The natural water cycle

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What is the "natural water cycle"?

The sun evaporates ocean water which rises to form clouds. The wind pushes the clouds over the continents where they join other clouds that have already formed. When it rains, snows or hails over the continents, part of the water in these precipitations returns more or less rapidly to the atmosphere, either directly through evaporation or due to the transpiration of plants and animals. Another part of the precipitation flows over the soil and, more or less quickly, meets up with a river, in which it flows to the sea. The rest of the precipitation infiltrates the soil where it is stored, at least in part, in aquifers. This water will also end up in the ocean, but over a long or very long time span, because aquifers also feed into rivers. At the same time, the sun continues to evaporate ocean water which rises to form clouds…

It is this perpetual movement of water, in its various phases, that is called the natural water cycle.

 

Is there less water today on Earth than previously?

Contrary to most other natural resources, such as oil or coal which are limited in quantity, water continues to circulate in the natural water cycle. There is just as much water on Earth today as there was when humans became humans. The quantity of fresh water, however, varies on the continents, over both time and space, which can result at particular times and places in shortages (drought) or in excess quantities (flooding). These phenomena will probably be amplified, in terms of their intensity, duration and location, in the future by climate change. We may expect them to create serious problems for access to fresh water in many parts of the world, including France, and for all living species.

Why is there more and more talk about water shortages?

For a number of reasons, e.g. an increase in population, competition for water between different uses (agriculture, industry and tourism) in many places, etc., needs for fresh water may exceed local resources.

• Aquifer levels can drop little by little because more water is drawn off than is naturally replaced, thus hindering normal recharging of the aquifer.

• Larger abstractions in rivers can create shortages and ecological problems for the environment, including the death of fish, losses of biodiversity, etc.

 

The quality of water resources has, in general, dropped over the years, which explains why laws now impose higher quality standards for both environmental and public-health reasons.