The Natural Water Circle
Water (H₂O), which is only a bond of the elements oxygen and hydrogen, is the most important and most frequent chemical compound on the blue planet – with a total volume between 1.4 and 1.6 billion km³, which corresponds to an earth surface water coverage of around 71%. However, this high quantity is by no means equal to the actual amount of drinking water - as only 2.5% of our blue resources are actually fresh water with 1.3 % of surface water, 30.1% groundwater and another 68.6% are stored in glaciers and ice. Of the many processes involved in this cycle, the most important are:
- Evaporation → If water changes from a liquid to a gas or vapor, leaving the Earth’s surface to its atmosphere, we speak of evaporation.
- Transpiration → If water is evaporating from the leaves of plants - e.g. through pores - it is classified as transpiration.
Evaporation and transpiration summed up, will result in Total Evaporation. Main drivers for evaporation are temperature, humidity, wind speed, as well as solar radiation.
- Condensation → Evaporated water rises up in the atmosphere and cools down the higher it gets. If this vapor is returning to a more liquid stage, we speak of condensation; Clouds are built.
- Precipitation → By condensation, and if clouds can not hold back the amount of moisture anymore, water is returning to the Earth in the shape of rain, snow or ice-pellets.
- Runoff → Precipitation that hits the Earth's surface can (1) be returned back to the atmosphere as part of the evaporation process, (2) be absorbed by vegetation, (3) infiltrate into the soil and nourish aquifers or can be (4) united in streams, lakes and the sea.
Based on the concept of the natural cycle, water cannot be lost in a sense that total water resources decrease – as we are talking of a cycle. However, overexploitation, water pollution and unsustainable consumption are responsible for a shift of available resources. For example, if groundwater resources are used for industrial purposes and are not released properly treated back to the environment (in order to recharge ground- or surface water resources), one might consider this water as ’lost’ for other purposes – e.g. drinking water for households. Without proper management and governance of water resources, virtual water is bond to products as for example fancy fashion and travels the world – leaving the regions of their origin with increasing water stress related problems.
- Shiklomanov, I.A.; Rodda, John C: World Water Resources at the Beginning of the 21st Century
- Manier, G.: Wasser in der Atmosphäre, in : Wasser: eine Einführung in die Umweltwissenschaften. S. 8 f. ; Höll, K.:Wasser: Nutzung im Kreislauf, Hygiene, Analyse und Bewertung. S. 16
- Wasser: Nutzung im Kreislauf, Hygiene, Analyse und Bewertung - K. Höll - 2002