The Water Balance

Question 1

What is the Water Balance?

Answer 1

The Water Balance shows the balance between inputs (precipitation) and outputs (potential evapotranspiration). The water balance affects how much water is stored in the basin. The general water balance in the UK shows seasonal patterns.

It can be illustrated by a water budget graph.

Question 2

• Draw the Water Balance for a temperate zone e.g. the UK
• Explain what: Soil moisture Surplus is, what Soil Moisture Utilisation is, what Soil Moisture Deficiency is, what Soil Moisture Recharge is and what the last Soil Moisture Surplus is.

Answer 2

• Drawing.

1. **Soil Moisture Surplus **- In wet seasons, precipitation is greater than evapotranspiration. The soil water store is full and there is a soil moisture surplus for plant use, surface runoff and ground water recharge. River levels rise due to more surface runoff and higher discharge.
2. **Soil Moisture Utilisation **- In drier seasons, potential evapotranspiration is greater than precipitation. The water store is being used up by plants or lost by evaporation (soil moisture utilisation).
3. **Soil moisture Deficiency **- There is a deficiency of soil water as the store is used up and potential evapotranspiration is greater than precipitation. Plants must have adaptations to survive and crops must be irrigated.
4. **Soil Moisture Recharge **- Precipitation is greater than potential evapotranspiration. The soil water store will start to fill again (soil moisture recharge).
5. **Last Soil Moisture Surplus **- The soil water store is full. Field capacity has been reached. Additional rainfall will percolate down to the water table, and groundwater stores will be recharged.