Water cycle 1

• Hydrological cycle


  The continuous movement of water on, above and below the Earth's surface
• Global hydrological cycle


  • It is a closed system - there are no external inputs or outputs, water is not lost or gained from space
  • It is powered by the sun - the sun heats water which evaporates, condenses and precipitates
  • It involves energy exchange, leading to local temperature fluctuations - as water evaporates it cools the environment, and as it condenses it releases heat
• Global hydrological cycle


  1. Evaporation

  2. Condensation

  3. Flows (runoff, groundwater)
• Gravitational potential energy (GPE)


  The potential energy a raindrop has due to its position high above sea level
• Kinetic energy


  The energy a raindrop has due to its motion as it moves down a hill slope
• Main stores of water in the global hydrological cycle


  • Oceans (saline water)
  • Ice in the cryosphere (68.7% of freshwater)
  • Groundwater (30.1% of freshwater)
  • Atmospheric water vapour (0.2% of freshwater)
  • Liquid freshwater (1% of freshwater)
• Freshwater makes up just 2.5% of all Earth's water
• Water


  Colourless, tasteless, transparent, odourless liquid that forms the seas, rivers and precipitation
• Stores of freshwater


  • 68.7% as ice within the cryosphere
  • 30.1% is groundwater
• In total, just 0.9% of the Earth's total freshwater, is accessible to humans
• Major stores of water


  • Oceans (saline water)
  • Ice (cryosphere)
  • Groundwater (aquifers)
  • Atmosphere (water vapour)
• Frozen water in the cryosphere = 68.7%
• Liquid water in the hydrosphere = 1%
• Water vapour in the atmosphere = 0.2%
• Groundwater in the lithosphere = 30.1%
• Water is stored unevenly around the globe because of the uneven spread of land to sea and permeable or porous rock which enable aquifers to form
• Hydrological cycle


  Transfers water, the flows which enable this are known as fluxes
• Annual flux


  Variations in flows due to temperature, seasons and location
• Evaporation


  Will be greatest in warmer areas due to increased heating from the sun e.g. at the equator
• Precipitation


  Will be high at the equator too due to the high rates of evaporation
• Ice caps


  Getting smaller as a result of climate change
• Ocean stores


  Increasing in size as a result of climate change
• Global water budget


  The difference between the inputs and outputs from the different stores
• Residence time


  The time water is held in a store
• Factors dictating the size of water stores and residence time


  • Flows/transfers (e.g. evaporation)
  • Global factors (e.g. climate change)
  • Local factors (e.g. human activity on a hillslope)
• More precipitation


  Generally increases the availability of water for storage
• Intense rainfall


  Reduces the opportunity for infiltration and water storage
• During the last Ice Age (approx. 18,000 yrs ago), roughly a third of Earth's surface was covered in ice sheets and glaciers
• Increased ice cover during the Ice Age

  Increased the magnitude (size) of the cryosphere's stores
• Increased ice cover during the Ice Age


  Lowered the hydrosphere's store (no flow of liquid water) and sea levels were over 100 m lower than present day
• Inter-Tropical Convergence Zone (ITCZ)


  Low-pressure zone at the Equator with high rates of evaporation and precipitation
• The ITCZ (also called the 'thermal equator') tracks with the seasonal movement of the Sun, north and south of the equator bringing intense low-pressure rain/monsoon conditions with the movement
• Global atmospheric circulation determines cloud and precipitation on a global scale
• The second largest store of water is ice and 95% is locked as the ice sheets of Antarctica and Greenland
• Melting of the ice sheets


  Adds water to the hydrosphere store of the oceans
• Melting of ice shelves


  Triggers ice calving, these icebergs subsequently melt; adding to the hydrosphere store and rising sea levels
• The total melting of the ice sheets could result in a 60 m sea level rise
• Melting of ice sheets and shelves

  Creates a positive feedback loop