ADGEO Advances in Geosciences ADGEO Adv. Geosci. 1680-7359 Copernicus Publications Göttingen, Germany 10.5194/adgeo-18-15-2008 A global comparison of four potential evapotranspiration equations and their relevance to stream flow modelling in semi-arid environments Weiß M. 1 Menzel L. 1 Center for Environmental Systems Research, University of Kassel, Kurt-Wolters-Str. 3, 34109 Kassel, Germany 20 06 2008 18 15 23 Copyright: © 2008 M. Weiß 2008 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://adgeo.copernicus.org/articles/18/15/2008/adgeo-18-15-2008.html The full text article is available as a PDF file from https://adgeo.copernicus.org/articles/18/15/2008/adgeo-18-15-2008.pdf

This study compares four different potential evapotranspiration equations according to Priestley Taylor, Kimberly Penman, Penman Monteith (FAO-56) and Hargreaves on a global basis to demonstrate their difference, and assess their impact on the calculation of stream flows. The various equations of potential evapotranspiration show great differences in magnitude. But due to the limited availability of validation data, it is difficult to assess which method is the physically most reasonable to be applied. According to this study, the radiation-based Priestley Taylor equation proved to be most suitable for a global application. For the calculation of stream flows, however, the processes involved in the derivation of actual evapotranspiration values from potential evapotranspiration values appear more relevant than the absolute value of the potential evapotranspiration itself.

 References Alcamo, J., Leemans, R., and Kreileman, E.: Global Change Scenarios of the 21st Century. Results of the IMAGE 2.1 Model, Pergamon, Oxford, 1998. Alcamo, J. M., Döll, P., Henrichs, T., Kaspar, F., Lehner, B., Rösch T., and Siebertl S.: Development and testing of the WaterGAP 2 global model of water use and availability, Hydrol. Sci., 48(3), 317–337, 2003. Allen, R. G., Jensen, M. E., Wright, J. L., and Burman, R. D.: Operational Estimates of Reference Evapotranspiration, Agro. J., 81, 650–662, 1989. Allen, R. G., Pereira, L. S., Raes, D., and Smith, M.: Crop evapotranspiration – Guidelines for computing crop water requirements, FAO, Rome, 1998. ASCE: Hydrology Handbook. ASCE Manuals and Reports on Engineering Practice, ASCE, New York, 1996. Bergström, S.: The HBV model. In: V. P. Singh, Computer models of watershed hydrology, Highlands Ranch, Water Resources Publications, 443–476, 1995. Bloemen, G. W.: A high-accuracy recording pan-evaporimeter and some of its possibilities, J. Hydrol., 39, 159–173, 1978. Brutsaert, W.: Evaporation into the atmosphere. Theory, History, and Applications, Kluwer Academic Publisher, Dordrecht, Boston, London, 1982. Burman, R. and Pochop, L. O.: Evaporation, Evapotranspiration and climatic data, Elsevier Science B.V., Amsterdam, 1994. Döll, P., Kaspar F., and Lehner, B.: A global hydrological model for deriving water availability indicators: model tuning and validation, J. Hydrol., 270, 105–134, 2003. Döll, P. and Lehner, B.: Validation of a new global 30-min drainage direction map, J. Hydrol., 258, 214–231, 2002. Doorenbos, J. and Pruitt, W. O.: Crop water requirements, FAO, Rome, 1977. Droogers, P. and Allen, R. G.: Estimating Reference Evapotranspiration Under Inaccurate Data Conditions, Irrigation and Drainage Systems, 16(1), 33–45, 2002. DVWK: Ermittlung der Verdunstung von Land- und Wasserflächen (evaporation from land and water areas, in German), 1996. FAO: Digital Soil Map of the World and Derived Soil Properties, Rome, FAO, 1995. GRDC: Long Term Mean Monthly Discharges and Annual Characteristics of Selected GRDC Stations, The Global Runoff Data Centre, Koblenz, Germany, 2004. Hargreaves, G. H. and Allen, R. G.: History and Evaluation of Hargreaves Evapotranspiration Equation, Journal of Irrigation and Drainage Engineering, 129(1), 53–63, 2003. Hargreaves, G. L., Hargreaves, G. H. and Riley, J. P.: Agricultural Benefits for Senegal River Basin, Journal of Irrigation and Drainage Engineering, 111(2), 113–124, 1985. Jensen, M. E., Burman, R. D. and Allen, R. G.: Evapotranspiration and irrigation water requirements, New York, 1990. Linacre, E. T.: Estimating U.S. Class-A pan evaporation from few climate data, Water International 19, 5–14, 1994. Maidment: Handbook of hydrology, McGraw-Hill, New York, 1992. Menzel, L.: Modellierung der Evapotranspiration im System Boden-Pflanze-Atmosphäre (simulation of evapotranspiration at the soil-vegetation-atmosphere interface; in German), Zürcher Geographische Schriften No 67, Swiss Federal Institute of Technology (ETH), Zürich, 1997. Menzel, L.: Flächenhafte Modellierung der Evapotranspiration mit TRAIN (areal modelling of evapotranspiration with TRAIN; in German), Potsdam-Institute for Climate Impact Research, 1999. Menzel, L., Teichert, E., and Weiß, M.: Climate change impact on the water resources of the semi-arid Jordan region. In: Proc 3rd International Conference on Climate and Water, edited by: Heinonen, M., Helsinki, 320-325, 2007. Mitchell, T. D. and Jones, P. D.: An improved method of constructing a database of monthly climate observations and associated high-resolution grids, International Journal of Climatology, 25(6), 693–712, 2005. MM5: MM5 Community Model Homepage, Retrieved 06/2007, from http://www.mmm.ucar.edu/mm5/, 2007. Monteith, J.: Evaporation and environment, Symp Soc Exp Biol., 19, 205–234, 1965. New, M., Hulme, M., and Jones, P.D.: Representing twentieth century space-time climate variability. Part 1: development of a 1961-90 mean monthly terrestrial climatology. , J. Clim., 12, 829–856, 1999. Penman, H. L.: Natural evaporation from open water, bare soil and grass, Proc. Proc. Roy. Soc. London, 120–146, 1948. Penman, H. L.: Evaporation: An Introductory Survey, Proc. Proc. Inf. Meeting on Physics in Agric., Neth. J. Agric. Sci., 9–29, 1956. Priestley, C. B. H. and Taylor, R. J.: On the assessment of surface heat flux and evaporation using large scale parameters, Monthly Weather Review, 100, 81–92, 1972. UNEP: Global Environment Outlook: environment for development (GEO-4), Progress Press, Ltd. Valletta, Malta, 2007. USGS, U.S. Geological Survey, EROS Data Center: Global Land Cover Characterization, Retrieved 8~June~2007, from http://edcsns17.cr.usgs.gov/glcc/ 2007. Wright, J. L.: Crop coefficients for estimates of daily crop evapotranspiration, Irrig. Scheduling for Water and Energy Conserv. in the 80's, Am. Soc. of Agric. Engrs. Dec., 1981. Wright, J. L.: New evapotranspiration crop coefficiennts, J. Irrig. and Drain. Div., ASCE, 108, 57–74, 1982.