Evaluation of Estimation Methods for Monthly Reference Evapotranspiration in Arid Climates
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YSTEMATIC STUDY OF ARID TERRITORIES
Evaluation of Estimation Methods for Monthly Reference Evapotranspiration in Arid Climates M. Nazaria, M. R. Chaichib, H. Kamelc, M. Grismerd, and S. M. M. Sadeghib, c, *, ** a
Department of Plant Science, McGill University Canada, Quebec H9X 3V9, Ste-Anne-de-Bellevue, Canada bDepartment of Plant Science, California State Polytechnic University, Pomona, CA 91768 United States c Department of Forestry and Forest Economics, University of Tehran Iran, Karaj, 261 Iran dDepartment of Land, Air, and Water Resources, University of California, Davis, CA 95616-8627 United States *e-mail: [email protected] **e-mail: [email protected] Received January 20, 2020; revised March 1, 2020; accepted March 1, 2020
Abstract– Reference evapotranspiration (ET0) plays a key role in irrigation system design as well as water management of agricultural ecosystems under irrigated and rainfed conditions. While many methods for estimating the ET0 have been developed during the past several decades, method selection essentially depends on the availability of measured climatic variables. The FAO-56PM method recommended by experts from Food and Agriculture Organization of the United Nations is widely used in agricultural and environmental research to estimate the ET0. However, it requires several climatic parameters that are not always available in developing countries, especially in arid regions. Here, we compare and evaluate the performance of 13 widely- and commonly-used equations for estimating ET0 against that predicted using the FAO-56PM model using climatic data from nine meteorological stations located in arid regions across Iran. On average, the best three methods that could be used as an alternative to the FAO-56PM equation were the Irmak (Irmak et al., 2003), Hargreaves-Samani (Hargreaves and Samani, 1985), and Hargreaves (1975) equations. Keywords: evapotranspiration, Iran, water availability, water budgets, water management DOI: 10.1134/S2079096120040150
Limited water availability is a key factor affecting crop production and accurate assessment of crop water needs is critical towards irrigation system design and management in arid and semiarid regions. Accurate estimation of evapotranspiration (ET) is essential in agricultural, climatological, drought monitoring, and hydrological studies for irrigation planning and management (Sentelhas et al., 2010; Attarod et al., 2015a, 2016). ET measurement has always been challenging, especially on the landscape spatial scale with a level of accuracy desired for farm-specific water management planning in regions lacking micrometeorological stations. Unlike directly measurable rainfall and streamflow, ET is usually estimated from mass transfer, energy transfer, or water budget methods (Enku and Melesse, 2013). Traditional measurements of ET using evaporation pan and lysimeter methods are mainly for smaller-scale applications or experimental studies and can be labor and cost intensive. Micrometeorological methods for estimating actual ET, such as ener
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