1.2- Changes In The Water Cycle Over Time Flashcards Preview

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Flashcards in 1.2- Changes In The Water Cycle Over Time Deck (21):

Changes in the water cycle over time time to include natural variation including:

- storm events
- seasonal changes


Changes in the water cycle over time time to include human impact including:

- farming practices
- land-use change
- water abstraction


Explain the impacts of storm events

- the amount and intensity of precipitation can affect the amount of runoff relative to infiltration
- heavy storms with a lot of water entering a drainage basin over a short period of time results in higher discharge, as is less time for infiltration to take place


Explain the impacts of drought

- can impact on stores and transfers of the water cycle- it causes:
- a reduction in water stored in rivers and lakes
- die back in vegetation reducing transpiration, interception and infiltration processes
- GROUNDWATER FLOW become more important
- initial rates of evapotranspiration to be high due to heat and dry air but declines in time as water on the ground dries up and trees die back
- soils to dry out- soil water store is reduced and throughflow ceases


What are the impacts of seasonal changes?

- temperature
- precipitation time and amount
- soil moisture


Explain the impacts of temperature (seasonal changes)

- seasonal changes in temperature can have an impact on the water cycle
- in the Uk, higher summer temperatures lead to greater evapotranspiration
- warm air can hold more moisture and vegetation will grow more rapidly
- in winter, evapotranspiration rates decline leading to higher channel flow and run off


Explain the impacts of precipitation type and amount (seasonal changes)

- precipitation and amount also varies within the seasons
- in summer, total rainfall may be less but storms are more frequent
- in winter, greater quantities of rainfall are likely resulting in huger channel flow
- if precipitation is in the form of snow however the lag time is likely to be greater (snow takes time to melt before the water enters the channel)
- when there is rapid melting of snow the peak discharge could be high leading to possible flooding


Explain the impacts of soil moisture (seasonal changes)

- soil moisture will vary with the seasons
- 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 winter, greater quantities of rainfall can lead to soils becoming saturated, leading to overland flow and higher discharge


Explain the impacts of farming practices

- ploughing breaks up the topsoil and allows greater infiltration resulting in less runoff and longer lag times- contour ploughing on slopes can help prevent the rapid run off of water downslope but poor ploughing practices can increase surface run off and result in soil erosion

- irrigation by farmers leads to the additional input of water to the local water cycle

- drainage systems tend to lead to more rapid transfer of water to the nearest river channel- there is evidence that that moorland drainage ditches are partly responsible for the increased flood risk in the city of York

- where grass crops replace more dense vegetation like forest there may be a reduction in transpiration and an increase in infiltration- after harvest, bare soils may lead to greater run-off and higher discharge

- large numbers of livestock on small areas can lead compacted soils increasing overland flow


What are the impacts of land use-change?

- urbanisation
- deforestation


Explain the impacts of urbanisation

- replacement of vegetated ground with impermeable surfaces such as tarmac and concrete
- water cannot infiltrate = increased overland flow making flooding more likely
- soil water and groundwater stores are reduced as most settlements are designed to transfer water as quickly as possible away from human activity to the nearest river achieved through road camber, building design and drainage systems


Explain the impacts of deforestation

- removal of trees leading to increased surface run off and soil erosion and reducing soil water stores
- deforestation reduces interception rates allowing rainwater to hit the surface directly
- if soil is washed into river channels the risk of flooding is increased
- less transpiration
- lack of vegetation roots means less infiltration resulting in flashy hydrograph


Explain the impacts of extensive deforestation

- can result in less water vapour available in the atmosphere so precipitation levels fall
- less water gets to the river channel and so flow may actually reduce = POSITIVE FEEDBACK


There is some concern that if the rate of deforestation in tropical South America continues the loss of vegetation could be extensive leading to

Significant changes in the water cycle


Explain how deforestation in the Amazon may have global implications for climate

- at present around 10% of the rainforest has been converted to cattle pasture and agriculture but most of this loss has focused within the last 50 years
- studies have shown that impacts are likely to be significant if there is 50% loss or greater
- given that the Amazon generates more than 1/4 of the world’s discharge changes in water resources caused by the atmospheric feedbacks associated with extensive deforestation, will be spread throughout the whole Amazon region and may have global implications for the climate


What is water abstraction?

Extraction of water from rivers or groundwater aquifers is referred to as water abstraction


Water that is abstracted for irrigation, industry and domestic purposes can have significant effects on the local water cycle. In the Middle East, for example irrigation has had a significant impact on

Water stores (aquifers and rivers) and transfer processes (evaporation and infiltration)


In places, water is being abstracted from aquifers formed thousands of years ago and they are at serious risk of becoming depleted as

The rate of recharge is much slower than the rate of use


In addition to the depletion of aquifers they can also become contaminated by

Inflowing saltwater if the water table drops below sea level which has become an issue with the chalk aquifer beneath London


What’s an example (mini case study) of an aquifer?

- about 40% of public water supplies in the Thames Basin comes from groundwater principally from the chalk aquifer
- precipitation on the exposed chalk hills infiltrated the porous rock where it is stored
- throughout history water has been extracted from wells that penetrate down to the chalk
- abstraction peaked in 1960s when groundwater levels beneath central London dropped to 88m below sea level
- since then, industries such as brewing that were responsible for much of the abstraction were relocated or closed down leading to gradual rebounding of the water table


What occurs today regarding chalk aquifer?

- aquifer carefully managed
- since 2000 groundwater levels have risen in West London but fallen in central, eastern, northern and southern London
- in east London there is a risk of saline intrusion