1.2.4 Factors affecting changes in the water cycle

Question 1

Physical factors affecting changes in the water cycle

Answer 1

• Seasonal changes and vegetation
• Storms and precipitation

Question 2

Human factors affecting changes in the water cycle

Answer 2

• Farming practices
• Land use change
• Water abstraction

Question 3

[Physical factors affecting changes in the water cycle]

How do storms and precipitation affect changes in the water cycle?

Answer 3

• Intense storms generate more precipitation and greater peak discharges than light rain showers.
• The larger input of water causes flows (e.g. runoff) and stores (e.g. groundwater) to increase in size.
• Some flows (e.g. infiltration) may not be able to occur rapidly enough for the size of the input, increasing runoff.

Question 4

[Physical factors affecting changes in the water cycle]

How do seasonal changes and vegetation affect changes in the water cycle?

Answer 4

• The size of inputs, flows and stores in the water cycle varies with the seasons – e.g. in the UK, summer is normally drier than winter.
• During the winter, temperatures may drop below 0C, causing water to freeze. This can reduce the size of flows through drainage basins, while the store of frozen water grows. When temperatures increase again, flows through drainage basins (outputs) can be much larger as the ice melts.
• Most plants show seasonal variation (e.g. vegetation usually dies back in winter). Vegetation intercepts precipitation and slows its movement to the river channel. Interception is highest when there’s lots of vegetation and deciduous trees have their leaves.
• The more vegetation there is in a drainage basin, the more water is lost (through transpiration and evaporation directly from the vegetation) before it reaches the river channel, reducing runoff and peak discharge.

Question 5

[Human factors affecting changes in the water cycle]

Farming practices

Answer 5

Infiltration is a key part of the water cycle. When rain hits the surface, what can’t infiltrate runs off instead. Farming practices can affect infiltration in several ways:

• Ploughing breaks up the surface so that more water can infiltrate, reducing the amount of runoff.
• Crops increase infiltration and interception compared to bare ground, reducing runoff. Evapotranspiration also increases, which can increase rainfall.
• Livestock, such as cattle, trample and compact the soil, decreasing infiltration and increasing runoff.
• Irrigation (artificially watering the land) can increase runoff if some of the water can’t infiltrate. Groundwater or river levels can fall if water is extracted for irrigation.

Question 6

[Human factors affecting changes in the water cycle]

Land use change:

How does deforestation affect changes in the water cycle?

Answer 6

Deforestation reduces the amount of water that is intercepted by vegetation, increasing the amount that reaches the surface.

In forested areas, dead plant material on the forest floor helps to hold the water, allowing it to infiltrate the soil rather than run off. When forest cover (and dead material) is removed, the amount of infiltration that can take place decreases.

Question 7

[Human factors affecting changes in the water cycle]

Land use change:

How does urbanisation affect changes in the water cycle?

Answer 7

Urbanisation and the construction of new buildings and roads** creates an impermeable layer over the land, preventing infiltration. This massively increases runoff,** resulting in water passing through the system much more rapidly and making flooding more likely.

Question 8

[Human factors affecting changes in the water cycle]

How does water abstraction affect changes in the water cycle?

Answer 8

• More water is abstracted (taken from stores) to meet demand in areas where population density is high. This reduces the amount of water in stores such as lakes, rivers, reservoirs and groundwater.
• During dry seasons, even more water is abstracted from stores (especially groundwater and reservoirs) for consumption and irrigation, so stores are depleted further.
• In many coastal areas, salt water intrusion can happen into aquifers, where water tables have sunk.