Evaluation of 32 Simple Equations against the Penman–Monteith Method to Estimate the Reference Evapotranspiration in the Hexi Corridor, Northwest China

Evapotranspiration plays an inevitable role in various fields of hydrology and agriculture. Reference evapotranspiration (ET0) is mostly applied in irrigation planning and monitoring. An accurate estimation of ET0 contributes to decision and policymaking processes governing water resource management, efficiency, and productivity. Direct measurements of ET0, however, are difficult to achieve, often requiring empirical methods. The Penman–Monteith FAO56 (PM-FAO56) method, for example, is still considered to be the best way of estimating ET0 in most regions of the globe. However, it requires a large number of meteorological variables, often restricting its applicability in regions with poor or missing meteorological observations. Furthermore, the objectivity of some elements of the empirical equations often used can be highly variable from region to region. The result is a need to find an alternative, objective method that can more accurately estimate ET0 in regions of interest. This study was conducted in the Hexi corridor, Northwest China. In it we aimed to evaluate the applicability of 32 simple empirical ET0 models designed under different climatic conditions with different data inputs requirements. The models evaluated in this study are classified into three types of methods based on temperature, solar radiation, and mass transfer. The performance of 32 simple equations compared to the PM-FAO56 model is evaluated based on model evaluation techniques including root mean square error (RMSE), mean absolute error (MAE), percentage bias (PBIAS), and Nash–Sutcliffe efficiency (NSE). The results show that the World Meteorological Organization (WMO) and the Mahringer (MAHR) models perform well and are ranked as the best alternative methods to estimate daily and monthly ET0 in the Hexi corridor. The WMO and MAHR performed well with monthly mean RMSE = 0.46 mm and 0.56 mm, PBIAS = 12.1% and −11.0%, and NSE = 0.93 and 0.93, before calibration, respectively. After calibration, both models showed significant improvements with approximately equal PBIAS of −2.5%, NSE = 0.99, and RMSE of 0.24 m. Calibration also significantly reduced the PBIAS of the Romanenko (ROM) method by 82.12% and increased the NSE by 16.7%.

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Global comparison of 20 reference evapotranspiration equations in a semi-arid region of Iran

Hydrology Research ◽

10.2166/nh.2018.174 ◽

2018 ◽

Vol 50 (1) ◽

pp. 282-300 ◽

Cited By ~ 10

Author(s):

Hadi Farzanpour ◽

Jalal Shiri ◽

Ali Ashraf Sadraddini ◽

Slavisa Trajkovic

Keyword(s):

Arid Region ◽

Reference Evapotranspiration ◽

Meteorological Data ◽

Irrigation Scheduling ◽

Climatic Conditions ◽

Accurate Estimation ◽

Management Scenarios ◽

Global Comparison ◽

Semi Arid Region ◽

Semi Arid

Abstract Accurate estimation of reference evapotranspiration (ETo) is a major task in hydrology, water resources management, irrigation scheduling and determining crop water requirement. There are many empirical equations suggested by numerous references in literature for calculating ETo using meteorological data. Some such equations have been developed for specific climatic conditions while some have been applied universally. The potential for usage of these equations depends on the availability of necessary meteorological parameters for calculating ETo in different climate conditions. The focus of the present study was a global cross-comparison of 20 ETo estimation equations using daily meteorological records of 10 weather stations (covering a period of 12 years) in a semi-arid region of Iran. Two data management scenarios, namely local and cross-station scenarios, were adopted for calibrating the applied equations against the standard FAO56-PM model. The obtained results revealed that the cross-station calibration might be a good alternative for local calibration of the ETo models when proper similar stations are used for feeding the calibration matrix.

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Comparative Analysis of Artificial Intelligence Models for Accurate Estimation of Groundwater Nitrate Concentration

Sensors ◽

10.3390/s20205763 ◽

2020 ◽

Vol 20 (20) ◽

pp. 5763 ◽

Cited By ~ 1

Author(s):

Shahab S. Band ◽

Saeid Janizadeh ◽

Subodh Chandra Pal ◽

Indrajit Chowdhuri ◽

Zhaleh Siabi ◽

...

Keyword(s):

Artificial Intelligence ◽

Water Resource Management ◽

Nitrate Concentration ◽

Evaluation Criteria ◽

Absolute Error ◽

Coefficient Of Determination ◽

Accurate Estimation ◽

Support Vector ◽

Topographic Wetness Index ◽

Agricultural Areas

Prediction of the groundwater nitrate concentration is of utmost importance for pollution control and water resource management. This research aims to model the spatial groundwater nitrate concentration in the Marvdasht watershed, Iran, based on several artificial intelligence methods of support vector machine (SVM), Cubist, random forest (RF), and Bayesian artificial neural network (Baysia-ANN) machine learning models. For this purpose, 11 independent variables affecting groundwater nitrate changes include elevation, slope, plan curvature, profile curvature, rainfall, piezometric depth, distance from the river, distance from residential, Sodium (Na), Potassium (K), and topographic wetness index (TWI) in the study area were prepared. Nitrate levels were also measured in 67 wells and used as a dependent variable for modeling. Data were divided into two categories of training (70%) and testing (30%) for modeling. The evaluation criteria coefficient of determination (R2), mean absolute error (MAE), root mean square error (RMSE), and Nash–Sutcliffe efficiency (NSE) were used to evaluate the performance of the models used. The results of modeling the susceptibility of groundwater nitrate concentration showed that the RF (R2 = 0.89, RMSE = 4.24, NSE = 0.87) model is better than the other Cubist (R2 = 0.87, RMSE = 5.18, NSE = 0.81), SVM (R2 = 0.74, RMSE = 6.07, NSE = 0.74), Bayesian-ANN (R2 = 0.79, RMSE = 5.91, NSE = 0.75) models. The results of groundwater nitrate concentration zoning in the study area showed that the northern parts of the case study have the highest amount of nitrate, which is higher in these agricultural areas than in other areas. The most important cause of nitrate pollution in these areas is agriculture activities and the use of groundwater to irrigate these crops and the wells close to agricultural areas, which has led to the indiscriminate use of chemical fertilizers by irrigation or rainwater of these fertilizers is washed and penetrates groundwater and pollutes the aquifer.

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Alternative Methods of Reference Evapotranspiration for Brazilian Climate Types

Revista Brasileira de Meteorologia ◽

10.1590/0102-7786333015 ◽

2018 ◽

Vol 33 (3) ◽

pp. 567-578 ◽

Cited By ~ 3

Author(s):

Bruno César Gurski ◽

Daniela Jerszurki ◽

Jorge Luiz Moretti de Souza

Keyword(s):

Reference Evapotranspiration ◽

Climatic Conditions ◽

Least Square ◽

Alternative Methods ◽

Climate Type ◽

Critical Gap ◽

Climatic Regions ◽

Sunshine Hours ◽

And Performance ◽

Semi Arid

Abstract The choice of consistent alternative methods is essential for the improvement of reference evapotranspiration (ETo) estimation for different climatic regions. Due to a critical gap in knowledge concerning the most adequate alternative ETo methods for the climatic conditions in Paraná, Brazil, this study aimed to test and to evaluate the main estimation alternative methods (Thornthwaite - EToTH; Camargo - EToC; Hargreaves and Samani - EToHS; Linacre - EToL; and, Budyko - EToB) for the subtropical (Cfb) and semi-arid (Bsh) climate types in Brazil. We compared our results with standard EToPM (Penman-Monteith) estimated between 1970 and 2015, using the minimum and maximum air temperature (T), sunshine hours (n), relative humidity (RH) and wind speed (U2). Least square regression analysis of ETo estimated by alternative methods vs EToPM were used to calibrate the methods for each analyzed climate type. The performance of calibrated and noncalibrated methods was evaluated by index of agreement “d” and performance “c”, root mean square error (RMSE) and mean error (ME). Our results showed the importance of calibration process of alternative methods for the improvement of ETo estimations in Brazil. The Hargreaves and Samani and Linacre calibrated methods showed better performance in the subtropical and semi-arid climates, respectively. Also, the Linacre and Budyko calibrated methods were particularly robust in subtropical and semi-arid climates, outlining the importance of continuous measurements of T used in the EToL and EToB modeling effort. The results presented here showed the importance to calibrate the alternative methods on ETo estimations and outlined the need for improvement and proposition of new ETo methods based on a limited number of climatic variables commonly available in subtropical and semi-arid climates in Brazil.

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Evaluation of FAO-56 Procedures for Estimating Reference Evapotranspiration Using Missing Climatic Data for a Brazilian Tropical Savanna

Water ◽

10.3390/w13131763 ◽

2021 ◽

Vol 13 (13) ◽

pp. 1763

Author(s):

Luiz Claudio Galvão do Valle Júnior ◽

George L. Vourlitis ◽

Leone Francisco Amorim Curado ◽

Rafael da Silva Palácios ◽

José de S. Nogueira ◽

...

Keyword(s):

Wind Speed ◽

Relative Humidity ◽

Water Resource Management ◽

Reference Evapotranspiration ◽

Meteorological Data ◽

Climatic Conditions ◽

Climatic Variables ◽

Climatic Data ◽

Wet Season ◽

Radiation Data

The Brazilian savanna (Cerrado) has been heavily impacted by agricultural activities over the last four to five decades, and reliable estimates of reference evapotranspiration (ETo) are needed for water resource management and irrigation agriculture. The Penman–Monteith (PM) is one of the most accepted models for ETo estimation, but it requires many inputs that are not commonly available. Therefore, assessing the FAO guidelines to compute ETo when meteorological data are missing could lead to a better understanding of which variables are critically important for reliable estimates of ETo and how climatic variables are related to water requirements and atmospheric demands. In this study, ETo was computed for a grass-dominated part of the Cerrado from April 2010 to August 2019. We tested 12 different scenarios considering radiation, relative humidity, and/or wind speed as missing climatic data using guidelines given by the FAO. Our results presented that wind speed and actual vapor pressure do not affect ETo estimates as much as the other climatic variables; therefore, in the Cerrado’s conditions, wind speed and relative humidity measurements are less required than temperature and radiation data. When radiation data were missing, the computed ETo was overestimated compared to the benchmark. FAO procedures to estimate the net radiation presented good results during the wet season; however, during the dry season, their results were overestimated because the method could not estimate negative Rn. Our results indicate that radiation data have the highest impact on ETo for our study area and presumably for regions with similar climatic conditions. In addition, those FAO procedures for estimating radiation are not suitable when radiation data are missing.

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Prediction of the Reference Evapotranspiration Using a Chaotic Approach

The Scientific World JOURNAL ◽

10.1155/2014/347625 ◽

2014 ◽

Vol 2014 ◽

pp. 1-13 ◽

Cited By ~ 2

Author(s):

Wei-guang Wang ◽

Shan Zou ◽

Zhao-hui Luo ◽

Wei Zhang ◽

Dan Chen ◽

...

Keyword(s):

Correlation Dimension ◽

Reference Evapotranspiration ◽

Chaotic Behavior ◽

Meteorological Data ◽

Absolute Error ◽

Local Approximation ◽

Climatic Conditions ◽

Nonlinear Dynamical ◽

Wide Range ◽

Correlation Dimension Method

Evapotranspiration is one of the most important hydrological variables in the context of water resources management. An attempt was made to understand and predict the dynamics of reference evapotranspiration from a nonlinear dynamical perspective in this study. The reference evapotranspiration data was calculated using the FAO Penman-Monteith equation with the observed daily meteorological data for the period 1966–2005 at four meteorological stations (i.e., Baotou, Zhangbei, Kaifeng, and Shaoguan) representing a wide range of climatic conditions of China. The correlation dimension method was employed to investigate the chaotic behavior of the reference evapotranspiration series. The existence of chaos in the reference evapotranspiration series at the four different locations was proved by the finite and low correlation dimension. A local approximation approach was employed to forecast the daily reference evapotranspiration series. Low root mean square error (RSME) and mean absolute error (MAE) (for all locations lower than 0.31 and 0.24, resp.), high correlation coefficient (CC), and modified coefficient of efficiency (for all locations larger than 0.97 and 0.8, resp.) indicate that the predicted reference evapotranspiration agrees well with the observed one. The encouraging results indicate the suitableness of chaotic approach for understanding and predicting the dynamics of the reference evapotranspiration.

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Comparative evaluation of different reference evapotranspiration models

Journal of Applied and Natural Science ◽

10.31018/jans.v9i1.1239 ◽

2017 ◽

Vol 9 (1) ◽

pp. 609-613

Author(s):

C. K. Arya ◽

R. C. Purohit ◽

L. K. Dashora ◽

P. K. Singh ◽

Mahesh Kothari ◽

...

Keyword(s):

Water Resource Management ◽

Meteorological Parameters ◽

Reference Evapotranspiration ◽

Potential Evapotranspiration ◽

Accurate Estimation ◽

Climatic Data ◽

Pan Evaporation ◽

Alternative Method ◽

Monteith Equation

The study was carried out to select best alternative method for the estimation of reference evapotranspi-ration (ET0). Accurate estimation of potential evapotranspiration is a necessary step in water resource management. Recently, the FAO-56 version of Penman-Monteith equation has been established as a standard for calculating ref-erence evapotranspiration (ET0) which requires measurement of a number of meteorological parameters namely, air temperature, relative humidity, solar radiation, and wind speed which may not be available in most of the meteoro-logical stations. Still there are different approaches (requiring less data) which estimate ET0 closely to Penman- Monteith (P-M) method for different climatological conditions. The present study is based on analysis of long term of 13 years (2000 to 2012) climatic data to calculate monthly reference evapotranspiration for Capsicum production (September–March) and also to compare the performance of evapotranspiration equations for Jhalawar district of Rajasthan with the standard FAO-56 Penman-Monteith method on the basis of the least root mean square error (RMSE) analysis. Hargreaves method and Pan evaporation (E-Pan) method overestimated the values of ETo when compared with FAO-56 Penman-Monteith method. On the basis of lowest value of RMSE, Pan evaporation method is found best alternative method to FAO-56 Penman-Monteith method in the study area.

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Empirical methods for reference evapotranspiration estimation

Scientia Agraria Paranaensis ◽

10.18188/sap.v19i3.21487 ◽

2020 ◽

Vol 19 (3) ◽

pp. 203-210

Author(s):

Oswaldo Palma Lopes Sobrinho ◽

Wady Lima Castro Júnior ◽

Leonardo Nazário Silva dos Santos ◽

Gerlange Soares da Silva ◽

Álvaro Itaúna Schalcher Pereira ◽

...

Keyword(s):

Reference Evapotranspiration ◽

Meteorological Data ◽

Physical Phenomenon ◽

Climatic Conditions ◽

Alternative Methods ◽

Empirical Methods ◽

Class A ◽

Evapotranspiration Estimation ◽

Almost All ◽

Meteorological Elements

The reference evapotranspiration (ETo) is a parameter applied in meteorological, climatological and hydrological studies being of great importance for the planning, management and management of water resources. Due to the need for knowledge about the loss of water from vegetated surfaces, researchers have developed a variety of methods for estimating ETo, some of which are well accepted, while others are criticized, such as the Penman-Monteith-FAO (PM-FAO) meteorological data, which is not always available by limiting its use. The PM-FAO method has been used for decades to be considered internationally and most appropriate for ETo estimates. This method represents the physical phenomenon of evapotranspiration that involves almost all meteorological elements analyzed in automatic and conventional meteorological stations. On the other hand, when this method is impossible to apply due to the lack of some input data, alternative methods are justified (Hargreaves-Samani, Blaney-Criddle, Priestley-Taylor, Jensen-Haise, Camargo, Makkink, Kharrufa , Linacre, Class A tank, Thornthwaite and solar radiation) according to soil and climatic conditions.

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Effect of Elevation on Variation in Reference Evapotranspiration under Climate Change in Northwest China

Sustainability ◽

10.3390/su131810151 ◽

2021 ◽

Vol 13 (18) ◽

pp. 10151

Author(s):

Wei Liu ◽

Linshan Yang ◽

Meng Zhu ◽

Jan F. Adamowski ◽

Rahim Barzegar ◽

...

Keyword(s):

Climate Change ◽

Land Surface ◽

Reference Evapotranspiration ◽

Sunshine Duration ◽

Northwest China ◽

Temporal Variations ◽

Climatic Conditions ◽

Dominant Factor ◽

Mountainous Regions ◽

Meteorological Observations

Through its effects on water and energy cycles, elevation plays an important role in modulating the spatial distribution of climatic changes in mountainous regions. A key hydrological indicator, reference evapotranspiration (ET0) reflects the maximum amount of water transferred to the atmosphere from the land surface. The current scarcity of information regarding elevation’s impact on variation in ET0 under climate change limits our understanding of the extent to which elevation modulates interactions between ET0 and climate change and of the attendant processes involved. Drawing upon long-term (1960–2017) meteorological observations from 84 stations in Northwest China (NWC), we examined (i) spatial and temporal variations in ET0; (ii) the sensitivity and contribution of air temperature (T), sunshine duration (SD), relative humidity (RH), and wind speed (WS) to ET0; (iii) the existence of a relationship between elevation and ET0 trends; and (iv) the major factor in controlling this relationship by using attribution analysis. Overall, annual ET0 in NWC showed a declining trend between 1960 and 2017, though at a change point in 1993, the trend shifted from a decline to a rise. A significant correlation between temporal change in ET0 and elevation confirmed the existence of a relationship between elevation and ET0 variation. The effect of elevation on changes in ET0 depended mainly on the elevation-based tradeoff between the contributions of T and WS: WS was the primary factor contributing to the decrease in ET0 below 2000 m, and T was the dominant factor contributing to the increase of ET0 above 2000 m. The rate of reduction in WS declined as elevation increased, thereby diminishing its contribution to variation in ET0. The present study’s results can serve to guide agricultural irrigation in different elevation zones under NWC’s evolving climatic conditions.

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Modeling daily reference evapotranspiration in middle south Saurashtra region of India for monsoon season using most dominant meteorological variables and the FAO-56 Penman-Monteith method

MAUSAM ◽

10.54302/mausam.v68i1.401 ◽

2021 ◽

Vol 68 (1) ◽

pp. 1-8

Author(s):

MANOJ GUNDALIA ◽

MRUGEN DHOLAKIA

Keyword(s):

Reference Evapotranspiration ◽

Monsoon Season ◽

Absolute Error ◽

Alternative Methods ◽

Meteorological Variables ◽

Coefficient Of Determination ◽

Efficiency Coefficient ◽

Study Region ◽

Proposed Model ◽

Meteorological Observations

Many methods are available to estimate reference evapotranspiration (ETo) from standard meteorological observations. The FAO-56 Penman-Monteith method is considered to be the most physical and reliable method and is often used as a standard to verify other empirical methods. However, it needs a lot of different input parameters. Hence, in the present study, a model based on most dominant meteorological variables influencing ETo is proposed to estimate ETo in the Middle South Saurashtra region of Gujarat (India). The performance of five different alternative methods and proposed model is compared with the standard FAO-56 Penman-Monteith method. The five quantitative standard statistical performance evaluation measures, Nash-Sutcliffe efficiency coefficient (E), coefficient of determination (R2), refined Willmott’s index (dr), root mean square of errors-observations standard deviation ratio (RSR) and mean absolute error (MAE) are employed in evaluating the performance of the selected methods and proposed model. The results show that the developed model and Hargreaves and Samani (1985) method with recalibrated parameters provide the most reliable results in estimation of (ETo) and it can be recommended for estimating (ETo) in the study region.

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