water

• solar energy and gravity drive the operation of the global hydrological cycle
• closed system: there is a transfer of energy but not matter between the system and its surroundings, so the same amount of water is kept within the hydrological cycle and circulated continuously
• inputs: the movement of matter or energy into a system from the environment
• outputs: the movement of matter or energy out of a system, in the hydrological cycle closed system this would be from one store to another
• stores: where matter or energy is kept for a long period of time
• flows: the amount of matter transferred from one place to another
• solar energy: heat energy from the sun causes changes in the state of water and drives some processes the hydrological cycle, like evaporation
• some sources are considered non-renewable because they are not replaced:

  • fossil water stored underground in rocks
  • glaciers melting due to climate change
• the annual balance between the flows and size of water stores is known as the global water budget
• water is considered a renewable resource because there is a constant circulation and replenishment of stores without any losses from the planet
• the availability of water may vary throughout the year, especially if there's a very dry season when plant absorption, evaporation and transpiration rates are higher
• the water budget determines what is available because some regions or areas have more precipitation than others, some have more rivers and some have more groundwater
• some of these stores constantly replenish so people have enough water each year but fossil reserves are not and the water budget may be changing due to climate change
• precipitation patterns- orographic (relief)

  • caused when humid air is forced to rise over mountains
  • when the air cools over at higher altitudes, moisture condenses, forms clouds and droplets of water which falls due to gravity
• precipitation patterns- frontal

  • caused when warm humid air is forced to rise at a warm front or cold front, usually part of a depression
  • the air cools, condenses and rain follows
• precipitation patterns- convectional

  • when the ground and lower atmosphere are heated by the sun causing rising thermals of air
  • humidity in the air condenses when it cools at higher altitudes, followed by intense rainfall
• flows:

  • interception- vegetation intercepts rain before it reaches the ground
  • infiltration- the movement of water downwards through soil
  • through flow- the movement off water downslope through the soil towards a base level (river)
  • overland flow- if soil spaces are full, water runs off the surface
  • direct runoff- rain falling on the ground when it cannot infiltrate
  • percolation- the movement of water downwards through porous or permeable rocks
  • groundwater flow- downwards and sideways movement of water in rock layers under the influence of gravity
• outputs

  • evaporation- change in state of water from liquid to a gas when heated by the sun
  • transpiration- plants absorb water through the soil through their roots, transpiring moisture to the surface of their leaves
• evapotranspiration- evaporation + transpiration
• Physical factors influencing the water cycle

  • Climate
  • Vegetation
  • Soils
  • Geology
• Climate influence on the water cycle

  1. Inputs: amount of precipitation

  2. Flows: more direct runoff when precipitation is greater or more intense

  3. Outputs: evaporation increases when its hotter
• Vegetation influence on the water cycle

  1. Inputs: high transpiration rates increase local rainfall

  2. Flows: large forests intercept a lot of rain slowing infiltration

  3. Outputs: extensive tree cover will increase evapotranspiration and reduce channel flow
• Soil influence on the water cycle

  Flows: soil with more spaces will allow more water to infiltrate, reducing overland flow
• Geology influence on the water cycle

  1. Flows: permeable or porous rocks allow more percolation and increase groundwater flow

  2. Outputs: impermeable rock prevent percolation
• human disruptions

  • deforestation- removal of tree cover reduces interception and evapotranspiration
  • abstracting water- people take water from the ground faster than it can be replaced
• water budget: the balance between inputs and outputs which are influenced by climate
• water balance equation:

  p= q + e +/- s

  • p is precipitation
  • q is channel discharge
  • e is evapotranspiration
  • s is change in storage