Water Cycle

• Water Cycle meaning


  water (hydrological) cycle is the continuous transfer of water

  between the land, atmosphere and oceans.
• Inputs meaning


  where matter or energy is added to the system
• Outputs meaning


  where matter or energy leaves the system
• Stores meaning


  where matter or energy builds up in the system
• Flows meaning


  where matter or energy moves in the system
• Boundaries meaning


  limits to the system
• What is the purpose of a systems approach?


  Simplifies the complexity of life. It organises and presents complex relationships between the different components of the physical environment.
• Systems are


  - Bounded

  - A generalisation of reality e.g. used to produce global climate models to predict potential impacts of rising levels of CO2 in the atmosphere

  - Have inputs, outputs, stores and flows

  - Are studied at a range of scales (local to global)
• Open System meaning


  Matter and energy can be transferred from the system across the boundary into the surrounding environment

  
  

  e.g. Water flowing through a drainage or hydrological cycle
• Closed System meaning


  Has a transfer of energy both into and beyond the system boundary but not a transfer of matter. Are when energy inputs equal outputs.

  
  

  e.g. Continual cycling of carbon
• Dynamic Equilibrium meaning


  when inputs equal outputs despite changing conditions
• Feedback meaning


  is how a system is trying to achieve dynamic equilibrium
• Positive Feedback meaning


  Where the effects of an actions are amplified or multiplied by subsequent knock-on effects
• Negative Feedback meaning


  Where the effects of an action are nullified by its subsequent knock-on effects
• Example of positive feedback in a system


  1. Human burning of fossil fuels

  2. Increasing atmospheric CO2 and other greenhouse gases

  3. Raises global temperatures

  4. Melts tundra permafrost

  5. Release of stored cryospheric methane (CH4) and CO2

  6. Increasing atmospheric CO2 and other greenhouse gases

  
  

  1. Human burning of fossil fuels

  2. Increasing atmospheric CO2 and other greenhouse gases

  3. Raises global temperatures

  4. Increased melting of sea ice

  5. Reduces polar albedo, increases solar absorption

  6. Raises global temperatures
• Examples of negative feedback in a system


  1. Human burning of fossil fuels

  2. Increasing atmospheric CO2 and other greenhouse gases

  3. Raises global temperatures

  4. More evaporation and precipitation

  5. More CO2 dissolved in rainwater then stored

  6. Carbon stores increases

  7. Climate cools

  
  

  1. Human burning of fossil fuels

  2. Increasing atmospheric CO2 and other greenhouse gases

  3. Raises global temperatures

  4. Encourages more plant growth

  5. Plants take in CO2

  6. Carbon stores increase

  7. Climate cools
• On a local scale, are carbon and water cycles open or closed systems?


  Open
• On a global scale, are carbon and water cycles open or closed systems?


  Closed
• Albedo Effect meaning


  - Lighter surfaces reflect the sun's energy/light e.g. ice, snow

  - Darker surfaces absorb the sun's energy/light e.g. oceans, water
• Open/Closed systems contain inputs, outputs, flows and stores. Example of Sea Ice near Kulusuk, Greenland


  Inputs- include precipitation and radiation from the sun

  
  

  Stores- water stored in the form of liquid water, ice and snow

  
  

  Flows- water transferred between the hydrosphere and atmosphere by processes such as evaporation and sublimation

  
  

  Outputs- includes water and dissolved carbon

  
  

  Positive Feedback- warmer temperatures causes ice melt, which increases exposure of dark surfaces (rock, water) which further increases temperature and so on
• At the global level the Earth has four major subsystems, which are?


  Atmosphere, Lithosphere, Hydrosphere, Biosphere (perhaps cryosphere)
• Atmosphere meaning


  the layers of gases surrounding the planet
• Lithosphere meaning


  solid, outer parts of earth, includes the brittle upper portion of the mantle and the crust, the outermost layers of Earth's structure
• Hydrosphere meaning


  includes water that is on the surface of the planet, underground, and in the air
• Biosphere meaning


  is made up of the part of Earth where life exists; extends from the deepest root systems of trees, to the dark environment of ocean trenches, to lush rainforests and high mountaintops
• Cryosphere meaning


  is the frozen ice and snow on the planet
• Where is the Earth's water stored?


  - Largest store is oceans, which contains 97% of global water

  - Only 2.5% of stores are freshwater, of which 69% is glaciers, ice caps and ice sheets and 30% is groundwater

  - Surface and other freshwater only accounts for 1.% of freshwater and is made up of permafrost, lakes, swamps, marshes, rivers, atmosphere and living organisms
• Aquifier meaning


  A body of permeable rock which can contain or transmit groundwater
• Where are the global stores of water?


  Major regional aquifer systems are spread relatively evenly throughout the Northern and Southern hemisphere.

  - South America, particularly Argentina, has a large aquifer system - the Guarani aquifer.

  - The majority of Europe is also home to a large underground water store.

  - The Indo Gangetic Plain lies North of India, where you would find the Himalayas but India itself does not have any underground stores.

  - North America, notably Canada is also lacking aquifers. - Central Australia is home to the large Great Artesian basin. - North and Central Africa also has a large system.
• Oceanic Water


  The water contained in the Earth's oceans and seas but not inland seas like the Caspian Sea.

  - Oceans dominate the amount of available water

  - Exact amount is unknown with figures varying from 1,320,000,000 to 1,370,000,000km^3 with an average depth of 3682m

  - Cover 72% of the planet's surface

  - Contain dissolved salts that allow it to stay as liquid water below 0C

  - Are alkaline with an average pH of 8.14

  - pH has fallen from 8.25 in the last 250 years and is falling. This change in pH is linked to the increase in atmospheric carbon
• Cryospheric Water


  - Those portions of the Earth's surface where water is in solid form.

  Five Locations of cryospheric water:

  - Sea Ice e.g. the Ross Ice Shelf

  - Permafrost e.g. the Alaska North Slope

  - Alpine glaciers e.g. Mer de Glace, France

  - Ice sheets e.g. the Greenland ice sheet

  - Ice caps e.g. the Iceland ice cap
• Cryospheric Water: Sea Ice


  Ice formed when water in the oceans is cooled to temperatures below freezing. Much of the Arctic Ocean is frozen; the amount of which grows in winter and shrinks in summer. Sea ice does not raise sea level when it melts, because it forms from ocean water.
• Cryospheric Water: Ice Sheets

  An ice sheet is a mass of glacial land ice extending more than 50,000 km2.

  - Ice sheets form in areas where snow that falls in winter does not melt entirely over the summer. Over thousands of years, the layers of snow pile up into thick masses of ice, growing thicker and denser as the weight of new snow and ice layers compresses the older layers

  - Constantly in motion, slowly flowing downhill under their own weight
• What are the 2 major ice sheets on Earth today?


  - Greenland

  - Antartica
• Greenland Ice Sheet


  - Greenland ice sheet is the second largest ice body in the world containing 8% of the total global fresh water.

  - The ice sheet is almost 2400 km long and its greatest width is 1100m. Thickness is generally more than 2km ad over 3km at its thickest point.

  - Not only the ice mass of Greenland- isolated glaciers and small ice caps cover between 76,000 and 100,000 square km.

  - If the entire 2,850,000 cubic km of ice were to melt, it would lead to a global sea level rise of 7.2m

  - Scientists have discovered melting is starting much earlier and reduces the albedo rate of the surface ice, increasing the absorption of incoming solar radiation, which leads to increased ice melt. Rising atmospheric temperatures are throught to be the main cause for increasing melt of the ice sheet.
• Cryospheric Water: Ice Caps


  - Are thick layers of ice on land that are smaller than 50,000km^2

  - Usually found in mountainous areas

  - Ice caps tend to be dome-shaped and are centred over the highest point of an upland area

  - They flow outwards, covering almost everything in their path and becoming the major source for many glaciers
• Cryospheric Water: Alpine Glaciers


  - Alpine glaciers are thick masses of ice found in deep valleys or in upland hollows.

  - Most valley glaciers are fed by ice from ice caps or smaller corrie glaciers.

  - These glaciers are particularly important in the Himalayas where about 15,000 Himalayan glaciers form a unique reservoir which supports perennial rivers such as the Indus and the Ganges
• Himalayan Glaciers


  - Aletsch is the largest ice cap in the Alps (23-km) long

  - The glacier, which covers 86 square kilometres in the Swiss Alps and holds about 11 billion tonnes of ice

  - Glacier would lose 50 percent of its volume and length by the year 2100 (due to climate change)
• Cryospheric Water: Permafrost


  - Permanently frozen layer of soil beneath the surface of the ground.

  - Remains at or below 0°C for at least two consecutive years. - - The thickness of permafrost varies from less than one metre to more than 1,500 m.

  - Around 15% of the Northern Hemisphere is underlain by permafrost, covering a total area of around 18 million km2

  - Includes large areas of Alaska, Canada, Greenland, and Siberia

  - About 85% of Alaska's land area is underlain by permafrost.
• Has permafrost begun to melt as climate warms?


  Yes

  - this melting is releasing large amounts of carbon dioxide and methane, potentially potentially affecting global climates