4.1 The Hydrological Cycle



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

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].