WATER - The Global Hydrological Cycle

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  • The Global Hydrological Cycle
    • It  is a closed system with no external inputs or outputs. This means global water is finite and constant.
    • POWER drives the cycle. Solar energy (heat), and Gravitational energy (causes down flow of rivers and precipitation to fall).
    • Stores
      • reservoirs where water is held. (OCEANS, GLACIERS/ ICE SHEETS,(cryosphere accounts for 69% of all global freshwater) SURFACE RUNOFF - rivers, lakes, groundwater, ATMOSPHERE.
    • flows
      • transfers of water from one store to another - precipitation, evaporation, transpiration and vapour transport.
      • Processes
        • Infiltration, surface run-off, sub-surface throughflow, deep groundwater flow, percolation, precipitation, interception, stem flow.
    • Fluxes
      • the rates of flow between stores.
    • Processes
      • Infiltration, surface run-off, sub-surface throughflow, deep groundwater flow, percolation, precipitation, interception, stem flow.
    • The Global Water Budget - the balance between precipitation, evaporation and surface run-off. (indicates water available for human use.
      • only 2.5% of the budget is freshwater, the rest is in oceans. however, 70% of this freshwater is locked up in glaciers, leaving just 1% of accessible freshwater.
        • Accessible freshwater can be found in lakes (52%), soil moisture, atmosphere, rivers and plants (in order)
        • The 1% of freshwater is the major water source for all human use.
      • P=E+R(+-)S Where S is storage.
    • Residence time - the average time a water molecule spends in a store.
      • can be from 10 days (atmosphere) to 3,600 years (oceans), 15,000 (ice caps).

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