The Water Cycle and Water Insecurity
5.1 The hydrological cycle and its importance
Water on earth comes from:
1. Outgassing which is the release of vapour in volcaniceruptions (gaseous water from earth’s
crust).
2. Comets and debris from space made mainly from ice. These decompose and breakdown upon
reaching the atmosphere joining our planet after (vapour showers from terrestrial).
What is the issue of accessing groundwater stores?
● Lowers water tables draining rivers and soil of water and killing wildlife like plants.
● Land surface cracks or subsides.
● Deteriorates the water quality and contaminates it.
● The replenishment speed is far too low.
As the system is continuous outputs govern inputs as nothing is lost or gained. The only thing that
changes is the state the water exists.
Gravitational Potential Energy- The energy an object possesses because of its position in a
gravitational field.
Solar energy- Energy emitted by the sun which drives the hydrological cycle.
Solar energy and GPE drives the hydrological system:
● GPE provides the energy for rates of water movement through the system influencing the
speed in which water completes the cycle.
● Solar energy provides energy for evaporation, condensation, precipitation and transpiration
speeding up the system. This explains cloud cover and precipitation as climate changes.
Fluxes and stores
Flux is the rate of flow between stores. The greatestflux is in between oceans and the atmosphere via
evaporation (400,000 km cubed a year). The smallest is surface runoff between land and oceans
(30,000 km cubed a year).
Interception loss is when water is retained by vegetation and lost by evapotranspiration. This is
greatest at the start of a storm and coniferous forests allow more water accumulation. Wind speed
decreases this loss and so does rainfall levels.
Climate change means in the hydrosphere (water on earth) we are going to see increasing
evaporation. Over oceans increasing precipitation as there will always be enough water to evaporate
to allow for saturation, greater intensity and variability in this. The cryosphere, increased evaporation
but as a store it is likely to decline due to reduced snowfall and increased rainfall.
Water is in 4 main stores, the largest oceans, which contain 97% of global water. Only 3% of storesare
freshwater of which 77% is cryosphere (glaciers, ice caps and ice sheets), (rest is surface water) 22%
is groundwater. Surface and other freshwater only accounts for 1% of global stores which is easily
accessible for human use. Other surface and freshwater are made up of permafrost, lakes, swamps,
marshes, rivers and living organisms. The atmosphere is also a store.
Fossil water or paleowater is an ancient body of waterthat has been contained in some undisturbed
space, typically groundwater in an aquifer, for millennia. Biosphere is all ecosystems on earth.
This leaves a small amount of water that is useful for humans as the rest is mainly inaccessible or in a
saline form. For example, 70% of London’s water comes from the River Thames. Though technology
e.g. desalination is being used to extend available water.
Residence time is the average length of time a watermolecule is in a store or reservoir. There is large
variation in residence time between stores. The atmospheric moisture residence time is only 10 days
whilst water can stay in ice caps for up to 15,000 years. Higher pollution and longer residence times
are correlated
,There is a difference in residence time due to some water e.g. the atmospheric water is moving whilst
ground water is not. On top of this some areas are difficult for humans to access like groundwater
meaning the water remains there longer whilst humans can access lakes easily.
Global warming will decrease time stores e.g. ice caps. On top of this increased temperatures and
thus evaporation and precipitation moves water at a quicker rate between stores decreasing the
residence time. Some stores may decrease in volume also residence time is going to change due to
human demand.
Proportional flow lines are lines that size or width are proportional to the flow size.
The hydrological cycle which is the continuous movement of water on, above and below earth is a
closed system (nothing is lost). Though we have water transfers from one store to another.
Drainage basins are a sub level of the hydrological system and occur regionally and locally they have
inputs and outputs and are open as water movement between these are part of the wider cycle. They
are an open system.
INPUTS
Precipitation- The transfer of water from the atmosphereto
surface by rain, sleet, snow, hail and dew.
STORAGE
Interception- The catching of precipitation by vegetation,
preventing it from reaching the ground.
Vegetation storage- Moisture taken up by vegetation and
held by plants.
Surface storage- Surface water in lakes, ponds etc
Groundwater storage- Water in permeable rock (aquifer)
Groundwater- Water stored in bedrock.
Soil moisture- Water held in soil.
Channel storage- Water held in streams and rivers.
FLOWS AND PROCESSES
Infiltration- Water transfers from the surface into the soil.
Throughflow- Movement of water through the soil.
Percolation- Transfer of water from soil to the bedrockbelow.
Stem flow- Water flowing down plant stems or drain pipes.
Groundwater flow- Movement of water through bedrock.
Surface run off- The movement of water across theland surface usually in reverse but can include
glaciers and man-made channels.
Channel flow- Volume of water flowing within the riverchannel (discharge/runoff).
OUTPUT
Transpiration- The transfer of water from within plantsand animals into the atmosphere as water
vapour.
Evaporation- The conversion of water to water vapourby heating. Affected by hours of sunshine,
temperature, wind speed, water storage type and humidity.
Condensation- The conversion of water vapour to waterwhich can cause clouds to accumulate.
Blue water is water stored in rivers, streams, lakes, groundwater in liquid form.
Green water is water stored in soil and vegetation (not visible).
Percolines are lines of concentrated water flow betweensoil horizons to the river channel.
5.2 The drainage basin with the hydrological cycle
The drainage basin is an open system with inputs, stores, outputs and
processes.
Watershed- The area of highest land that separatesone drainage basin from
another.
Mouth- The end of the river where it meets the sea.
Confluence- When a tributary joins a larger river.
Tributary- A smaller river feeding into a larger one.
Source- The starting point of a river.
Catchment area- The entire area drained by a river.
Antecedent conditions are the conditions that precede a precipitation event.
So for example the amount of moisture in the soil or bedrock. This has a
huge impact on the infiltration rate, the type of flow, the rates of overland
,flow.
What factors affect the flow in the drainage basin?
The extent of the effect is seen through:
● The amount of factors it affects.
● The scale of the effect (amount of the basin).
● Seasonality
PHYSICAL
Basin shape and size -
● Long basin means the water can get into the river quite quickly but evenly.
● Round may mean that it takes a while to reach the river due to higher friction levels but more
likely will enter the river all at once.
● Larger basins collect more precipitation and have larger discharge levels.
● Very significant as it is where all the discharge occurs.
EXAMPLE: The amazon river is the largest basin in the world of 7 million square km resulting in its
discharge carrying 20% of all water carried to rivers by oceans.
Number of tributaries and stream order-
● Lots of tributaries mean water is able to get into the river much faster as channel flow is the
fastest form of water movement.
● Fewer means a greater distance for flows which leads to increased friction of water.
Reservoirs hold water back blocking the flow.
● If lots of rivers join the river quickly in a close proximity it results in large water entering the
river at one point.
● If the pattern is more spaced out and regular, the water will enter the river at more constant
points throughout the river.
● This is not that significant as it mainly just affects discharge levels and velocity.
EXAMPLE: Many tributaries result in a large river discharge e.g The Thames has a large discharge of
65.8m3/s due to most of the tributaries joining before it enters London.
Soil type and geology -
● Results in different percolation and infiltration rates due to different geology types.
● Impermeable soils and rocks cause surface saturation decreasing the speed of flow of that
water.
● Permeable soils and rocks allow a recharge of groundwater.
● More compact surface types inhibit infiltration and result in less infiltration.
● Soil type controls the rate of infiltration, soil moisture storage and rate of throughflow.
● The geology normally varies over a basin so its effects are localised though it is extremely
important in the local area in terms of water storage.
● It also has an important role in the land use around due to ground water storage potential
which will then impact the store and flows.
● Soil moisture and geology affect vegetation levels. E.g. baked soils mean vegetation cannot
grow whilst chalk promotes fertile soils (Southdown from Thames is great for farming and
groundwater storage).
EXAMPLE: Granite has little percolation e.g. The Thames in Aberdeenshire (granite) has high levels of
discharge and no percolation leading to also highly saturated soils and throughflow. The Thames has
multiple different bands of rock types and thus different levels of percolation and groundwater.
Topography/gradient-
● The type of hills and gradient affects the speed of the drainage basin.
● The steeper the gradient the more surface runoff resulting in a faster speed of flow of water in
the basin. Steep slopes also result in shorter storage times.
● Shallow gradients promote infiltration.
● The gradient affects the stores and flows mainly. This is more significant if it has the same
gradient throughout as gradient normally changes. Only affects infiltration and surface runoff
, pace.
EXAMPLE: A high gradient results in a faster speed of the river e.g. the upper swale is the steepest
river in England and is the fastest flowing river in England.
Vegetation amount and type -
● More vegetation results in more interception meaning there is less likely to be high levels of
surface runoff due to mitigated intense rainfall and a temporary storage for water.
● It also stops water entering the basin through increasing evapotranspiration.
● Vegetation also breaks up the soil promoting infiltration.
● Vegetation cover may also reduce sunlight reducing evaporation.
● This has more localised impacts though the amount being removed increases over time, with
many organisations working to replant it. Not a large effect as it only affects flows and
evaporation output a bit.
EXAMPLE: Large vegetation levels results in large stores of water in vegetation leading to little surface
discharge e.g. The new forest has the large vegetation levels in the UK resulting in it having small
rivers with its largest one being 14.5km.
Climate -
● This affects the vegetation type in the basin.
● An increase in precipitation in winter means the discharge increases and there is a higher
velocity as there is more surface runoff especially with intense rainfall exceeding the
infiltration capacity and rate. On top of this it may cause the water table to rise decreasing
infiltration levels.
● It also affects evaporation levels with higher levels reducing surface runoff.
● It also results in seasonal variation of water input throughout the year, in winter there is higher
water flows.
● In winter areas get snowfall reducing the amount of flow. Snow can also increase the amount
of water in a basin when it melts.
● A storm will erode the basin increasing its size and discharge levels. Baked soils also result in
higher surface run off levels.
● This has a significant impact on everything but especially inputs and outputs as it decides
precipitation (only input so significant) and evaporation levels, it also decides the vegetation.
The precipitation type is also important. Though in some places precipitation is the same all
year round.
● Evapotranspiration accounts for 100% of output in arid areas and 75% in humid areas.
EXAMPLE: Evaporation levels that are high and lower precipitation levels lead to low surface water
discharge e.g. the highest level of evaporation happens in sub saharan Africa and lowest levels of
precipitation this results in them having 90% of the region being arid with few rivers. e.g. Meltwater is
stored largely at the top of the Tarim basin which is released in growing seasons resulting in river
fluctuations and is vital for irrigation of China’s desert.
Rock types:
Porous rock (sandstone, chalk) allows water to percolate through the pore spaces.
Pervious rock (limestone) both types of rock are characterisedby a lack of surface drainage and have
high rates of infiltration, it allows it to go along joints areas.
Impermeable rock (granite, shale, clay) impedes drainage by restricting percolation. These areas are
characterised by high rates of overland flow or surface runoff. - Clays can absorb some water but at
very low levels due to the tight pack of the rock.
Factors affecting infiltration:
● Through a period of rainfall, infiltration capacity decreases as the ground has an increased
amount of moisture absorbed in it reducing its infiltration capacity.
● Soil texture influences the rate of infiltration e.g.sandy soils are 3-12mm hr faster than clay.
● Vegetation increases infiltration levels as the vegetation means more water can be absorbed
at a faster rate and also store more water.
● Compact surfaces inhibit infiltration and result in splashing of water from the ground.
Vegetation makes soils less compact.
5.1 The hydrological cycle and its importance
Water on earth comes from:
1. Outgassing which is the release of vapour in volcaniceruptions (gaseous water from earth’s
crust).
2. Comets and debris from space made mainly from ice. These decompose and breakdown upon
reaching the atmosphere joining our planet after (vapour showers from terrestrial).
What is the issue of accessing groundwater stores?
● Lowers water tables draining rivers and soil of water and killing wildlife like plants.
● Land surface cracks or subsides.
● Deteriorates the water quality and contaminates it.
● The replenishment speed is far too low.
As the system is continuous outputs govern inputs as nothing is lost or gained. The only thing that
changes is the state the water exists.
Gravitational Potential Energy- The energy an object possesses because of its position in a
gravitational field.
Solar energy- Energy emitted by the sun which drives the hydrological cycle.
Solar energy and GPE drives the hydrological system:
● GPE provides the energy for rates of water movement through the system influencing the
speed in which water completes the cycle.
● Solar energy provides energy for evaporation, condensation, precipitation and transpiration
speeding up the system. This explains cloud cover and precipitation as climate changes.
Fluxes and stores
Flux is the rate of flow between stores. The greatestflux is in between oceans and the atmosphere via
evaporation (400,000 km cubed a year). The smallest is surface runoff between land and oceans
(30,000 km cubed a year).
Interception loss is when water is retained by vegetation and lost by evapotranspiration. This is
greatest at the start of a storm and coniferous forests allow more water accumulation. Wind speed
decreases this loss and so does rainfall levels.
Climate change means in the hydrosphere (water on earth) we are going to see increasing
evaporation. Over oceans increasing precipitation as there will always be enough water to evaporate
to allow for saturation, greater intensity and variability in this. The cryosphere, increased evaporation
but as a store it is likely to decline due to reduced snowfall and increased rainfall.
Water is in 4 main stores, the largest oceans, which contain 97% of global water. Only 3% of storesare
freshwater of which 77% is cryosphere (glaciers, ice caps and ice sheets), (rest is surface water) 22%
is groundwater. Surface and other freshwater only accounts for 1% of global stores which is easily
accessible for human use. Other surface and freshwater are made up of permafrost, lakes, swamps,
marshes, rivers and living organisms. The atmosphere is also a store.
Fossil water or paleowater is an ancient body of waterthat has been contained in some undisturbed
space, typically groundwater in an aquifer, for millennia. Biosphere is all ecosystems on earth.
This leaves a small amount of water that is useful for humans as the rest is mainly inaccessible or in a
saline form. For example, 70% of London’s water comes from the River Thames. Though technology
e.g. desalination is being used to extend available water.
Residence time is the average length of time a watermolecule is in a store or reservoir. There is large
variation in residence time between stores. The atmospheric moisture residence time is only 10 days
whilst water can stay in ice caps for up to 15,000 years. Higher pollution and longer residence times
are correlated
,There is a difference in residence time due to some water e.g. the atmospheric water is moving whilst
ground water is not. On top of this some areas are difficult for humans to access like groundwater
meaning the water remains there longer whilst humans can access lakes easily.
Global warming will decrease time stores e.g. ice caps. On top of this increased temperatures and
thus evaporation and precipitation moves water at a quicker rate between stores decreasing the
residence time. Some stores may decrease in volume also residence time is going to change due to
human demand.
Proportional flow lines are lines that size or width are proportional to the flow size.
The hydrological cycle which is the continuous movement of water on, above and below earth is a
closed system (nothing is lost). Though we have water transfers from one store to another.
Drainage basins are a sub level of the hydrological system and occur regionally and locally they have
inputs and outputs and are open as water movement between these are part of the wider cycle. They
are an open system.
INPUTS
Precipitation- The transfer of water from the atmosphereto
surface by rain, sleet, snow, hail and dew.
STORAGE
Interception- The catching of precipitation by vegetation,
preventing it from reaching the ground.
Vegetation storage- Moisture taken up by vegetation and
held by plants.
Surface storage- Surface water in lakes, ponds etc
Groundwater storage- Water in permeable rock (aquifer)
Groundwater- Water stored in bedrock.
Soil moisture- Water held in soil.
Channel storage- Water held in streams and rivers.
FLOWS AND PROCESSES
Infiltration- Water transfers from the surface into the soil.
Throughflow- Movement of water through the soil.
Percolation- Transfer of water from soil to the bedrockbelow.
Stem flow- Water flowing down plant stems or drain pipes.
Groundwater flow- Movement of water through bedrock.
Surface run off- The movement of water across theland surface usually in reverse but can include
glaciers and man-made channels.
Channel flow- Volume of water flowing within the riverchannel (discharge/runoff).
OUTPUT
Transpiration- The transfer of water from within plantsand animals into the atmosphere as water
vapour.
Evaporation- The conversion of water to water vapourby heating. Affected by hours of sunshine,
temperature, wind speed, water storage type and humidity.
Condensation- The conversion of water vapour to waterwhich can cause clouds to accumulate.
Blue water is water stored in rivers, streams, lakes, groundwater in liquid form.
Green water is water stored in soil and vegetation (not visible).
Percolines are lines of concentrated water flow betweensoil horizons to the river channel.
5.2 The drainage basin with the hydrological cycle
The drainage basin is an open system with inputs, stores, outputs and
processes.
Watershed- The area of highest land that separatesone drainage basin from
another.
Mouth- The end of the river where it meets the sea.
Confluence- When a tributary joins a larger river.
Tributary- A smaller river feeding into a larger one.
Source- The starting point of a river.
Catchment area- The entire area drained by a river.
Antecedent conditions are the conditions that precede a precipitation event.
So for example the amount of moisture in the soil or bedrock. This has a
huge impact on the infiltration rate, the type of flow, the rates of overland
,flow.
What factors affect the flow in the drainage basin?
The extent of the effect is seen through:
● The amount of factors it affects.
● The scale of the effect (amount of the basin).
● Seasonality
PHYSICAL
Basin shape and size -
● Long basin means the water can get into the river quite quickly but evenly.
● Round may mean that it takes a while to reach the river due to higher friction levels but more
likely will enter the river all at once.
● Larger basins collect more precipitation and have larger discharge levels.
● Very significant as it is where all the discharge occurs.
EXAMPLE: The amazon river is the largest basin in the world of 7 million square km resulting in its
discharge carrying 20% of all water carried to rivers by oceans.
Number of tributaries and stream order-
● Lots of tributaries mean water is able to get into the river much faster as channel flow is the
fastest form of water movement.
● Fewer means a greater distance for flows which leads to increased friction of water.
Reservoirs hold water back blocking the flow.
● If lots of rivers join the river quickly in a close proximity it results in large water entering the
river at one point.
● If the pattern is more spaced out and regular, the water will enter the river at more constant
points throughout the river.
● This is not that significant as it mainly just affects discharge levels and velocity.
EXAMPLE: Many tributaries result in a large river discharge e.g The Thames has a large discharge of
65.8m3/s due to most of the tributaries joining before it enters London.
Soil type and geology -
● Results in different percolation and infiltration rates due to different geology types.
● Impermeable soils and rocks cause surface saturation decreasing the speed of flow of that
water.
● Permeable soils and rocks allow a recharge of groundwater.
● More compact surface types inhibit infiltration and result in less infiltration.
● Soil type controls the rate of infiltration, soil moisture storage and rate of throughflow.
● The geology normally varies over a basin so its effects are localised though it is extremely
important in the local area in terms of water storage.
● It also has an important role in the land use around due to ground water storage potential
which will then impact the store and flows.
● Soil moisture and geology affect vegetation levels. E.g. baked soils mean vegetation cannot
grow whilst chalk promotes fertile soils (Southdown from Thames is great for farming and
groundwater storage).
EXAMPLE: Granite has little percolation e.g. The Thames in Aberdeenshire (granite) has high levels of
discharge and no percolation leading to also highly saturated soils and throughflow. The Thames has
multiple different bands of rock types and thus different levels of percolation and groundwater.
Topography/gradient-
● The type of hills and gradient affects the speed of the drainage basin.
● The steeper the gradient the more surface runoff resulting in a faster speed of flow of water in
the basin. Steep slopes also result in shorter storage times.
● Shallow gradients promote infiltration.
● The gradient affects the stores and flows mainly. This is more significant if it has the same
gradient throughout as gradient normally changes. Only affects infiltration and surface runoff
, pace.
EXAMPLE: A high gradient results in a faster speed of the river e.g. the upper swale is the steepest
river in England and is the fastest flowing river in England.
Vegetation amount and type -
● More vegetation results in more interception meaning there is less likely to be high levels of
surface runoff due to mitigated intense rainfall and a temporary storage for water.
● It also stops water entering the basin through increasing evapotranspiration.
● Vegetation also breaks up the soil promoting infiltration.
● Vegetation cover may also reduce sunlight reducing evaporation.
● This has more localised impacts though the amount being removed increases over time, with
many organisations working to replant it. Not a large effect as it only affects flows and
evaporation output a bit.
EXAMPLE: Large vegetation levels results in large stores of water in vegetation leading to little surface
discharge e.g. The new forest has the large vegetation levels in the UK resulting in it having small
rivers with its largest one being 14.5km.
Climate -
● This affects the vegetation type in the basin.
● An increase in precipitation in winter means the discharge increases and there is a higher
velocity as there is more surface runoff especially with intense rainfall exceeding the
infiltration capacity and rate. On top of this it may cause the water table to rise decreasing
infiltration levels.
● It also affects evaporation levels with higher levels reducing surface runoff.
● It also results in seasonal variation of water input throughout the year, in winter there is higher
water flows.
● In winter areas get snowfall reducing the amount of flow. Snow can also increase the amount
of water in a basin when it melts.
● A storm will erode the basin increasing its size and discharge levels. Baked soils also result in
higher surface run off levels.
● This has a significant impact on everything but especially inputs and outputs as it decides
precipitation (only input so significant) and evaporation levels, it also decides the vegetation.
The precipitation type is also important. Though in some places precipitation is the same all
year round.
● Evapotranspiration accounts for 100% of output in arid areas and 75% in humid areas.
EXAMPLE: Evaporation levels that are high and lower precipitation levels lead to low surface water
discharge e.g. the highest level of evaporation happens in sub saharan Africa and lowest levels of
precipitation this results in them having 90% of the region being arid with few rivers. e.g. Meltwater is
stored largely at the top of the Tarim basin which is released in growing seasons resulting in river
fluctuations and is vital for irrigation of China’s desert.
Rock types:
Porous rock (sandstone, chalk) allows water to percolate through the pore spaces.
Pervious rock (limestone) both types of rock are characterisedby a lack of surface drainage and have
high rates of infiltration, it allows it to go along joints areas.
Impermeable rock (granite, shale, clay) impedes drainage by restricting percolation. These areas are
characterised by high rates of overland flow or surface runoff. - Clays can absorb some water but at
very low levels due to the tight pack of the rock.
Factors affecting infiltration:
● Through a period of rainfall, infiltration capacity decreases as the ground has an increased
amount of moisture absorbed in it reducing its infiltration capacity.
● Soil texture influences the rate of infiltration e.g.sandy soils are 3-12mm hr faster than clay.
● Vegetation increases infiltration levels as the vegetation means more water can be absorbed
at a faster rate and also store more water.
● Compact surfaces inhibit infiltration and result in splashing of water from the ground.
Vegetation makes soils less compact.
