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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
agricultural and biological sciences
A recommendation on standardized surface resistance for hourly calculation of reference ET
o
by the FAO56 Penman-Monteith method
Agricultural Water Management, Volume 81, No. 1-2, Year 2006
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Description
Continued development of networks of electronic weather stations worldwide has increased the availability of weather data for calculating ETo on an hourly basis. There has been question and debate as well as studies on the appropriate expression and parameterization for the surface resistance (r s) parameter of the Penman-Monteith (PM) equation and the associated coefficient for the reduced form FAO-PM equation when applied hourly. This paper reviews the performance of the FAO-PM method using rs = 70 s m -1 for hourly periods and using a lower rs = 50 s m -1 value during daytime and rs = 200 s m-1 during nighttime. Variability in hour to hour trends in rs among locations and dates makes it difficult, if not impossible, to establish a consistent algorithm for rs. However, the relatively good and consistent accuracy in ETo when using a constant rs = 50 s m-1 during daytime gives good reason to recommend this value as a standardized parameter and coefficient for calculating ETo. Based on a national study in the U.S. and studies by European and American researchers, the authors recommend that the FAO-PM ETo method from FAO56, when applied on an hourly or shorter basis, use rs = 50 s m-1 for daytime and rs = 200 s m-1 for nighttime periods. This use will provide, on average, good agreement with computations made on a 24-h time step basis. No changes are suggested for the FAO-PM method for daily (24-h) time steps, where use of rs = 70 s m-1 should continue. © 2005 Elsevier B.V. All rights reserved.
Authors & Co-Authors
Allen, Richard Glen
United States, Moscow
University of Idaho
Pruitt, William O.
United States, Davis
University of California, Davis
Wright, James L.
United States, Washington, D.c.
United States Department of Agriculture
Howell, Terry A.
United States, Bushland
Usda Ars Conservation and Production Research Laboratory
Ventura, Francesca
Italy, Bologna
Alma Mater Studiorum Università Di Bologna
Snyder, Richard
United States, Davis
University of California, Davis
Itenfisu, Daniel
Canada, Edmonton
Alberta Agriculture and Rural Development
Steduto, Pasquale
Italy, Rome
Food and Agriculture Organization of the United Nations
Berengena, Joaquin
Spain, Cordoba
Centro Ifapa Almeda Del Obispo
Yrisarry, Javier Baselga
Unknown Affiliation
Smith, Martin
Madagascar, Antananarivo
Fao
Pereira, Luis S.
Portugal, Lisbon
Instituto Superior de Agronomia, Universidade de Lisboa
Raes, Dirk
Belgium, Leuven
Ku Leuven
Perrier, Alain
France, Palaiseau
Agroparistech
Alves, Isabel
Portugal, Lisbon
Instituto Superior de Agronomia, Universidade de Lisboa
Walter, Ivan
Unknown Affiliation
Elliott, Ronald
United States, Stillwater
Oklahoma State University
Statistics
Citations: 560
Authors: 17
Affiliations: 13
Identifiers
Doi:
10.1016/j.agwat.2005.03.007
ISSN:
03783774