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1.
Two different artificial neural network (ANN) techniques, multi-layer perceptrons (MLP) and radial basis neural networks (RBNN), are employed in the estimation of monthly pan evaporation. The monthly climatic data, air temperature, solar radiation, wind speed, pressure and humidity, of three stations operated by the U.S. Environmental Protection Agency in California are used as inputs to the ANN models to estimate monthly evaporation. In the first part of the study, the accuracy of MLP and RBNN are compared with each other. The multi-linear regression (MLR) and the Stephens–Stewart (SS) methods are also considered for the comparison. The concern of second part of the study is to investigate the ability of neural computing techniques, MLR and SS models in evaporation estimation using data from nearby station(s). The performances of the models are evaluated using mean square errors, mean absolute relative errors and determination coefficient (R 2). The effect of periodicity on model’s estimation performance is also investigated. Based on the comparisons, it is found that the MLP and RBNN computing techniques could be employed successfully in modeling monthly evaporation process.  相似文献   

2.
The study investigates the ability of artificial neural networks (ANN) with artificial bee colony (ABC) algorithm in daily reference evapotranspiration (ET0) modeling. The daily climatic data, solar radiation, air temperature, relative humidity, and wind speed from two stations, Pomona and Santa Monica, in Los Angeles, USA, are used as inputs to the ANN–ABC model so as to estimate ET0 obtained using the FAO-56 Penman–Monteith (PM) equation. In the first part of the study, the accuracy of ANN–ABC models is compared with those of the ANN models trained with Levenberg–Marquardt (LM) and standard back-propagation (SBP) algorithms and those of the following empirical models: The California Irrigation Management System (CIMIS) Penman, Hargreaves, and Ritchie methods. The mean square error (MSE), mean absolute error (MAE) and determination coefficient (R2) statistics are used for evaluating the accuracy of the models. Based on the comparison results, the ANN–ABC and ANN–LM models are found to be superior alternative to the ANN–SBP models. In the second part of the study, the potential of the ANN–ABC, ANN–LM, and ANN–SBP models in estimation ET0 using nearby station data is investigated.  相似文献   

3.
 Field experiments were conducted for 2 years (1997 and 1998) on sandy loam soil in northwestern Botswana to study the effect of five levels of pan evaporation replenishment (20, 40, 60, 80 and 100%) on marketable yield, yield components, irrigation production efficiency and economic return of winter broccoli, carrot, rape and cabbage under a drip irrigation method. The highest mean marketable yield (2 years) of broccoli (19.1 t/ha), carrot (58.9 and 32.9 t/ha), rape (61.8 t/ha) and cabbage (97.2 t/ha) was recorded at 80% of pan evaporation replenishment. The irrigation production efficiency of broccoli (5.9 kg/m3), rape (14.6 kg/m3) and cabbage (23.6 kg/m3) was maximum at 80, 20 and 60% of pan evaporation replenishment respectively. Irrigation replenishment up to 80% of pan evaporation loss did not influence the irrigation production efficiency for total and root yield of carrot. The results revealed that a further increase in irrigation amount resulting from 100% of pan evaporation replenishment did not increase the marketable yield of crops but reduced the irrigation production efficiency significantly. The seasonal water applied and marketable yield of broccoli, carrot, rape and cabbage showed quadratic relationships (R 2 = 0.85–0.98), which can be used for allocating irrigation water within and between the crops. The net return increased with the increase in pan evaporation replenishment. The results revealed that the rape crop is the most remunerative, followed by cabbage, broccoli and carrot. Received: 2 November 1998  相似文献   

4.
Measurement of evaporation (E) rate from various natural surfaces is known as the key element in any hydrological cycle and hydrometeorological studies. Due to the shortage of pan evaporation (E P) data, the estimation of E P for such studies seems necessary. The main aim of this paper was to estimate daily E P using artificial neural network (ANN) and multivariate non-linear regression (MNLR) methods in semi-arid region of Iran. Five different ANN and MNLR models comprising various combinations of daily meteorological variables, that is, relative humidity (RH), air temperature (T), solar radiation (SR), wind speed (U) and precipitation (P) were developed to evaluate degree of effect of each of these variables on E P. The comparison of models estimates showed that the ANN 5 model characterized by Delta-Bar-Delta learning algorithm and Sigmoid activation function which uses all input parameters (T, U, SR, RH, P) performed best in prediction of daily E P. The sensitivity analysis revealed that the estimated E P data are more sensitive to T and U, respectively. A comparison of the model performance between ANN and MNLR models indicated that ANN method presents the best estimates of daily E P.  相似文献   

5.
利用东江流域1956~2000年15个气象台站的小型蒸发皿观测资料,分析了流域蒸发皿蒸发量的变化趋势及其可能原因。结果表明,东江流域年蒸发皿蒸发量整体的下降趋势非常显著,在1986年前后发生了非常明显的下降突变,下降速率达30.9 mm/10a,45年来下降了约139.0 mm;流域下降趋势存在明显的区域差异性和较大的空间异质性。东江蒸发量下降的原因主要是日照时数和平均风速的显著下降,抵消了气温上升所引起的蒸散量的上升,反而使蒸散量呈现为显著下降趋势;平均日较差的显著下降在蒸发皿蒸发量减少趋势中可能也起着重要作用。  相似文献   

6.
Summary The water use of two soybean cultivars (Bragg and Ruse) was measured for three seasons for a range of irrigation treatments. The seasonal totals of plant and soil evaporation ranged from 450 to 750 mm or from 36 to 64% of class A pan evaporation for the same period. Both cultivars extracted approximately 60% of the total extractable soil water in the top 1.2 m of soil before actual evaporation (Ea) dropped below potential evaporation (Eo). Up to this point the ratio between Ea and class A pan evaporation averaged 0.8. Ruse used water at a faster rate than Bragg but Ruse was not as effective in extracting the deep (below 1.0 m) soil water as Bragg. Water use efficiency (kg seed ha–1 mm–1 water) showed a small but general increase with decreasing irrigation water application. Runoff losses varied from zero for non-irrigated Ruse in 1977/78 to 352 mm for frequently-irrigated Bragg in 1976/77, generally increasing with the number of irrigations.  相似文献   

7.
An experiment was carried out in a naturally ventilated greenhouse to study the relationship between banana (Musa sp.) plant transpiration (Tr) measured with load cells, reference crop evapotranspiration (ETo) calculated with five widely used models (i.e. the Priestley-Taylor, FAO radiation, Hargreaves, FAO Penman and FAO Penman-Monteith models) and pan evaporation (Epan) measured with a standard Chinese 20 cm pan. Microclimatic conditions were measured inside the greenhouse. Results show that vapor pressure deficit and air temperature had good linear correlations to banana Tr with R2 of 0.67 and 0.62, respectively. Among the five models tested, banana Tr and ETo calculated with the FAO-Penman model yielded the highest determination coefficient (R2 = 0.67), followed by the FAO-PM model (R2=0.63), the FAO radiation model (R2=0.52), the Hargreaves model (R2=0.49) and the Priestley-Taylor model (R2=0.47). Banana transpiration Tr vs. Epan yielded an R2 of 0.83, which is higher than the five models tested. In conclusion, the 20 cm pan can be useful for estimating banana Tr in greenhouses.  相似文献   

8.
Accurate reference evapotranspiration (ET0) data are essential to water resources project planning and farm irrigation scheduling. Evaporation pans are widely used to estimate reference ET0. Via the pan coefficient (K p), ET0 is estimated from evaporation pan data. Four common K p equations (Orang in Potential accuracy of the popular non-linear regression equations for estimating pan coefficient values in the original and FAO-24 tables, unpublished report, 1998; Allen and Pruitt in J Irrig Drain Eng 117(5):758–773, 1991; Cuenca in Irrigation system design: an engineering approach, p 133, 1989; Snyder in J Irrig Drain Eng 118(6):977–980, 1992) to calculate daily K p coefficients to estimate ET0 were evaluated using a 10-year mean climate dataset for a subtropical climate (north of Iran). Overall results showed that ET0 calculated using the daily K p values from Orang (Potential accuracy of the popular non-linear regression equations for estimating pan coefficient values in the original and FAO-24 tables, unpublished report, 1998) provided more accurate daily, monthly, and annual total estimates compared to the others equations.  相似文献   

9.
We address a need for a rapid technique to estimate the leaf area index (LAI) of pre-existing natural vegetation. This is required to determine the effects of agroforestry plantings on deep drainage from agricultural land. Previous work shows: (1) a relationship between the hydrologic ‘footprint’ of tree belts and their lineal leaf area (leaf area per metre of belt, LLA, m2 m−1), relative to the LAI of natural vegetation and (2) that the LAI of natural vegetation is related to plant-available soil moisture and climate. We evaluated relationships between LAI measured at 37 sites across southern Australia and (1) annual average rainfall, P; (2) annual average pan evaporation, E0; (3) ‘available rainfall’—annual average rainfall, P, minus annual average pan evaporation, E0; (4) a climate wetness index P/E0; (5) Specht's soil evaporative index, k = 0.0045 + 71.57/E0. P was the best indicator for the data set used, i.e. LAI = 0.003P + 0.41 (r2 = 0.80).  相似文献   

10.
The objective of this study was to test an artificial neural network (ANN) for converting pan evaporation data (E p) to estimate reference evapotranspiration (ET0) as a function of the maximum and minimum air temperature. The conventional method that uses Pan coefficient (K p) as a factor to convert E p to ET0, is also considered for the comparison. The ANN has been evaluated under semi-arid conditions in Safiabad Agricultural Research Center (SARC) in the southwest of Iran, comparing daily estimates against those from the FAO-56 Penman–Monteith equation (PM), which was used as standard. The comparison shows that, the conventional method underestimated ET0 obtained by the PM method. The ANN method gave better estimates than the conventional method that requires wind speed and humidity data.  相似文献   

11.
Based on evaporation from a 20 cm diameter pan placed above the crop canopy, sprinkler irrigation scheduling of winter wheat was studied in the North China Plain (NCP) in the 2001–2004 winter wheat seasons. Results showed that pan evaporation (E pan,C) was closely related to actual evapotranspiration (ET) measured using weighing lysimeters. The combined pan–crop coefficient (K c,pan), the ratio of ET to E pan,C, was closely related to leaf area index (LAI ) and plant height. Data from the 2002–2003 season were used to establish the relationships between K c,pan and LAI (method A) or plant height (method B), and used to determine the crop coefficient (method C). ET computed by the three methods was compared with measured ET using lysimeters in the 2001–2002 and 2003–2004 seasons. Mean relative error of estimated daily ET by the three methods ranged from 20 to 30%, and the relative error in cumulative ET in the experimental periods ranged from 1 to 19%. Among the three methods, results from methods A and B were not significantly different from each other (P > 0.01), and were closer to the lysimeter data than results from method C (P < 0.001). Method B, being easier to measure, was recommended for ET estimation in NCP.  相似文献   

12.
Actual evapotranspiration (ETc) of three mature sweet orange orchards (cv. Salustiana and Washington Navel on sour orange), under border irrigation and typical cultural practices was measured by the water balance method during 1981 to 1984. Soil water content was measured at 7 to 10 day intervals using a neutron meter and soil sampling of the 0–10 cm surface layer. Zero flux plane was calculated by measurements with mercury tensiometers. Irrigation water in these and other 5 similar orchards was measured by broad crested weirs. Rainfall and other climatic data for calculation of reference evapotranspiration by FAO's methods (ETo) were collected in a nearby meteorological station. Average yearly ETc ranged from 750 to 660 mm and mean monthly maximum was 3.7 and 3.2 mm/day in July for Salustiana and W. Navel orchards, respectively.ETo estimates for the different methods used were highly correlated (r 20.94). Monthly crop coefficients (Kc) based on pan evaporation ranged from 0.5–0.6 in spring and summer to 0.8 in autumn and were about 10% higher than those for Penman or radiation methods. Average annual Kc for the three plots studied was 0.64, 0.61 and 0.51, respectively, and correlated well (r 2=0.99) with tree ground cover. Irrigation efficiency was about 50% for orchards with soils with less water holding capacity and more applied water per irrigation and 70–80% in orchards with deeper soils or with a higher water holding capacity. Increasing irrigation frequency and applying smaller amounts of water per irrigation with good uniformity can improve on-farm irrigation efficiency.  相似文献   

13.
In 2005 and 2006, a study was conducted to determine the effect of subsurface and surface drip irrigation systems and to determine optimum irrigation water using six different irrigation levels imposed on muskmelon (Cucumis Melo L. cv. Ananas F1) under semi-arid climatic conditions. Irrigation treatments received 0, 25, 50, 75, 100, and 125% of class A pan evaporation rates. In 2005, average yield from subsurface and surface drip irrigation systems ranged from 16.2 (I 0) to 31.1 (I 75) t ha−1 and from 16.2 (I 0) to 43.8 (I 75) t ha−1, respectively. While in 2006, fruit yields for the same systems ranged from 8.2 (I 0) to 40.4 (I 75) t ha−1 and from 8.2 (I 0) to 38.9 (I 100) t ha−1. Regression analysis of the yield data indicated no significant (P > 0.05) difference between years and irrigation systems. The highest muskmelon yields from subsurface and surface drip irrigation systems were obtained at 83 and 92% of class A pan. Bigger fruits were obtained with optimum irrigation amounts for both of the irrigation systems. However, there was no clear indication of irrigation water amounts on total soluble solid and flesh thickness of muskmelon fruits.  相似文献   

14.
The major problem when dealing with modeling evapotranspiration process is its nonlinear dynamic high complexity. Researchers developed reference evapotranspiration (ET-ref) estimation models in rich and poor data situations. Thus, the well-known Penman-Monteith (PM) model always performs the highest accuracy results of ET-ref from a rich data situation. Its application in many areas particularly in developing countries such as Burkina Faso has been limited by the unavailability of the enormous climatic data required. In such circumstances, simple empirical Hargreaves (HARG) equation is often used despite of its non-universal suitability. The present study assesses the artificial neural network (ANN) performance in ET-ref modeling based on temperature data in Bobo-Dioulasso region, located in the Sudano-Sahelian zone of Burkina Faso. The models of feed forward backpropagation neural network (BPNN) algorithm type ANN and Hargreaves (HARG) were employed to study their performance by comparing with the true PM. From the statistical results, BPNN temperature-based models perform better than HARG. Beside, when wind speed is introduced into the neural network models, the coefficient of determination (r2) increases significantly up to 9.52%. While, sunshine duration and relative humidity might cause only 3.51 and 6.69% of difference, respectively. Wind is found to be the most effective variable extremely required for modeling with high accuracy the nonlinear complex process of ET-ref in the Sudano-Sahelian zone of Burkina Faso.  相似文献   

15.
The aim of this study was to assess the magnitude of evaporation loss from the agricultural water reservoirs (AWRs) for irrigation at a regional scale and to analyze its impact on water storage efficiency. To this end, we identified the extant AWRs for irrigation in the Segura River Basin (SRB) in southeastern Spain, and calculated the water loss from each AWR per month and year. In order to accomplish this, we determined the monthly and yearly values of the pan coefficient, Kp, taking into account the geometric dimensions (area and depth) of the AWRs and local climate conditions through a function of air vapour pressure deficit (VPD). AWR areas were identified by interpreting aerial images, while climate conditions were assessed using daily meteorological data obtained from 74 automated agro-meteorological stations located in irrigated areas. Regional evaporation losses were estimated using aggregation GIS techniques. A total of 14,145 AWRs covering 4901 ha were identified, which represents 0.26 and 1.81% of the total area of SRB and the irrigated land, respectively. Results indicated that annual water loss at a basin scale reaches 58.5 × 106 m3, which corresponds to 1.404 m of water depth over the flooded area and to 8.3% of irrigation water use in the basin. This quantity is higher than the industrial demand and similar to the environmental demand, and is equivalent to 27% of the domestic water use in a region with approximately two million inhabitants. The method used, based on annual Kp, appears the most straightforward to assess regional evaporative losses from AWRs, and can be extended to other regions and climates, provided that the VPD-dependent function that gives the pan coefficient is available.  相似文献   

16.
《Agricultural Systems》1999,59(1):41-55
Environmental fate models are increasingly used to evaluate potential impacts of agrochemicals on water quality to aid in decision making. However, errors in predicting processes like evapotranspiration (ET), which is rarely measured during model validation studies, can significantly affect predictions of chemical fate and transport. This study compared approaches and predictions for ET by GLEAMS, Opus, PRZM-2, and RZWQM and determined effects of the predicted ET on simulations of other hydrology components. The ET was investigated for 2 years of various fallow–corn growing seasons under sprinkler irrigation. The comparison included annual cumulative daily potential ET (ETp), actual ET, and partitioning of total ET between soil evaporation (Es) and crop transpiration (Et). When measured pan evaporation was used for calculating ETp (the pan evaporation method), Opus, PRZM-2, and RZWQM predicted 74, 65, and 59%, respectively, of the 10-year average ET reported for a nearby site. When the energy-balance equations were used for calculating ETp (the combination methods), GLEAMS, Opus, PRZM-2, and RZWQM predicted 84, 105, 60, and 72% of the reported ET, respectively. The pan evaporation method predicted a similar amount of ET to the combination methods for bare soil, but predicted less ET when both Es and Et occurred. RZWQM reasonably predicted partitioning of ET to Es, while GLEAMS and Opus over-predicted this partitioning. A close correlation between soil water storage in the root zone and ET suggests that accurate soil water content predictions were fundamental to ET predictions. ©  相似文献   

17.
Summary The evapotranspiration rates of five-year-old coconut palms (Cocos nucifera Linn. cv West Coast Tall) grown in an Oxisol on the West coast of India were quantified from soil moisture depletion studies and lysimetric measurements. The rates increased from 2.9 mm day–1 in December to 5.5 mm day–1 in April and reduced to 2.3 mm day–1 in June following the onset of monsoon rain. Ratios of evatranspiration to class A pan evaporation were 0.87–0.88 in the moderate rainfall period (September and October), 0.78–0.85 in the winter period (November–February), 0.87–0.96 in the summer period (March–May) and 0.60–0.68 in the rainy period (June–August).  相似文献   

18.
【目的】为估算参考作物蒸散发(ET0)和灌溉实时预报调度、区域农业干旱评估提供依据。【方法】以滇中高原上洱海湖滨灌区的大理气象站为例,探究“蒸发悖论”现象出现的时期,采用气象因子线性回归模型、蒸发皿折算系数Kp模型、气象因子+蒸发皿蒸发(Epan)多元回归模型、Normal Copula模型等4种方法计算逐日ET0进行预测对比,并与Penman-Monteith公式计算所得的ET0进行对比。【结果】①1954—2018年大理站20 cm蒸发皿蒸发量呈下降趋势,ET0和气温呈上升趋势,但ET0的上升趋势更平缓;虽然在长时间序列上ET0和蒸发皿蒸发量有相反的变化趋势,但在年代际存在显著的差异性,1960年和2000全年以及四季均出现“蒸发悖论”,1970年则是全年以及夏、秋、冬三季出现“蒸发悖论”,1990年仅夏季出现“蒸发悖论”,2010年秋季出现“蒸发悖论”。②在未出现“蒸发悖论”时期,加入Epan后的气象因子多元回归模型法(ET0,Epan+Metr)所得逐日ET0预测结果与标准值的误差最小,其次为单纯的气象因子多元线性回归模型法(ET0,Metr),最差为Kp模型法(ET0,Kp);加入Epan后的气象因子多元回归模型(ET0,ET0,Epan+Metr)逐日ET0预测的相对误差(ERR)小于15%、20%、25%的样本数达到了79.18%~90.16%、89.32%~97.23%、94.79%~98.36%。③出现“蒸发悖论”时,蒸发皿蒸发与ET0的变化趋势相反,只能采用Copula联合分布函数模型预测,构建T-Tmax二维Normal Copula模型的精度更高,ERR小于15%、20%、25%的样本数为73.70%~86.56%,82.51%~92.95%,89.89%~98.52%。【结论】通过M-K检验判别是否处于“蒸发悖论”期,以决策选用加入Epan后的气象因子多元回归模型,还是T-Tmax二维Normal Copula模型,二者均可显著提高逐日ET0预测模拟的精度。  相似文献   

19.
Over the last few decades, precipitation has decreased as a result of climate change. This change increases crop water requirements, while irrigation water is wasted because of improper irrigation scheduling. Soil moisture sensors could be used to improve irrigation scheduling and save both water and energy. The objective was to study the energy and water savings, and the gross margin achieved, when using an intelligent surface drip irrigation method on sorghum bicolor (L.) Moench. In the years 2008 and 2009, a study was conducted at the farm of the University of Thessaly, Central Greece. A Class A evaporation pan and an automated frequency domain reflectometry soil moisture sensor were used for irrigation scheduling. Two treatments in four replications were organized in a randomized complete block design: (1) pan surface drip irrigation (PSDI100) and amount of water equal to 100 % of the daily evapotranspiration (ETd), as determined by a Class A evaporation pan, and (2) automated surface drip irrigation (ASDI100) and amount of water equal to 100 % of the ETd, as determined by an automated soil moisture sensor. The mean dry biomass production and the gross margin were greater in the PSDI100 treatment. The fully automated treatment remained profitable despite the high first costs. The mean water saving was 12.5 %, while the mean energy saving was 12.4 %, and the irrigation water-use efficiency was higher in the ASDI100 treatment.  相似文献   

20.
Soil water is an important factor affecting photosynthesis, transpiration, growth, and yield of crops. Accurate information on soil water content (SWC) is crucial for practical agricultural water management at various scales. In this study, remotely sensed parameters (leaf area index, land cover type, and albedo) and spatial data manipulated using the geographic information system (GIS) technique were assimilated into the boreal ecosystem productivity simulator (BEPS) model to monitor SWC dynamics of croplands in Jiangsu Province, China. The monsoon climate here is characterized by large interannual and seasonal variability of rainfall causing periods of high and low SWC. Model validation was conducted by comparing simulated SWC with measurements by a gravimetric method in the years 2005 and 2006 at nine agro-meteorological stations. The model-to-measurement R2 values ranged from 0.40 to 0.82. Nash-Sutcliffe efficiency values were in the range from 0.10 to 0.80. Root mean square error (RMSE) values ranged from 0.028 to 0.056 m3 m−3. Simulated evapotranspiration (ET) was consistent with ET estimated from pan evaporation measurements. The BEPS model successfully tracked the dynamics and extent of the serious soil water deficit that occurred during September-November 2006. These results demonstrate the applicability of combining process-based models with remote sensing and GIS techniques in monitoring SWC of croplands and improving agricultural water management at regional scales in a monsoon climate.  相似文献   

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