Water Cycle

• Global water budget


  balance of water fluxes and size of water stores involved in hydrological cycle each year
• Closed system


  Transfer of energy but no matter between the system and its surroundings
• Open system


  Receives inputs from and transfers outputs of energy and matter to other systems
• Oceans water store


  96.9%
• Continents water store


  3.02% (Groundwater 1.1%, River/Lake 0.1%, Soil moisture 0.01%, Atmosphere moisture 0.001%, Biological 0.0001%)
• Fluxes


  Martime to Continental Atmosphere 40 (10(3)km3)

  Continental Atmos. to Continents 113 (reverse 73)

  Continents to Oceans 40

  Oceans to Maritime Atmos. 413 (reverse 373)
• Fossil water


  Water contained in an undisturbed space for longer than 1,000 years
• Blue water


  Water in its liquid form (Rivers)
• Green water


  Water evaporated from soil and plants
• Grey water


  Relatively clean water waste from baths, sinks and kitchen appliances
• Ogallala Aquifer USA


  Used for agriculture in Midwest, declined 300ft in some areas since 1940s, would take 6,000 years to replenish
• Water budget equation


  Precipitation (Input) = Channel discharge + evapotranspiration (Output) +/- changes in storage
• Drainage Basin


  Area drained by a river and its tributaries, separated by high land called watershed (open system)
• Interception


  Water impeded by vegetation, varies due to temperature, leaf type, age and density
• Infiltration


  Rate water enters pores in the soil (mm/hour) - changes due to saturation levels
• Overland flow


  Water moving across the surface
• Saturated overland flow


  Rainwater forced to run off the surface when maximum soil saturation is reached
• Infiltration-excess overland flow


  When rainfall intensity is higher than infiltration capacity, causing the additional water to run over the surface
• Groundwater flow


  Slow movement of percolated water through rocks to a river
• Percolation


  Water moving vertically downwards through rocks
• Evapotranspiration


  Total amount of water removed from a drainage basin from liquid water to gas and water in the soil taken through plants that is e from the stomata
• Channel runoff


  Total water output from the catchment at river mouth
• Human disruption to interception

  Varied crops, deforestation, urbanisation
• Human disruption to infiltration

  Trampling, urbanisation, deforestation, ploughing
• Human disruption to channel runoff

  River extraction reducing flow (Colorado River)
• Human disruption to evapotranspiration

  Dams, global warming, vegetation changes
• London Aquifer


  Decline 65m 1845-1967

  Water table rise became threat - 1998 increase in abstraction (70 million litres / day)
• Convectional rainfall

  
• Relief rainfall

  
• Frontal rainfall

  
• Soil moisture budget


  Used to compare inputs and outputs from soil
• Soil moisture graph

  
• River regime


  Annual variation in discharge per year (displayed in hydrograph)
• Perennial Channel


  River with continual flow all year
• Intermittent Channel


  River with lack of flow for a few weeks/months a year
• Ephemeral Channel


  River that only flows for a few hours/days (Wadi)
• River regime factors


  Climate (desert mostly ephemeral), drainage area, altitude, geology, land use
• River Wye Regime


  Lowest flow in late summer (more evapotranspiration), highest flow in winter
• Storm Hydrograph

  
• Amazon drought


  Rainfall decline causing reduced nutrient input into streams and rivers

  2005 = 70 million ha forest experienced drought

  Canopy dieback occured