Impacts on the Water Cycle (AQA A Level Geography)
Revision Note
Written by: Jacque Cartwright
Reviewed by: Bridgette Barrett
Natural Impacts on the Water Cycle
Inputs, outputs, stores and flows/transfers of the water cycle change over time and space for a variety of reasons
Natural climate change - the impact of ice ages or interglacial periods will change the availability of water within the system
Extreme climatic events, such as drought, impact the water cycle by reducing the amount available within the system
Ecosystem changes - plant succession may alter the dominant vegetation in an area, which can alter interception rates. Animal burrowing leaves tiny voids which water can infiltrate instead of transferring to groundwater
Seasonal changes- wet and dry seasons change the availability of water within the system
Table Showing Seasonal Impacts on the Water Cycle
Water Cycle Component | Winter Factor | Summer Factor |
|---|---|---|
Precipitation | Usually greater levels of precipitation, snow will delay the availability of water until melted | Usually, precipitation is less, however, summer storms can bring flash flooding |
Evaporation | Lower temps reduce the rate | Higher temps increase the rate |
Soil moisture | Saturated soils lead to increased overland flow and loss of water within the cycle | Soils may dry out, reducing the availability of water, although any rain infiltrates quickly. Hard, the baked ground is initially impermeable |
Vegetation | Vegetation dies back, reducing interception and transpiration | Vegetation grows, increasing rates of transpiration and interception |
River channel flow | Higher discharge rates are usual with winter storms | Lower discharge rates as levels of precipitation drop |
Human Impacts on the Water Cycle
Climate change
Farming practices
Deforestation
Land use change
Water abstraction
Table Showing Human Impacts on the Water Cycle
Human Factor | Impact on Water Cycle |
|---|---|
Climate change | Increasing global temperatures reduce mountain glacial ice and the availability of freshwater for communities dependent on this water |
Water abstraction | The growth of the global population has increased the demand for water supplies. Excessive removal of aquifer water means that recharge cannot keep up and stores are depleted. This can allow seawater ingress if the water table drops below sea water or salinisation if the water table rises and evaporation leaves natural salt concentrations behind |
Land use change | Changes to an urbanised landscape increase impermeable surfaces, leading to increased runoff and reduced infiltration. City drainage systems remove water quickly but can lead to flooding when river channels cannot discharge excess runoff quickly |
Deforestation | Vegetation removal for agriculture, urbanisation or firewood for fuel supply, impacts an important water storage and transfer capability. Soil moisture is reduced, transpiration declines and less precipitation occurs at a local level which can lead to a dry river system |
Farming practices | Wells used as the main source of irrigation for plants can lower groundwater and river channel levels. Farming in arid or semi-arid regions can lead to desertification and reduces the soil's capacity to store water. Ploughing fields, which removes vegetation, can break up compacted soil, allowing for infiltration and storage, however, it can also increase surface runoff if furrows are ploughed so they act as channels (vertical furrows down a slope, rather than horizontal) |
Examiner Tips and Tricks
Questions using 'assess' want you to show what you know, but also to decide (assess) how important it is
For example, if you were asked to assess the impact of farming practices on the water cycle, you would need to discuss the different processes and say which processes had the biggest impact
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