Water Budgets

Test your knowledge with free interactive questions on Seneca — used by over 10 million students.

Global Water Budget

The balance between water being evaporated from the oceans and precipitated onto the land is referred to as the water budget.

Limited water for human use

Only 2.5% of the Earth's water is freshwater and of that, less than 1% is accessible for direct human use.
The access and quality of water differ depending on your location in the world. It is often the Earth's geology that plays a part in affecting water availability.

Water store residence time

The water found in the oceans is stored there for longer than the short amount of time that water is held in the atmosphere.

Non-renewable stores

Fossil water is the name given to non-renewable, untouched, ancient freshwater stores. We can find fossil water beneath deserts and in polar areas.
New technology is now allowing us to access more of this water. For example, the extension of oil drilling technology and the use of satellite imagery can increase use of these fossil aquifers.
The cryosphere (glaciers and ice caps) is another non-renewable store as it continues to melt.

Polar Hydrology

Water budgets differ in tropical, temperate and polar areas climates. Temperature, precipitation and seasonality influence the amount of water held in stores.

Polar hydrology

The Polar area is also referred to as the cryosphere (ice-sheets and glaciers).
There is very little vegetation due to low temperature and limited light, so the ability for plants to grow is reduced.

During winter

During the winter, the ground, lakes and rivers are frozen in the cryosphere. Winter snow and ice mean that 85% of solar radiation is reflected.
Permafrost is soil that is permanently frozen.

During spring/summer

In the spring and summer frozen water thaws in the cryosphere causing rapid surface runoff, resulting in increased evaporation.
As ice and soils thaw, biogenic gases (gases produced by or used by organisms e.g. methane) are released into the atmosphere.

The tropics receive a high concentration of solar radiation so there is a lot of ocean evaporation, resulting in high rainfall. The following are characteristics of the water budget in tropical areas:

Tropical hydrology

In the tropical rainforest, there is little seasonal variation due to the consistent temperature, high rainfall and consistent sunlight.
There is a high density of vegetation that collects the majority of precipitation.
Around 50% of the precipitation is returned via evapotranspiration.
Rainforests are able to generate their own water cycle due to convectional rainfall.
Convectional rainfall is when the forest floor is warm and so the air on the surface heats up and expands. This air rises and condenses, forming rain clouds.

Tropical rainforest deforested

Deforestation reduces evapotranspiration which in turn reduces precipitation levels and water supply as less water is being put back into the cycle via plants. It instead will have to flow through streams and rivers, taking longer to cycle through.
Vegetation is crucial for the area’s convectional rainfall.
Rainfall is essential for all rainforest life, so severe deforestation would have devastating knock-on effects on the rest of the ecosystem.