The water cycle and water insecurity - What are the processes operating within the hydrological cycle from global to local scale? Flashcards
1
Q
Why is the global hydrological cycle a closed system?
A
It is a closed system of linked processes so there are no external inputs or outputs. For this reason, the amount of global water is finite and constant. The only thing that does change is the state in which the water exists (liquid, vapour or ice). The proportion of global water held in each state vary over time with changes in climate.
2
Q
Where does the power that drives the global hydrological cycle come from?
A
The power that drives the global hydrological cycle comes from two sources:
1 solar energy: in the form of heat
2 gravitational energy: causes rivers to flow downhill and precipitation to fall to the ground
3
Q
Name a climate change that would alter the proportion of water held in different states.
A
Global warming
4
Q
What are stores?
A
Stores are ‘reservoirs’ where water is held.
5
Q
What are the four main stores?
A
There are four main stores: (1) the oceans, (2) glaciers and ice sheets (cryosphere), (3) surface runoff and (4) the atmosphere.
6
Q
What does surface runoff consist of?
A
Surface runoff consists of rivers and lakes, as well as groundwater.
7
Q
What percentage of all the global freshwater does the cryosphere account for?
A
Of these freshwater stores, the cryosphere is the largest, accounting for 60% of all the global freshwater.
8
Q
What percentage of groundwater does the cryosphere account for?
A
30%
9
Q
Less than what percentage of groundwater is stored in the biosphere (vegetation and soil moisture)?
A
Less than 1% is stored in the biosphere (vegetation and soil moisture).
10
Q
What are flows?
A
Flows are the transfers of water from one store to another.
11
Q
What are the four main flows?
A
There are four main flows: precipitation, evaporation, transpiration and vapour transport.
12
Q
What are fluxes?
A
Fluxes are the rates of flow between stores.
13
Q
Where do the greatest fluxes occur?
A
The greatest fluxes occur over the oceans.
14
Q
What is surface runoff?
A
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15
Q
What is groundwater?
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16
Q
What does the global water budget take into account?
A
The global water budget takes into account all the water that is held in the stores and flows of the global hydrological cycle.
17
Q
What percentage of all the water that is held in the stores and flows of the global hydrological cycle is freshwater?
A
2.5%
18
Q
What percentage of all the freshwater that is held in the stores and flows of the global hydrological cycle is ‘easily accessible surface freshwater’?
A
1%
19
Q
What percentage of all the water that is held in the stores and flows of the global hydrological cycle is locked up in glaciers and ice sheets?
A
Nearly 70% is locked up in glaciers and ice sheets.
20
Q
What is residence time?
A
This is the average time a molecule of water will spend in one of the stores. Residence times vary from 10 days in the atmosphere to 3,600 years in the oceans and 15,000 years in an ice cap.
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31
What two water stores are non-renewable?
It has been claimed that two water stores fossil water and the cryosphere are non-renewable. The latter is to be questioned because come another glacial period, more water will once again become locked in glaciers and ice sheets.
32
What are the main stores of easily accessible surface freshwater?
Ice caps & glaciers (69%)
| Groundwater (30%)
33
What is a drainage basin?
The drainage basin is a subsystem within the global hydrological cycle. It is an open system with external inputs and outputs. Since those inputs vary over time, so does the amount of water in the drainage basin.
34
What is the main input in the drainage basin?
The main input is precipitation, which can vary in a number of different ways.
35
What characteristics of precipitation can have a significant impact on the drainage cycle/
- Form: rain, snow or hail. Clearly, with snow, entry of water into the drainage system will be delayed.
- Amount: this will affect the amount of water in the drainage basin and fluxes within it.
- Intensity: the greater the intensity, the greater the likelihood of flooding.
- Seasonality: this is likely to result in the drainage basin system operating at different flow levels at different times of the year.
- Distribution: this is significant in very large basins, such as the Nile and the Ganges, where tributaries start in different climate zones.
36
How does solar energy affect the drainage basin system?
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37
What characteristics of precipitation can have a significant impact on the drainage cycle?
- Form: rain, snow or hail. Clearly, with snow, entry of water into the drainage system will be delayed.
- Amount: this will affect the amount of water in the drainage basin and fluxes within it.
- Intensity: the greater the intensity, the greater the likelihood of flooding.
- Seasonality: this is likely to result in the drainage basin system operating at different flow levels at different times of the year.
- Distribution: this is significant in very large basins, such as the Nile and the Ganges, where tributaries start in different climate zones.
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43
What are the seven types of flows that are important in transferring precipitation that has fallen on the land into the drainage network?
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1 Interception
2 Infiltration
3 Percolation
4 Throughflow
5 Groundwater flow
6 Surface runoff
7 River or channel flow
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44
What is interception?
Interception: the retention of water by plants and soils which is subsequently evaporated or absorbed by the vegetation.
45
What is infiltration?
Infiltration: the process by which water soaks into, or is absorbed by the soil.
46
What is percolation?
Percolation: similar to infiltration, but a deeper transfer of water into permeable rocks.
47
What is throughflow?
Throughflow: the lateral transfer of water downslope through the soil.
48
What is groundwater flow?
Groundwater flow: the very slow transfer of percolated water through pervious or porous rocks. Also known as base flow.
49
What is surface runoff?
Surface runoff: the movement of water that is unconfined by a channel across the surface of the ground. Also known as overland flow.
50
What is river of channel flow?
River or channel flow: takes over as soon as the water enters a river or stream; the flow is confined within a channel.
51
What are the three main outputs of the drainage basin?
1 Evaporation
2 Transpiration
3 Discharge
52
What is evaporation?
Evaporation: the process by which moisture is lost directly into the atmosphere from water surfaces, soil and rock.
53
What is transpiration?
Transpiration: the biological process by which water is lost from plants through minute pores and transferred to the atmosphere.
54
What is discharge?
Discharge: (also known as channel flow) into another, larger drainage basin, a lake or the sea.
55
What is the difference between throughflow and groundwater flow?
Throughflow: the lateral transfer of water downslope through the soil.
Groundwater flow: the very slow transfer of percolated water through pervious or porous rocks. Also known as base flow.
56
Which of the flows is perhaps the most important?
Surface runoff
57
What physical factor mainly impacts on the inputs and outputs?
Climate
58
Which of the flows is perhaps the most important?
Surface runoff
59
What are the physical factors affecting drainage basin systems?
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Climate
Soils
Geology
Relief
Vegetation
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60
How does climate affect drainage basin systems?
Climate has a role in influencing the type and amount of precipitation overall and the amount of evaporation, i.e. the major inputs and outputs. Climate also has an impact on the vegetation type
61
How do soils affect drainage basin systems?
Soils determine the amount of infiltration and throughflow and, indirectly, the type of vegetation
62
How does geology affect drainage basin systems?
Geology can impact on subsurface processes such as percolation and groundwater flow (and, therefore, on aquifers). Indirectly, geology affects soil formation
63
How does relief affect drainage basin systems?
Relief can impact on the amount of precipitation. Slopes can affect the amount of runoff
64
How does vegetation affect drainage basin systems?
The presence or absence of vegetation has a major impact on the amount of interception, infiltration and occurrence of overland flow, as well as on transpiration rates
65
What are the four impacts of human activities on drainage basin systems?
River management
Deforestation
Changing land use - agriculture
Changing land use - urbanisation
66
What is the impact of river management on drainage basin systems?
- Construction of storage reservoirs holds back river flows
- Abstraction of water for domestic and industrial use reduces river flows
- Abstraction of groundwater for irrigation lowers water tables
67
What is the impact of deforestation on drainage basin systems?
- Clearance of trees reduces evapotranspiration, but increases infiltration and surface runoff
68
What is the impact of changing land use - agriculture on drainage basin systems?
- Arable to pastoral: compaction of soil by livestock increases overland flow
- Pastoral to arable: ploughing increases infiltration by loosening and aerating the soil
69
What is the impact of changing land use - urbanisation on drainage basin systems?
- Urban surfaces (tarmac, tiles, concrete) speed surface runoff by reducing percolation and infiltration
- Drains deliver rainfall more quickly to streams and rivers, increasing chances of flooding
70
What components of the drainage basin system are most affected by humans?
The components of the drainage basin most affected by humans are:
- evaporation and evapotranspiration
- interception
- infiltration
- groundwater
- surface runoff
71
What is evapotranspiration?
Evapotranspiration is the combined effect of evaporation and transpiration, such as occurs from most vegetated surfaces.
72
What would be the effects of afforestation on drainage basin flows?
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73
How has deforestation disrupted the Amazon drainage basin cycle?
Deforestation here has disrupted the drainage basin cycle in a number of ways, including:
- a lowering of humidities
- less precipitation
- more surface runoff and infiltration
- more evaporation, less transpiration
- more soil erosion and silt being fed into the rivers
74
What is a water budget?
A water budget is the annual balance between precipitation, evapotranspiration and runoff.
75
What formula is used to calculate a water budget?
It is calculated from the formula:
P = E + R + S
where P is precipitation, E is evapotranspiration, R is runoff and S represents changes in storage over a period of time, usually one year.
76
What do water budgets at a national or regional scale provide a useful indication of?
Water budgets at a national or regional scale provide a useful indication of the amount of water that is available for human use (for agriculture, domestic consumption, etc.)
77
At a local scale, what can water budgets inform about?
At a local scale, water budgets can inform about available soil water. This is valuable to users, such as farmers, who can use it to identify when irrigation might be required, and how much.
78
What is available soil water?
Available soil water is the amount of water that can be stored in the soil and is available for growing crops.
79
What is a river regime?
A river regime is the annual variation in the discharge or flow of a river at a particular point, and is usually measured in cumecs.
80
What is the discharge or flow of a river at a particular point (river regime) usually measured in?
Cumecs
81
What factors influence the character of a river's regime?
The character of a river's regime is influenced by a number of variable factors:
- the size of the river and where discharge measurements are taken along its course
- the amount, seasonality and intensity of the precipitation
- the temperatures, with possible meltwater and high rates of evaporation in summer
- the geology and soils, particularly their permeability and porosity; groundwater noted in permeable rocks is gradually released into the river as base flow
- the type of vegetation cover: wetlands can hold water and release it slowly into the river
- human activities aimed at regulating a river's discharge
82
What is the difference between river regimes and storm hydrographs?
Whereas river regimes are usually graphed over the period of a year, storm hydrographs show discharge changes over a short period of time, often no more than a few days.
83
What do storm hydrographs show?
Storm hydrographs show discharge changes over a short period of time, often no more than a few days.
84
What are the two things that the storm hydrograph plots?
The storm hydrograph plots two things: the occurrence of a short period of rain (maybe a heavy shower or storm) over a drainage basin and the subsequent discharge of the river.
85
What are the main features of a storm hydrograph?
- Once the rainfall starts, the discharge begins to rise; this is known as the rising limb
- Peak discharge is reached sometime after the peak rainfall because the water takes time to move over and through the ground to reach the river
- The interval between peak rainfall and peak discharge is known as the lag time
- Once the input of rainwater into the river starts to decrease, so does the discharge; this is shown by the falling or recessional limb
- Eventually the river's discharge returns to its normal level of base flow
86
What happens in a storm hydrograph once the rainfall starts?
Once the rainfall starts, the discharge begins to rise; this is known as the rising limb
87
What is the term for once the rainfall starts, the discharge begins to rise?
Rising limb
88
When and why is peak discharge reached?
Peak discharge is reached some time after the peak rainfall because the water takes time to move over and through the ground to reach the river
89
What does lagtime refer to?
The time interval between peak rainfall and peak discharge is known as the lag time
90
What happens once the input of rainwater into the river starts to decrease?
Once the input of rainwater into the river starts to decrease, so does the discharge, this is shown by the falling or recessional limb
91
What is another term for when the river's discharge returns to its normal level?
Base flow
92
What is the difference between 'flashy' hydrographs and 'flat' hydrographs?
Some hydrographs have very steep limbs, especially rising limbs, high peak discharge and a short lag. These are often referred to as 'flashy' hydrographs. In contrast, there are some hydrographs with gently inclined limbs, low peak discharge and long lag time. These are often called 'delayed' or 'flat' hydrographs.
93
What are the effects of urbanisation on hydrological processes?
- Construction work leads to the removal of vegetation cover. This exposes the soil and increases overland flow.
- Bare soil is eventually replaced by a covering of concrete and tarmac, both of which are impermeable and increase surface runoff.
- The high density of buildings means that rain falls on roofs and then is swiftly fed into drains by gutters and pipes.
- Drains and sewage reduce the distance and time rainwater travels before reaching a stream or river channel.
- Urban rivers are often channelised with embankments to guard against flooding. When floods occur, they can be more devastating.
- Bridges can restrain the discharge of floodwaters and act as local dams, thus prompting upstream floods.
94
What problem means that the effects of urbanisation on hydrological processes are made worse?
The problem is made worse by the fact that so many towns and cities are located close to rivers.
95
Apart from a steady rainfall, what other factors contribute to a 'delayed' hydrograph?
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96
What interacting factors affect the shape of two different storm hydrographs?
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Weather/climate
Rock type
Soils
Relief
Basin size
Shape
Drainage density
Vegetation
Pre-existing (antecedent) conditions
Human activity
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97
What would the difference in hydrograph be for a 'flashy' river compared to a 'flat' river?
'Flashy' river
Short lag time, high peak, steep rising limb
'Flat' river
Long lag time, low peak, gently sloping rising limb
98
How would weather/climate affect the shapes of two different storm hydrographs for a 'flashy' river and a 'flat' river?
'Flashy' river
Intense storm that exceeds the infiltration capacity of the soil
Rapid snowmelt as temperatures suddenly rise above zero
Low evaporation rates due to low temperatures
'Flat' river
Steady rainfall that is less than the infiltration capacity of the soil
Slow snowmelt as temperatures gradually rise above zero
High evaporation rates due to high temperatures
99
How would rock type affect the shapes of two different storm hydrographs for a 'flashy' river and a 'flat' river?
'Flashy' river
Impermeable rocks, such as granite, which restrict percolation and encourage rapid surface runoff
'Flat' river
Permeable rocks such as limestone, which allow percolation and so limit rapid surface runoff
100
How would soils affect the shapes of two different storm hydrographs for a 'flashy' river and a 'flat' river?
'Flashy' river
Low infiltration rate, such as clay soils (0-4mm/h)
'Flat' river
High infiltration rate, such as sandy soils (3-12mm/h)
101
How would relief affect the shapes of two different storm hydrographs for a 'flashy' river and a 'flat' river?
'Flashy' river
High, steep slopes that promote surface runoff
'Flat' river
Low, gently slopes that allow infiltration and percolation
102
How would basin size affect the shapes of two different storm hydrographs for a 'flashy' river and a 'flat' river?
'Flashy' river
Small basins tend to have more flashy hydrographs
'Flat' river
Larger basins have more delayed hydrographs; it takes time for water to reach gauging stations
103
How would shape affect the shapes of two different storm hydrographs for a 'flashy' river and a 'flat' river?
'Flashy' river
Circular basins have shorter lag times
'Flat' river
Elongated basins tend to have delayed or attenuated hydrographs
104
How would drainage density affect the shapes of two different storm hydrographs for a 'flashy' river and a 'flat' river?
'Flashy' river
High drainage density means more streams and rivers per unit area, so water will move more quickly to the measuring point
'Flat' river
Low drainage density means few streams and rivers per unit area, so water is more likely to enter the ground and move slowly through the basin
105
How would vegetation affect the shapes of two different storm hydrographs for a 'flashy' river and a 'flat' river?
'Flashy' river
Bare/low density, deciduous in winter, means low levels of interception and more rapid movement through the system
'Flat' river
Dense, deciduous in summer, means high levels of interception and a slower passage through the system; more water lost to evaporation from vegetation surfaces
106
How would pre-existing (antecedent) conditions affect the shapes of two different storm hydrographs for a 'flashy' river and a 'flat' river?
'Flashy' river
Basin already wet from previous rain, water table high, soil saturated so low infiltration/percolation
'Flat' river
Basin dry, low water table, unsaturated soils, so high infiltration/percolation
107
How would human activity affect the shapes of two different storm hydrographs for a 'flashy' river and a 'flat' river?
'Flashy' river
Urbanisation producing impermeable concrete and tarmac surfaces
Deforestation reduces interception
Arable land, downslope ploughing
'Flat' river
Low population density, few artificial impermeable surfaces
Reforestation increases interception
Pastoral, moorland and forested land
