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Station 2: The Water Cycle

The natural water cycle is one of the most important cycles on earth. In this cycle the sun plays a very important part, acting as a type of engine for the cycle. Without it, water cannot evaporate and this would preclude cloud formation and subsequent precipitation. The weather, particularly precipitation and the sun, constitutes a very important foundation for the water cycle.

A certain amount of precipitation evaporates, while another portion is led into runoff. Runoff can be subdivided into above-ground runoff (rivers, lakes and other bodies of water), and underground runoff (seepage into the groundwater). Only a small amount of the precipitation that falls in woodland areas actually reaches the forest floor directly. For the most part precipitation falls on the tallest of vegetation, the trees. From this height, the water falls to lower-lying vegetation, and from there it can finally trickle down to the earth’s surface. There is quite a delay between precipitation reaching the forest canopy and when the water droplets reach the forest floor; often the water only reaches the ground long after the actual precipitation has ceased. Precipitation is usually absorbed in short order by the forest floor; even on steep slopes absorption is comparably rapid. Because of this sponge-like quality, the forest can be regarded as a massive water reservoir. Only a very small percentage of precipitation runs rapidly along the surface, creating streams and rivers. Also in the forest the process of evaporation is delayed. The leaves, needles and branches retain a certain amount of moisture from the precipitation until this evaporates. Not to be forgotten are the plants that absorb part of the water seepage, and subsequently release this moisture into the air through transpiration. This process occurs over an extended period that often exceeds the duration of actual precipitation.

The aforementioned processes undergo fundamental changes as soon as the clearing of a forest begins. When the land is freed of its forest canopy, precipitation reaches the ground directly and without delay. As the earth can only absorb a certain small percentage of water at one time, seepage is reduced. Most of the water is led into above-ground run off, and this takes with it soil components. This leads to a diminished rate of groundwater formation and, because of evaporation directly off the ground, leads to dried-out earth [Bibliographisches Institut GmbH 2012, o. S.].

Except for the evaporation of water from the vegetation, many of the same processes mentioned previously occur over the surface water (rivers, lakes, seas, etc.). The sun heats the bodies of water, thus converting the water surface into water vapour. Because of the latter’s lower density in relation to air, the water vapour begins to rise. At higher altitudes this water begins to condense, accumulating in clouds. The more water particles amass and build up in a cloud, the higher the chances for precipitation. If a cloud is heavy and dense enough, there will be rain. The cycle will then begin anew.