WCC: Water Cycle - Factors affecting change in the water cycle over time

Question 1

How does drought affect vegetation and subsequent water processes?

Answer 1

Vegetation dies back, reducing transpiration, interception and infiltration

Question 2

How does drought affect soil and subsequent water processes?

Answer 2

Soils dry out, reducing soil water stores and throughflow

Question 3

How does drought affect evapotranspiration?

Answer 3

Initial rates of evapotranspiration are high due to thea heat and dry air. This declines in time as surface water dries up and vegetation dies back.

Question 4

What are the physical variations affecting change in the water cycle?

Answer 4

Storm events
Drought
Seasonal changes

Question 5

What types of seasonal changes affect the water cycle?

Answer 5

Temperature
Precipitation type and intensity
Soil moisture

Question 6

How do seasonal changes in temperature in the UK affect the water cycle?

Answer 6

Higher summer temperatures lead to greater evapotranspiration - warm air can hold more moisture and vegetation will grow more rapidly. In the winter evapotranspiration will decrease leading to higher channel flow and runoff.

Question 7

How do seasonal changes in precipitation in the UK affect the water cycle?

Answer 7

In summer total rainfall may be less but storm are more frequent. In winter greater quantities of rain fall are likely resulting in higher channel flow. If precipitation is in the form of snow the lag time is likely to be greater as it takes time to melt before water enters the river channel. When there is rapid melting of snow the peak discharge could be high leading to possible flooding.

Question 8

How do seasonal changes in soil moisture in the UK affect the water cycle?

Answer 8

Dry soils in summer encourage infiltration, although in drought conditions soils can become hard and baked encouraging rapid overland flow and the risk of flash flooding. In the winter, greater quantities of rainfall can lead to soils becoming saturated, leading to overland flow and higher discharge.

Question 9

What are the human activities affecting change in the water cycle?

Answer 9

Land use change
Farming
Water abstraction

Question 10

What two land use changes impact the water cycle the most?

Answer 10

Urbanisation

Deforestation

Question 11

How does urbanisation make flooding more likely?

Answer 11

Vegetated ground is replaced with impermeable concrete and tarmac, so water cannot infiltrate into the soil, increasing overland flow.

Question 12

Why does urbanisation reduce soil and groundwater stores?

Answer 12

Most settlements are designed to transfer water as quickly as possible away from human activity to the nearest river

Question 13

Give 3 ways settlements designed to transfer water as quickly as possible away from human activity.

Answer 13

Road camber
Building design
Drainage systems

Question 14

What determines the scale to which deforestation impacts the water cycle?

Answer 14

The extent of deforestation:
Localised deforestation leads to local change
Extensive deforestation leads to regional change

Question 15

What 5 farming practices affect the water cycle?

Answer 15

Ploughing
Irrigation
Drainage systems
Grass crops
Livestock

Question 16

How does ploughing impact the water cycle?

Answer 16

Ploughing breaks up the topsoil and allows greater infiltration resulting in less runoff.
Contour ploughing on slopes can help prevent rapid runoff downslope
Poor ploughing practices can increase surface runoff and result in soil erosion

Question 17

How does irrigation impact the water cycle?

Answer 17

It leads to the additional input of water to the local water cycle

Question 18

How do grass crops impact the water cycle?

Answer 18

When grass crops replace more dense vegetation there may be a reduction in transpiration and an increase in infiltration

Question 19

How can livestock impact the water cycle?

Answer 19

Large numbers of livestock in a small area can compact the soil leading to greater overland flow

Question 20

How can drainage systems impact the water cycle?

Answer 20

They lead to the more rapid transfer of water to the nearest river channel. This increases flood risk and the flashiness of river regimes.

Question 21

How does subsurface drainage remove excess water from the soil profile?

Answer 21

A network of perforated tubes installed 60-120cm below the soil surface allows water to flow through them when the water table exceeds the height of the tube. Drain tiles allow excess water to leave the field, lowering the water table to the depth of the tube over the course of several days.

Question 22

What are 3 disadvantages associated with soil drainage?

Answer 22

Higher flood risks and flashier river regimes
Soil erosion
Nitrate loss

Question 23

How does soil drainage lead to soil erosion?

Answer 23

The dry topsoil becomes more vulnerable to wind erosion if not properly protected

Question 24

What kind of soils are vulnerable to wind erosion?

Answer 24

Sandy and peaty soils e.g in East Midlands and East Anglia

Question 25

Compare the severity of soil erosion by wind and water.

Answer 25

The proportion of a field subject to wind erosion is likely to be greater than that subject to water erosion

Question 26

Explain by nitrate loss is a major concern regarding soil drainage.

Answer 26

It can lead to eutrophication as water draining from fields enters local watercourses and enriches ponds with nitrogen or phosphorous. Increased growth of algal blooms disturbs the water quality.

Question 27

What is one way to overcome some of the problems arising from soil drainage?

Answer 27

Controlled drainage - keeping the water table high during the off-season when crops aren’t growing

Question 28

How does controlled drainage reduce the impacts of nitrate loss?

Answer 28

The high water table increases the rate of dentirifcation so more nitrates are converted to nitrogen gas as soon as the saturated soils warm up in the spring, reducing nitrate loss to local watercourses.

Question 29

When is over-abstraction likely to occur?

Answer 29

When demand for water exceeds the amount available during a certain period

Question 30

What kind of areas is over-abstraction likely to occur in?

Answer 30

Areas with low rainfall and high population density, as well as areas with intensive agricultural or industrial activity

Question 31

What is water abstraction?

Answer 31

The extraction of water from rivers or groundwater aquifers

Question 32

What is over-abstraction?

Answer 32

The extraction of water at a faster rate than the rate of recharge

Question 33

What impacts can over-abstraction have?

Answer 33

Sinking water tables and depletion of aquifers
Reduced surface stores
Saline inrtusion

Question 34

What is saline intrusion?

Answer 34

When the water table falls below sea level and inflowing seawater contaminates the freshwater store

Question 35

Give an example of an area experiencing widespread saline intrusion. What is causing over-abstraction here?

Answer 35

The Mediterranean coastlines of Italy, Spain and Turkey. The major cause of over-abstraction is demands of tourist resorts.

Question 36

Give some examples of the impacts over-abstraction has on the Mediterranean coastline.

Answer 36

Malta - most groundwater can no longer be used for domestic consumption of irrigation because of saline intrusion.; they have resorted to expensive desalination plants.
Italy - over-exploitation of the Po River in the region of the Milan aquifer has led to a 25-40m decrease in groundwater levels over the past 80 years.
Spain - over 1/2 of abstracted groundwater volume is obtained from areas facing over-exploitation problems.

Question 37

Briefly describe how water abstraction has affected London over time.

Answer 37

• 40% of public water supplies in the Thames Basin come from groundwater, principally the Chalk aquifer which forms exposed chalk hills to the north and south of the London Basin. Precipitation soaks into the porous chalk where it is stored.
• Throughout history water has been abstracted from wells and boreholes that penetrate down to the chalk.
• Abstraction peaked in 1960s when groundwater levels beneath central London dropped to 88m below sea level.
• The industries responsible for much of the abstraction have since relocated or closed down leading to a gradual rebounding of the water table.
• Today the aquifer is carefully managed.
• Since 2000 groundwater levels have risen in W London but fallen in central, E and S London.

Question 38

In general, how does deforestation cause changes in the water cycle?

Answer 38

Less vegetation leads to:

• reduced interception
• reduced evapotranspiration
• reduced infiltration and throughflow

Question 39

What is a major difference between the impacts of localised and extensive deforestation?

Answer 39

Localised deforestation can increase precipitation rates, whereas extensive deforestation decreases precipitation rates

Question 40

Why does deforestation reduce infiltration rates?

Answer 40

Unimpeded flow causes soil compaction and erosion

Question 41

Why does deforestation reduce throughflow?

Answer 41

Compacted soil

Lack of roots to widen soil pores

Question 42

What are the impacts of increased overland flow due to localised deforestation?

Answer 42

Higher discharge

Increased risk of localised flooding

Question 43

After extensive deforestation, how does water initially leave the area? Why?

Answer 43

Through the river channel as evapotranspiration rates are low

Question 44

How will localised deforestation impact soil stores?

Answer 44

Impacts are likely to be limited; there will be less vegetation taking up and intercepting water, however infiltration rates will be lower

Question 45

How will extensive deforestation impact soil stores?

Answer 45

Soil stores will decrease as precipitation and infiltration reduce

Question 46

If localised deforestation reduces evapotranspiration rates, why would precipitation rates not reduce?

Answer 46

Atmospheric circulation

Vegetation breezes

Question 47

Explain why atmospheric circulation can mean localised deforested areas can continue receiving the same amount of precipitation. Where is this more likely to occur?

Answer 47

As deforestation is localised, clouds formed from nearby forested areas can travel across the deforested areas to maintain precipitation levels there. This is more likely to occur in temperate forests as the cycle of water between the trees and the atmosphere is slower here.

Question 48

Explain how vegetation breezes increase precipitation in localised deforested areas. Where is this more likely to occur?

Answer 48

Air over cleared land warms faster as cleared land reflects more solar radiation. It rises more quickly and creates localised low pressure, drawing moist air in from forested areas. This results in an increase in cloud coverage, thunderstorms and precipitation over the cleared land at the expense of forested areas. This is more likely to occur in tropical rainforests.

Question 49

Why is atmospheric circulation less likely to maintain precipitation levels in tropical rainforests?

Answer 49

Tropical rainforests recycle water very quickly between the trees and the atmosphere, so rain formed in one place stays and falls in the same region.

Question 50

Why do tropical rainforests recycle water so quickly between the trees and the atmosphere?

Answer 50

The trees’ large soil water supply means they can afford to move and lose more water than other plants. Increased evapotranspiration accelerates the formation of rain.

Question 51

Over time, how will extensive deforestation change water cycle stores and transfers?

Answer 51

Less precipitation
Less overland flow
Smaller soil stores

Question 52

Why does extensive deforestation reduce precipitation rates?

Answer 52

1. There are not enough nearby forested areas for atmospheric circulation to bring precipitation to the cleared land
2. There are not enough nearby forested areas for vegetation breezes to occur

Question 53

How can reduced precipitation in extensively deforested areas lead to a positive feedback cycle?

Answer 53

Less water gets to the river and channel flow is reduced. Evapotranspiration decreases further, precipitation decreases further.

Question 54

How does extensive deforestation impact the wider region?

Answer 54

Changes due to atmospheric feedbacks will not be limited to the catchment areas where deforestation has occurred but will be spread unevenly throughout the forest area due to atmospheric circulation

Question 55

Give an example of how extensive deforestation can impact the wider region.

Answer 55

For more than 60% of tropical land surface, air that has passed over extensive forest in the preceding days produced at least twice as much rain that has passed over little forest.

Question 56

Give an example of how intended future land use contributes to the impacts of deforestation.

Answer 56

The deliberate burning of forest areas to clear for agriculture produces airborne aerosols around which water vapour condenses. This reduces rainfall as the subsequent smaller droplets that occur in clouds are too small to precipitate.

Question 57

What process can deforestation lead to that will change the ecosystem of the area?

Answer 57

Desertification

Question 58

Which type of deforestation would lead to desertification?

Answer 58

Extensive