4.1 The Hydrological Cycle

Figure 4.1.1 Flows within the hydrological cycle

(Source: Impee Cambridge [see reference4],[see reference5])
Figure 4.1.1 sourced from The ImpEE Project, The Cambridge-MIT institute. The ImpEE wesbite is designed as an educational resource. It may be reproduced, modified and used freely for educational purposes
http://www-g.eng.cam.ac.uk/impee/?section=topics&topic=water&page=slideshow

Annually, around 505,000km³ of water is evaporated from the oceans, and 72,000km³/year is evaporated from land surfaces to join the hydrological cycle. This gives a total of around 577,000km³/year active in the global water cycle. Of this total, approximately 458,000km³/year (80%) falls back onto the oceans and only 20% (119,000km³/year) falls onto the land.

Of the 20% freshwater falling on land as precipitation, most is transpired back into the atmosphere almost immediately, leaving only 8% of the total active volume on the

ground. Much of this forms groundwater that may become inaccessible and/or polluted and surface water which may become polluted.

Globally, 7,000km³ more water is stored on land in March than in September when 600km³ more is stored in the atmosphere than in March. [see reference 6].