Content

• Earth is one of the lucky places that has liquid water, unlike some other places in our solar system
• Liquid water on Earth enables it to support life
• Ways in which water affects the thermal conditions on Earth

  • Absorbs and stores solar radiation, then slowly releases it
  • Water evaporates and forms clouds, which reflect solar radiation and lower surface temperature
• Albedo effect

  How reflective a surface is
• Nearly a fifth of all solar radiation is reflected by clouds
• Water vapor

  A greenhouse gas that absorbs and radiates infrared radiation, warming the atmosphere
• If there was no water vapor, conditions on Earth would be 15-20 degrees lower
• Too much water vapor or other greenhouse gases can lead to enhanced greenhouse effect and climate change
• How plants use water

  • For photosynthesis
  • Respiration releases water
  • To stay rigid and transport nutrients
  • To cool down through transpiration
• How animals use water

  • For chemical reactions and transporting nutrients and oxygen
  • To cool down through sweating, panting and evaporation
• Economic activities involving water

  • Farming and irrigation
  • Hydroelectric power generation
  • Manufacturing
  • Drinking water supply
  • Sewage systems
  • Leisure activities
• Finite resource

  Water on Earth is a closed system, with no net loss or gain
• Hydrological system

  Driven by energy from the sun, with water cycling through the system
• Drainage basin

  An open system where energy, water and other matter can enter and leave
• Water can enter a drainage basin through precipitation from the surrounding area, and leave through outflows
• Stores of water in the global system

  • Oceans (97%)
  • Glaciers (2%)
  • Groundwater (aquifers)
  • Lakes
  • Soils
  • Atmosphere
  • Rivers
  • Biosphere
• Most of the water on Earth is saline (salty), and fresh water is a tiny proportion of the overall amount of water stored
• Residence time

  The average time a water molecule spends in the atmosphere is about 9 days

  There is a rapid cycling of water from the atmosphere back into a store
• Hydrological cycle

  The stores and processes of the water cycle at a global scale
• Processes in a drainage basin

  1. Condensation

  2. Evaporation

  3. Evapotranspiration

  4. Streamflow

  5. Surface run off

  6. Percolation

  7. Infiltration

  8. Groundwater flow
• Stores in a drainage basin

  • Clouds/atmosphere
  • Leaves
  • Ice/Glaciers
  • Snow
  • Oceans
  • Rivers
  • Aquifers
  • Lakes/reservoirs
• Inputs to a drainage basin

  • Precipitation
  • Energy from the sun
• Outputs from a drainage basin

  • Rivers
  • Human extraction and use
  • Groundwater flow into another basin
• Localized carbon cycle

  Open system with inputs and outputs, carbon can be lost from one area to another
• Carbon stores ranked by importance


  • Sedimentary rocks (60-100 million gigatons)
  • Oceans (40,000 gigatons)
  • Seafloor sediment
  • Fossil fuels
  • Soil
  • Atmosphere
  • Land plants
• Oceans

  • Not a singular system, different layers store different amounts of carbon
  • Surface stores some carbon, but deep ocean stores most
• Land plants don't store much carbon compared to other stores
• Importance of carbon


  • Used by plants in photosynthesis and respiration
  • Building block for life, forms stable bonds easily
  • Used by humans and animals in carbohydrates, proteins, and lipids
  • Fossil fuels and wood/paper are carbon-based resources
• Atmosphere stores little carbon but is key in the circulation of carbon (residence time of 6 years)
• Oceans, sea floor sediments and sedimentary rocks store more carbon and have a long residence time

  • Surface ocean: 25 years
  • Deep ocean: 1250 years
  • Sedimentary rocks: 240 - 300 million years
• Water balance equation

  Precipitation = Evapotranspiration + Stream flow +/- Changes in storage
• Precipitation higher than evapotranspiration

  Water surplus
• Evapotranspiration higher than precipitation

  Water deficit
• Recharge

  When precipitation exceeds evapotranspiration, refilling depleted stores
• Precipitation

  Water falling from the atmosphere, can be liquid or solid
• Precipitation in mountains/high latitudes

  • Often falls as snow, takes longer to reach rivers
• Intense precipitation(10-15mm per hour)

  Exceeds infiltration capacity, leads to surface runoff and potential flooding
• Long duration precipitation

  Fills up ground stores, leads to surface runoff and potential flooding
• Seasonal precipitation patterns

  Affect flows and stores in the water cycle

  Some regions experience most of their precipitation during a rainy season
• Transpiration

  Water uptake by plant roots, travels through plant, and is released into the atmosphere through stomata via diffusion