Proper methods and its calibration for estimating reference evapotranspiration using limited climatic data in Southwestern China

Proper methods for estimating reference evapotranspiration (ET₀) using limited climatic data are critical, if complete weather data are unavailable. Based on the weather data of 19 stations in Guizhou Province, China, several simple methods for ET₀ estimation, including the Hargreaves, Priestley–Taylor, Irmak–Allen, McCloud, Turk, and Valiantzas methods, were involved in comparison with the standard FAO-56 Penman–Monteith (PM) method. The Turk equation performs well for estimating ET₀ in humid locations. Both the Turk method and the Valiantzas method initially performed acceptably with mean root-mean-square difference (RMSD) of 0.1472 and 0.1282 mm d^?1, respectively, with only requiring parameters of temperature (T), relative humidity (RH), and sunshine duration (n). The corresponding calibration formulas to Turk and Valiantzas method were suggested as the most appropriate method for ET₀ estimation with the RMSD of 0.0098 and 0.0250 mm d^?1, respectively. The local calibrated Hargreaves–Samani method performed well and can be applied as the substitute of FAO-56 PM method under the condition that only the daily mean, maximum, and minimum temperatures were available, and local calibrated McCloud method was acceptable if only the mean temperature was available.     

Evaluation and calibration of simple methods for daily reference evapotranspiration estimation in humid East China

The current study aims to improve the performance of simple methods for the estimation of daily reference evapotranspiration (ET₀) in humid East China, namely Priestley–Taylor 1972 (P-T 1972), Hargreaves–Samani 1985 (H-S 1985) and Turc 1961 (TU 1961). These methods were evaluated and calibrated based on well-watered grass lysimeter experiments. The FAO-56 Penman–Monteith equation (FAO-56 PM) is the best method, and the radiation-based methods (TU 1961 and P-T 1972) perform much better than the temperature-based method (H-S 1985). In the simple methods, the coefficients are calibrated to: 1.34 for P-T 1972; 0.0186, 23.47 and 17.06 for TU 1961; and 0.0027 and 0.449 for H-S 1985. The locally calibrated TU 1961 and P-T 1972 perform much better than the original, with either the observed ET_0r or the ET_0c obtained by FAO-56 PM as standard. However, local calibration does not significantly improve the performance of the H-S 1985 method. In humid East China, FAO-56 PM is the best method for daily ET₀ calculation. TU 1961, especially if locally calibrated, is the optimal choice as a simple substitute for FAO-56 PM when solar radiation is available. Otherwise, serious local calibration is strongly recommended before applying H-S 1985 for daily ET₀ estimation.     

Calculation of the shortwave radiation flux from weather station data in evapotranspiration studies

A statistical relationship between the measured daily flux of short-wave radiation, the extra-terrestrial radiation and the duration of bright sunshine was established. Used were continuous daily data from the Weather Service station of Göttingen, West Germany (51°33′N, 9°57′E) for the period 1969–1980. The analysis was similar to the procedure proposed by Kimball (1927). Daily values for the extra-terrestrial short-wave radiation and for the maximum possible duration of sunshine were calculated from expressions developed by Swift (1976). It was found that in Göttingen, for an assumed solar constant radiative flux of 1352 W.m^?2, the constants A and B in the Kimball equation were 0.18 and 0.47. It was also found that these average values varied from year to year and also for different seasons of the year. It is pointed out that if radiation values calculated with the Kimball equation are used to estimate the daily evapotranspiration, care must be taken that proper regional constants are used.     

Estimation of daily reference evapotranspiration by neuro computing techniques using limited data in a semi-arid environment

In this paper, the daily reference evapotranspiration (ET₀) for Bulawayo Goetz was estimated from climatic data using neuro computing techniques. The region lacks reliable weather data and experiences inconsistencies in the measuring process due to inadequate and obsolete measuring equipment. This paper aims to propose neuro computing techniques as an alternative methodology to estimating evapotranspiration. Firstly, ET₀ was calculated using FAO-56 Penman-Monteith (PM) equation from available climatic data. Data was divided into training, testing and validation for neuro computing purposes. The study also investigated the effect of different normalisation techniques on neuro computing ET₀ estimation accuracy. In another application, neuro-computing ET₀ estimates were compared against those obtained using empirical methods and their calibrated versions. The Z-score normalisation technique for all data sets gave best results with a Multi-layer perceptron (5–5-1) model having RMSE, MAE and R² values in the range 0.12–0.25 mm day^?1, 0.08–0.15 mm day^?1 and 0.94–0.99 respectively. There were no significant differences in ET₀ estimation accuracy by neuro computing techniques due to normalisation technique. The Neuro computing techniques were superior to empirical methods in ET₀ estimation for Bulawayo Goetz. The Neuro computing techniques are recommended for use in cases of limited climatic data at Bulawayo Goetz.     

小流域水文循环过程中蒸散发量模拟方法评价

蒸散发(ET)在农业灌溉和水资源管理中起着重要作用。ET可通过FAO-Penman-Monteith方法(ET_(FPM))进行准确估算,ET_(FPM)方法是ET估算的标准参考方法,此方法需要提供更为详实的气象数据。对于ET的估算,需要寻找使用较少的输入数据,而不会影响预测准确性的替代方法。研究运用5个基于辐射的模型,包括Makkink(ET_(MAK))、Priestley和Taylor(ET_(PT))、Abtew(ET_(ABT))、Jensen-Haise(ET_(JH))、McGuinness和Bordne(ET_(MB)),3个基于温度的模型,包括Hargreaves and Samani(ET_(HS))、Hamon(ET_(HAM))和Linacre(ET_(LIN)),以及1个基于空气动力学的模型Penman(ET_(PEN)),通过使用韩仓河流域周边6个气象水文站的长期数据,将选取的模型与ET_(FPM)模型在月尺度和生长季节尺度上进行比较评价。结果表明,ET_(JH)、ET_(HAM)分别是67%,33%研究区域每月ET的最佳预测方法。在研究区域中,基于辐射的方法优于基于温度的方法。植被生长季节ET累积值表明,Jensen-Haise和Hamon方法在暖季和秋冬季生长期表现最佳,而春季生长期最佳预测方法仅包括Jensen-Haise方法。最佳替代方法和ET_(FPM)方法之间的差异表明,最佳替代方法在某些地区的估算可信度不高,因此在使用之前应考虑ET模型可预测性能的时空变化。     

Adjustment of radiation use efficiency of winter wheat by air temperature at different irrigation regimes and nitrogen rates

In this research, radiation use efficiency (RUE) of winter wheat was determined under different irrigation regimes and nitrogen application rates in experimental field at southwest Iran (semi-arid region) in 2009–2010 and 2010–2011. The experiment was laid out as a split plot design, with irrigation treatments as main plots and N fertilization as sub-plots with three replications. Irrigation treatments were 1.2 (I4), 1.0 (I3), 0.8 (I2), and 0.5 (I1) times of the full irrigation requirements and N treatments were 0 (N1), 46 (N2), 92 (N3), and 136 (N4) kg ha^?1. Air temperature had significant effects on RUE that was adjusted by multiplication of hourly temperature factor to the hourly values of solar radiation (RUE _a ). The values of RUE _a were significantly different from the values of RUE in both growing seasons. The values of RUE _a ranged from 1.44 to 1.83 g MJ^?1 and 1.45 to 1.81 g MJ^?1 in 2009–2010 and 2010–2011, respectively. In both growing seasons, minimum and maximum values of RUE were at I1N1 and I4N4 treatments, respectively. The methods of daily maximum and minimum air temperature were modified for considering the effects of air temperature on RUE at locations where hourly air temperature and radiation were not available.     

Determination of the potential evapotranspiration and crop coefficient for saffron using a water-balance lysimeter

Agriculture is the major consumer of water and it is possible to decrease water consumption in this sector by proper irrigation scheduling. Irrigation scheduling is based on crop water requirements. Saffron is an important crop in Iran. The main purpose of this study was to determine the potential evapotranspiration and crop coefficient for saffron using single and dual crop coefficients, in Badjgah region, College of Agriculture, Shiraz University, Shiraz, Iran. Three water-balance lysimeters were used for this experiment in a two-year study. Total saffron potential evapotranspiration values were 523 and 640 mm in the first and second growing seasons, respectively. The maximum evapotranspiration rates for saffron were 4.5 and 6.1 mm d^?1 in the first and second growing seasons, respectively. Based on the results of this study, different saffron growing stages for evapotranspiration were 30, 40, 70 and 60 days. Crop coefficient (K _c) values for the initial, mid- and late-season growth stages were 0.41–0.45, 0.93–1.05 and 0.29–0.31 in both years, respectively. Basal crop coefficient (K _cb) values for the initial, mid- and late-season growth stages were 0.15–0.16, 0.41–0.65 and 0.15–0.17 in both years, respectively.     

蒸散量双线性曲面回归模型的改进及验证

潜在蒸散发是水文循环和能量循环的一项重要组成,准确估算蒸散发对农业水资源有效利用具有重要的理论和现实意义。为获得精度稳定可靠的蒸散发估计值同时只需较少的气象资料,以沂沭河上游流域(临沂控制站)为研究区,提出改进的双线性曲面回归模型(bilinear surface regression model,BSRM)计算站点的潜在蒸散量。以实测蒸发数据折算的陆面潜在蒸散量为标准,同时以彭曼公式(P-M)为参考与之对比,检验和评价3种BSRM模型的精度,并分析各气象因子对潜在蒸散量的影响。结果表明:3种BSRM模型中,基于日照百分率、气温和相对湿度建立的双线性曲面回归模型模拟精度最高,以基于日照百分率计算的太阳辐射、气温、相对湿度建立的双线性曲面回归模型次之,以基于Hargreaves-Allen方程计算的太阳辐射、气温和相对湿度建立的双线性曲面回归模型模拟精度最差。基于日照百分率、气温和相对湿度建立的BSRM模型的模拟精度略优于P-M公式,但所需的气象因子较少,计算方法简单;且受气象因子的变化影响较少,模拟精度稳定可靠,是一种有效的替代方法。     

利用估算的太阳辐射计算浑善达克沙地参考作物蒸散速率的精度分析

利用FAO推荐的Penman—Monteith公式。以内蒙浑善达克沙地三个气象站太阳辐射实测值计算的参考作物蒸散速率（ET0）为背景值，分析了利用估算的太阳辐射计算ET0时的精确度。结果表明：太阳实际日照时数短时。ET0的计算误差比较明显，必须利用适当的方法予以修正。     

Short-term forecasting of daily crop evapotranspiration using the ‘Kc-ETo’ approach and public weather forecasts

Short-term forecasting of daily crop evapotranspiration (ET_c) is essential for real-time irrigation management. This study proposed a methodology to forecast short-term daily ET_c using the ‘K_c-ET_o’ approach and public weather forecasts. Daily reference evapotranspiration (ET_o) forecasts were obtained using a locally calibrated version of the Hargreaves-Samani (HS) model and temperature forecasts, while the crop coefficient (K_c) was estimated from observed daily ET_o and ET_c. The methodology was evaluated by comparing the daily ET_c forecasts with measured ET_c values from a field irrigation experiment during 2012–2014 in Yongkang Irrigation Experimental Station, China. The overall average of the statistical indices was in the range of 0.96–1.27 mm d^?1 for the mean absolute error (MAE), 1.53–2.55 mm d^?1 for the mean square error (MSE), 1.77–2.30 mm d^?1 for the normalized mean square error (NMSE), 27.5–29.4% for the mean relative error (MRE), 0.71–0.44 for the correlation coefficient (R) and 0.46–0.05 for the mean square error skill score (MSESS). Sources of error werewere K_c estion, temperature forecasts and HS model that does not consider wind speed and humidity, and.the largesourceof error is K_c determination, which suggested that care should be taken when forecasting ET_c with estimated K_c values in the study area.     

基于气象资料的日辐射模型在中国西北地区适用性评价

地表总辐射(Rs)是作物生长模型率定、蒸散量估算、灌溉制度制定和太阳能资源利用的重要基础数据。为有效提高辐射资源利用率,该文基于中国西北地区10个气象站点1993-2016年气象数据对9种不同日辐射模型进行适用性评价。采用非线性回归分析法对Bristow-Campbell(B-C)模型进行参数属地化修正,得到B-C校正模型。模型适用性评价结果表明:9种模型在西北地区的辐射模拟值和实测值均呈极显著相关(P0.01);基于日照时数的日辐射模型(?ngstr?m-Prescott、Ogelman、Bahel、Louche、Almorox-Hontoria、Glower-Mc Culloch,其R2介于0.875~0.954)计算精度高于基于温度的模型(Hargreaves-Samani、Annandale、Bristow-Campbell,其R2介于0.652~0.813);其中基于日照时数的模型中Bahel模型精度最高,其次是Ogelman和Glower-Mc Culloch模型,其RMSE分别为2.282、2.309和2.313 MJ/(m~2·d),n RMSE分别为14.0%、14.2%和14.2%,MAE分别为1.666、1.701和1.697 MJ/(m~2·d),Nash-Sutcliffe系数(NS)分别为0.905、0.903和0.902;基于温度的日辐射模型中B-C校正模型精度最高,其RMSE为3.819 MJ/(m~2·d),n RMSE为23.3%,MAE为2.680 MJ/(m~2·d),NS为0.741。因此,西北地区日辐射计算当仅有日照时数资料时推荐使用Bahel模型,当仅有温度资料时推荐使用Bristow-Campbell校正模型。     

Evaluation of some equations for estimating evapotranspiration in the south of Iran

The Penman–Monteith (PM) equation is the most common method of estimating reference crop evapotranspiration (ET _o) for different climates of the world. This equation needs full weather data, however, few stations with complete weather data exist in Fars Province, in the south of Iran. Therefore, other equations based on more readily available weather data, such as temperature and rainfall, can be used instead of the PM equation in Fars Province. Four calibrated equations have been proposed in previous studies for Fars Province using weather data up to 2000. These equations were the Hargreaves equation (H), a new equation based on monthly temperature and rainfall (R), the Thornthwaite equation (T) and the Blaney–Criddle equation (B). Using weather data for 2001 to 2006 from 14 stations in Fars Province and outside the province, this study determined the best equations for estimating ET _o in each month and each station, rather than using the PM equation. The results revealed that equations H, R, T and B showed a good correlation to the PM equation, and can be used to estimate monthly ET _o in the study area. Also, the best equation for each location in Fars Province in each month of the year can be determined by using prepared distribution maps. Furthermore, the results showed that there was no specific relationship between the climate at the station and the best equation for estimating ET _o.     

Calibration of Hargreaves–Samani and Priestley–Taylor equations in estimating reference evapotranspiration in the Northwest of Iran

Accurate estimation of reference evapotranspiration (ET_o) is essential for water resources management and irrigation systems scheduling, especially in arid and semiarid regions such as Iran. In the present research, constant coefficients of Hargreaves–Samani (C_H–S) and Priestley–Taylor (C_P–T) equations were locally calibrated to estimate the ET_o based on the FAO–Penmen–Monteith (PM) method as standard method. For this purpose, meteorological data of eight synoptic stations located in the northwest of Iran were used during the period of 1997–2008. The outcomes showed that the values of C_H–S and C_P–T were 0.0026 (instead of 0.0023) and 1.68 (instead of 1.26), respectively. Also, at stations with high wind speed, the values of calibrated coefficients of C_H–S and C_P–T were maximum. Then, the estimated ET_o values using adjusted C_H–S and C_P–T coefficients were compared to the obtained actual ET_o values by PM method using root mean square error and mean bias error indices. The results indicated that the new calibrated H–S and P–T equations have good agreement with the PM method for estimation of the ET_o. Moreover, the equation of Ravazzani et al. was calibrated in the studied region. It was concluded that in general, the mentioned equation was shown better performance than original H–S equation.     

Evaluation of inoculation with nitrogen and phosphorus biofertilizers on yield and radiation use efficiency of black cumin (Nigella sativa L.) under Mashhad climatic conditions

The purposes of this study were evaluate the effects of biofertilizers inoculation on growth indices, yield and radiation use efficiency (RUE) in black cumin under Mashhad climatic conditions. This field experiment was carried out based on a randomized complete block design with three replications. This experiment was performed at Agricultural Research Station, Ferdowsi University of Mashhad, Iran, during two growing seasons 2007–2008 and 2008–2009. Treatments were (A) Azotobacter paspali, (B) Azospirillum brasilense, (C) Rhizophagus irregularis, A + C, B + C, A + B, A + B + C and control. In all treatments, except control, 100 g of seeds were inoculated with15 mg of each biofertilizer. Results indicated that leaf area index (LAI) and accumulative dry matter (DM) showed an increasing trend up to 1863°Cd and a short declining trend afterwards. The relation between accumulative DM and absorbed photosynthesis active radiation (PARa) was linear. Radiation use efficiency (RUE) fluctuated from 0.55 gMJ^?1 (control) to 0.89 gMJ^?1 (B+C). Inoculation with biofertilizers enhanced root development and hence availability of moisture and nutrients, particularly nitrogen and phosphorus. Since these ecological fertilizers produce many growth regulators for the plant which promote LAI and accumulative DM and therefore yield, PARa and RUE enhanced.     

四川省不同区域地表太阳总辐射模型适用性评价

选用1994−2016年四川省7个辐射站气象数据,在3个辐射区（川西高原I区、川东盆地II区和川西南山地III区）中评价了6种地表太阳总辐射（Rs）估算模型在3种天气类型（晴、多云、阴）下的适用性,并分析基于天气类型的组合模型在不同区域的模拟效果,以探寻最适宜全省不同区域的Rs估算方法。结果表明：（1）各经验模型在四川省整体表现良好（决定系数R2介于0.554～0.934,P <0. 001）,I区（甘孜和红原站）模拟效果最好的为日照时数模型A−P（平均绝对误差MAE为2.210±0.714MJ∙m⁻²∙d⁻¹）,II区（成都、绵阳和泸州站）、III区（峨眉山和攀枝花站）模拟效果最佳的均为混合模型Chen（II区MAE为1.510±0.027MJ∙m⁻²∙d⁻¹,III区为1.930±0.006MJ∙m⁻²∙d⁻¹）;（2）6个模型在四川省3种天气类型下的模拟效果呈晴天>多云>阴天的规律,日照时数模型（A−P和Ba模型）能更好地模拟晴天时的Rs,混合模型（Chen和Ab模型）则在多云和阴天时模拟效果更佳,I区在晴天、多云、阴天3种天气下模拟效果最好的模型分别是A−P（整体评价指标GPI为0.850）、Ab（1.294）、Ba（0.862）,II区分别为A−P（0.381）、Chen（1.358）、Chen（1.742）,III区分别为Chen（0.204）、Chen（0.857）、Chen（0.526）;（3）基于天气类型的组合模型（M新）模拟各区Rs的效果均比未组合前各模型的效果好（3个区GPI分别为0.558、0.582、0.134）。因此,推荐使用基于天气类型的组合模型来估算四川省Rs。     

Temperature,activity and field sighting in the mediterranean spur-thighed or common garden tortoise Testudo graeca L

Daylight observations on NW African and W Turkish populations of the Mediterranean spur-thighed tortoise Testudo graeca L. showed that activity, depending upon maturity, sex and size, is influenced by air temperature and sunshine. Tortoises are active above 18°C while refuge from sunshine during the middle of the day occurs above 28°C. Morning basking increases body temperature, which under glass in S England was shown to be thermoregulated at about 35°C. With movements in and out of sunshine, most heat is dissipated through the plastron. Field sighting frequency (no.man-h^?1) as a relative index of abundance in low density populations is influenced by activity and behaviour type. This is discussed with regard to tortoise detection being increased by locomotory rustling and mating sounds in thick vegetation.     

利用地面气象资料建立四川省日总辐射计算模型

利用四川省6个辐射观测站2016?2018年日总辐射和地面气象资料,应用“个案排秩”、一元线性回归和逐步回归方法,建立四川省日总辐射计算模型（模型Ⅰ）,并按日照时数是否为0建立有日照总辐射计算模型（模型Ⅱ）和无日照总辐射计算模型（模型Ⅲ）。结果表明：模型Ⅰ、模型Ⅱ和模型Ⅲ均通过0.01水平显著性检验;模型Ⅰ、模型Ⅱ和模型Ⅲ回代检验的MAPE分别为12.62%、10.02%、16.34%,NRMSE分别为16.17%、12.23%、28.40%;4个典型日应用这3个模型的MAPE分别为7.59%、4.50%、36.53%,NRMSE分别为9.22%、5.93%、40.98%;对于4个典型日在日照时数为0时不用模型Ⅲ而改用模型Ⅰ、日照时数不为0时用模型Ⅱ,其MAPE为5.79%、NRMSE为7.47%,比全部资料用模型Ⅰ模拟分别提高1.80个和1.75个百分点。建立的3个日总辐射计算模型均具有应用价值;四川省日总辐射最佳模拟方法是日照时数为0时用模型Ⅰ计算,日照时数不为0时用模型Ⅱ计算;海拔、天气状况和日照长短决定四川各地日总辐射量的大小,其中海拔和天气状况是造成四川各地日总辐射差异的主要因素。     

基于GEP和地理位置信息的湘鄂地区月参考作物腾发量模拟计算

参考作物腾发量(ET0)是计算植被蒸散发的关键因子,准确估算ET0对水资源管理、灌溉制度设计等具有重要意义。本研究利用湘鄂地区46个气象站点1955—2005年的逐月气象数据,包括月最高气温、最低气温、平均风速、日照时数以及相对湿度,用FAO-56 Penman-Monteith法计算各站的逐月ET0值。然后结合基因表达式编程(GEP)算法挖掘公式的能力,以各站点的地理位置信息(纬度、经度、海拔)及月序数为输入,以多年逐月平均ET0值为输出,建立基于地理位置信息的月ET0模型,并与传统ET0模型的计算结果进行比较。结果表明,所建立的模型具有足够的精度,校正、检验阶段的决定系数(R2)和均方根误差(RMSE)分别为0.934、0.951和10.050 mm、8.628 mm;与Hargreaves和Priestley-Taylor法相比,基于地理位置信息建立的GEP模型的结果均方根误差最小,变化范围为8.628~9.967 mm。本研究所建立的月ET0模型具有明确的表达式,简单易用,在湘鄂地区仅利用地理位置信息计算逐月ET0是可行的,可以利用该模型进行月尺度的灌溉制度设计和植被蒸散发的估算。     

Effect of nitrogen and wheat residue on cotton (Gossypium hirsutum L.) yield and weed control

Wheat (Triticum aestivum L.) residues and nitrogen (N) management are the major problems in the southern part of Iran where irrigated wheat–cotton (Gossypium hirsutum L.)–wheat rotation is a common practice. A 2-year (2009–2011) field experiment was conducted as a split plot design with four replications at a cotton field (Darab), Fars Province, Iran, to determine the influence of different rates of wheat residue (0%, 25%, 50%, and 75%) incorporation and N rates (150, 200, 300, and 400 kg ha^?1) on weed suppression, yield, and yield components of cotton. Results showed that a higher residue incorporation and a lower N rate improved weed suppression in both years. For treatments receiving 150 kg N ha^?1 and 75% of wheat residues (2250 kg ha^?1), weed biomass and density were significantly lower compared to treatments receiving 400 kg N ha^?1. The highest cotton lint yield (about 2400–2700 kg ha^?1) was obtained by 300 kg N ha^?1 in the absence of residue application, in both years. Incorporation of 25% of wheat residue (750 kg ha^?1) and application of 300 kg N ha^?1 are recommended to guarantee an optimum level of cotton lint yield and weed suppression in a wheat–cotton–wheat rotation in this region.     

Comparison of artificial neural networks and prediction models for reference evapotranspiration estimation in a semi-arid region

Estimation of reference evapotranspiration (ET_o) is essential for determination of crop water requirements. In this research, Penman–FAO (P-FAO) and Penman–Monteith (PM) equations were calibrated and validated by lysimeter-measured ET_o with six and four weather parameters. Furthermore, two input structures (six and four weather parameters) to artificial neural networks (ANNs) were investigated. Results showed that the accuracy of the PM equation is greater than that of the P-FAO equation. An empirical equation was developed to estimate daily ET_o using mean daily temperature and relative humidity, and sunshine hours. The accuracy of the equation to estimate daily ET_o using smooth weather data is greater than that of an equation using original data. Furthermore, ANNs were able to estimate ET_o properly. The accuracy of ANNs with six inputs is higher than that obtained using the P-FAO equation and is similar to that determined using the PM equation. A decrease in number of inputs to ANNs generally decreased the accuracy of estimation, however, ANNs were able to estimate ET_o properly when wind speed and solar radiation were unavailable. Furthermore, the accuracy of ANNs, with four input parameters is greater than that obtained using the PM equation and is similar to that obtained with P–FAO and the developed empirical equations.