Water Cycle

• How much water does the hydrosphere contain?

  1.4 sextillion litres of water
• Describe most of the water stored in the hydrosphere?

  Saline water in oceans

  Less than 3% is freshwater (which most of Earth's species need for survival)
• Of the Earth's fresh water, how much is FROZEN IN THE CRYOSPHERE?


  69% is frozen in the cryosphere
• Of the Earth's fresh water, how much is groundwater?


  30%
• what is groundwater?


  Water stored underground in the lithosphere
• Of the Earth's fresh water, how much is LIQUID FRESHWATER on the EARTH'S SURFACE?


  0.3% is liquid freshwater on the Earth's surface in lakes, rivers etc
• Of the Earth's fresh water, what % is stored as water vapour in the atmosphere??


  0.04%
• What must water be

  Physically and economically accessible for humans to use, and as a result, only a small amount of water on the planet can be used by humans
• Problem with groundwater


  Hard to access, so may not be cost effective to extract it
• What can water change between?

  Solid, liquid and gaseous forms
• What must water do for it to boil or melt?


  must gain energy (eg from the Sun)
• What must water do for it to condense or freeze


  lose energy
• What does water do continuously?


  water is continuously cycled between different stores. This is known as the GLOBAL HYDROLOGICAL CYCLE
• What type of system is the global hydrological system?


  closed systems- no inputs or outputs of water
• What does the amount of water present in each store vary over?

  A range of scales from LOCAL to GLOBAL
• What does the magnitude of each store depend on?


  the minimum amount of water flowing between them
• what can long-term changes in the climate affect?

  the magnitude of evaporation
• When does evaporation occur?

  When liquid water changes state into a gas, becoming water vapour.

  It GAINS energy (usually from solar radiation)
• What does evaporation cause an increase in?


  the amount of water stored in the atmosphere
• What does the magnitude of the evaporation flow vary by?

  Location & season.

  • If there's lots of solar radiation,
  • a large supply of water and warm, dry air,
  • the amount of evaporation will be HIGH
• When will evaporation be LOW?

  If there's not much solar radiation, little available liquid water and COOL AIR that is already nearly saturated (unable to absorb any more water vapour)
• when does condensation occur?


  when water vapour changes state to become a liquid - it loses energy to the surroundings
• when does condensation happen?


  When air containing water vapour cools to to its dew point
• what is a dew point?


  the temperature at which water vapour will change from a gas to a liquis
• why do temps fall at night?


  due to heat being lost to space
• what can water droplets do?

  stay in the atmosphere or flow to other subsystem
• what does the magnitude of the condensation flow depend on?


  The amount of water vapour in the atmosphere and the temperature
• when is condensation high?


  • lots of water vapour in the air
  • if there is a large or rapid drop in temperature
• why is precipitation an essential part of the water cycle?


  Precipitation is the main flow of water from the atmosphere to the ground
• when do clouds form?

  When warm air cools down, causing the water vapour in it to condense into water droplets, which gather as clouds
• what happens when droplets get big enough?

  They fall as precipitation
• what THREE THINGS can cause warm air to cool, leading to precipitation?


  1. Other air masses
  2. Topography
  3. convection
• How do other air masses cause warm air to cool, leading to precipitation?

  Warm air less dense than cool air . as a result, when warm and cool air meet, the warm air - forced up above cool air

  it cools down as it rises

  results in FRONTAL PRECIPITATION
• How does TOPOGRAPHY cause warm air to cool, leading to precipitation?

  When warm air meets mountains, it is forced to rise, causing it to cool. = results in orographic precipitation
• How does CONVECTION cause warm air to cool, leading to precipitation?


  When sun heats up ground, moisture on ground evaporates and rises up in a column of warm air

  • As it gets higher, it cool
  • = results in convective precipitation
• Give details about water droplets caused by condensation?


  too small to form clouds on their own

  • For clouds to form, must be tiny particles of other substances
  • (eg dust, soot) to act as CLOUD CONDENSATION NUCLEI.
  • They give water a surface to condense on
  • = ENCOURAGES clouds to form,
  • rather than allowing the moist air to dispere
• What can vary SEASONALLY?


  Cloud formation and precipitation

  • can vary seasonally - more rain in winter
  • can vary by location - precipitation higher in tropics than poles
• give 2 examples of cryospheric processes?


  Accumulation

  Ablation
• what do cryospheric processes do?


  change the amount of water stored as ice in the cryosphere
• what varies with temp?


  the balance of accumulation and ablation