carbon and water

• Systems are composed of:

  • Inputs: Where matter or energy is added to the system
  • Outputs: Where matter or energy leaves the system
  • Stores: Where matter or energy builds up in the system
  • Flows: Where matter or energy moves in the system
  • Boundaries: Limits to the system (e.g. watershed)
• Open systems receive inputs and transfer outputs of energy or matter with other systems
• Positive feedback amplifies the impacts of the original event

  • Negative feedback nullifies the impacts of the original event, leading to dynamic equilibrium
• On a local scale, the carbon and water cycles are open systems

  • On a global scale, they are closed systems
  • Each system contains flows/transfers, inputs, outputs, and stores/components
• The Water Cycle: Local Scale

  • Water may be lost as an output through evapotranspiration and runoff
  • More water may be gained as an input through precipitation
  • Inputs and outputs are not balanced, making it an open system
• Precipitation: Any water that falls to the surface of the earth from the atmosphere including rain, snow, and hail

  • Convectional, Relief, and Frontal are types of rainfall
• Evapotranspiration: Compromised of evaporation and transpiration

  • Evaporation occurs when water is heated by the sun, causing it to become a gas and rise into the atmosphere
  • Transpiration occurs in plants when they respire through their leaves, releasing water they absorb through their roots
• Infiltration: Water moving from above ground into the soil

  • Infiltration capacity refers to how quickly infiltration occurs
  • If precipitation falls at a greater rate than the infiltration capacity, overland flow will occur
• Groundwater Flow: Water moves through the rocks

  • Ensures water in rivers even after long dry periods
  • Usually slow but variable
• Streamflow: Water that moves through established channels

  • Fast
  • Stemflow: Flow of water intercepted by plants or trees, down a stem, leaf, branch, or other part of a plant
• Soil Water: Water stored in the soil utilized by plants

  • Mid-term
  • Groundwater: Water stored in the pore spaces of rock
  • Long-term
• The Water Balance: Precipitation = Total Runoff + Evapotranspiration +/- (change in) Storage

  • Used to express water storage and transfer in a drainage basin system
  • Important for explaining droughts or floods
• Changes to the Water Cycle:

  • Deforestation leads to less interception by trees, increasing surface runoff
  • Storm events quickly saturate the ground, increasing surface runoff
  • Seasonal changes affect vegetation growth and surface runoff
• Agriculture:

  • Pastoral farming reduces infiltration due to trampling by livestock
  • Arable farming increases infiltration by ploughing
  • Hillside terracing increases surface water storage
• Urbanisation:

  • Impermeable surfaces reduce infiltration but increase surface runoff
  • Green roofs and Sustainable Urban Drainage Systems help reduce urban flooding
• The Soil Water Budget:

  • Shows the annual balance between inputs and outputs in the water cycle
  • Dependent on type, depth, and permeability of the soil and bedrock
• Seasonal Variation of the Soil Water Budget:

  • Autumn: Water surplus occurs
  • Winter: Refills soil water stores
  • Spring: Water surplus
  • Summer: Soil water stores deplete
• The Global Water Cycle:

  • Comprised of many stores, with oceans containing 97% of global water
  • Only 2.5% of stores are freshwater, with glaciers and ice caps being the largest portion
• Water can be stored in four areas:

  • Hydrosphere: Any liquid water
  • Lithosphere: Water stored in the crust and upper mantle
  • Cryosphere: Any water that is frozen
  • Atmosphere: Water vapour
• Aquifers are underground water stores that are unevenly distributed on a global scale
• Shallow groundwater aquifers can store water for up to 200 years
• Deeper fossil aquifers, formed during wetter climatic periods, may last for 10,000 years
• Glaciers may store water for 20-100 years, feeding lakes that store water for 50-100 years
• Seasonal snow cover and rivers store water for 2-6 months
• Soil water acts as a temporary store, holding water for 1-2 months
• The global atmospheric circulation model determines cloud formation and rainfall
• The Inter-Tropical Convergence Zone (ITCZ) is a low-pressure zone on the equator with heavy rainfall, partly responsible for monsoons
• The ITCZ moves during the seasons as the sun's position changes
• Unstable weather occurs where the Ferrel and Hadley cells meet, moved by the jet-stream, causing changeable weather in the UK
• Seasonal changes include less precipitation and more evapotranspiration in summer, reduced flows in the water cycle in winter, reduced interception in winter, and increased evapotranspiration in summer
• Storm events cause sudden increases in rainfall, leading to flooding and replenishment of water stores
• Droughts cause major water store depletion and decreased activity of flows in the water cycle
• El Niño and La Niña effects occur every 2-7 years, impacting global temperatures in a predictable way
• Glaciers and icecaps have stored significant proportions of freshwater in the past through accumulation
• Currently, almost all of the world's glaciers are shrinking, causing sea levels to rise
• If all the world's glaciers and icecaps were to melt, sea levels would rise by around 60 meters
• Human impacts on the water cycle include farming practices, land use change, and water abstraction
• Flood hydrographs represent rainfall and discharge of a river, with key components like discharge, rising limb, falling limb, lag time, baseflow, stormflow, and bankfull discharge
• Flashy hydrographs have short lag time and high peak discharge, while subdued hydrographs have long lag time and low peak discharge
• Factors that increase surface runoff, decrease lag time, and increase peak discharge to create a flashy hydrograph include high rainfall intensity, antecedent rainfall, impermeable underlying geology, high drainage density, small basin, circular basin, low temperatures, precipitation type, and vegetation cover