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Lou Y.,China Agricultural University | Kang S.,China Agricultural University | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water saving Agriculture in Hill Areas of Southern China | And 2 more authors.
Sichuan Daxue Xuebao (Gongcheng Kexue Ban)/Journal of Sichuan University (Engineering Science Edition) | Year: 2014

Connotation of water-saving irrigation was elaborated, and the factors of water-efficient irrigation developing were analyzed. Three items of sub-indices of engineering, agriculture and management water-saving were adopted. Firstly, main ingredients with thirty-three indices of the sub-indices were extracted to reduce the number of evaluation indices and establish index system of regional water-saving irrigation developing level evaluation model. Secondly, combination weights were formed from both of objective weight determined by entropy weight method and subjective weight determined by analytic hierarchy process method. Finally, the set pair analysis was selected for analysis. The evaluations showed that two regions are of general, seven regions are of relatively poor, twelve regions are of poor, and the rations of them in all regions are 9%, 33% and 58%, respectively. The results indicated that water-efficient irrigation developing level of every region is still lower, and the overall of Sichuan province is evaluated with level of poor. Therefore, the model has a strong practicality to evaluate the water-saving irrigation development in different regions.


Jia Y.,University of Sichuan | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Wei X.,University of Sichuan | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2016

In order to making true the exact calculation of reference crop evapotranspiration (ET0) and increase the accuracy with the lack of meteorological data in the large area, the Yangtze River Basin is divided into upstream, midstream and downstream according to the altitude of the stations. A new method of space distribution based on Inverse Distance Weighted Interpolation method is raised which can present every substream, including upstream, midstream and downstream. This method can include the connection of different stations. There are 102 meteorological stations which can provide 50 years of daily meteorological data from 1963 to 2013. In this research, we used the methods of Penman-Monteith (P-M), Hargreaves-Samani (H-S), Irmark-ALLEN (I-A), Pristley-Taylor (P-T), Makkink (M-K), Penman-Van Bavel (PVB), 1948 Penman (48-PM) to calculate daily ET0 of every stations of the Yangtze River Basin. The method of Penman-Monteith can be used to be the standard method to calculate standard daily ET0 to evaluate other methods because of its accuracy. The coefficient of Nash-Sutcliffe, the daily relative root mean square error, the consistency coefficient of Kendall can be used to evaluate the precision index of the method. The result showed that the best method of daily ET0 imitative effect compared with P-M is PVB in the three substreams, because the slope of the imitative equation of PVB in upstream is 0.946, the slope in midstream is 1.065, and the slope in downstream is 1.005. The method of Pristley-Taylor has a better effect in the midstream and downstream, and the slopes of the imitative equation are 1.030 and 1.201.The method of Makkink also has a good effect in the midstream and downstream, and the slopes are 0.857 and 0.936. The determination coefficient of daily ET0 imitative equation of these six methods all achieved very significant levels (α =0.01) in three substreams. The methods of Pristley-Taylor and Penman-Van Bavel have high calculation accuracy in all area of the Yangtze River Basin, and the highest absolute error of monthly ET0 is 0.55 mm/d using the method of Pristley-Taylor, at the same time the highest absolute error of monthly ET0 is 0.48 mm/d using the method of Penman-Van Bavel. The effect of the methods of Hargreaves-Samani and Irmark-ALLEN are worse than other methods to calculate monthly ET0 in the whole Yangtze River Basin. The method of Pristley-Taylor is the best method to calculate ET0 in the upstream of the Yangtze River Basin, because the daily relative root mean square error is 0.341 mm/d, the coefficient of Nash-Sutcliffe is 0.886, and the consistency coefficient of Kendall is 0.829. The method of Penman-Van Bavel is the best method to calculate ET0 in the midstream and downstream of the Yangtze River Basin. In the midstream, the daily relative root mean square error is 0.201 mm/d, the coefficient of Nash-Sutcliffe is 0.973, and the coefficient of Nash-Sutcliffe is 0.926. In the downstream, the daily relative root mean square error is 0.306 mm/d, the coefficient of Nash-Sutcliffe is 0.954, and the consistency coefficient of Kendall is 0.869. In the Yangtze River Basin, the relative error of Pristley-Taylor and Penman-Van Bavel are the lowest among these methods which are less than 35%, the relative error of is the highest among these methods which is more than 40%. In conclusion, the method of Pristley-Taylor and Penman-Van Bavel are the best methods to calculate ET0 in the Yangtze River Basin, the calculation process are simple at the same time. The method of Pristley-Taylor and Penman-Van Bavel can be a simplified recommendation of calculating ET0 in the Yangtze River Basin. © 2016, Chinese Society of Agricultural Engineering. All right reserved.


Feng Y.,Chinese Academy of Sciences | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Zhao L.,University of Sichuan | And 2 more authors.
Journal of Hydrology | Year: 2016

Reference evapotranspiration (ET0) is an essential component in hydrological ecological processes and agricultural water management. Accurate estimation of ET0 is of importance in improving irrigation efficiency, water reuse and irrigation scheduling. FAO-56 Penman-Monteith (P-M) model is recommended as the standard model to estimate ET0. Nevertheless, its application is limited due to the lack of required meteorological data. In this study, trained extreme learning machine (ELM), backpropagation neural networks optimized by genetic algorithm (GANN) and wavelet neural networks (WNN) models were developed to estimate ET0, and the performances of ELM, GANN, WNN, two temperature-based (Hargreaves and modified Hargreaves) and three radiation-based (Makkink, Priestley-Taylor and Ritchie) ET0 models in estimating ET0 were evaluated in a humid area of Southwest China. Results indicated that among the new proposed models, ELM and GANN models were much better than WNN model, and the temperature-based ELM and GANN models had better performance than Hargreaves and modified Hargreaves models, radiation-based ELM and GANN models had higher precision than Makkink, Priestley-Taylor and Ritchie models. Both of radiation-based ELM (RMSE ranging 0.312-0.332 mm d-1, Ens ranging 0.918-0.931, MAE ranging 0.260-0.300 mm d-1) and GANN models (RMSE ranging 0.300-0.333 mm d-1, Ens ranging 0.916-0.941, MAE ranging 0.2580-0.303 mm d-1) could estimate ET0 at an acceptable accuracy level, and are highly recommended for estimating ET0 without adequate meteorological data. © 2016 Elsevier B.V.


Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Zhao L.,University of Sichuan | Zhao L.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | And 2 more authors.
Sichuan Daxue Xuebao (Gongcheng Kexue Ban)/Journal of Sichuan University (Engineering Science Edition) | Year: 2016

The monthly meteorological data from 1960 to 2012 in 8 stations in Sichuan agricultural regions was used to calculate the precipitation satisfied degree, and the grain production and reduction due to drought in Sichuan from 1988 to 2007 were used to calculate the grain reduction rate in “wheat-rice” and “wheat-corn-sweet potato” cropping systems, respectively. The drought risk probability of the precipitation satisfied degree was calculated by normal distribution function, and the grain reduction rate due to drought was studied by information diffuse theory. The results showed that under the two cropping systems precipitation can't satisfy the crop water requirement in one year every five years in most agricultural regions of Sichuan province, so the irrigation is needed. In “wheat-rice” and “wheat-corn-sweet potato”, the probability of medium drought, heavy drought and severe drought is 39.7%, 10.9%, 4.9% and 32.7%, 6.1%, 3.2%, respectively. The precipitation satisfied degree is well related with the grain reduction rate. When the grain reduction rate shows medium or heavy drought, the precipitation satisfied degree anomaly must indicate the occurrence of drought. However, when the precipitation satisfied degree anomaly indicates the occurrence of drought, the grain reduction rate does not necessarily judge the medium or heavy drought. © 2016, Editorial Department of Journal of Sichuan University (Engineering Science Edition). All right reserved.


Li C.,University of Sichuan | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Wei X.,University of Sichuan | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2015

Reference crop evapotranspiration (ET0) is an important part of water cycle and water balance. Accurate estimation of ET0 becomes vital in planning and optimizing irrigation schedules and irrigation systems management. Numerous methods have been proposed for estimating ET0, among which Penman-Monteith (P-M) model recommended by Food and Agriculture Organization of the United Nations (FAO) in 1998 since it provids the highest accurate results across the world wherever in an arid or humid environment. But the main problems computing ET0 by P-M model are its complicated nonlinear process and requirements of many climatic variables. Thus, there is an urgent need to develop a much simpler and more appropriate model in areas with limited data, such as the Hargreaves-Samani (HS) method, which is modified in this paper. In order to obtain more accurate HS model of ET0 in hilly area of central Sichuan Basin, 3 parameters (including temperature index, temperature coefficient and temperature constant) were calibrated based on Bayesian Theory using daily meteorological data from 1953 to 2002. Then, the daily and monthly ET0 from 2003 to 2013 were computed by the modified HS model, original HS model and PM model. Compared with the value recommended by FAO (the temperature index, temperature coefficient and temperature constant are 0.0023, 0.5 and 17.8, respectively), the 3 parameters obtained from the modified HS model were much smaller, and increased by latitude (0.00213, 0.46 and 16.5 in north zone, 0.00217, 0.44 and 16.36 in central zone, 0.00212, 0.44 and 16.21 in south zone). The ET0 calculated by PM model was taken as the standard, the relative error of modified HS model decreased form 14.2%-60.9% to -1.1%-33.4% in north, 40.6%-92.6% to 16.9%-61.1% in central, 31.3%-96.0% to 8.5%-64.4% in south, and 32.1%-82.7% to 9.5%-52.6% in whole hilly area of central Sichuan Basin. Through the correlation analysis, the slope of regression curve between ET0 calculated by PM model and ET0 calculated by modified HS model were 1.16 in north (R2=0.91), 1.02 in central (R2=0.88), 0.99 in south (R2=0.88), and 1.13 in whole hilly area of central Sichuan Basin (R2=0.91), respectively. The trend analysis based on monthly ET0 showed that the trend of ET0 based on modified HS model was the same as that from PM model, which performed as the downwards Quadratic parabola in one year but increasing slightly in years from 2003 to 2013. The relative error of ET0 obtained from the modified and original HS model was above zero, and the former was smaller. Therefore, the modified Hargreaves-Samani model based on Bayesian Theory is more adaptive and accurate, and can be used as a simple method for the calculation of ET0 in hilly area of central Sichuan Basin. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved.


Feng Y.,University of Sichuan | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Gong D.,Chinese Academy of Sciences | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2015

Reference crop evapotranspiration (ET0) is an essential parameter of water resource planning and management. Accurate estimation of ET0 becomes vital in planning and optimizing irrigation schedules and irrigation systems management. Numerous methods have been proposed for estimating ET0, among which Penman-Monteith (P-M) model recommended by Food and Agriculture Organization of the United Nations (FAO) in 1998 is the best one. FAO accepted the P-M model as the standard and sole equation for ET0 estimation since it provided the most accurate results across the world wherever in an arid or humid environment. But the main problems for computing ET0 by the P-M model are its complicated nonlinear process and requirements of many climatic variables. Thus, it is urgent to develop a simpler and more appropriate model in areas with limited data especially in developing countries like China. In the current study, the applicability of extreme learning machine (ELM) in ET0 modeling based on limited data was assessed in the humid environment in hilly area of central Sichuan, China. In addition, four climate-based models (Hargreaves, Priestley-Taylor, Makkink and Irmark-Allen) and the ELM model were tested against the P-M model to study their performance by using three commonly used criteria: root mean square error (RMSE), coefficient of determination (R2) and efficiency coefficient (Ens). From the statistical results, the ELM model performed well in expressing the nonlinear relationship between ET0 and meteorological factors; when based on temperature data, the ELM model performed better than Hargreaves model which is an empirical temperature-based model. When radiation and temperature data were introduced in the ELM model, the error decreased significantly, and it was much more accurate than the Priestley-Taylor, Makkink and Irmark-Allen model. It was found that the ELM model, which required maximum air temperature, minimum air temperature and sunshine duration input variables, had the best accuracy and was the optimal approach to estimate ET0 when the complete weather data required by the P-M model were not available. The further assessment of ELM was conducted and it was confirmed that the model could provide a powerful tool in estimating ET0 in the humid environment like hilly area of central Sichuan when lack of meteorological data. The research could provide a reference to accurate ET0 estimation in hilly area of central Sichuan. ©, 2014, Chinese Society of Agricultural Engineering. All right reserved.


Feng Y.,Chinese Academy of Agricultural Sciences | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Gong D.,Chinese Academy of Agricultural Sciences | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2016

As the only connecting parameter between energy balance and water balance, evapotranspiration (ET) is the most excellent indicator for the activity of climate change and water cycle, and therefore, accurate estimation of ET is of importance for hydrologic, climatic and agricultural studies. ET is commonly computed by reference evapotranspiration (ET0), and this paper investigated the performance of generalized regression neural network (GRNN) algorithm in modeling FAO-56 Penman-Monteith (PM) ET0 only with the temperature data in 19 meteorological stations located at the western, middle, and eastern part of Sichuan basin, southwest China. Data of meteorological variables containing maximum air temperature (Tmax), minimum air temperature (Tmin) for the period of 1961-1990 were used as input variables to train the GRNN model, and data for the period of 1991-2014 were used to validate the GRNN model. The performance of GRNN model was compared with the empirical temperature-based Hargreaves (HS1) and calibrated Hargreaves (HS2) models considering the PM ET0 as the benchmarks. The evaluation criteria of root mean squared error (RMSE) and model efficiency (Ens) were used for the comparison. The statistical results indicated that the RMSE values of the GRNN, HS1 and HS2 models were 0.41, 1.16 and 0.70 mm/d, respectively, and the Ens values of the GRNN, HS1 and HS2 models were 0.88, 0.13 and 0.67, respectively, which manifested the performance of the GRNN model was encouraging. The RMSE of the HS1 model was the biggest every year at temporal scale in all 3 sub-zones of Sichuan basin, followed by the HS2 model, and the RMSE of the GRNN model was the smallest; the Ens of the GRNN model was bigger than HS1 and HS2 model every year at temporal scale in all 3 sub-zones. The RMSE of the HS1 model was the biggest in every meteorological station of Sichuan basin at spatial scale, followed by the HS2 model, and the RMSE of the GRNN model was the smallest; the Ens of the GRNN model was bigger than HS1 and HS2 model in every meteorological station at spatial scale. Based on the RMSE and Ens, the errors of GRNN, HS1 and HS2 models showed an increasing tendency, which indicated the error of all the 3 models would become bigger in the future. The ranges of the ET0 values computed by the PM, GRNN, HS1 and HS2 model were 695~837, 709~820, 1029~1178 and 818~975 mm, all of which showed an increase tendency with a rate of 2.7, 2.0, 2.2 and 2.4 mm/a respectively in recent 24 years. Compared with the PM model, GRNN, HS1 and HS2 overestimated the ET0 value by 0.8%, 45.1% and 17.3%, respectively. The analysis of the performance of GRNN, HS1 and HS2 models at temporal and spatial scale confirmed the good ability of the GRNN model in estimating ET0 when the data for PM model were not fully available, and thus the GRNN model should be adopted to compute ET0. This paper can provide the reference for estimating the crop water requirement in Sichuan basin when only temperature data are accessible. © 2016, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.


Feng Y.,Chinese Academy of Agricultural Sciences | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Gong D.,Chinese Academy of Agricultural Sciences | Wei X.,University of Sichuan
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2016

Reference evapotranspiration (ET0) is an important component of agricultural water management, analysis on the change trend and spatial distribution characteristics of ET0 under the climate change scenarios can be used as references for estimation of crop water requirement. In the current study, daily meteorological data from 11 meteorological stations were obtained from 1961 to 2013 in hilly area of central Sichuan, Southwest China. ET0 during 1961-2013 were calculated by FAO-56 Penman-Monteith equation, ET0 during 2014-2099 were downscaled from HadCM3 (Hadley Centre Coupled Model version 3) outputs under two emission scenarios of high (A2) and low (B2) emission by statistical downscaling model (SDSM 4.2 software). Temporal trend and spatial distribution of ET0 during 1961-2099 were analyzed by Mann-Kendall trend test and Inverse Distance Weighted Interpolation method. The results indicated that ET0 decreased non-significantly (P>0.05) during baseline period (1961-2010) with a tendency rate of -5.2 mm/10a, annual mean ET0 was 757 mm, and the highest values of ET0 were found in the north and south region while the lowest values were in the central region; HadCM3 projected a statistically significant (P<0.05) and continuous increase in ET0 during 2020s (2011-2040), 2050s (2041-2050) and 2080s (2071-2099) with a rate of 8.9, 17.5 and 13.2 mm/10 a under A2 emission scenario and 12.1, 21.5 and 4.3 mm/10 a under B2 emission scenario, respectively. Averaged for the whole area, the projected increase were 7.9%, 10.9% and 16.7% under A2 emission scenario and 7.1%, 4.9% and 12.8% under B2 emission scenario for the three periods 2020s, 2050s and 2080s, respectively. The increase under A2 emission scenario was slightly higher than that under B2 scenario which may be caused by higher air temperature and solar radiation under A2 emission scenario. The highest values of ET0 were found in the northwest and south region while the lowest values were in the central region both under A2 and B2 emission scenarios for the three periods 2020 s, 2050 s and 2080 s, and the greater increase in ET0 was found in south central region while lower increase was in central, south and north region both under A2 and B2 emission scenarios for the three periods 2020 s, 2050 s and 2080 s. GCMs and SDSM were applied to project the climate changes in the future, which may lead some uncertainties in the results due to the uncertainties of GCMs, SDSMs and selection of predictors. In order to reduce the uncertainties of climate projection and improve the simulating abilities of SDSMs on future climate, more GCMs, downscaling methods and emission scenarios should be selected for the projection of ET0. This research provided possible temporal trend and spatial distribution of ET0 in the future in hilly area of central Sichuan, which can provide valuable information for irrigation schedule planning. © 2016, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.


Feng Y.,University of Sichuan | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Wei X.,University of Sichuan | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2014

Reference crop evapotranspiration (ET0) is of importance to estimate crop water requirement and make plans of irrigation scheme. Research on temporal and spatial variation of ET0 is important for regional agricultural water management and regional water allocation. The purpose of this study was to make a better understanding of the variation characteristics of ET0 in hilly area of central Sichuan where the agricultural water mostly depends on irrigation. Penman-Monteith equation recommended by Food and Agriculture Organization (FAO) in 1998 was applied to calculate the daily ET0 for 13 meteorological stations within 52 years (1961-2012). Kriging of GIS was introduced to draw the maps of ET0 that could present a clear spatial distribution of ET0. Mann-Kendall trend test was used to analyze temporal distribution characteristics of ET0, and the causes of ET0 change were manifested by sensitivity analysis based on path analysis method. The results showed that: annual ET0 change had a conspicuous decreasing trend in hilly area of central Sichuan in the past 52 years, especially in Langzhong,Yibin and Ziyang station where ET0 decreased significantly (α=0.05). However, in Mianyang station, ET0 increased within 52 years; The temporal distribution characteristics indicated that, during 1961-1979, ET0 increased gradually then decreased until 2003. The trend of ET0 change in a year was a single peak curve, and the change accounting for 85.82% of the year was mostly between March and October. The maximum of ET0 was 3.46 mm/d in July and the minimum was 0.79 mm/d in December. The spatial distribution of ET0 revealed that ET0 decreased gradually from northeast and southeast to the center. During 1961-1970 and 1981-1990, there were several sudden changes in spatial distribution. Compared with the average value within 52 years, the ET0 was smaller in Bazhong station but bigger in Ziyang and Neijiang station. Considering the uneven distribution of ET0 within a year and the sudden changes, the conclusion could be attained that the variation characteristics of ET0 in hilly area of central Sichuan was influenced by the change of weather greatly. The path analysis between meteorological factors and ET0 revealed that the path coefficient of sunshine duration (n), wind speed (u2), relative humidity (RH) and temperature (T) were 0.61, 0.37, -0.25 and 0.019, respectively. Their overall contribution to R2 were 0.48, 0.28, 0.13 and 0.001, respectively. When n, u2, RH and T were removed respectively in sensitivity analysis, R2 values were reduced from 0.89 to 0.596, 0.81,0.84 and 0.88, respectively. R2 had the biggest change when n was removed, and thus ET0 was more sensitive to n and n was the key meteorological factor affecting ET0 in hilly area of central Sichuan. The coefficient of determination between actual and estimated ET0 in four quarters was 0.93, 0.97, 0.96 and 0.94, respectively, when average quarter temperature instead of T was used to estimate ET0, which indicated that it was reasonable to use average quarter temperature to calculate ET0 when meteorological data in hilly areas of central Sichuan was lacking. This research provided information for agricultural production in hilly area of central Sichuan.


Li C.,University of Sichuan | Cui N.,University of Sichuan | Cui N.,Provincial Key Laboratory of Water Saving Agriculture in Hill Areas of Southern China | Feng Y.,University of Sichuan | Wei X.,University of Sichuan
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2016

Reference crop evapotranspiration (ET0) is an important parameter for water cycle and water balance. Accurate estimation of ET0 becomes vital in water resource evaluation and agricultural water resource utilization. Numerous methods have been proposed for estimating ET0, among which the Penman-Monteith (P-M) model recommended by Food and Agriculture Organization of the United Nations (FAO) in 1998 is the best one to compute ET0 at present due to its foundation in physics and comprehensively considering the relationships. FAO has accepted the P-M model as the standard equation for the estimation of ET0 since it provides the highest accurate results across the world no matter in an arid or humid environment. But the main problems on computing ET0 by the P-M model are its complicated nonlinear process and requirements of many climatic variables. Thus, there is an urgent need to develop a much simpler and more appropriate model in the areas with limited data. This paper compares the accuracy of the Hargreaves-Samani (HS) method, Makkink method, Priestley-Taylor (PT) method, Irmark-Allen (IA) method, Penman-Van Bavel (PVB) method and 48PM method. To obtain the best calculation methods and assess its adaptability, the Sichuan Province is divided into 4 regions (including the eastern basin (I), the moist mountainous area (II), the southwest valley area (III) and the western plateau zone (IV)), and the daily ET0 in 46 stations from 1954 to 2013 is calculated. Then, this paper takes the ET0 calculated by the P-M model as a standard, and makes a comparison among the 6 methods. The results show that all methods are obviously variable in different regions. The HS method, the PT method and the PVB method are more accurate while the 48 PM method, the IA method and the Makkink method have a larger error. Unfortunately, there is no method that performs good in all of 4 regions except the PT and PVB methods due to the different terrain or climate in different area. The HS method is relatively accurate in Area I and II which have a lower altitude; the 48PM method has a relative error more than 50% in the shallow hilly area and plateau area, while its relative error is lower in basin areas, such as -25%-11.1% in Batang and Dege, and 11.2%-37.5% in southeast area. Finally, we find that the best methods in the area of I and II are the HS method (root mean square error (RMSE) 0.58 mm/d, mean absolute error (MAE) 0.45 mm/d, mean relative error (MRE) 0.02) and the PVB method (RMSE 0.61 mm/d, MAE 0.39 mm/d, MRE-0.15), and the best method in the area of III and IV is the PT method (RMSE 0.55-0.6 mm/d, MAE 0.44-0.45 mm/d, MRE 0.02-0.06). Therefore, the HS method can be attained as the best one for calculating ET0 in the eastern basin, the PVB method can be the best one for the moist mountainous area, and the PT method can be similarly chosen in the southwest valley area and the western plateau zone in Sichuan. © 2016, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.

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