The water cycle and water insecurity (DONE) Flashcards
1
Q
What approach is the global hydrological cycle typically studied as?
A
- The global hydrological cycle is typically studied and understood using a systems approach, which is a central concept for the study of physical geography.
2
Q
What does the systems theory allow us to do?
A
- Systems theory allows us to conceptualise the main water stores and pathways at a global scale, as well as understand the role of local hydrological processes within this wider global system.
- This complex system adjusts and changes as a result of physical and human factors over short and long timescales.
3
Q
What is a system?
A
- A system is any set of interrelated components that are connected together to form a working whole, characterised by inputs, stores, processes (or fiows) and outputs.
- There are two types: closed system and open system.
4
Q
What is a closed system?
A
- A closed system occurs when there is transfer of energy but not matter between the system and its surroundings (the inputs come from within the system).
5
Q
What is an open system?
A
- An open system receives inputs from and transfers outputs of energy and matter to other systems.
6
Q
Why is the hydrological cycle a closed system?
A
- The global hydrological cycle is a closed system because all the water is continually circulated through the stores and there is a constant amount of water in the system.
- The system does not change because there are no gains from or losses to other systems.
7
Q
What drives the global circulation of water in the hydrological cycle?
A
- The global circulation of water is driven by solar energy;
- When heated by the Sun, the water on the Earth’s surface evaporates into the atmosphere.
- When the humid air rises, condensation occurs at the cooler temperatures, forming clouds, and this eventually leads to precipitation and water is returned back to the land and oceans on the Earth’s surface.
8
Q
What energy transfers occur in the hydrological cycle?
A
- On land, gravitational potential energy is converted to kinetic energy as the water moves through the system by plant interception, or over land as surface runoff.
9
Q
How can water flow through soil in the hydrological cycle?
A
- Water also flows through the soil by the processes of infiltration and throughflow.
- Here, it may be stored as soil moisture or, if the bedrock is permeable or porous, will percolate into the rock where it is stored as groundwater.
- Some of this water will return to the oceans via streams and rivers, which may take some time if it is stored in lakes or glaciers en route.
10
Q
What is the largest water store in the global hydrological cycle?
A
- Oceans are the largest:
- 96.9% of water is stored here.
- 1,335,040 x 10^3 Km3
11
Q
Which water store in the hydrological cycle has the largest residence time?
A
- ice caps and glaciers have the largest residence time of 15,000 years.
12
Q
What is the smallest water store in the global hydrological cycle?
A
- Biological water (biosphere).
- 1 x 10^3 Km3
- 0.0001% of water is stored there.
13
Q
Which water store in the hydrological cycle has the smallest residence time?
A
- Biological water (biosphere).
- 1 week residence time.
14
Q
What is the global water budget?
A
- The global water budget is the annual balance of water fiuxes (flows) and the size of the water stores - oceans, atmosphere, biosphere, cryosphere, groundwater and surface water.
15
Q
Why is water generally considered as a renewable resource?
A
- The water stores have different residence times, but the constant circulation, albeit at variable speeds, means that water is generally considered a renewable resource, replenished naturally.
16
Q
What type of water is not considered as a renewable resource?
A
- Fossil water is an exception; this is water that has been contained in an undisturbed space, usually groundwater in an aquifer, for millennia or longer.
17
Q
In what areas is fossil water being extracted an how does this impact the resource?
A
- In arid regions such as the Sahara Desert, the fossil water in these aquifers may be extracted for human purposes (agriculture, industry and consumption), but there is little to no significant recharge, effectively making this type of groundwater a non-renewable resource.
18
Q
What is a drainage basin?
A
- A drainage basin is an area of land that is drained by a river and its tributaries, and separated from neighbouring drainage basins by a ridge of high land called a watershed or divide.
19
Q
What type of system is a drainage basin?
A
- A drainage basin is an open system, so it is linked to other systems by inputs and outputs and involves a number of linked processes and stores.
20
Q
What is precipitation?
A
- Precipitation is any form of water (liquid or solid) falling from the sky.
- Precipitation includes rain, sleet, snow, hail and drizzle.
21
Q
What is the major input into any drainage basin system?
A
- Precipitation is the major input into any drainage basin system.
- The volume of the input varies according to its type and intensity over time and space, linked to the climatic season and associated weather systems.
22
Q
Where are highest precipitation inputs found?
A
- The highest precipitation inputs to drainage basins are found in the tropics, due to the lntertropical Convergence Zone (ITCZ), and in some places during the monsoon seasons.
23
Q
Why does the ITCZ cause large volumes of precipitation?
A
- In the ITCZ, intense solar radiation fuels the convection of warm humid air, resulting in condensation and precipitation (convectional precipitation).
24
Q
Where is the highest average precipitation in the world?
A
- The highest average annual rainfall is in Mawsynram in India, with 11,873 mm of rain per year, mostly during the monsoon season between June
and September.
25
Q
Where is the lowest average precipitation in the world?
A
- The lowest precipitation inputs are found in stable areas of high atmospheric pressure, such as Quillagua in the Atacama Desert, which is the driest place on Earth, receiving less than 0.2 mm of rain per year.
26
Q
How can continentality influence the distribution of precipitation?
A
- The distribution of precipitation can be influenced by continentality (distance from the sea).
- Continental interiors, such as the Gobi Desert in Asia or the Alice Springs region in Australia, are far from the moisture of maritime air masses.
27
Q
How can relief impact the distribution of precipitation?
A
- Relief, such as mountains, and prevailing winds complicate the pattern.
- with high levels of precipitation occurring where prevailing winds are forced to rise over higher altitudes, forming orographic precipitation.
28
Q
What are the physical macros which affect drainage basin flows?
A
- interception
- infiltration and throughflow
- direct runoff (overland flow)
- ## percolation and groundwater flow
29
Q
What is interception?
A
- Interception is the process by which raindrops are prevented from falling directly on to the
ground surface by the presence of a layer of vegetation; the leaves, branches and stems of these plants catch the water first.
30
Q
How does vegetation cause interception?
A
- Leaves, branches
and stems of plants catch the water before it reaches the ground. - The water later reaches the soil via stem flow (water flowing down the vegetation stems to the ground below) or throughfall, where the
water drips to the ground. - The undergrowth may intercept again some of the water falling from the canopy (secondary interception), and some of the water will return to the atmosphere
via evapotranspiration (known as interception loss).
31
Q
What is secondary interception?
A
- This is where the undergrowth may intercept some of the water falling from the canopy.
32
Q
What is interception loss?
A
- Where water will return to the atmosphere via evapotranspiration during the process of interception.
33
Q
How does precipitation impact the rate of interception?
A
- Interception is greatest when the precipitation is light and of short duration, as dry leaves and stems have the greatest water storage capacity.
- As vegetation becomes wetter or rainfall intensity increases, more water will drip or flow to the ground and interception effectiveness will decrease.
34
Q
How does vegetation impact rate of interception?
A
- The vegetation type and cover also influence the amount of interception: denser types of vegetation, such as many coniferous forests, intercept more rainfall than sparser deciduous forests.
- This is especially so in winter, when temperate deciduous trees shed their leaves; and forests intercept more than grasses or crops.
35
Q
What is infiltration and infiltration capacity?
A
- Infiltration is the movement of water vertically downwards through pores in the soil.
- And the infiltration capacity is the maximum rate at which the soil can absorb precipitation .
36
Q
What factors impact the rate of infiltration?
A
- The rate of infiltration will depend on a number of factors, especially the amount of water already in the soil - the degree of saturation .
- Once in the soil, water moves both vertically and laterally through it by the process of throughflow - this is a downslope movement under the influence of gravity towards a stream or river.
37
Q
What is direct runoff/overland flow and what are the 2 types?
A
- Water flowing over the surface of the ground is known as direct runoff or overland flow.
- There are two types: saturated overland flow and infiltration-excess overland flow .
38
Q
When and where does saturated overland flow occur?
A
- Saturated overland flow occurs when water accumulates in the soil until the water table reaches or ponds on the surface, forcing further rainwater to run off the surface.
- This is particularly common where there are thin soils of moderate permeability.
- Concavities near a stream or riverbank often have high moisture levels and may produce saturated overland flow early in a rainstorm cycle.
39
Q
When does infiltration-excess overland flow occur?
A
- Infiltration-excess overland flow occurs when the rainfall intensity exceeds the infiltration capacity, so the excess water flows over the ground surface.
- Any surface runoff will quickly deliver water into river channels, increasing the risk of flooding downstream.
40
Q
How does percolation lead to groundwater storage in aquifers?
A
- When infiltrating water reaches permeable underlying bedrock, it will continue to move slowly downwards into the rock by the process of percolation.
- When the permeable layer lies above an impermeable rock layer the water can percolate no further, creating a saturated zone.
- The water will fill the spaces within the permeable or porous rock, creating groundwater storage and an aquifer (a permeable rock which stores water).
41
Q
How can percolation cause groundwater flow?
A
- When the water percolates through permeable rock and reaches an impermeable layer, it will fill in cracks and create aquifers which will cause a saturated zone.
- The upper level of this zone is known as the water table.
- Water may then move laterally as groundwater flow if the geological structure allows.
42
Q
How does the porosity of rocks impact the rate of percolation and groundwater flow?
A
- The rate of percolation and groundwater flow will depend on the permeability
of the rock, which is linked to its porosity or perviousness. - Porosity relates to the total volume of pore spaces, and is greatest in coarse-grained rocks such as sandstone.
- While pervious rocks such as limestone have joints and bedding planes along which water can flow.
- Therefore percolation and groundwater flow rates will increase with porosity and perviousness.
- Impermeable rocks such as granite, however, will prevent any percolation or water movement through the ground.
43
Q
How is the rate of groundwater flow impacted by the angle of the rock strata?
A
- The rate of groundwater flow will also increase according to the angle of the rock strata, as a steeper gradient will allow gravity to operate more effectively.
44
Q
What physical factors affect drainage basin outputs?
A
- Evaporation and transpiration.
- Channel flow.
45
Q
How does evapotranspiration impact drainage basin outputs?
A
- Evapotranspiration is the total amount of moisture removed from a drainage basin by processes of evaporation and transpiration; together, these processes can represent a significant output.
- Evaporation is the process by which liquid water is transformed into water vapour (a gas).
- Transpiration is the biological process by which water is drawn upwards from the soil by plants and evaporated through the minute pores, called stomata, in leaves.
46
Q
What factors impact the rate of evapotranspiration?
A
- Temperature: the rate of evaporation increases with temperature. The main energy source is solar radiation, so evaporation and temperature will increase with sunshine hours.
- Wind: will increase the rate of evaporation by reducing the relative humidity and preventing saturation of the air.
- Vegetation cover: transpiration will increase with increased vegetation cover, which will depend on the type of vegetation and the season. Vegetation with a low albedo, such as dark forests will absorb more solar radiation, increasing evaporation.
- Soil moisture content: will determine the amount of water available for transpiration. It is dependant on the soil and rock permeability.
47
Q
How can you study evapotranspiration losses using potential and actual evapotranspiration?
A
- potential evapotranspiration is the amount of evapotranspiration that could take place given unlimited supplies of water in an environment, whereas actual evapotranspiration is the amount of evapotranspiration that takes place given the actual water availability.
48
Q
What is channel flow?
A
- Channel flow is water that has collected to flow in a rivulet, stream or river, and is another output from the drainage basin system.
- This is essentially the discharge of a river which is the volume of water passing a specific gauging station per unit of time and is measured in cubic metres per second (or cumecs).
49
Q
What is discharge and therefore channel flow dependant on?
A
- Discharge is dependent on the amount of precipitation falling directly into the channel.
- And also on contributions from drainage basin stores via surface runoff, throughflow or groundwater flow.
50
Q
In general, how can human activities disrupt the drainage basin cycle?
A
- Human activities can disrupt a drainage basin cycle by changing the speed of processes, creating new stores or by abstracting water.
- Significant disruption is also caused by hard engineering schemes, such as channelisation, to manage river flooding and, to a lesser extent, soft engineering schemes, such as overflow areas.
51
Q
How does cloud seeding disrupt the drainage basin cycle?
A
- This is the attempt to change the amount or type of precipitation by dispersing substances into the air that serve as cloud condensation nuclei (hygroscopic nuclei).
- New technology and research claims to have produced reliable results that
make cloud seeding a dependable and affordable water-supply practice for many regions, but its effectiveness is still debated.
52
Q
Which places have used cloud seeding and in turn disrupted the drainage basin cycle?
A
- China used cloud seeding in Beijing just before the 2008 Olympic Games to create rain to clear the air of pollution.
- It is used in the Alpine Meadows ski area in California to improve snow cover, and was used in 2015 in Texas to reduce the impact of drought.
53
Q
How does urbanisation disrupt the drainage basin cycle?
A
- Urbanisation creates impermeable surfaces that reduce infiltration and increase surface runoff and throughflow through artificial drains; stream and river discharges often increase rapidly as a result.
54
Q
Which places have disrupted the drainage basin cycle through urbanisation?
A
- Across the UK, urbanisation has increased flood risk in many towns and cities such as Winchester and Maidenhead (2014 floods) and Carlisle, York and Manchester (2015 floods).
55
Q
How does dam construction disrupt the drainage basin cycle?
A
- Dams increase surface water stores and evaporation and reduce downstream river discharge.
56
Q
Which places have disrupted the drainage basin cycle through the construction of dams?
A
- Lake Nasser behind the Aswan Dam in Egypt is estimated to have evaporation losses of 10 to 16 billion cubic metres every year.
- This represents
a loss of 20 to 30 per cent of the Egyptian water volume from the River Nile.
57
Q
How does groundwater abstraction disrupt the drainage basin cycle?
A
- In some locations, 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.
58
Q
Which places have disrupted the drainage basin cycle through groundwater abstraction?
A
- Groundwater is used to irrigate more than 40 per cent of China’s farmland and provides about 70 per cent of the drinking water in the dry northern and north-western regions.
- Groundwater extraction is increasing by about 2.5 billion cubic metres per year, and consequently groundwater levels in the arid North China Plain dropped by as much as a metre a year between 1974 and 2000.
- Groundwater rebound has occurred in some of the UK’s major conurbations, including London, Birmingham, Nottingham and Liverpool, as a result of reduced abstraction for industry.
59
Q
What are water budgets?
A
- Water budgets show the annual balance between inputs (precipitation) and outputs (evapotranspiration and channel flow).
- A water budget can be expressed as:
Precipitation (P) =channel discharge (Q) + evapotranspiration (f) ± change in storage (S)
60
Q
What does the equation for water budgets allows us to do?
A
- This gives a direct comparison of natural water supply and demand.
- Making it possible to identify the time periods when precipitation exceeds evapotranspiration (resulting in a positive water balance), or times when there is a negative water balance (evapotranspiration exceeds precipitation) and an increased drought risk.
