importance to life

• What type of system is the global hydrological cycle classified as?

  A closed system
• What does the global hydrological cycle consist of?

  The circulation of water around the earth
• Why is the amount of global water considered finite and constant?

  Because there are no external inputs or outputs in a closed system
• What changes in the global hydrological cycle over time?

  The state in which water exists (liquid, vapor, ice)
• What are the two main sources of energy that drive the global hydrological cycle?

  Solar energy and gravitational potential energy
• How does gravitational potential energy affect the hydrological cycle?

  It causes rivers to flow downhill and precipitation to fall to the ground
• What are the main water stores in the global hydrological cycle?

  • Oceans (largest)
  • Glaciers and ice sheets (cryosphere, second largest)
  • Surface runoff (including rivers, lakes, groundwater, soil moisture)
  • Atmosphere
• What percentage of global freshwater is held in the cryosphere?

  69%
• What percentage of global freshwater is held in groundwater?

  30%
• What percentage of global freshwater is stored in the biosphere?

  Less than 1%
• What are flows in the context of the global hydrological cycle?

  Transfers of water from one store to another
• What is the annual evaporation from oceans to the atmosphere?

  400,000 km³
• What is the annual precipitation from the atmosphere to the oceans?

  370,000 km³
• What is the annual evaporation from landmasses to the atmosphere?

  60,000 km³
• What is the annual precipitation from the atmosphere to landmasses?

  90,000 km³
• What is the annual surface runoff from landmasses to the oceans?

  30,000 km³
• What is the significance of the global water budget?

  It limits water available for human use
• What percentage of the global water budget is freshwater?

  2.5%
• What is the percentage of easily accessible surface freshwater in the global water budget?

  1%
• What is the residence time of water in the atmosphere?

  10 days
• What is the residence time of water in the oceans?

  3,600 years
• What is the residence time of water in an ice cap?

  15,000 years
• Why are fossil water and cryosphere considered non-renewable?

  Because they are not replenished within a human timescale
• What is fossil water?

  Ancient, deep groundwater made from wetter periods in the geological past
• What does the cryosphere consist of?

  Areas of the world where water is frozen into snow or ice
• Is the cryosphere considered non-renewable?

  It is questioned because more water will be locked in glaciers during another glacial period
• Why is accessible surface water critical for human use?

  Because it is the major source of water for human use
• What does the small percentage of accessible surface water indicate about water as a resource?

  It emphasizes that water is a scarce resource needing careful management
• What are the percentages of water distribution in the global water budget?

  • 97.5% in oceans
  • 2.5% freshwater
  • 69% in ice caps and glaciers
  • 30% in groundwater
  • 1% as easily accessible surface water
  • 52% in lakes
  • 38% as soil moisture
  • 8% as atmospheric water vapor
  • 1% in rivers
  • 1% as accessible water in plants