds and lakes

  
  

  vegetation - water taken up by plants

  
  

  groundwater - stored in the ground/rocks. aquifers are porous rocks that hold water (have holes in them)

  
  

  soil - moisture in soil

  
  

  channel - water held in a river/stream channel

  
• flows of a drainage basin

  -Infiltration - water soaking into the soil, influenced by soil type, structure and current concentration of water

  
  

  -Overland Flow (surface runoff) - more frequent when rainfall is on the ground faster than infiltration

  
  

  -Throughflow - water moving slowly downhill through the soil, and is faster through "pipes" like cracks in the soil

  
  

  -stemflow - water running down trees

  
  

  -percolation, water seeping though the soil into the water table

  
  

  -groundwater flow - water flowing below the water table, through permeable rock, faster groundwater occurs with more permeable rock, like limestone

  
  

  -Baseflow - groundwater that feeds into the river through the bank and riverbed

  
  

  -interflow - water flowing downhill, through permeable rock above the water table

  
  

  -channel flow - water flows in the rivers and streams

  
• Outputs of a drainage basin

  Rivers Discharge/ river flow

  
  

  Evaporation - turning water into water vapour

  
  

  Transpiration - evaporation from leaves - plants and trees take up water through roots and transport it to their leaves where it evaporates

  
• river regimes


  The annual variation in the flow of a river
• storm hydrographs


  - peak discharge = highest point on graph, when river discharge at its greatest

  
  

  -lag time= delay between peak rainfall and peak discharge - it takes time for the rain water to flow into the river. Short lag time can increase peak discharge because water reaches the river in a shorter amount of time

  
  

  - rising limb = river discharge increases when rain water flows into river

  
  

  -falling limb =period when a river's discharge is falling
• water cycle varies due to physical factors

  storms and precipitation - intense storms generate more precipitation and greater peak discharges than light showers

  
  

  seasonal changes and vegetation - the more vegetation there is the more water is lost in drainage basin before it reaches channel rivers - reduces peak discharge and runoff

  
  

  - During the winter, the size of flows can be reduced through drainage basins, whilst frozen water grows. When the temperatures rise, the peak of discharge is much larger due to ice melting

  
  

  - Most vegetation dies in winter, it intercepts precipitation and slows its movement to river channel
• effects of water abstraction

  Water abstraction - more water abstracted (taken from stores) to meet demand in areas where population density is high, reduces the amount of water in stores like lakes and rivers. Even more water is taken from stores (especially groundwater) for irrigation so many stores are depleted (used up)
• effect of land use changes

  deforestation - reduces amount of water intercepted by vegetation as more will then reach the surface. Dead plant material help hold water, which infiltrates the soil instead of it being run-off - however if removed then infiltration decreases.

  
  

  - Construction of new buildings and roads causes impermeable surfaces which prevents infiltration. This increases run-off to rapidly cause flooding
• effect of farming practice

  - ploughing can break up the surface so more water can infiltrate, reducing amount of run-off

  
  

  - crops increase infiltration and interception reducing run-off. Evapotranspiration increases + increases rainfall

  
  

  -animals like cattle compact the soil, decreasing infiltration and increasing run-off

  
  

  - irrigation can increase runoff if some water cannot infiltrate. Ground water can fall if water is extracted for irrigation