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WATER CYCLE (Supporting Life (Uses (Economic Activity (Industry demands…

- - - - Made up of water particles and ice crystals
      - Reflect 1/5 of incoming solar radiation and lowers surface temperatures
    - - Potent greenhouse has
      - Absorbs long wl radiation - helps maintain global temps. almost 15 degrees higher than they would be otherwise
  - - - Crucial to their growth, reproduction and other metabolic functions
    - - Photosynthesis
        
        Occurs in leavs
        
        Combines CO2, sunlight, and water
        
        Makes glucose and starches
      - Respiration
        
        Converts glucose into energy thru its reaction with 02
        
        Releases CO2 + H20
      - Maintains rigidity in plants
      - Transports mineral nutrients form the soil
      - Transpiration
        
        Transp. from leaf surfaces cools plant via evapotransp.
    - - Essential resource for economic activity
      - Generates electricity
      - Irrigates crops
      - Provides recreational facilities
      - Satisfies public demands
        
        Drinking water
        
        Sewage disposal
      - Industry demands
        
        Food manufacturing
        
        Brewing
        
        Paper making
        
        Steel making
- - - - Precipitation
      - Evaporation
      - Transpiration
      - Runoff
      - Infiltration
      - Percolation
      - Throughflow
    - - Precip. varies in character and this impacts the water cycle at the drainage basin scale
        
        Most rain fows quickly into streams and rivers
        
        In high lattitudes and mountanious catchments, precip. often falls as snow and may remain on the ground for several months = considerable time lag between snowfall and runoff
        
        Intensity is the amount of precip. falling in a given time
        
        High intensity (10-15 mm/hr) moves rapidly overland into streams and rivers
        
        Prolonged precip. events, linked to depressions and frontal systems = large amounts of precip. + river flooding
        
        During the rainy season, river discharge is high and flooding is common where precip. is concentrated in that season
      - Formation
        
        Clouds form when water vapour cools to its dew point
        
        Dew point is the critical temperature when air becomes saturated (100% relative humidity) and can hold no more vaopur
        
        Dew point = condensation bc excess vapour changes state to form liquid droplets
        
        Aggregated, these droplets form clodus
        
        Rain develops thru the process of droplets coalescing or ice crystals growing within clouds
        
        Rain, snow, hail, sleet, drizzle
    - - Is the diffusion of water vapour to the atmosphere from leaf pores (stomata)
      - Is responsible for 10% of moisture in the atmosphere
      - Influenced by temperature, wind speed, water availability to plants
        
        Deciduous trees shed leaves in climates with either dry or cold seasons to reduce moisture thru transp.
    - - Is the phase change of vapour to liquid water
      - Occurs when air is cooled to its dew point
        
        At the dew point where it reaches its critical temperature, air becomes saturated with vapour = condensation
      - Clouds form through condensation in the atmosphere
      - Cumuliform clouds
        
        Flat bases and considerable vertical development
        
        Most often form when air is heated locally through contact with the E's surface
        
        = heated air particles rise freely thru the atmosphere (convection), expand (due to fall in pressure with altitude) and cool
        
        When cooling reaches the dew point, condensation begins and clouds form
      - Stratiform clouds
        
        Air mass moves horizontally across a cooler surface (often ocean)
        
        This process, mixing and turbulence is ADVECTION
        
        Layered
      - Cirrus clouds
        
        Form at higyh altitude
        
        Consist of tin ice crystals
        
        Have little influence on water cycle bc they do not produce precipitation
        
        Wispy
      - Condensationa t/nrea ground = dew/fog
        
        Deposits large amounts of moisture on veg. + other surfaces
    - - Clouds are visible aggregates of water and/or ice that float in the free air
      - Clouds form when vapour is cooled to its dew point. Cooling occurs when:
        
        Air warmed by contact w ground/sea, rises and so pressure falls = it cools by expansion ADIABATIC EXPANSION
        
        The vertical movement of air is CONVECTION
        
        Clouds formed by convection
        
        Ground heated by Sun warms the air in contact with the surface to 18 degrees
        
        The air is less dense and more bouyant bc it is warmer than its surroundings (13 degrees)
        
        This atmospheric instability = air rising freely in a convection current
        
        When its internal temp. reaches dew point (8 degrees), condensation occurrs adn clouds form
        
        The air continues to rises so long as its internal temperature is higher than the surrounding atmosphere
        
        Air masses move horizontally across as relative cooler surface - ADVECTION
        
        A relatively warm air mixes with a cooler one
      - Lapse rates (LR)
        
        Vertical distribution of temperature in the lower atmosphere
        
        The temperature changes that occur within an air parcel as it rises vertically away form the ground
        
        Three types
        
        Environmental LR
        
        Is the vertical temp. profile of the lower atmosphere at any given time
        
        Temp. falls by 6.5 degrees for every km of height gained
        
        Dry Adiabatic LR
        
        Rate of which a parcel of dry air cools
        
        Dry parcel - under 100% humidity so condensation is not occurring
        
        Cooling by adiabatic expansion is 10 degrees/km
        
        Saturated Adiabatic LR
        
        Rate at which a saturated parcel of air cools as it rises thru the atmospehre
        
        Saturated parcels - condensation is occurring
        
        Bc condensation releases latent heat, the SALR is lower than the DALR, at 7 degrees/km
        
        Their interaction explains the formation of clouds
  - - - Phase change of liquid to vapour
      - Main pathway for water to enter atmosphere
      - The energy input does not increase temp.
      - Heat brings about evaporation and breaks molecular bonds
      - Energy is absorbed ass latent heat and is released later in condensation
      - This process allows huge quantities of heat to be transferred globally
    - - Vegetation intercepts a proportion of precipitation, storing it temporarily on branches, leave and stems
      - The moisture either evaporates (interception loss) or falls to ground
      - Rainwater briefly intercepted before reaching ground is throughfall
      - Prolonged/intense rainfall = intercepted rainwater to flow to ground along stems + branches (stemflow)
      - Factors of Interception Loss
        
        Interception storage capacity
        
        Before rainfall, veg. surfaces are dry and unsaturated. As rainfall continues, surfaces become saturated = increased stemflow and throughfall
        
        Wind speed
        
        Evapo. rates increase w. wind speed. Turbulence also increases = additional thrufall
        
        Vegetation Type
        
        Greater interception loss from grasses than agricultural crops. Trees have higher interception losses bc of surface area + aerodynamic roughness
        
        Tree Species
        
        Greater interception losses from evergreens than broad-leaved deciduous trees
        
        Most conifers have leaves year-round + water adheres to spaces between conifer needles = increased evap.
    - - Rain reaching ground and not entering storage follows one of the 2 flowpaths to streams + rivers
        
        Infiltration
        
        By gravity into the soil and lateral movement or throughflow to stream and river channels
        
        Overland flow
        
        Across ground surface, either as a sheet or trickles and rivulets to stream and river channels
        
        When intensity exceeds infil. capacity
        
        Only occurs when soil becomes saturated and the water table rises to the surface - saturated overland flow
      - Groundwater flow
        
        Water percolates deep underground when soil is underlain by permeable rocks
        
        The water migrates slowly thru the pores and joints as groundwater flow
        
        Emerges at surface as springs + seepages
        
        Groundwater levels on the chalk in S England has a distinct seasonal pattern
        
        Late Oct. - water tables beginning to rise as temps. + evapotransp. fall
        
        This recharge continues until late Jan.
        
        Groundwater levels then decline thru late winter, spring + summer (lowest point in early autumn)
    - - Ablation - loss of ice from snow, ice sheets and glaciers due to melting, evaporation and sublimation
      - Meltwater is imp. to river flow in high latitudes and mountain catchments
- - - - Oceans 97%
        
        Store 97% of all global water
      - Polar ice + glaciers 2%
        
        Freshwater comprises a small proportion
        
        75% of freshwater is stored in icecaps of Greenland and Antarctica
      - Groundwater 0.7%
        
        Water stored below ground in permeable rocks amounts to 1/5 of all freshwater
      - Lakes 0.01%
      - Soils 0.05%
      - Atmosphere 0.001%
        
        Is a small store but plays an important role
        
        Rapid flux of water into and out of the atmosphere
        
        Average residence time of a water molecule in the atmosphere is 9 days
      - Rivers 0.0001%
      - Biosphere 0.00004%
  - - - Water vapour evaporated from oceans, soils, lakes and rivers
      - Vapour transpired from plant leaves
      - Together these processes = evapotranspiration
    - - Most rivers flow to the oceans; some in the continental drylands, drain in inland basins
      - A large amount of precip. on land reaches rivers thru infiltration and through flow
    - - This groundwater eventually reaches the surface as springs or contributes to runoff