Water cycle

• saline water percentage 


  97 %
• freshwater percentage 


  3 %
• cryosphere percentage


  69 %
• how much water is held within the hydrosphere

  1.4 sextillion liters of water
• water vapor percentage


  0.04 %
• evaporation 


  process of liquid water turning into water vapor

  gains energy from solar radiation

  increases the atmospheric store
• magnitude of evaporation


  seasons -> the summer has higher evaporation due to the longer daylight hours increasing the amount of time that surfaces are exposed to sunlight

  latitude -> the poles experience less evaporation as the solar radiation is highly disperse
• scale: why is there lots of water on earth but still water shortages

  not all water is physically and economically accessible to use

  example: ground water is out of reach in most areas which means it is not cost effective to extract
• condensation


  process where water vapor turns into liquid water

  looses energy to the surroundings

  decreases the atmospheric store

  water cools at the dew point
• condensation magnitude


  time of day -> higher rates at night as more heat is lost to space
• lithosphere percentage


  30 %
• cloud formation


  process of warm air rising, cooling, and condensing around condensation nuclei which are small particulate matter that provide a surface for water vapor to condense on
• cloud formation magnitude

  rate of evaporation -> influences how much water vapor is in the atmosphere

  urban areas -> have a higher concentration of condensation nuclei which encourages cloud formation

  pressure belts -> higher rates under low pressure
• precipitation causes

  • when two air masses meet -> when warm and cold air meet, warm air is forced above the cold air as it is less dense - this allows it to cool and condense creating frontal rainfall
  • topography -> when warm air is forced to rise above a hill it creates orographic rainfall
  • convection -> when surface heat rises it cools and condenses creating convectional rainfall
• cryospheric processes

  accumulation and ablation create short term fluctuations in the amount of water stored in the cryosphere

  scale: the last glacial maximum ended 11000 years ago and the amount of water storage has decreased since then
• inputs of a drainage basin

  precipitation
• storage of water in a drainage basin

  • channel flow (in the river itself)
  • pedosphere (in the soil)
  • biosphere (in vegetation)
• groundwater storage

  stored in rock and soil deep underground
• water table

  highest point of the zone of saturation
• aquifers

  porous rocks that hold water
• interception


  process by which water is prevented from reaching the soil by vegetation and infrastructure

  scale: its a temporary store

  • evaporation
  • through fall (where water flows through one leaf to another)
• stem flow

  process by which water flows down a trunk or stem
• infiltration

  process by which water is absorbed by the soil

  porosity and permeability are huge influencers
• overland flow


  process by which water flows over the surface of the land
• channel flow


  process by which water flows through a river channel
• river discharge


  the amount of water flowing through a river basin per second
• water balance

  wet season -> there is a water surplus

  • precipitation is greater than evaporation
  • this increases ground water and discharge ~

  dry season -> there is a water deficit

  • evaporation is greater than precipitation
  • this decreases ground water stores
• factors that affect run off

  1. size of the river basin -> increased size leads to an increase in discharge peak - the lag time therefore increases as there is a higher distance to travel
  2. relief of the land -> water flows faster down hill on a gradient due to gravity - this would decrease the lag time and interception rates leading to an increase in overland flow
• storm events

  increased intensity of rainfall increases peak discharge

  precipitation increases in a small amount of time which leads to overland flow and a risk of flooding
• seasonal changes

  winter -> the temperatures fluctuate around 0 degrees which means that water is frozen - when the water melts there will be a rapid increase in discharge - there will also be reduced throughflow as vegetation are deciduous and lose their leaves

  summer -> interception from vegetation increases lag time
• farming practices

  1. ploughing -> decreases run off as the top soil is broken up
  2. crop planting -> increases infiltration
  3. irrigation -> increases run off as the soil remains constantly saturated
• land use change

  1. deforestation -> increase surface run off as there are less stemflow and interception
  2. infrastructure -> higher amount of impermeable surfaces which increases the risk of flooding