Water cycle

• Conventional rainfall

  sun warms the earths surface, which warms overlying air.

  warm air expands becoming less dense and rises.

  rising air begins to cool, reducing its ability to hold moisture.

  water vapour condenses as air reaches saturation and dew point.

  condenses around condensation nuclei - clouds form - rainfall
• Orographic rainfall

  air is forced to rise up the stoss side( side exposed to wind).

  air cools with altitude increase, reducing ability to hold moisture.

  air reaches saturation and dew point.

  condensation forms around condensation nuclei - clouds form - rainfall.

  rainshadow forms on leeward side

  eg. Tibetan plateau
• Frontal Rainfall

  eg. mid-latitudes UK

  when warm and and cool air mass meet, the warm air is forced to rise due to it being less dense.

  air then cools with increasing altitude, reducing its ability to hold moisture.

  air reaches saturation and dew point.

  condensation forms around condensation nuclei - clouds form - rainfall.
• Drainage basins are open systems
• Inputs out puts and flows

  
• Precipitation can vary due to?

  amount

  type

  seasonality

  intensity

  distribution
• how does vegetation affect drainage basin flows?

  Influences rate of interception, density and type influences how much takes place
• how does soil affect drainage basin flows?

  influences infiltration capacity eg. sandy vs clay permeability
• how does geology affect drainage basin flows?

  influences degree to which percolation can take place, due to porosity
• how does volume and intensity affect drainage basin flows?

  influences rate of saturated over land flow, due to infiltration not taking place, therefore also influencing channel flow
• how does relief affect drainage basin flows?

  influences speed of overland flow and through flow due to force of gravity
• how does temperature and climate affect drainage basin flows?


  Influences rate of evapotranspiration
• which two forces drive movement?

  solar

  gravity
• oceans store? 


  96.9% total water
• rivers and lakes store?

  0.01% total water
• Green water?


  water stored in soil + vegetation
• biosphere?


  Ecological systems integrating all living things
• River regimes 


  Measure of annual variations in river discharge
• Majority river discharges are determined my climate, due to majority of base flow comes from groundwater flow - fewer fluctuations
• river Indus

  Precipitation locked in cryosphere in Himalayas during N. Hemisphere winter.

  increased temps in spring leads to ice melt and increased overland flow, over frozen soil to river.

  increased discharge.
• Movement of ITCZ north in summer means increased conventional rainfall.

  also, increased saturation and saturated over land flow as infiltration capacity is exceeded.
• River Yukon

  Precipitation falls as snow, so is in temporary cryosphere store.

  temp increases in spring leads to snow melt and over land flow over frozen soils.

  increased discharge.
• In summer ground thaws, increased infiltration and through flow + precip as rain.

  after short summer, ground re-freezes and slow return to winter discharge as river is fed by increased volumes of ground water flow.
• Amazon river

  Influenced by climate and size of drainage basin. 2.9 millions sq miles

  river located in S. hemisphere, so increased rainfall in Feb/march.

  die to size, river takes 4/5 months to reach peak discharge.
• river Oak v river Lamburn

  Identical climate different geology
• Lamburn 


  Contains porous rock, underlying chalk, meaning once infiltrated water can undergo percolation.

  therefore, river fed mainly by groundwater flow ( slower flow ).

  meaning less volatility in regime throughout year.
• Oak

  Drains on impermeable clay, meaning less infiltration and increase in overland flow to feed the river.

  = More volatility as over land flow = faster flow
• type of storm hydrographs?

  flashy and Delayed
• Flooding process


  water reaches point in channel at similar times

  steep rising limb

  higher peak discharge

  short lag time

  exceeds bank full discharge
• Sandy

  permeable

  3-12 mm/hr
• Clay

  impermeable

  0-4mm/hr
• High drainage density

  More tributaries per unit area

  channel flow is fastest transfer

  more water moves more quickly to main channel

  reducing lag time
• Human influences of drainage basin?

  Urbanisation

  agriculture

  deforestation

  mid-management
• Urbanisation

  tarmac/concrete form impermeable surface, so no infiltration.

  water travels over low friction, direct route to channel.

  water arrive rapidly at similar times

  flashy hydrograph
• Urbanisation URBAN HEAT ISLAND EFFECT

  buildings made of concrete also have low albedo. absorb and re- radiate heat.

  warms overlying air leading to increased conventional rainfall formation.

  URBAN HEAT ISLAND EFFECT

  incrwasd intensity and volume of inputs overwhelming infiltration capacity.
• Deforestation

  reduced volume uptake from soils and reduced evapotransporation.

  25% of inputs return to the atmosphere in forested area.

  unforested means more water in drainage basin = higher water table = soil more likely to be Saturated = increased saturated overland flow
• deforestation

  Decreases global photosynthesis = increased CO2 in Atmosphere = increased EGHE = rise in global temps = increased conventional rainfall

  1• increase in temp = 7% more moisture in atmosphere

  Increased intensity, overwhelming infiltration capacity
• Deforestation

  Decreases shading, and increases exposure to direct sunlight.

  increases soil baking = reducing permeabilit.

  reducing infiltration and increased over land flow = flashy OR less recharge of aquifers (applies to all deforestation)
• Agriculture

  often includes deforest to make room for livestock farming. in addition, livestock leads to trampling of ground = soil compaction = reduced infiltration = increased overland flow = flashy
• Agriculture 


  Mechanisation in arable land.

  ploughing channels water.

  compaction of soil through heavy machinery.

  reduces infiltration and increased overland flow.

  flashy