Water Budget (key terms)

Question 1

What is a surplus?

Answer 1

When precipitation is greater than potential evapotranspiration and the soil water store is full so there is a surplus of soil moisture for plant use, runoff and recharging groundwater. Soil is at field capacity.

Question 2

What is utilisation?

Answer 2

Potential evapotranspiration increases and exceeds precipitation, so there is more water evaporating from the ground surface and being transpired by plants than is falling as rain. The water is gradually used up.

Question 3

What is a deficit?

Answer 3

The soil water store has been used up by high rates of evapotranspiration and low precipitation. Plants can only survive if they are adapted to periods of drought or are irrigated. e.g. Cacti have spines reducing surface-area = = less area to evaporate.

Question 4

What is (soil) recharge?

Answer 4

This occurs when potential evapotranspiration decreases so that is lower than precipitation and the soil starts to fill up again.

Question 5

What is field capacity?

Answer 5

The soil is full of water and cannot hold any more. Further precipitation could lead to surface-runoff and flooding.

Question 6

What is potential evapotranspiration?

Answer 6

The amount of evapotranspiration that occurs as a result of temperature and vegetation (time of year) as long as there is water available.

Question 7

What is non-equation equation for change is store volume?

Answer 7

P = E + Q (+/-) S
P = Precipitation (in)
E = Evapotranspiration (out)
Q = Discharge (out)
S = Charge in store