Water and the hydrological cyle are paramount for supporting life on earth
Works as a closed system
Driven by solar energy and gravitational potential energy
Begins with evaporation - water vapour from the ocean is lifted and condensed in the atmosphere to form clouds
Moisture is then transported around the globe and returns to the surface as precipitation
When reaching the ground - some water will evaporate back into the atmosphere - some may percolate the ground to form groundwater
Balance of the water that remains on the surface of the earth is called runoff and is emptied into lakes, rivers and streams - carry it back to oceans for process to start again
Majority of water is stored in oceans and fresh water is mainly in icecaps and glaciers - 1% accessible to humans
Some stores of water are fossil water - not renewable
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Drainage basins
drainage basin is the area of land drained by a river - water collected here travels downstream
flows
interception: precipitation that does not reach the soil because it is intercepted by vegetation and the forest floor
infiltration: water on the ground soaking into the soils and porous rocks
throughflow: the flowing of water within the soil - moving towards the river
percolation: movement of water through the soil or underlying porous rock, being stored as groundwater
outputs
evaporation
transpiration
channel flow
physical factors that affect the importance of inputs, outputs and flows
climate
temperature, precipitation patterns determine availability and vary according to latitude
equatorial areas recieve the most rainfall - mountain snow can be released as water in warmer temperatures - increasing the amount of easily accessible water
river systems
drainage basins - collect precipitation and channels towards the coast
availability - depends on land use, basin size and shape and precipitation type
flow increases downstream but climate creates variation in discharge and water loss
climate can also produce river regimes where water is supplied through glacial and snow melt
geology
determines underground storage - according to permeability, pourous rock stores water
metamophic rock (aquicludes) cause runoff but do not store water
gravels store best if unconsolidated and bounded by impermeable
humans disrupt the drainage basin - accelerating processes such as deforestation and changing land use
digging deep wells - high risk of salinization, contaminates water sources and can cause shortages
urbanisation increases the proportion of impermeable surfaces - prevents precipitation penetrating the ground - less stored and less availability
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Water budgets and river systems at local scales
water budgets show annual balance between inputs (precipitation) and outputs (through evapotranspiration) - their impact on soil water availability
water budgets influenced by climate types
temperate: mild temperatures and steady climate
tropical: tropical wet, tropical monsoon, or tropical wet and dry seasons
polar: tundra and ice caps climate - tundra summer are short and in ice cap season - temperatures not above zero
river regimes indicate the annual variation in discharge of a river - give an indication of the climate, geology and soils
storm hydrograph shape depends on human factors (land use and urbanisation) and physical features:
shape: circular shape = rapid drainage, long narrow basin means it takes water longer to reach the basin
size: smaller basin = shorter lag time
drainage density: the higher density = greater risk of flooding
rock type: impermeable rocks = greater surface run off and more rapid increase in discharge than permeable rocks
soil and vegetation: roots of plants take in water - reducing through flow, overall reducing discharge
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