Impacts on the Water Cycle (AQA A Level Geography)

• 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

• 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)