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global water store
closed water system because water cannot enter or leave the Earth and its atmosphere
stores
water stored as either water vapour, ice, saline or freshwater.
oceans
lakes
aquifers (underground lakes)
cryosphere (glaciers and ice sheets)
local stores
vegetation storage
surface storage
soil moisture
groundwater storage
flows
how water moves from one store to another
infiltration
throughflow
percolation
stem flow
base flow
channel flow
surface runoff
processes
what drives the flows between stores
precipitation
evaporation
transpiration
cryosphere exchanges
runoff
total global water supply
96.5% of Earth's water is in the oceans and seas
2.5% of Earth’s water is in freshwater (not salty)
0.9% of Earth’s water is in other saline (salty) water sources
freshwater supply
68.8% of Earth's freshwater is in the cryosphere
30% of Earth's freshwater is groundwater
1.2% of Earth's freshwater is surface water
hydrological cycle in a drainage basin
smaller, open systems. The main features of the drainage basin hydrological cycle are:
inputs
outputs
flows
orographic rainfall
when air masses rise over mountains causing it to condense and rain
frontal rainfall
when two air masses meet at an area of low pressure creating rain
convectional rainfall
rainfall caused by water turning to water vapour due to solar radiation
evaporation
when water turns to water vapour and leaves the drainage basin
transpiration
when water leaves plants through holes in their leaves
channel flow (output)
the volume of water that is flowing in a river channel
interception
when plants capture precipitation in their leaves
infiltration
when precipitation enters into the soil
percolation
the vertical flow of water between soil and rock layers
direct runoff
when water from precipitation or snowmelt flows across the ground’s surface because the surface is impermeable i.e. tarmac
saturated overland flow
when the ground is full of water resulting in runoff
throughflow
the horizontal flow of water through soil/rock layers
groundwater flow
the flow of water horizontality once it has reached the water table
physical factors affecting drainage basins
soil type, rock type, climate, relief of the land, vegetation cover
soil type
impermeable soils can stop infiltration and lead to surface saturation resulting in increased surface runoff, where there are permeable soils, infiltration and percolation can occur allowing groundwater to recharge
rock type
some rocks are impermeable and can stop the infiltration of water into the ground, causing the ground to saturate which leads to surface runoff and increase flows in rivers; permeable rocks allow for infiltration and percolation to happen
climate
cold climates allow for precipitation to fall as snow, the water can be stored and held back until it melts, this reduces the channel flow during the winter but leads to an increase during spring and summer due to glacial melt
relief of the land
steeper slopes mean faster surface runoff and shorter times for water storage
vegetation cover
when an area has a high coverage of vegetation, the interception and evapotranspiration increases but the surface runoff decreases
human factors affecting drainage basins
reservoirs, urbanisation, over-abstraction, deforestation
reservoirs
reservoirs - man-made stores that disrupt the natural water flow by delaying the flow and increasing water lost from evaporation
when vegetation grows on the reservoir’s surface, an increase in evapotranspiration happens and increases the salinity of the water
dams - reduce the water flow further downstream resulting in the loss of vegetation
urbanisation
a change of land use that results in moving away from the natural environment to towns and cities
leads to a large number of impermeable surfaces i.e. concrete, which reduce infiltration whilst increasing surface runoff
abstraction
when humans remove water from underground water stores e.g. aquifers
over-abstraction
when the volume of water being removed is greater than the volume of groundwater being replenished, leading to rivers drying up during periods of low rainfall
deforestation
reduces interception and consequently, rainfall strikes soil directly, leading to soil compaction.
soil compaction and the removal of tree roots reduces infiltration
causes an increase in surface runoff (soil saturation occurs faster), resulting in more soil erosion and flooding
water budget
balance between water being evaporated from the oceans and precipitated onto the land
global water budget: limited water for human use
only 2.5% of the Earth's water is freshwater and of that, less than 1% is accessible for direct human use
access and quality of water differs depending on location in the world - usually geology that plays a part in affecting water availability
global water budget: water store residence time
water found in the oceans is stored there for longer than the short amount of time that water is held in the atmosphere
global water budget: non-renewable stores
fossil water is the name given to non-renewable, untouched, ancient freshwater stores. We can find fossil water beneath deserts and in polar areas
new technology is now allowing us to access more of this water, e.g., the extension of oil drilling technology and the use of satellite imagery can increase the use of these fossil aquifers
cryosphere is another non-renewable store as it continues to melt
cryosphere hydrology
very little vegetation due to low temperature and limited light, so the ability for plants to grow is reduced
during the winter, the ground, lakes and rivers are frozen in the cryosphere, winter snow and ice mean that 85% of solar radiation is reflected
in spring and summer, frozen water thaws in the cryosphere, causing rapid surface runoff and increasing evaporation
as ice and soils thaw, biogenic gases (gases produced by or used by organisms e.g. methane) are released into the atmosphere
permafrost
soil that is permanently frozen
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