WCC: Water Cycle - Factors affecting change in the water cycle over time Flashcards
Changes in the water cycle over time: Natural variation - storm events and seasonal changes Human impacts - farming practices, land use change and water abstraction
How does drought affect vegetation and subsequent water processes?
Vegetation dies back, reducing transpiration, interception and infiltration
How does drought affect soil and subsequent water processes?
Soils dry out, reducing soil water stores and throughflow
How does drought affect evapotranspiration?
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.
What are the physical variations affecting change in the water cycle?
Storm events
Drought
Seasonal changes
What types of seasonal changes affect the water cycle?
Temperature
Precipitation type and intensity
Soil moisture
How do seasonal changes in temperature in the UK affect the water cycle?
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.
How do seasonal changes in precipitation in the UK affect the water cycle?
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.
How do seasonal changes in soil moisture in the UK affect the water cycle?
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.
What are the human activities affecting change in the water cycle?
Land use change
Farming
Water abstraction
What two land use changes impact the water cycle the most?
Urbanisation
Deforestation
How does urbanisation make flooding more likely?
Vegetated ground is replaced with impermeable concrete and tarmac, so water cannot infiltrate into the soil, increasing overland flow.
Why does urbanisation reduce soil and groundwater stores?
Most settlements are designed to transfer water as quickly as possible away from human activity to the nearest river
Give 3 ways settlements designed to transfer water as quickly as possible away from human activity.
Road camber
Building design
Drainage systems
What determines the scale to which deforestation impacts the water cycle?
The extent of deforestation:
Localised deforestation leads to local change
Extensive deforestation leads to regional change
What 5 farming practices affect the water cycle?
Ploughing Irrigation Drainage systems Grass crops Livestock
How does ploughing impact the water cycle?
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
How does irrigation impact the water cycle?
It leads to the additional input of water to the local water cycle
How do grass crops impact the water cycle?
When grass crops replace more dense vegetation there may be a reduction in transpiration and an increase in infiltration
How can livestock impact the water cycle?
Large numbers of livestock in a small area can compact the soil leading to greater overland flow
How can drainage systems impact the water cycle?
They lead to the more rapid transfer of water to the nearest river channel. This increases flood risk and the flashiness of river regimes.
How does subsurface drainage remove excess water from the soil profile?
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.
What are 3 disadvantages associated with soil drainage?
Higher flood risks and flashier river regimes
Soil erosion
Nitrate loss
How does soil drainage lead to soil erosion?
The dry topsoil becomes more vulnerable to wind erosion if not properly protected
What kind of soils are vulnerable to wind erosion?
Sandy and peaty soils e.g in East Midlands and East Anglia
Compare the severity of soil erosion by wind and water.
The proportion of a field subject to wind erosion is likely to be greater than that subject to water erosion
Explain by nitrate loss is a major concern regarding soil drainage.
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.
What is one way to overcome some of the problems arising from soil drainage?
Controlled drainage - keeping the water table high during the off-season when crops aren’t growing
How does controlled drainage reduce the impacts of nitrate loss?
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.
When is over-abstraction likely to occur?
When demand for water exceeds the amount available during a certain period
What kind of areas is over-abstraction likely to occur in?
Areas with low rainfall and high population density, as well as areas with intensive agricultural or industrial activity
What is water abstraction?
The extraction of water from rivers or groundwater aquifers
What is over-abstraction?
The extraction of water at a faster rate than the rate of recharge
What impacts can over-abstraction have?
Sinking water tables and depletion of aquifers
Reduced surface stores
Saline inrtusion
What is saline intrusion?
When the water table falls below sea level and inflowing seawater contaminates the freshwater store
Give an example of an area experiencing widespread saline intrusion. What is causing over-abstraction here?
The Mediterranean coastlines of Italy, Spain and Turkey. The major cause of over-abstraction is demands of tourist resorts.
Give some examples of the impacts over-abstraction has on the Mediterranean coastline.
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.
Briefly describe how water abstraction has affected London over time.
- 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.
In general, how does deforestation cause changes in the water cycle?
Less vegetation leads to:
- reduced interception
- reduced evapotranspiration
- reduced infiltration and throughflow
What is a major difference between the impacts of localised and extensive deforestation?
Localised deforestation can increase precipitation rates, whereas extensive deforestation decreases precipitation rates
Why does deforestation reduce infiltration rates?
Unimpeded flow causes soil compaction and erosion
Why does deforestation reduce throughflow?
Compacted soil
Lack of roots to widen soil pores
What are the impacts of increased overland flow due to localised deforestation?
Higher discharge
Increased risk of localised flooding
After extensive deforestation, how does water initially leave the area? Why?
Through the river channel as evapotranspiration rates are low
How will localised deforestation impact soil stores?
Impacts are likely to be limited; there will be less vegetation taking up and intercepting water, however infiltration rates will be lower
How will extensive deforestation impact soil stores?
Soil stores will decrease as precipitation and infiltration reduce
If localised deforestation reduces evapotranspiration rates, why would precipitation rates not reduce?
Atmospheric circulation
Vegetation breezes
Explain why atmospheric circulation can mean localised deforested areas can continue receiving the same amount of precipitation. Where is this more likely to occur?
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.
Explain how vegetation breezes increase precipitation in localised deforested areas. Where is this more likely to occur?
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.
Why is atmospheric circulation less likely to maintain precipitation levels in tropical rainforests?
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.
Why do tropical rainforests recycle water so quickly between the trees and the atmosphere?
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.
Over time, how will extensive deforestation change water cycle stores and transfers?
Less precipitation
Less overland flow
Smaller soil stores
Why does extensive deforestation reduce precipitation rates?
- There are not enough nearby forested areas for atmospheric circulation to bring precipitation to the cleared land
- There are not enough nearby forested areas for vegetation breezes to occur
How can reduced precipitation in extensively deforested areas lead to a positive feedback cycle?
Less water gets to the river and channel flow is reduced. Evapotranspiration decreases further, precipitation decreases further.
How does extensive deforestation impact the wider region?
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
Give an example of how extensive deforestation can impact the wider region.
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.
Give an example of how intended future land use contributes to the impacts of deforestation.
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.
What process can deforestation lead to that will change the ecosystem of the area?
Desertification
Which type of deforestation would lead to desertification?
Extensive
