Computing FAO56 reference grass evapotranspiration PM-ETo from temperature with focus on solar radiation

Published on Apr 1, 2019in Agricultural Water Management 3.18
· DOI :10.1016/j.agwat.2018.12.014
Paula Paredes18
Estimated H-index: 18
(Instituto Superior de Agronomia),
Luis S. Pereira50
Estimated H-index: 50
(Instituto Superior de Agronomia)
Abstract The computation of the reference crop evapotranspiration (ET o ) using the FAO Penman-Monteith equation (PM-ET o ) requires data on maximum and minimum air temperatures (T max , T min ), vapour pressure deficit (VPD), solar radiation (R s ) and wind speed at 2 m height (u 2 ). However, those data are often not available, or data sets may be incomplete or have questionable quality. Various procedures were proposed in FAO56 to overcome these limitations and an abundant literature has been and is being produced relative to alternative computational methods. Studies applied to a variety of climates, from hyper-arid to humid, have demonstrated that improved methods to compute PM-ET o from temperature only (PMT approach) have appropriate accuracy. These methods refer to estimating: (i) the dew point temperature (T dew ) from T min or, in case of humid climates, from the mean temperature, T mean ; (ii) R s from the temperature difference (TD = T max -T min ); and (iii) u 2 using default global or regional values. Greater difficulties refer to the need for locally calibrating the radiation adjustment coefficient (k Rs ) used with the R s equation. Therefore, considering that calibrated k Rs values were made available by past studies for a large number of locations and diverse climates, the current study developed and tested simple computational approaches relating locally calibrated k Rs with various observed weather variables – TD, relative humidity (RH) and average u 2 . The equations were developed using CLIMWAT monthly full-data relative to all the Mediterranean countries. The equations refer to all available data, or to data grouped as hyper-arid and arid, semi-arid, dry and moist sub-humid, and humid climates. To test those k Rs equations, ET o computed from temperature and using the predicted k Rs values were compared with ET o computed with full data sets of the same Mediterranean locations and of Iran, Inner Mongolia, Portugal and Bolivia. RMSE average values result then small, ranging from 0.34 to 0.54 mm day −1 , therefore not very far from values obtained when a trial and error procedure was used for all the same locations, from 0.27 to 0.46 mm day −1 . These indicators allow to propose the use of k Rs obtained from the predictive equations instead of locally calibrated k Rs values, which greatly eases computations and may largely favour the use of the PMT approach.
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J. L. Monteith22
Estimated H-index: 22
2,575 Citations
Published on Oct 1, 2015in Journal of Hydrology 3.73
Pau Martí17
Estimated H-index: 17
(Polytechnic University of Valencia),
Manuel Zarzo14
Estimated H-index: 14
(Polytechnic University of Valencia)
+ 1 AuthorsJoan Girona1
Estimated H-index: 1
Summary The application of simple empirical equations for estimating reference evapotranspiration (ET o ) is the only alternative in many cases to robust approaches with high input requirements, especially at the local scale. In particular, temperature-based approaches present a high potential applicability, among others, because temperature might explain a high amount of ET o variability, and also because it can be measured easily and is one of the most available climatic inputs. One of the mos...
19 Citations Source Cite
George H. Hargreaves8
Estimated H-index: 8
Zohrab Samani15
Estimated H-index: 15
Increasing population and needs for an augmented food supply give greater importance to improved procedures for estimating agricultural water requirements both for irrigation and for rain-fed agriculture. Four methods for estimating potential evapotranspiration are compared and evaluated. These are the Class A evaporation pan located in an irrigated pasture area, the Hargreaves equation, the Jensen-Haise eguation, and the Blaney-Criddle method. The evaporation pan is rated as superior to the oth...
834 Citations
Published on Jan 1, 2002in Irrigation and Drainage Systems
Peter Droogers22
Estimated H-index: 22
(International Water Management Institute),
Richard G. Allen46
Estimated H-index: 46
(University of Idaho)
Reference evapotranspiration (ET0) estimates have been computed on a global scale using a high-resolution monthly climate dataset. Penman-Monteith (PM) and Hargreaves (HG) methods have been compared, showing very reasonable agreement between the two methods. Fitting the two parameters of HG using the PM derived ET0 values did not improve estimates by the HG method substantially. Modifying the original Hargreaves method to a Modified-Hargreaves (MH) method by including a rainfall term improved ET...
444 Citations Source Cite
Published on Jun 1, 2008in Agricultural Water Management 3.18
M. Jabloun1
Estimated H-index: 1
A Sahli5
Estimated H-index: 5
The Food and Agriculture Organization of the United Nations had improved the version of the Penman-Monteith method (FAO-56 PM) which has recently been proposed as the standard for estimating reference evapotranspiration (ETo). Unfortunately, some weather variables, especially solar radiation, relative humidity and wind speed, are often missing which could impede the estimation of ETo with the FAO-56 PM method. To overcome the problem of the availability of climatic parameters, procedures to esti...
149 Citations Source Cite
Published on Aug 1, 2015in Mountain Research and Development 1.22
Mario Córdova3
Estimated H-index: 3
(University of Cuenca),
Galo Carrillo-Rojas3
Estimated H-index: 3
(University of Marburg)
+ 2 AuthorsRolando Célleri13
Estimated H-index: 13
(University of Cuenca)
Reference evapotranspiration (ETo) is often calculated using the Penman-Monteith (FAO 56 PM; Allen et al 1998) method, which requires data on temperature, relative humidity, wind speed, and solar radiation. But in high-mountain environments, such as the Andean paramo, meteorological monitoring is limited and high-quality data are scarce. Therefore, the FAO 56 PM equation can be applied only through the use of an alternative method suggested by the same authors that substitutes estimates for miss...
28 Citations Source Cite
Published on May 1, 2004in Agricultural Water Management 3.18
Antonio Roberto Pereira16
Estimated H-index: 16
(University of São Paulo),
William O. Pruitt6
Estimated H-index: 6
(University of California, Davis)
Abstract A photoperiodic effective daily temperature is proposed as an alternative version of the Thornthwaite scheme for estimating daily evapotranspiration rates. Extensive lysimetric data sets from two contrasting climatic regions were used to test the proposed version. The well-known gross underprediction of the original Thornthwaite approach for arid climates became a slight overprediction under the new version, but it was equivalent to that obtained with the well-recommended Penman–Monteit...
110 Citations Source Cite
Published on Sep 1, 2009in Agricultural and Forest Meteorology 4.04
Xiaoying Liu7
Estimated H-index: 7
Xurong Mei8
Estimated H-index: 8
+ 4 AuthorsJohn R. Porter45
Estimated H-index: 45
(University of Copenhagen)
Abstract Estimation of global solar radiation ( R s ) from the daily range of air temperature (Δ T ) offers an important alternative in the absence of measured R s or sunshine duration because of the wide availability of air temperature data. In this paper, we assessed 16 R s models including modified versions of the Bristow and Campbell (B–C) and the Hargreaves (Harg) models across a wide range of agro-ecological conditions in China. Using long-term data from 15 sites in Northeast, North China ...
92 Citations Source Cite
Published on Oct 1, 2008in Agricultural and Forest Meteorology 4.04
A. Bandyopadhyay7
Estimated H-index: 7
A. Bhadra7
Estimated H-index: 7
(North Eastern Regional Institute of Science and Technology)
+ 1 AuthorsRajendra Singh23
Estimated H-index: 23
(Indian Institute of Technology Kharagpur)
Abstract Solar radiation ( R s ), a very important variable in agricultural meteorology, is measured at a very limited number of meteorological stations worldwide. However, a number of methods are reported in the literature for estimating R s from routinely measured air temperature extremes, the accuracy of which needs to be tested. R s was thus estimated by different methods for 29 stations distributed throughout India. The methods compared were Hargreaves [Hargreaves, G.H., 1994. Simplified co...
53 Citations Source Cite
Published on Jul 1, 1994in The Geographical Journal
David J. Nash27
Estimated H-index: 27
Nick Middleton15
Estimated H-index: 15
David S.G. Thomas49
Estimated H-index: 49
This text aims to summarize the state of scientific knowledge on the drylands of the globe. It explores the current stage of understanding of desertification as well as its extent and possible solutions. The book argues that desertification is one of the world's most pressing environmental problems and that it is a global issue which is accelerating. This edition has been revised and expanded to include updated computer images of desertification, as well as fuller descriptions and explanations o...
907 Citations Source Cite
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