All books

Professional

Apps About Coach Log in Start reading

Earth and Space Sciences · Glossary

What is Residence time?

Definition 9.3 High School Earth and Space Sciences · Chapter 9 — Freshwater Resources

The residence time of water in a reservoir is the average time that water spends in it between entering and leaving.

Residence times of water, computed as stock divided by flux from the global water cycle (blue), and the measured age of deep groundwater under the eastern Sahara (orange). Logarithmic axis: from one year on, each marked step is a hundredfold. Data: Trenberth and others (2007); U.S. Geological Survey; Sturchio and others (2004).
Residence times of water, computed as stock divided by flux from the global water cycle (blue), and the measured age of deep groundwater under the eastern Sahara (orange). Logarithmic axis: from one year on, each marked step is a hundredfold. Data: Trenberth and others (2007); U.S. Geological Survey; Sturchio and others (2004).

Examples

Example 9.5 (Water in the air)

The atmosphere holds 12 70012\,700 km3\mathrm{km}^{3} of water, and 486 000486\,000 km3\mathrm{km}^{3} fall out of it each year as rain and snow. Its residence time is 12 700/486 000≈0.02612\,700/486\,000 \approx 0.026 year, about 9.59.5 days: the water of the air is renewed every week or two. A cloud that rains today is made of water that left the ocean or the ground a few days ago.

Read in context →