Unit 3.1 - W&C - Water Deficit

Question 1

What is water deficit and how does it occur?

Answer 1

A deficit occurs when water cycle outputs (evaporation, transpiration and river discharge) are greater than inputs of precipitation. An unexpected and long-lasting water deficit is categorised as a drought. The balance between precipitation, evapotranspiration and run off is known as the water balance.

Question 2

What is the formula for drainage basin water balances?

Answer 2

P = Q + ET + ΔS

where:

P = precipitation

Q = total runoff (as river discharge)

ET = evapotranspiration

ΔS = positive or negative changes in water storage

Question 3

How will climate change affect the water balance in the UK?

Answer 3

For decades, UK climate scientists have been collecting and analysing evidence of how climate change may be affecting how the water cycle operates in and around the UK. While it is impossible to attribute any individual event to climate change, the increasing incidence of extreme weather is producing an overall pattern which is consistent with scientific predictions.
The weather of early 2020 is viewed by some scientists as a good example of what the ‘new normal’ could be by mid-century.

Question 4

What are aquifers and how are they used?

Answer 4

These important stores require that a layer of sedimentary rock is underlain by an impermeable layer. Water which percolates downwards under gravity into the sedimentary layer becomes trapped and stored there. It can be accessed by societies via wells and boreholes. However, over time aquifers may suffer from long-term depletion if water is extracted faster than new water naturally arrives. Mass balance is not maintained.

Question 5

What is surface store depletion?

Answer 5

Over-use of inland bodies of water leads to their long-term depletion.

Question 6

How can aquifers be recharged?

Answer 6

Natural recharge – reducing extraction allows recharge by the percolation of precipitation and surface water to the aquifer.
Artificial recharge - water is added to the ground surface or pits and basins are flooded, increasing the percolation rate. Alternatively, water is pumped (injected) back into the aquifer.