Water Cycle and Water Insecurity
The global hydrological cycle
where is the world’s water?
- lithosphere - rigid outer part of the Earth consisting of the crust and upper mantle
- hydrosphere - liquid component of the Earth, eg sea, lake, puddle, rain
- cryosphere - frozen water part of the Earth's system
- biosphere - plants and animals
- atmosphere - layer of gases surrounding the Earth (water vapour)
system - inputs, outputs, transfers and stores
the water system is a closed system because we can’t create or lose water, we just make it unusable to us
controls of this cycle:
- solar energy and gravitational energy
- variation between outputs and inputs over land and sea
there is a loss of stores as the Earth surfaces warm
Drainage basin hydrological cycle (DBHC)
factors affecting storage and flow in the DBHC
- landscape features such as areas for river storage of water
- land use and building will affect flows between the surface and soil/rocks
- gradient of the land (will accelerate surface and flow through)
- geology and rock type will affect infiltration and storage
- climate will affect evaporation rates and storage accelerating whole cycle
- amount of vegetation (cover) will affect interception and potentially increase stores
- weather factors such as wind systems can bring rain but the wind can also increase evaporation
- action of creating dams affects storage
- diverting water systems, human actions through irrigation
human actions disrupting drainage basin cycle
cloud seeding - the attempt to change the amount or type of precipitation by dispersing substances into the air
that serve as cloud condensation nuclei
urbanisation - creates impermeable surfaces that reduce infiltration and increase surface runoff and
throughflow through artificial drains; stream and river discharge often increase rapidly as a result
dam construction - dams increase surface water stores and evaporation and reduce downstream river
discharge
groundwater abstraction - in some places, groundwater is abstracted from aquifers faster than it is replaced,
causing reduced groundwater flow and a lower water table
in other locations, reduced industrial activity or deforestation has increased groundwater storage, increasing
the risk of groundwater flooding if the water table reaches the land surface
The water table is the boundary between the unsaturated
zone and the saturated zone underground. Below the
water table, groundwater fills any spaces between
sediments and within rock
,throughflow - water moving sideways through the soil, downslope under the influence of gravity
percolation - water moving vertically downwards through and into a permeable or porous rock
channel flow - water flowing in a rivulet, stream of river contained within its banks
water budgets show the annual balance between inputs and outputs
precipitation = channel discharge + evapotranspiration ± change in storage
Hydrographs
flashy hydrograph - short lag time and high peak discharge
subdued hydrograph - long lag time and low peak discharge
factor flashy hydrograph subdued hydrograph
drainage basin small basins - water will reach the large basins - water will take longer to reach
size channel rapidly, as it has a shorter the channel as it has a greater distance to
distance to travel travel
drainage basin circular basins - it will take less time for elongated basins - water will take a long
shape the water to reach the channel, as all the time to reach the channel from the
extremities are equidistant from the extremities of the drainage basin
channel
drainage basin steep slopes - water flows rapidly gentle slopes - water can infiltrate into the
relief downhill and reaches the channel ground and travel slowly to the channel
quicker through the soil and rock
soil type clay soils - low porosity and the grains sandy soils - high porosity, so water can
swell when they absorb water, so water infiltrate
infiltrates slowly deep / thick soils - allow more infiltration
thin soil - becomes saturated quickly
, factor flashy hydrograph subdued hydrograph
rock type impermeable rocks - water cannot permeable rocks - water percolates through
percolate into the rock, increasing pore spaces and fissures into the
surface runoff to rivers groundwater store
drainage density high drainage density - a large number low drainage density - a small number of
of surface streams per km² means the surface streams per km² means the water
storm water will reach the main channel travels slowly through the soil and rocks to
rapidly the river
natural vegetation thin grass - intercepts little water and forest and woodland - intercepts water and
there is little loss by evapotranspiration, has high rates of evapotranspiration, so
so more water reaches the channel less water reaches the channel, and more
rapidly slowly
land use urban - urban surfaces have more hard rural - vegetated surfaces intercept water
surfaces such as roads, and drains that and allow infiltration so water travels slowly
carry the water rapidly and directly to the to the river channel
river
precipitation high intensity - when rain falls faster low intensity - water can infiltration so water
intensity than the infiltration capacity, surface travels slowly through the soil to the river
runoff occurs and transports the water channel
rapidly to the channel
precipitation prolonged - the water table rises and the short duration - most of the water infiltrates
duration soil becomes saturated, causing surface into the soil and travels slowly through the
runoff, which travels rapidly to the river soil into the rocks before reaching the
channel channel
snowfall fast snowmelt - meltwater cannot slow snowmelt - the ground thaws with the
infiltrate into the frozen ground, so it snow, so the meltwater can infiltrate into the
flows rapidly over the surface into the soil and rocks before reaching the channel
river channel
evapotranspiration low rates - fewer losses from the high rates - high evapotranspiration losses
drainage basin system will increase will reduce discharge into the river channel
discharge into the river channel
River regimes - describes the difference in discharge in a river over the course of a year or longer
simple regimes
- occur when the river experiences a period of seasonally high discharge followed by low discharge
- typical of rivers where inputs depend on glacial meltwater, snowmelt or snowmelt storms
complex regimes
- occur where larger rivers cross different relief and climatic zones, and therefore experience the effects
of different seasonal climatic events
- human factors can also contribute to their complexity
Water balance
- the water balance affects how much water is stored in a system
- the general water balance in the UK shows seasonal patterns
The global hydrological cycle
where is the world’s water?
- lithosphere - rigid outer part of the Earth consisting of the crust and upper mantle
- hydrosphere - liquid component of the Earth, eg sea, lake, puddle, rain
- cryosphere - frozen water part of the Earth's system
- biosphere - plants and animals
- atmosphere - layer of gases surrounding the Earth (water vapour)
system - inputs, outputs, transfers and stores
the water system is a closed system because we can’t create or lose water, we just make it unusable to us
controls of this cycle:
- solar energy and gravitational energy
- variation between outputs and inputs over land and sea
there is a loss of stores as the Earth surfaces warm
Drainage basin hydrological cycle (DBHC)
factors affecting storage and flow in the DBHC
- landscape features such as areas for river storage of water
- land use and building will affect flows between the surface and soil/rocks
- gradient of the land (will accelerate surface and flow through)
- geology and rock type will affect infiltration and storage
- climate will affect evaporation rates and storage accelerating whole cycle
- amount of vegetation (cover) will affect interception and potentially increase stores
- weather factors such as wind systems can bring rain but the wind can also increase evaporation
- action of creating dams affects storage
- diverting water systems, human actions through irrigation
human actions disrupting drainage basin cycle
cloud seeding - the attempt to change the amount or type of precipitation by dispersing substances into the air
that serve as cloud condensation nuclei
urbanisation - creates impermeable surfaces that reduce infiltration and increase surface runoff and
throughflow through artificial drains; stream and river discharge often increase rapidly as a result
dam construction - dams increase surface water stores and evaporation and reduce downstream river
discharge
groundwater abstraction - in some places, groundwater is abstracted from aquifers faster than it is replaced,
causing reduced groundwater flow and a lower water table
in other locations, reduced industrial activity or deforestation has increased groundwater storage, increasing
the risk of groundwater flooding if the water table reaches the land surface
The water table is the boundary between the unsaturated
zone and the saturated zone underground. Below the
water table, groundwater fills any spaces between
sediments and within rock
,throughflow - water moving sideways through the soil, downslope under the influence of gravity
percolation - water moving vertically downwards through and into a permeable or porous rock
channel flow - water flowing in a rivulet, stream of river contained within its banks
water budgets show the annual balance between inputs and outputs
precipitation = channel discharge + evapotranspiration ± change in storage
Hydrographs
flashy hydrograph - short lag time and high peak discharge
subdued hydrograph - long lag time and low peak discharge
factor flashy hydrograph subdued hydrograph
drainage basin small basins - water will reach the large basins - water will take longer to reach
size channel rapidly, as it has a shorter the channel as it has a greater distance to
distance to travel travel
drainage basin circular basins - it will take less time for elongated basins - water will take a long
shape the water to reach the channel, as all the time to reach the channel from the
extremities are equidistant from the extremities of the drainage basin
channel
drainage basin steep slopes - water flows rapidly gentle slopes - water can infiltrate into the
relief downhill and reaches the channel ground and travel slowly to the channel
quicker through the soil and rock
soil type clay soils - low porosity and the grains sandy soils - high porosity, so water can
swell when they absorb water, so water infiltrate
infiltrates slowly deep / thick soils - allow more infiltration
thin soil - becomes saturated quickly
, factor flashy hydrograph subdued hydrograph
rock type impermeable rocks - water cannot permeable rocks - water percolates through
percolate into the rock, increasing pore spaces and fissures into the
surface runoff to rivers groundwater store
drainage density high drainage density - a large number low drainage density - a small number of
of surface streams per km² means the surface streams per km² means the water
storm water will reach the main channel travels slowly through the soil and rocks to
rapidly the river
natural vegetation thin grass - intercepts little water and forest and woodland - intercepts water and
there is little loss by evapotranspiration, has high rates of evapotranspiration, so
so more water reaches the channel less water reaches the channel, and more
rapidly slowly
land use urban - urban surfaces have more hard rural - vegetated surfaces intercept water
surfaces such as roads, and drains that and allow infiltration so water travels slowly
carry the water rapidly and directly to the to the river channel
river
precipitation high intensity - when rain falls faster low intensity - water can infiltration so water
intensity than the infiltration capacity, surface travels slowly through the soil to the river
runoff occurs and transports the water channel
rapidly to the channel
precipitation prolonged - the water table rises and the short duration - most of the water infiltrates
duration soil becomes saturated, causing surface into the soil and travels slowly through the
runoff, which travels rapidly to the river soil into the rocks before reaching the
channel channel
snowfall fast snowmelt - meltwater cannot slow snowmelt - the ground thaws with the
infiltrate into the frozen ground, so it snow, so the meltwater can infiltrate into the
flows rapidly over the surface into the soil and rocks before reaching the channel
river channel
evapotranspiration low rates - fewer losses from the high rates - high evapotranspiration losses
drainage basin system will increase will reduce discharge into the river channel
discharge into the river channel
River regimes - describes the difference in discharge in a river over the course of a year or longer
simple regimes
- occur when the river experiences a period of seasonally high discharge followed by low discharge
- typical of rivers where inputs depend on glacial meltwater, snowmelt or snowmelt storms
complex regimes
- occur where larger rivers cross different relief and climatic zones, and therefore experience the effects
of different seasonal climatic events
- human factors can also contribute to their complexity
Water balance
- the water balance affects how much water is stored in a system
- the general water balance in the UK shows seasonal patterns
