The Water Cycle - A Level Geography OCR

• Hydrosphere - all water on planet Earth


  97% Ocean

  3% locked up in fresh water
• What makes up the hydrosphere

  Oceanic water

  Cryospheric water

  Terrestrial water

  Atmospheric water
• Oceanic Water


  Largest store of water of earth (97% of Earth's water in total)

  - Cover 72% of the Earth's total surface

  - Typically salty

  - falling pH (becoming more acidic over time)
• What is Cryospheric Water?

  Water that is stored on Earth in solid form (ice)

  - sea ice

  - permafrost (water is frozen into the soil)

  - ice caps

  - ice sheets

  -glaciers
• Cryospheric processes

  Ablation
• Terrestrial Water


  Water that is fresh water and free flowing

  - surface water (rivers and lakes)

  - groundwater

  - soil water

  - biological water (biomass - plants and animals)
• Atmospheric Water


  Held in all three states - solid, liquid, gas (water vapour), clouds.

  
  

  Water held in the atmosphere acts as a greenhouse gas and is used to control the Earth's temperature.
• Factors driving the change in magnitude of water stores

  Solid to liquid (melting and freezing)

  Liquid to gas (evaporation)

  Gas to liquid (condensation)
• Liquid - gas (factors affecting)

  Controlled by a variety of factors:

  The process requires energy in the form of solar radiation (heat up water)

  Availability of water - no water, no gas forming

  Humidity - air is saturated with water vapour, makes it harder for liquid to turn into a gas.

  Temperature - too cold, the process won't take place, hot it increases the rate of evaporation.
• Gas - Liquid (factors affecting)

  The main form of precipitation (rain - condensation)

  - Air temp is reduced: hot air can hold more water vapour so when it cools it can no longer hold it and will return into the form of water.

  - volume of air increases without a temperature rise will cause water vapour to turn into a liquid.
• What is the drainage basin?

  Area of land drained by a river and it's tributaries.
• What is the water shed?

  Border around the drainage basin, marking the boundary of the drainage basin.
• Drainage basin


  - open system (energy and matter can transfer in and out of the system. water can come outside of the drainage basin e.g. through clouds)

  - cascading system (inputs and outputs of one open system within the drainage basin system flow into the inputs of another system)
• Drainage Basin System Diagram

  
• Inputs into the drainage basin system

  - precipitation (rain/snow)
• Stores in the drainage basin system

  - interception (trees and plants collect water, trapped in the vegetatation, stopping the water hitting the ground directly)

  - soil

  - rivers

  - lake
• Processes/flows in the drainage basin system

  = ways that water is moving within the drainage basin system, between the stores

  - stemflow (water moving down the stems of plants)

  - surface runoff (water flowing across the surface of the ground)

  - infiltration (water is moving downwards through the soil)

  - throughflow (faster movement of water through the soil)

  - percolation (water moving down through rocks)

  - groundwater flow/base flow

  - channel flow (water flowing within rivers)
• Outputs within the drainage basin system

  - evaporation

  - transpiration (evaporating straight from plants/transpiring)
• Transport within the Global Water Cycle

  - ocean-land-ocean

  - recirculation of water over land

  - ocean-ocean
• What is the water balance

  = inputs-outputs in the water system

  (e.g. drainage basin)
• Equation for Water Balance

  Precipitation (p) =Evapotranspiration + Streamflow +- storage
• Processes of the water cycle

  - precipitation

  - transpiration

  - condensation
• Transpiration


  = diffusion of water vapour to the atmosphere from stomata of plants.
• Factors influencing transpiration

  - temperature

  - wind speed

  -water availability to plants (e.g. deciduous trees shed their leaves in climates with dry or cold seasons to reduce moisture loss through transpiration)
• Condensation


  = the phase change of vapour to liquid water.

  - occurs when air is cooled to its dew point. At this temperature air becomes saturated with vapour resulting in condensation.
• Precipitation


  = water and ice that falls from clouds towards the ground (form of snow, hail, rain, sleet and drizzle)
• How does precipitation form?

  = vapour in the atmosphere cools to its dew point and condenses into tiny water droplets/ice particles to form clouds. These tiny droplets aggregate, reach a critical size and leave as precipitation.
• Environmental Lapse rate (ELR)


  = vertical temperature profile of the lower atmosphere at any given time. On average the temperature falls by 6.5c for every klm of height gained.
• Dry adiabatic lapse rate (DALR)


  = rate at which a parcel of dry air (less than 100% humidity so that condensation is not taking place) cools. Cooling, caused by adiabatic expansion is approximately 10c/km
• Saturated adiabatic lapse rate (SALR)


  = rate at which a saturated parcel of air (one at which condensation is occuring) cools as it rises through the atmosphere. Because condensation releases latent heat, the SALR at around 7c/km is lower than the DALR
• Clouds


  = visible aggregate of water or ices or both that float in the free air. Form when water vapour is cooled to its dew point.
• Absolute instability

  
• Absolute stability

  
• Conditional instability

  
• Soil Moisture graph

  
• What is a soil moisture graph?

  recording the amount of water held in the soils throughout the year - measuring precipitation and evapotranspiration.
• What is soil moisture recharge?

  = precipitation is greater than evapotranspiration, so there is more water entering the soil than leaving so there is a surplus.
• What is river discharge

  = volume of water passing a measuring point in a given time
• Factors affecting interception loss

  - interception storage capacity

  - wind speed

  - vegetation type

  -tree species
• Interception storage capacity

  Vegetation surfaces are dry before rainfall and ability to retain water is at a maximum. Initially most rainfall is intercepted. As vegetation becomes saturated, output of water through stemflow and throughfall increases. Interception depends on the duration and intensity of rainfall.