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Geography > The water cycle and water insecurity - What factors influence the hydrological system over short- and long-term timescales? > Flashcards

The water cycle and water insecurity - What factors influence the hydrological system over short- and long-term timescales? Flashcards

1
Q

What are short-term deficits within the hydrological cycle (i.e. droughts) the result of?

A

Short-term deficits within the hydrological cycle (i.e. droughts) are the result of physical processes, but can have significant impacts on people.

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2
Q

What are short-term surpluses within the hydrological cycle (i.e. floods) the outcome of?

A

Short-term surpluses within the hydrological cycle (i.e. floods) are the outcome of physical processes and can have significant impacts on people.

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3
Q

In the longer term, what can climate change have a significant impact on?

A

In the longer term, climate change can have a significant impact on the hydrological cycle, both globally and locally.

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4
Q

What is the definition of a drought?

A

Drought is defined in meteorological terms as a shortfall or deficiency of water over an extended period, usually at least a season.

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5
Q

What is a hydrological drought characterised by?

A

Meteorological drought is sometimes distinguished from hydrological drought. The latter is characterised by reduced stream flow, lowered groundwater levels and reduced water stores.

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6
Q

What is the impact if a drought can and does hit agricultural productivity hard?

A

This, in turn, can lead quickly to food shortages, famine and starvation.

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7
Q

What does research suggest that sea surface temperature anomalies are an important causal factor in?

A

Short-term precipitation deficits

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8
Q

What do sea surface temperature anomalies relate to?

A

Sea surface temperature anomalies relate to how much temperatures of the sea surface, recorded at a particular time, differ from the long-term average. Anomalies may be positive or negative. A positive anomaly occurs when the observed temperature is warmer than the average. A negative anomaly is when the observed temperature is cooler than the average.

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9
Q

What do temperature anomalies provide the key to, which, in turn, is thought to trigger the occurrence of droughts?

A

El Nino-Southern Oscillation (ENSO)

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10
Q

What happens to conditions during an El Niño event?

A

When this happens, cool water normally found along the coast of Peru is replaced by warmer water.

At the same time, the area of warmer water further west, near Australia and Indonesia, is replaced by cooler water.

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11
Q

What happens to cool water normally found along the coast of Peru during an El Niño event?

A

Cool water normally found along the coast of Peru is replaced by warmer water.

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12
Q

What happens to the area of warmer water further west, near Australia and Indonesia during an El Niño event?

A

The area of warmer water further west, near Australia and Indonesia, is replaced by cooler water.

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13
Q

How often do El Niño events usually occur?

A

El Niño events usually occur every three to seven years and usually last for 18 months.

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14
Q

Explain how El Niño episodes contribute to drought conditions.

A

g

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15
Q

What do La Niña episodes involve?

A

They involve the build-up of the cooler-than-usual subsurface water in the tropical part of the Pacific.

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16
Q

What does the build-up of cooler-than-usual subsurface water in the tropical part of the Pacific in La Niña episodes lead to?

A

This situation can also lead to severe drought conditions, particularly on the western coast of South America.

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17
Q

Explain how La Niña episodes contribute to drought conditions.

A

f

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18
Q

Which part of the globe is most affected by (a) El Niño events, and (b) La Niña episodes?

A

f

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19
Q

A normal year

A

g

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20
Q

An El Niño year

A

g

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21
Q

An La Niña year

A

g

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22
Q

What is desertification?

A

Desertification is the process by which once-productive land gradually changes into a desert-like landscape. It usually takes place in semi-arid land on the edges of existing deserts. The process is not necessarily irreversible.

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23
Q

What causes desertification?

A

The causes of desertification are essentially natural. They set in motion a downward spiral that runs roughly as follows:

  • changing rainfall patterns with rainfall becoming less reliable, seasonally and annually. The occasional drought year sometimes extends to several years
  • the vegetation cover becomes stressed and begins to die, leaving bare soil
  • the bare soil is eroded by wind and an occasional intense shower
  • when rain does fall, it is often only for very short, intense periods. This makes it difficult for the remaining soil to capture and store it
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24
Q

Explain why human factors do not cause drought but they act like a feedback loop.

A

Humans enhance the impacts of droughts by the over-abstraction of surface water from rivers and ponds, and of groundwater from aquifers.

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25
Q

What are the four human factors contributing to desertification?

A

Key human factors encouraging this are:

  • population growth
  • overgrazing
  • over-cultivation
  • deforestation.
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26
Q

How does population growth contribute to desertification?

A

Rapid population growth puts pressure on the land to grow more food. Migrants fleeing from one disaster area help to make another

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27
Q

How does overgrazing contribute to desertification?

A

Too many goats, sheep and cattle destroy the vegetation cover

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28
Q

How does over-cultivation contribute to desertification?

A

Intense use of marginal land exhausts the soil and crops will not grow

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29
Q

How does deforestation contribute to desertification?

A

Trees are cut down for fuel, fencing and housing. The roots no longer bind the soil and erosion ensues

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30
Q

In the case of the Sahel, how has the situation of desertification been made worse?

A

In the case of the Sahel, the situation has been made worse by frequent civil wars.

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31
Q

What are the impacts of desertification in the Sahel?

A

Crops, livestock and homes have been deliberately destroyed.

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32
Q

Of the four human factors contributing to desertification, which do you think is the most significant?

A

Deforestation

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33
Q

What percentage of Australia is affected by serious or severe rainfall deficiency?

A

Drought is a recurrent annual feature in Australia, with up to 30% of the country affected by serious or severe rainfall deficiency.

34
Q

What is the difference between droughts in the Sahel and droughts in Australia?

A

Unlike the Sahel, Australia has not followed the same downward spiral of desertification. Careful management of scarce water resources, and sorting out the competing demands of irrigation and urban dwellers, have stopped this happening. Other actions include the large-scale recycling of grey water, constructing desalinisation plants and devising new water conservation strategies.

35
Q

What is grey water?

A

Grey water is waste bath, shower, sink and washing water. It can be recycled, but not necessarily for human consumption.

36
Q

What is ecological resilience?

A

Ecological resilience is the capacity of an ecosystem to withstand and recover from a natural event (such as drought and flooding) or some form of human disturbance.

37
Q

What percentage of the Earth’s land surface is covered by wetlands?

A

Wetlands currently cover about 10% of the Earth’s land surface.

38
Q

What important functions do wetlands perform?

A

It is now understood that wetlands perform a number of important functions: from acting as temporary water stores to the recharging of aquifers, from giant filters trapping pollutants to providing nurseries for fish and feeding areas for migrating birds.

39
Q

How can drought have a major impact on wetlands?

A

With less precipitation, there will be less interception (as vegetation becomes stressed), as well as less infiltration and percolation. Water tables will fall. Evaporation will also increase. This, together with the decrease in transpiration, will reduce the valuable functions performed by wetlands.

40
Q

What remains the major challenge to the survival of wetlands?

A

While droughts pose a threat to wetlands, the major challenge to their survival still remains artificial damage.

41
Q

Why are wetlands a prime example of an undervalued ecosystem?

A

d

42
Q

What are forests responsible for?

A

They are responsible for much interception which, in turn, means reduced infiltration and overland flow.

43
Q

What are forests characterised by?

A

High levels of transpiration

44
Q

In the coniferous forests, what is drought causing?

A

In the coniferous forests, drought is not only causing direct psychological damage but is also increasing the susceptibility of pines and firs to fungal diseases. Tree mortality is on the increase.

45
Q

In the tropical forest, what appears to be having a greater impact on large trees?

A

The increased mortality attributed to drought appears to be having a greater impact on large trees.

46
Q

Why is it important to ensure that the ecological resilience of ecosystems is not overstretched by either the destructive activities of people or natural events such as droughts and floods?

A

As ecosystems play such as vital role within the hydrological cycle, it is important to ensure that their ecological resilience is not overstretched by either the destructive activities of people or natural events such as droughts and floods.

47
Q

What are the meteorological causes of flooding?

A

The meteorological causes of flooding are:

  • intense storms which lead to flash flooding, as in semi-arid areas but more commonly in mountainous areas
  • prolonged, heavy rain, such as during the Asian monsoon and with the passage of deep depressions across the UK
  • rapid snowmelt during a particularly warm spring, as on the plains of Siberia
48
Q

What is flash flooding?

A

Flash flooding is distinguished by its exceptionally short lag time - often minutes or hours.

49
Q

Why is Bangladesh a particularly flood-prone country?

A

Bangladesh is a particularly flood-prone country mainly because it is a land of floodplains and deltas built up by mighty rivers such as the Ganges, Padma and Meghna. These rivers are swollen twice a year by meltwater from the Himalayas and by the summer monsoon. Hilly tracts between the rivers and behind Chittagong are often victims of flash floods.

50
Q

Suggest reasons why flash floods often occur in mountainous areas.

A

d

51
Q

What does another type of flooding - tidal flooding - often result from?

A

Another type of flooding - tidal flooding - often results from storm surges or when high river flows meet particularly high spring tides in estuaries.

52
Q

What is a storm surge?

A

A storm surge is caused by very low air pressure which raises the height of the high-tide sea. Strong onshore winds then drive the ‘raised’ sea towards the coast, often breaching coastal defences and flooding large areas.

53
Q

What physical circumstances is the likelihood of flooding also increased by?

A

The likelihood of flooding is also increased by other physical circumstances:

  • in low-lying areas with impervious surfaces, as in towns and cities
  • where the ground surface is underlain by impermeable rocks
  • when ice dams suddenly melt and the water in glacial lakes are released
  • where volcanic activity generates meltwater beneath ice sheets that is suddenly released (jokulhaups)
  • where earthquakes cause the failure of dams or landslides that block rivers
54
Q

How else do plate tectonics contribute to flooding?

A

f

55
Q

How does channelisation reduce the risk of flooding?

A

An effective way of improving river discharge and reducing the flood risk.

56
Q

What is the problem of channelisation as a hard-engineering approach to reducing the risk of flooding?

A

The trouble is that it simply displaces that risk downstream. Some other location may well be overwhelmed by the increased discharge

57
Q

How do dams reduce the risk of flooding?

A

Block the flow of sediment down a river so the reservoir gradually fills up with silt; downstream there is increase river bed erosion

58
Q

What is the problem of dams as a hard-engineering approach to reducing the risk of flooding?

A

Downstream there is increased river bed erosion

59
Q

How do river embankments reduce the risk of flooding?

A

Designed to protect from floods of a given magnitude.

60
Q

What is the problem of river embankments as a hard-engineering approach to reducing the risk of flooding?

A

They can fail when a flood exceeds their capacity. Inevitably, when this happens, the scale of the flooding is that much greater

61
Q

What are some examples of soft-engineering methods of reducing the flood risk?

A

These include making greater use of floodplains as nature intended, namely as temporary stores of flood water, and using them only for nature conservation and perhaps agriculture and recreation.

62
Q

What is the difference between hard- and soft-engineering approaches to flood control?

A

f

63
Q

What are the socioeconomic impacts of flooding?

A

The impacts of flooding are all too familiar. They include:

  • death and injury
  • spread and water-borne diseases
  • trauma
  • damage to property, particularly housing
  • disruption of transport and communications
  • interruption of water and energy supplies
  • destruction of crops and loss of livestock
  • disturbance of everyday life, including work
64
Q

What are the environmental impacts of flooding?

A

The environmental impacts of flooding receive much less publicity. Perhaps it is because there are some positives, which include:

  • recharged groundwater stores
  • increased connectivity between aquatic habitats
  • soil replenishment
  • for many species, flood events trigger breeding, migration and dispersal
65
Q

What can the removal of soil and sediment by floodwaters lead to?

A

The removal of soil and sediment by floodwaters can lead to eutrophication of water bodies. That same floodwater can also leach pollutants into watercourses with disastrous effects for wildlife, while diseases carried by floodwater can weaken or kill trees.

66
Q

What is eutrophication?

A

Eutrophication is the process of nutrient enrichment that ultimately leads to the reduction of oxygen in rivers, lakes and ponds, and the consequent death of fish and other species.

67
Q

Which places in the UK were most affected during the 2016 floods?

A

During the 2016 floods, large areas of the UK received more than twice the average amount of rainfall for that time of year. Carlisle and Cockermouth in Cumbria were among the worst-hit places and were the focus of media attention.

68
Q

What factors were to blame for the 2016 floods?

A

The following were singled out for blame:

  • budget cuts in the amount of money being spent on flood defences
  • an EU Directive that puts environmental conservation ahead of the regular dredging of rivers
  • poor land management, resulting in blocked ditches
  • global warming
69
Q

How does precipitation have an impact on the inputs and outputs of the hydrological cycle?

A
  • A warmer atmosphere has a greater water-holding capacity
  • It is argued that the mode of precipitation may be more important than the amount in determining its impacts
  • Widespread increases in rainfall intensity are expected more than large increases in total amounts
  • Areas of precipitation increase include the tropics and high latitudes
  • The length and frequency of heatwaves are increasing in some locations and is resulting in the increased occurrence of drought
  • With climate warming, more precipitation in northern regions is falling as rain rather than snow
70
Q

How do evaporation and evapotranspiration have an impact on the inputs and outputs of the hydrological cycle?

A
  • Evaporation over large areas of Asia and North America appears to be increasing
  • Transpiration is linked to vegetation changes, which in turn are linked to changes in soil moisture and precipitation
71
Q

How does soil moisture have an impact on the inputs and outputs of the hydrological cycle?

A
  • Uncertain, as soil moisture depends on many factors, of which climate is only one
  • Where precipitation is increasing, it is likely that soil moisture will also increase
72
Q

What is significant about soil moisture?

A
  • Uncertain, as soil moisture depends on many factors, of which climate is only one
  • Where precipitation is increasing, it is likely that soil moisture will also increase
73
Q

What impact do surface runoff and stream flow have on flows and stores of the hydrological cycle?

A
  • More low flows (droughts) and high flows (floods)

- Increased runoff and reduced infiltration

74
Q

What impact does groundwater flow have on flows and stores of the hydrological cycle?

A
  • Uncertain, because of abstraction by humans
75
Q

What are the impacts of reservoir, lake and wetland storage on flows and stores of the hydrological cycle?

A
  • Changes in wetland storage cannot be conclusively linked to climate change
  • It appears that storage is decreasing as temperatures increase
76
Q

What impact does soil moisture have on flows and stores of the hydrological cycle?

A
  • Possibly little change, with higher precipitation and evaporation cancelling each other out
77
Q

What are the impacts of permafrost on flows and stores of the hydrological cycle?

A
  • Deepening of the active layer is releasing more groundwater
  • Methane released from thawed lakes may be accelerating change
78
Q

What are the impacts of snow on flows and stores of the hydrological cycle?

A
  • Decreasing length of the snow-cover season
  • Spring melt starting earlier
  • A decreasing temporary store
79
Q

What are the impacts of glacier ice on flows and stores of the hydrological cycle?

A
  • Strong evidence of glacial retreat and ice sheet thinning since the 1970s
  • Less accumulation because of more precipitation falling as rain
  • A decreasing store
80
Q

What are the impacts of oceans on flows and stores of the hydrological cycle?

A
  • More data on surface temperatures needed
  • Where there is ocean warming, there will be more evaporation
  • Possibly ocean warming leads to the generation of more cyclones
  • Storage capacity being increased by meltwater
  • Rising sea level
81
Q

Which stores are expected to increase?

A

f

82
Q

What are the impacts of short-term climate change on water supply?

A
  • Increases in annual temperature leads to greater evaporation from surface water and reservoirs in summer although spring discharge may increase
  • Greater rates of evapotranspiration, desiccation of forests store
  • Impact of oscillations, e.g. ENSO is leading to increasingly unreliable patterns of rainfall, e.g. less predictable monsoons
  • More frequent cyclone and monsoon events threaten water supplies immediately
  • Increased intensity and frequency of droughts as a result of global warming and oscillation is an issue for rainfed agriculturalists
  • Depleted aquifers leads to problems with groundwater
  • Decreasing rainfall in many areas as a result of global warming
  • Loss of snow and glaciers as a store threatens many communities in mountain areas, e.g. in Himalayas

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