Variations in Runoff and the water cycle

Question 1

Storms and Precipitation

Answer 1

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.

Question 2

Seasonal changes

Answer 2

During the winter, temperatures may drop below 0 °C, 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 (and outputs) can be much larger as the ice melts.

Question 3

Vegetation

Answer 3

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 4

Farming practices

Answer 4

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.

Question 5

Irrigation

Answer 5

(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

Land Use change

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.

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.