1.1.2 Water balance

Question 1

Water balance values in summer

Answer 1

Precipitation = 50 mm
Runoff = 30 mm
Evapotranspiration = 40 mm
Change in storage = -20 mm

Question 3

Water balance equation

Answer 3

used to express the process of water storage and transfer in a drainage basin system
Precipitation = Total Runoff + Evapotranspiration +/- (change in) Storage

Question 5

Factors that affect water cycle on a local scale

Answer 5

Deforestation, storm events, seasonal changes, agriculture, urbanisation

Question 6

Water balance values in winter

Answer 6

Precipitation = 150 mm
Runoff = 50 mm
Evapotranspiration = 10 mm
Change in storage = +90 mm

Question 7

Water cycle - Spring

Answer 7

More vegetation growth so more interception by vegetation.

Question 7

Water cycle - Summer

Answer 7

Likely to be less rain in summer. Ground may be harder and therefore more impermeable encouraging surface runoff

Question 8

Deforestation

Answer 8

There is less interception by trees so surface runoff increases. The soil is no longer held together by roots, so soil water storage decreases. There are fewer plants so transpiration decreases.

Question 8

Water cycle - Autumn

Answer 8

Less vegetation growth so less interception. Seasonally more rainfall.

Question 9

Water cycle - Winter

Answer 9

Frozen ground may be impermeable and encourage runoff. Snow discourages runoff and takes time to melt, slowing down the processes that occur within the water cycle.

Question 10

Water balance in wet seasons

Answer 10

precipitation > evapotranspiration.

Ground stores fill so more runoff, discharge and higher river levels. +ve water balance (water surplus)

Question 11

Agriculture

Answer 11

Pastoral, arable, hillside terracing (padi fields), irrigation

Question 12

Pastoral

Answer 12

Livestock such as Pigs, cattle, goats, sheep etc, trample the ground reducing infiltration.

Question 13

Water balance in dry seasons

Answer 13

Precipitation < evapotranspiration

plants absorb water, ground stores deplete. -ve water balance (water deficit)

Question 14

Arable

Answer 14

Ploughing increases infiltration by creating a
looser soil, which decreases surface runoff. However, digging drainage ditches (often seen around field edges) increases surface runoff and streamflow.

Question 15

Hillside Terracing

Answer 15

increases surface water storage and therefore decreases runoff.

Question 16

Irrigation

Answer 16

can lead to groundwater depletion.

Question 17

Storm events

Answer 17

Large amounts of rainfall quickly saturate the ground to its field capacity. No more water can infiltrate the soil, increasing the surface runoff. Storm events are therefore less effective at recharging water stores than prolonged rainfall.

Question 18

Urbanisation

Answer 18

Creating roads and buildings which have impermeable surfaces creates impermeable surfaces that reduce infiltration but increase surface runoff, reducing lag-time and increasing the flood risk.

Question 19

To tackle the problem of urban flooding…

Answer 19

Green roofs and sustainable urban drainage systems (SUDS). (use of grass)

Question 20

Soil Water budget

Answer 20

shows the annual balance between inputs and outputs in the water cycle and their impact on soil water storage/availability.

Question 21

Soil water budget depends on…

Answer 21

type, depth and permeability of the soil and bedrock.

Question 22

The maximum possible level of storage of water in the soil

Answer 22

Field capacity

Question 23

Rainfall after field capacity is reached…

Answer 23

is likely to cause flooding

Question 24

Soil water budget - Autumn

Answer 24

greater input from precipitation than there is an output from evapotranspiration as deciduous trees lose their leaves and the cooler temperatures mean that
the plants photosynthesise less. Soil moisture levels increase and the water deficit is recovered from the previous summer. Eventually a water surplus may occur.

Question 25

Soil water budget - winter

Answer 25

Potential evapotranspiration from plants reaches a minimum due to the colder temperatures and the precipitation continues to refill the soil water stores . Infiltration and percolation will also refill the water table.

Question 26

Soil water budget - spring

Answer 26

Around February and March, plants start to grow again and potential evapotranspiration increases as temperatures get higher and plants start photosynthesising more. There is still a water surplus in this time.

Question 27

Soil water budget - summer

Answer 27

The hotter weather leads to utilisation of soil water as evapotranspiration peaks and rainfall is at a minimum . The output from evapotranspiration is greater than the input from precipitation so the soil water stores are depleting. A water deficit may occur if there is a long
hot summer and spring, a lack of winter rainfall, or a drought the year before.