Water balance equation

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The general water balance equation , also known as the water balance , describes the relationship between the components and compartments of the water cycle . It forms the basis of the hydrological balance. The formula for a demarcated area and a specific period is

Precipitation + inflow = evapotranspiration (evaporation) + outflow + storage change (reserve - use up),

or abbreviated

N + Q in = ET + Q out + ΔS.

If the above and below ground catchment areas match , the water balance is shortened

N = ET + Q + ΔS.

In a certain area, the amount of precipitation is distributed among parts that evaporate from plants or open surfaces that run off above or below ground, as well as the part that contributes to the change in the amount of soil water or the groundwater supply. A negative discharge value is to be interpreted as an inflow value.

If one considers a sufficiently long period of time, one can assume the equality "reserve = consumption", which simplifies the water balance equation to

N = ET + Q.

If you also set up the global balance for the entire surface of the earth, then “runoff = 0” must apply in total, and you get the further simplification

N = ET.

In addition to the control variable precipitation, the climate, the type of soil, the geological situation and the vegetation / land use have an influence on the water balance equation, e.g. For example, a larger proportion of the precipitation evaporates in hot climates, so less is left for groundwater formation and runoff formation (simplified).

See also

literature

  • Markus Weiler, Konrad Miegel: Global and local water cycle . In: Nicola Fohrer (Ed.): Hydrology . UTB, Stuttgart 2016, ISBN 978-3-8252-4513-9 , pp. 29-45 .

Individual evidence

  1. ↑ Markus Weiler, Konrad Miegel: Global and local water cycle . In: Nicola Fohrer (Ed.): Hydrology . UTB, Stuttgart 2016, ISBN 978-3-8252-4513-9 , pp. 37 .
  2. ↑ Markus Weiler, Konrad Miegel: Global and local water cycle . In: Nicola Fohrer (Ed.): Hydrology . UTB, Stuttgart 2016, ISBN 978-3-8252-4513-9 , pp. 38 .
  3. ↑ Markus Weiler, Konrad Miegel: Global and local water cycle . In: Nicola Fohrer (Ed.): Hydrology . UTB, Stuttgart 2016, ISBN 978-3-8252-4513-9 , pp. 45 .
  4. ↑ Water balance equation. In: spectrum. Spektrum.de, 2001, accessed on January 22, 2018 .