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

Published on Apr 1, 2019in Agricultural Water Management 3.54
· DOI :10.1016/j.agwat.2018.12.014
Paula Paredes18
Estimated H-index: 18
(Instituto Superior de Agronomia),
Luis S. Pereira51
Estimated H-index: 51
(Instituto Superior de Agronomia)
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Abstract
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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Published on Nov 1, 2018in Agricultural Water Management 3.54
Paula Paredes18
Estimated H-index: 18
(IPN: Instituto Politécnico Nacional),
Diogo S. Martins6
Estimated H-index: 6
(Instituto Superior de Agronomia)
+ 2 AuthorsCarlos Pires10
Estimated H-index: 10
(University of Lisbon)
Abstract This study aims at assessing the accuracy of estimating daily grass reference evapotranspiration (PM-ET o ) computed with ERA-Interim reanalysis products, as well as to assess the quality of reanalysis products as predictors of daily maximum and minimum temperature, net radiation, dew point temperature and wind speed, which are used to compute PM-ET o . With this propose, ET o computed from local observations of weather variables in 24 weather stations distributed across Continental Por...
Published on Nov 1, 2018in Theoretical and Applied Climatology 2.72
Paula Paredes18
Estimated H-index: 18
(University of Lisbon),
J. C. Fontes4
Estimated H-index: 4
(University of the Azores)
+ 1 AuthorsLuis S. Pereira51
Estimated H-index: 51
(University of Lisbon)
Reference crop evapotranspiration (ETo) estimations using the FAO Penman-Monteith equation (PM-ETo) require a set of weather data including maximum and minimum air temperatures (T max, T min), actual vapor pressure (e a), solar radiation (R s), and wind speed (u 2). However, those data are often not available, or data sets are incomplete due to missing values. A set of procedures were proposed in FAO56 (Allen et al. 1998) to overcome these limitations, and which accuracy for estimating daily ETo...
Published on Oct 1, 2018in Theoretical and Applied Climatology 2.72
Paula Paredes18
Estimated H-index: 18
(University of Lisbon),
J. C. Fontes4
Estimated H-index: 4
(University of the Azores)
+ 1 AuthorsLuis S. Pereira51
Estimated H-index: 51
(University of Lisbon)
Reference crop evapotranspiration (ETo) estimations using the FAO Penman-Monteith equation (PM-ETo) require several weather variables that are often not available. Then, ETo may be computed with procedures proposed in FAO56, either using the PM-ETo equation with temperature estimates of actual vapor pressure (e a) and solar radiation (R s), and default wind speed values (u 2), the PMT method, or using the Hargreaves-Samani equation (HS). The accuracy of estimates of daily e a, R s, and u 2 is pr...
Published on Sep 1, 2018in Agricultural and Forest Meteorology 4.19
Isabel F. Trigo28
Estimated H-index: 28
(Instituto Português do Mar e da Atmosfera),
Henk Bruin6
Estimated H-index: 6
(WUR: Wageningen University and Research Centre)
+ 4 AuthorsRamón López-Urrea1
Estimated H-index: 1
Abstract This article presents validation results of the grass Reference Evapotranspiration (ET o ) product, which is provided operationally by the Satellite Applications Facility on Land Surface Analysis (LSA SAF). ET o is considered to be the evapotranspiration from a hypothetical extensive well-watered field covered with green grass (12 cm high and with 0.23 albedo), under the given down-welling short-wave radiation. The LSA SAF product is estimated from daily solar radiation at the surface v...
Published on Aug 1, 2018in Theoretical and Applied Climatology 2.72
P. Lobit1
Estimated H-index: 1
(UMSNH: Universidad Michoacana de San Nicolás de Hidalgo),
L. L. Perez1
Estimated H-index: 1
(UMSNH: Universidad Michoacana de San Nicolás de Hidalgo),
Jean-Paul Lhomme1
Estimated H-index: 1
We propose a new model to estimate daily global radiation from daily temperature range measurements. This model combines that of Majumdar et al. (Sol Energy 13(4):383–394, 1972) to estimate clear sky radiation with a Gompertz function to estimate the relation between temperature range and cloud transmittance. Model parameters are estimated from historical weather data: maximum and minimum temperatures and, if available, relative humidity; no other calibration is required. The model was parametri...
Published on Jul 1, 2018in Water Resources Management 2.99
Ali Mokhtari2
Estimated H-index: 2
,
Hamideh Noory6
Estimated H-index: 6
(UT: University of Tehran),
Majid Vazifedoust7
Estimated H-index: 7
(University of Gilan)
Reference evapotranspiration (ET0) from FAO-Penman-Monteith equation is highly sensitive to the surface incoming solar radiation (SISR) and therefore accurate estimate of this parameter would result in more accurate estimation of ET0. In this study, the accuracy of three main approaches for SISR estimation including empirical models (Angstrom and Hargreaves-Samani), physically-based data assimilation models (Global Land Data Assimilation System-Noah, GLDAS/Noah, and National Centers of Environme...
Published on Jan 1, 2018in Theoretical and Applied Climatology 2.72
Javier Almorox14
Estimated H-index: 14
(UPM: Technical University of Madrid),
Alfonso Senatore12
Estimated H-index: 12
(University of Calabria)
+ 1 AuthorsGiuseppe Mendicino11
Estimated H-index: 11
(University of Calabria)
When not all the meteorological data needed for estimating reference evapotranspiration ETo are available, a Penman–Monteith temperature (PMT) equation can be adopted using only measured maximum and minimum air temperature data. The performance of the PMT method is evaluated and compared with the Hargreaves–Samani (HS) equation using the measured long-term monthly data of the FAO global climatic dataset New LocClim. The objective is to evaluate the quality of the PMT method for different climate...
Published on Aug 1, 2017in Water Resources Management 2.99
Luis S. Pereira51
Estimated H-index: 51
(University of Lisbon)
Abstract Population growth, increasing demands for food, ever-growing competition for water, reduced supply reliability, climate change and climate uncertainty and droughts, decline in critical ecosystems services, competition for land use, changing regulatory environments, and less participatory water resources governance are contributing to increasing difficulties and challenges in water resource management for agriculture and food. The need for sustainable food security for our global populat...
Published on Jun 1, 2017in Renewable & Sustainable Energy Reviews 10.56
Babak Jahani2
Estimated H-index: 2
(Water Resources University),
Yagob Dinpashoh17
Estimated H-index: 17
(Water Resources University),
Atefeh Raisi Nafchi1
Estimated H-index: 1
(Shahid Chamran University of Ahvaz)
In this study, accuracy and suitability of eleven models from three different categories for estimating daily solar radiation in Iran were evaluated. For this purpose, daily meteorological data of 23 stations in Iran which record solar radiation was used. The models consist of temperature-, sunshine-based and complex models. Furthermore, four new models, namely; P1, P2, P3 and P4 were developed in the present study. The models P1 and P2 estimate daily solar radiation based on daily range of temp...
Published on Apr 1, 2017in International Journal of Climatology 3.60
Diogo S. Martins6
Estimated H-index: 6
(Instituto Superior de Agronomia),
Paula Paredes18
Estimated H-index: 18
(Instituto Superior de Agronomia)
+ 3 AuthorsLuis S. Pereira51
Estimated H-index: 51
(University of Lisbon)
Computing crop reference evapotranspiration (ETo) with the FAO Penman–Monteith method (PM-ETo) requires maximum and minimum air temperature, shortwave radiation, relative air humidity and wind speed. These data are often not available, thus requiring alternative computation procedures. Although some proposed approximations may provide ETo values with small estimation errors, the physics of the ET processes may then not be well described. The use of reanalysis data, which is common in climate stu...
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