Wisps of low fog rise above a calm lake on a frosty morning, with trees reflected in the water.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Catchment cutaway. conceptual stores and transfers, not to scale.

Surface runoff. Overland flow and rivers carry water downhill towards the outlet. Divides separate surface catchments.

How to read these results

Reservoir 10000 + human use 0 = 10,000 m³ (isolated teaching budget).

Water cycle stores and flows

Trace water between stores and explain how changes in rainfall or human use affect the amount held in a reservoir.

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Why it happens

Water moves between the atmosphere, land and ocean through evaporation, precipitation and flows at and below the surface. Naming the stores first makes it easier to trace where water comes from and where it goes.

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Evaporation fog over a lake. Water vapour mixes into colder air and condenses into droplets; invisible vapour itself cannot be photographed.

Try a comparison

Show the drainage basin, then increase Abstraction. Explain how removal from a local store changes the water available within the catchment.

Reading the result

The tracers identify transfer routes; their size and spacing do not measure the volume of water moving along each route.

A common misunderstanding

Because the global water cycle conserves water, a local reservoir cannot run out.

Water can leave a local store faster than it is replenished. Withdrawals, evaporation and downstream releases may exceed inflow, reducing the stored volume even while water remains elsewhere on Earth. A regional water balance therefore needs the amounts and timing of both inputs and outputs.

Cases

Exam language

Store

A quantity of material or energy held within part of a system, such as water in a lake or carbon in vegetation. Inputs and outputs change the amount stored. A store is an amount; a flux is a transfer rate.

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Tropical forest at Bodiman, Cameroon: living vegetation is a carbon store, exchanging carbon with the air and soil.

Transfer

The movement of material or energy between stores within a system. In a drainage basin, infiltration transfers water from the surface into soil. A transfer describes a pathway or process; a flux quantifies its rate.

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Snowmelt near Fourth of July Lake, Idaho. Seasonal melting transfers stored snow water into streams, soils and groundwater.

Watershed

In UK geography, the drainage divide separating basins. In US usage, watershed commonly means the entire drainage basin; check the context.

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ASTER, 24 September 2005: tributaries dissect sandstone in Canyonlands, Utah. A drainage network collects flow towards a main river.

Abstraction

The removal of water by people from a river, lake or aquifer for uses such as irrigation or drinking supplies. A store can shrink when abstraction and other losses exceed recharge, even though water continues circulating globally.

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Groundwater hand pump at Perambalur, India. Abstraction removes water from an aquifer; pumping may lower the water level around a well, which is measured below ground.

Interception

The temporary capture of precipitation on leaves, branches and other surfaces before it reaches the ground. Some water evaporates and some drips or flows down stems. Interception changes the timing and amount of water entering soil.

Residence time

The typical time material remains in a store. For a well-mixed store at steady state, mean residence time is its amount divided by its outflow rate.

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Glen Canyon Dam and Lake Powell, Arizona. Reservoir storage and controlled releases alter the timing and size of flows downstream.

Evapotranspiration

The combined transfer of water to the atmosphere through evaporation and plant transpiration. It links soil moisture, vegetation and weather in a drainage-basin water balance. Potential evapotranspiration describes demand under adequate water supply, not necessarily the amount that actually occurs.

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Leaf epidermis viewed through a microscope. Stomata regulate gas exchange and water-vapour loss; transpiration is one part of evapotranspiration.

Process0.40Abstraction0.00Follow a transfer