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Lesson 3.The Water Budget and River Regimes

The hydrological cycle influences water budgets and river systems at a local scale. It’s very important you understand what water budgets and river systems are; and the importance of understanding river regimes and the differences between that and the water budget. The global water budget is a specification of inflows, outflows and changes of stored volume of water for a defined water system during a specified period; some of this may be available to humans to use.

The water balance/budget shows the state of equilibrium in a drainage basin between the inputs and outputs received and lost. They can be used to monitor the amount of water held in stores. They are clearly influenced by type of climate(not just temperatures and precipitation, but also seasonality)

Where P input exceeds E loss there is a positive water balance

Where P input is lower than E losses there is a negative water balance

The climatic zones across the Earth have different water balances and climate change can cause changes in the water balance of different areas. These impacts on water availability. Since water budgets impact on the availability of water in the soil, they are therefore of great importance to farmers.

The variation of global water budgets with latitude.

***** You need to be aware of water budget characteristics in TROPICAL, TEMPERATE and

POLAR locations.

***** You need to be aware of water budget characteristics in TROPICAL, TEMPERATE and

POLAR locations.

The Water Balance and Climate

What are the impacts of different climate types, for instance, temperate, monsoonal or tropical, on water budgets, as well as the impacts of tundra environments on the budget?

Causes of Monsoons

2) How does climate affect global water budgets?

3) Why do you think it is important to understand the global water budget system? Think of the rivers such as The Nile that runs through many African countries.

Continental Variations

Continent Precipitation (mm/year)

Evapotranspiration (mm/year)

Difference (mm/year)

Run off (mm/year)

Surface Base flow

Europe 657 375 283 185 97

Asia 696 420 276 205 71

Africa 696 582 114 74 40

Australia (and Oceania)

803 534 269 205 64

North America 645 403 242 171 71

South America 1564 946 618 395 223

Run off is divided into surface flow and base flow. Surface flow = water flowing overland that hasn’t seeped through the soil and ground maybe due to full soil saturation.

Base flow= groundwater flow within permeable rocks (aquifers)

4. Looking at the table above what issues would Africa face?

5. Which continent in your opinion has the better water supply catchment and why?

Soil Moisture Budget – add notes and annotate

Write an explanation for this graph. Add annotations to help you

A water budget graph for southern England showing soil moisture status

• Used to show the annual balance between inputs (precipitation) and outputs (EVT). This gives an indication then of soil water availability

• In a drainage basin, this water balance can be represented by the following equation. Drainage basin discharge = precipitation — evapotranspiration +/— changes in storage, water on the surface, in the soil or groundwater

River Regimes

A river regime can be defined as the annual variation in discharge or flow of a river at a particular point or gauging station usually measured in cumecs. Much of this flow is not from immediate precipitation or run-off, but is supplied from groundwater between periods of rain. This can mask fluctuations in river flow caused by immediate precipitation as for example in Britain the River Kennet flows over chalk so it maintains its flow even at drier times due to the base flow being fed from chalk aquifers.

In pairs, write as many factors that you can think of that will affect river regime.

Write notes from PPT and complete the factors task.

River Regimes across the world and climatic regions

Notes

Comparing the River Regimes for two rivers –

Complete the questions 1, a-c on the next page. Please read through the information and analyse the graphs first.

Answers:

Further Analysis and interpretation of a river regime in UK – River Avon

Define ‘river regime’ –

State two reasons why a rivers regime will alter throughout the year (4 marks)