the water cycle

• What are the three components of the global hydrological cycle?


  The three components of the cycle are stores, flows and processes
• Examples of global stores of water

  • Oceans.
  • Lakes.
  • Aquifers (underground lakes).
  • The cryosphere (glaciers and ice sheets)
• Local stores of water include:

  • Interception.
  • Vegetation storage.
  • Surface storage.
  • Soil moisture.
  • Groundwater storage.
• Flows are how water moves from one store to another.
• Example of flows

  • Infiltration.
  • Throughflow.
  • Percolation.
  • Stem flow.
  • Base flow.
  • Channel flow.
  • Surface runoff.
• • The following processes drive the flows between the stores:
  • Precipitation.
  • Evaporation.
  • Transpiration.
  • Cryosphere (glaciers and ice sheets) exchanges.
  • Runoff.
• Water is found on earth as a gas called water vapour, as liquid water, and as solid ice. Although the amount of water in each store changes over the year, each store has a relative size.
• Total global water supply

  • 96.5% of Earth's water is in the oceans and seas.
  • 2.5% of Earth’s water is in freshwater (not salty).
  • 1% of Earth’s water is in other saline (salty) water sources.
• Freshwater sources

  • 68.8% of Earth's freshwater is in the cryosphere (glaciers, ice caps).
  • 30% of Earth's freshwater is groundwater.
  • 1.2% of Earth's fresh water is surface water.
• Surface water stores

  • 69% of Earth's surface water is in ground ice and permafrost.
  • 20% of Earth's surface water is in lakes.
  • 4% of Earth's surface water is in soil moisture.
  • 3% of Earth's surface water is in the atmosphere.
  • 3% of Earth's surface water is in swamps and marshes.
  • 0.5% of Earth's surface water is in rivers.
  • 0.5% of Earth's surface water is in the biosphere (living things).
• Drainage basins are open hydrological systems
• Inputs into drainage basins

  • There are three types of precipitation that input into a drainage basin:
  • Orographic - when air masses rise over mountains causing it to condense and rain.
  • Frontal - when two air masses meet at an area of low pressure creating rain.
  • Convectional - rainfall caused by water turning to water vapour due to solar radiation.
• Outputs from drainage basins

  • Evaporation - when water turns to water vapour and leaves the drainage basin.
  • Transpiration - when water leaves plants through holes in their leaves.
  • Channel flow - the volume of water that is flowing in a river channel.
• Flows

  • Interception
  • Infiltration
  • Direct runoff
  • Saturated overland flow .
  • Throughflow
  • Percolation
  • Groundwater flow
• Interception 


  when plants capture precipitation in their leaves.
• Infiltration 


  when precipitation enters into the soil.
• Direct runoff - when water from precipitation or snowmelt flows across the ground’s surface because the surface is impermeable i.e. tarmac.
• Saturated overland flow - when the ground is full of water, resulting in runoff.
• Throughflow - the horizontal flow of water through soil/rock layers.
• Percolation - the vertical flow of water between soil and rock layers.
• Groundwater flow - the flow of water horizontally once it has reached the water table.
• There are physical components that can impact the relative inputs, flows and outputs of a drainage basin.
• Physical Factors Affecting Drainage Basins

  Climate,Soil type,Vegetation cover,Relief of the land,Rock type
• Climate affecting Drainage Basins

  • Where cold climates allow for precipitation to fall as snow, the water can be stored and held back until it is thawed (melted).
  • This may reduce the channel flow during the winter but lead to an increase during the spring and summer months due to glacial melt water.
• Soil type affecting drainage basin

  • Impermeable soils can stop infiltration and lead to surface saturation resulting in increased surface runoff.
  • Where there are permeable soils, infiltration and percolation can happen. This can cause groundwater to recharge.
• Vegetation cover affecting drainage basin


  When an area has a high coverage of vegetation, the interception and evapotranspiration increases but the surface runoff decreases.
• Relief of the land affecting drainage basin


  Steeper slopes mean faster surface runoff and shorter times for water storage.
• Humans can impact the inputs, outputs, flows and stores of water in a drainage basin
• Rock type affecting drainage basin

  Some rocks are impermeable and can stop the infiltration of water into the ground. Similarly to impermeable soils, these types of rocks can cause the ground to saturate and lead to surface runoff and increase flows in rivers. -In contrast, permeable rocks allow for infiltration and percolation to happen.
• Human Factors Affecting Drainage Basins


  • Over-abstraction
  • Deforestation
  • Urbanisation
  • Reservoirs
• Urbanisation Affecting Drainage Basins


  • Urbanisation is a change of land use that results in moving away from the natural environment to towns and cities.
  • Urbanisation leads to a large number of impermeable surfaces i.e. tarmac, slate, concrete. These impermeable surfaces reduce infiltration, whilst increasing surface runoff.
• Over-Abstraction Affecting Drainage Basins

  • Abstraction is the process by which humans remove water from underground water stores (e.g. aquifers).
  • Over-abstraction is when the volume of water being removed is greater than the volume of groundwater being replenished.
  • Over-abstraction can lead to rivers drying up during periods of low rainfall.
• Deforestation affecting drainage basins

  • Deforestation is the term used to describe the removal of trees. The impact of deforestation reduces interception and consequently, rainfall strikes soil directly, leading to soil compaction.
  • Soil compaction and the removal of tree roots can reduce infiltration.
  • Ultimately deforestation causes an increase in surface runoff, resulting in more soil erosion and flooding.
• Reservoirs affecting drainage basins

  • Reservoirs are man-made stores that disrupt the natural water flow, by delaying the flow and increasing water lost from evaporation.
  • Dams reduce the water flow further downstream resulting in loss of vegetation.
  • When vegetation grows on the reservoir’s surface, an increase in evapotranspiration happens and in turn increase in salinity of the water.