Water

• Hydrologic Cycle


  1. Evaporation/Evapotranspiration

  2. Condensation

  3. Precipitation

  4. Interception

  5. Infiltration

  6. Runoff

  7. Storage
• Hydrologic Cycle


  • Evaporation and precipitation constantly circulate water through atmosphere, hydrosphere, lithosphere, and biosphere
  • More than 97% of water is in the ocean
  • Globally, oceans dominate evaporation
  • More than 70% of the world is covered by ocean
  • Globally, oceans also dominate precipitation
• Composition of Earth's water

  • Saltwater oceans & seas (>97%)
  • Freshwater (ice caps/glaciers, groundwater, freshwater lakes, saline lakes, soil moisture, atmosphere, rivers and streams) (<3%)
• Over land


  Precipitation > Evaporation + Transpiration
• Over water


  Evaporation > Precipitation
• Advection


  Each year land gains 8% of water while oceans lose 8% of water, replaced by runoff
• Moisture Balance of the Atmosphere

  • Evaporation (ocean) (86%) (Input)
  • ET (land) (14%)(Input)
  • Precipitation (ocean) (78%) (Output)
  • Precipitation (land) (22%) (Output)
• Evaporation


  Sun heats up liquid water and changes it to a gas
• Transpiration


  Water evaporates from plants
• Condensation


  Water vapor cools and becomes liquid again, forming clouds
• Precipitation


  Water in clouds falls back to Earth
• Groundwater formation


  Precipitation is absorbed into the ground, forming pockets of water
• Runoff


  Water collects in rivers, streams, and oceans
• Water Budget components


  • Actual Evapotranspiration
  • Potential Evapotranspiration
  • Precipitation
  • Soil Moisture Storage/Deficit
  • Surplus and Runoff
• Actual Evapotranspiration (ACTET)


  The amount of water evapotranspired (transpiration + evaporation from soil) from an area of continuous, uniform vegetation that covers the whole ground and that is well supplied with water
• Potential Evapotranspiration (POTET)


  The maximum amount of water that could potentially evaporate/transpire under optimum conditions, determined by atmospheric energy (latitude, temperature)
• Precipitation (PRECIP)


  The water "input" to the surface in the surface water balance, compared to POTET it determines moisture conditions
• Soil Moisture Storage


  The amount of water that saturated soil retains against gravity, with field capacity as the theoretical maximum and wilting point as the threshold below which plants won't be nourished
• Water Balance


  Change of Storage = Inflow - Outflow
• Types of Drought


  • Meteorological - based on the degree of dryness/rainfall deficit.
  • Agricultural - impacts on agriculture.
  • Hydrological - impact on water supply by lack of rain.
  • Socioeconomic - impact of drought conditions on supply and demand.
• Groundwater is the largest potential freshwater source, accounting for >22% of freshwater (excluding cryosphere)
• Aquifer


  A subsurface layer of permeable rock or unconsolidated materials through which groundwater can flow
• Groundwater recharge


  Precipitation infiltrates the subsurface soil and rock, accumulating over millions of years
• Water Table


  The top of the surface where ground water occurs
• Artesian Well


  A well that taps into a confined aquifer, where the water rises to the surface due to pressure