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Gaussen Index

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The Gaussen Index (or Bagnouls-Gaussen Index) or xerothermic index is a method of calculating and comparing aridity.

According to Henri Gaussen (French botanist and biogeographer), a given period is said to be arid, when: .[1][2]

(P: total precipitation in millimeters over the given period, T: average temperature in °C over the given period)

The resulting index number indicates the number of biologically dry days in a year for a given location (it therefore ranges between 0 and 365). The data includes not only precipitation stricto sensu but also fog, dew and humidity of the air.

In general, it is accepted that an environment is non-arid when the index is less than 100, semi-arid between 100 and 290, arid between 290 and 350, and hyperarid between 350 and 365.

This index is very useful for the use of an ombrothermic diagram [fr], the latter always constructed on the scale model: 1 °C = 2 mm precipitation.

Other indices such as the Louis Emberger rainfall quotient (which is not unique) have been defined. However, the Gaussen index which is simple and precise is still preferable.[3] Indeed Henri Gaussen defines precisely the 4 nuances of Mediterranean climate just against this index,[4] while Emberger defines the level of humidity in a region of Mediterranean climate but does not support precisely this Mediterranean climate.[3]

The calculation does not reflect reality because it is based on averages. For example, according to the calculation, we find a total of 0 biologically dry days in Lyon, for 60 biologically dry days in Marseille.[5]

References

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  1. ^ Gaussen and Bagnouls 1952, pp. 10–11.
  2. ^ Gaussen and Bagnouls 1957, p. 194.
  3. ^ a b Tassin, Claude (31 May 2012). Paysages végétaux du domaine méditerranéen : bassin méditerranéen, Californie, Chili central, Afrique du Sud, Australie méridionale [Mediterranean Vegetation Landscapes : Mediterranean basin, California, Central Chile, South Africa, South Australia] (in French). Marseille: IRD Éditions. ISBN 978-2-7099-1731-5.
  4. ^ Gaussen and Bagnouls 1957, p. 200.
  5. ^ Gaussen and Bagnouls 1952, p. 12.

Bibliography

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