Processes water cycle

• Moves around 1000x more carbon per year
• Processes of water cycle

  1. Precipitation

  2. Evaporation

  3. Condensation

  4. Cloud formation

  5. Lapse rates
• Precipitation


  Several forms - rain, snow, hail, sleet and drizzle
• Precipitation formation


  1. Water vapour in atmosphere cools to dew point

  2. Condenses into droplets or ice to form clouds

  3. Eventually aggregates and reaches critical size to leave cloud as precipitation
• Dew point


  Atmospheric temperature below which water vapour begins to condense
• Particles like dust and smoke are essential for precipitation as condensation nuclei</b>
• Convectional rainfall


  1. Sun warms darker areas of Earth's surface

  2. Warmer, less dense air rises

  3. Air cools and relative humidity increases until dew point

  4. Condensation occurs to create cumuliform clouds

  5. Latent heat given off allows further air rise and deepens low pressure, causing intense rainfall
• Convectional rainfall is most common in tropical locations due to intense ground heating
• Frontal rainfall


  1. Cold air from poles and warm air from tropics form low pressure systems

  2. Warmer, moist tropical air rises at front creating instability and low pressure

  3. As air cools, relative humidity increases until saturated (dew point)

  4. Latent heat given off allows air to continue upwards, bringing heavier rainfall
• Frontal rainfall is common in mid-latitude locations
• Orographic rainfall


  1. Moist air meets mountain barrier

  2. Air rises and cools, relative humidity increases until dew point

  3. Latent heat allows further rise and cooling, creating more precipitation

  4. Rain shadows occur on leeward side of mountains
• Absolute humidity


  Actual amount of water vapour held in air
• Relative humidity


  Percentage of capacity of air to hold water
• Colder air can hold less moisture than warmer air
• Increased precipitation in world due to higher temperatures
• In UK, downpours could increase by 5% in South and 15% in North
• Condensation


  1. Physical process where water vapour changes into liquid

  2. Occurs when air cooled to dew point or saturated

  3. Water molecules condense on to nuclei or surfaces
• Dew/Frost formation


  1. Condensation of moisture on leaves and plants overnight

  2. Occurs when heat from surface is released to space, cooling the ground
• Cloud formation


  1. Cumuliform clouds form when heated air rises and expands, cooling to dew point

  2. Stratiform clouds form when air mass moves horizontally across cooler surface
• Lapse rates


  • Environmental variable temperature profile of lower atmosphere
  • Dry adiabatic rate - dry air cools at 10°C/km
  • Saturated adiabatic rate - saturated air cools at 6.5°C/km due to latent heat release
• Cloud formation by convection

  1. Ground heated by sun warms air above

  2. Warmer, less dense air rises freely in convection currents

  3. Reaches dew point, condensation begins to form clouds
• Transpiration


  • Diffusion of water vapour to atmosphere from leaf pores (stomata)
  • Influenced by temperature, wind speed, seasons, water availability
• Evaporation


  • Phase change from liquid water to vapour
  • Absorbs latent heat
  • Sublimation - solid water transforms directly to vapour
• Interception


  • Vegetation intercepts proportion of precipitation, storing temporarily
  • Either evaporates or falls as throughflow
• Factors affecting interception loss: vegetation type, rainfall intensity, wind speed
• Runoff


  1. Infiltration into soil

  2. Overland flow across surface to streams/rivers

  3. Overland flow occurs when rainfall exceeds infiltration capacity
• Cryospheric processes


  • Ablation - removal of snow/ice by melting or evaporation
  • Accumulation - inputs to glacial system from snow
• Catchment hydrology


  • Drainage basin - area of land drained by a river and tributaries
  • Percolation - movement of water vertically into rocks and groundwater flow
• Factors affecting permeability, infiltration, throughflow: permeable, gradient, porous
• Carbon cycle


  Processes include photosynthesis, respiration, decomposition, combustion