- That portion of total precipitation used to satisfy vegetation needs.
- The actual availability of precipitation used in plant development.
Availability is affected by such factors as precipitation intensity, season, temperature, ground cover, sod type, etc. The dependence of precipitation effectiveness on temperature and/or evaporation has been expressed in many ways: Köppen's formulas for defining desert climate, Lang's moisture factor, De Martonne's index of aridity, Gorczyński's aridity coefficient, Angström's humidity coefficient, Transeau's precipitation–evaporation quotient, and Thornthwaite's precipitation-effectiveness index.
Transeau, E. N. 1905. Forest Center of Eastern America. American Naturalist. 39. 875–899.
Thornthwaite, C. W. 1948. An approach toward a rational classification of climate. Geogr. Rev.. 38. 55–94.
Köppen, W. 1931. Grundriss der Klimakunde. Walter die Gruyter Co., Berlin.
Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact email@example.com. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.