Turc Method Research Articles

Comparison of Empirical Methods to Estimated Reference Evapotranspiration

Evapotranspiration plays an important role in agricultural water management and crop modelling. Estimating reference Evapotranspiration (ETo) using meteorological variables, both theoretical and empirical methods, is highly recommended considering the availability of weather data in several locations. The estimation method recommended as the standard method is FAO Penman Monteith (FAOPM), but due to the limited meteorological data in a region and the difficulty and complexity of FAOPM, it is recommended to use the empirical method which is easier and only requires a few simple meteorological variables. The aim of this research is to compare and evaluated empirical methods for estimating ETo against the FAOPM. The statistical analysis using in this research are RSME, MAE, coefficient Correlation, NSE, Average bias, index of agreement, and confidence index (c). Evaluation for the best models based on statistic analyzed shows that several empirical methods show terrible performance in estimating the monthly average ETo (mm/day), which are Thornthwaite-Mather, Hargraves-Samani, Makkink, Hamon, Romaneko, and Kharauffa. Modified Blaney-Criddle method showed a good performance method, while PMAWS showed very good performance The Turc and Hansen method showed excellent performance with RMSE, MAE, NSE, and C values ​​for the Turc method, are 0.12, 0.11, 0.78, 0.92 respectively, and for the Hansen method are 0.12, 0.1, 0.8, and 0.89 respectively.

Potential Alternative Evapotranspiration Estimation Methods for Batu Pahat Climatic Condition: A Quantitative Comparison

Urbanisation had replaced the vegetation and soil cover, increasing heat retention by reducing the benefits of natural cooling mechanisms provided by evapotranspiration. The objective of this study is to investigate the potential of the alternative estimation performance for selected evapotranspiration (ET) methods for Batu Pahat station; for further prediction on the changes of future climatic parameters. Since the data is limited, ET0 estimation using temperature-based used are the Thornthwaite, Blaney-Criddle (original) and FAO Blaney-Criddle methods. Standard data formulation based on Batu Pahat latitude for meteorological parameters were used to estimate ET0 using basic radiation-based, the Penman (original) and Turc methods. Correlation results show that all three temperature-based methods estimated a similar range of ET0. For the radiation-based method, the Turc method seems slightly overestimated than the other four methods. However, these estimation needs to be explored further using the benchmark method, i.e., the FAO-56 Penman-Monteith, for the accuracy and reliabilities of these methods. Apart from temperature, it was found that ET0 did not correlate with rainfall and evaporation.

Applicability and improvement of different evapotranspiration methods of reference crops in Jiangxi Province

To achieve accurate evaluation of evapotranspiration of reference crops (ET0) in Jiangxi, China, in the absence of systematic climatological data, with reference to the FAO-56 Penman–Monteith (P-M) equation, the Priestley-Taylor (P–T) method, the Makkink method, the Hargreaves-Samani (H–S) method, the Irmak-Allen (I-A) method, the Penman1948 (48PM) method, the Penman-Van Bavel (PVB) method, the Baier-Robertson (B-R) method, the improved Baier-Robertson (M-B-R) method, the Schendel (Sch) method, the Turc method, the Jensen-Haise (J-H) method, and the Brutsaert-Stricker (B-S) method were used to evaluate the daily climatological data collected by 26 weather stations in Jiangxi, China, and 17 weather stations in adjacent provinces. The results were compared with each other and parameter rate determination was conducted. The results indicated that the Turc method exhibited optimized applicability before parameter rate determination and the average root mean square error (RMSE) and the average normalized root mean square error (NRMSE) by this method were 0.39 mm/d and 0.157 mm, respectively. However, parameter rate determination led to negligible improvement in accuracy for this method. The Turc method could be directly applied in Jiangxi (except Nanchang). For special distribution of error after parameter rate determination, all methods exhibited significant errors in Northern Jiangxi. Herein, the 48PM method and the B-S method showed good applicability after parameter rate determination and RMSE and NRMSE of data by these methods ranged in 0.06 ~ 0.34 mm/d and 0.08 ~ 0.27, 8 ~ 27%, respectively, and their d-indices were close to 1. The annual over-estimations in weather stations in Jiangxi were below 30 mm. In the absence of data about relative humidity and wind speed, the P–T method was an appropriate simplified method for Jiangxi. In this case, α was slightly lower than the default value (1.05 ~ 1.18), RMSE was within 0.21 ~ 0.66 mm/d, and NRMSE was within 0.08 ~ 0.308 ~ 30%. Accuracy of RMSE, d-index, and NRMSE of data by the P–T method, the I-A method, and the PVB method was consistent with all stations, while that by the Mak method was slightly lower, which could be attributed to severe over-estimation in July and August. RMSE of the H–S method, the B-R method, the M-B-R method, the J-H method, and the Sch method were above 0.75 mm/d and these methods were not suitable for accurate evaluation of ET0 in Jiangxi, China. The annual ET0 was calculated by various methods (except the 48PM method and the B-S method) exhibited significant variation around 2003. This may be attributed to significant changes in certain meteorological factors over recent years.

Annual Actual Evapotranspiration Estimation via GIS Models of Three Empirical Methods Employing Remotely Sensed Data for the Peloponnese, Greece, and Comparison with Annual MODIS ET and Pan Evaporation Measurements

Actual evapotranspiration (ETa) has been insufficiently investigated in Greece. This study aimed to estimate annual ETa by empirical methods (Turc, modified Turc, and Coutagne) for the Peloponnese, Greece, a Mediterranean testbed, between 2016–2019, four of the warmest years since the preindustrial era, and compare them to MODIS ET. Furthermore, measurements of annual pan evaporation (Epan) were performed for two Class A pan stations in the Peloponnese with different reliefs and conditions. The empirical methods and statistical formulae (RMSD, MB, and NMB) were developed as models in ArcMap. The outcomes of the Turc method resembled MODIS ET ranges for all years, followed by those of Coutagne. The estimates by the modified Turc method were almost identical to MODIS ET. Therefore, the modified Turc method can be used as an alternative to MODIS ET (and vice versa) for the Peloponnese for 2016–2019. Moreover, the Epan at Patras University station (semiurban, low elevation) exhibited an upward trend resembling the trends of the empirical methods over the study years, whereas the Epan at Ladonas station (higher elevation, lakeside) required investigation on a monthly time scale. Additionally, the gradual decrease of pan-water icing at Ladonas in December (from 20 d in 2016 to 0 d in 2019) could imply an undergoing decrease in snowpack storage retention across the mountains of the Peloponnese.

The Role of DEM Resolution and Evapotranspiration Assessment in Modeling Groundwater Resources Estimation: A Case Study in Sicily

The reliability of hydrological response simulated by distributed hydrological models in river basins with complex topographies strictly relies on the adopted digital elevation model (DEM) resolution. Furthermore, when the objective is to investigate hydrologic processes over a longer period, including both wet and dry conditions, the choice of a proper model for estimating actual evapotranspiration can play a key role in water resources assessment. When dealing with groundwater-fed catchment, these aspects directly reflect on water balance simulations and consequentially on groundwater resource quantification, which is fundamental for effective water resources planning and management at the river basin scale. In the present study, a DEM-based inverse hydrogeological balance method is applied to estimate the active mean annual recharge of the northern Etna groundwater system within the upstream part of the Alcantara river basin in Sicily region (Italy). Despite this area representing a biodiversity hot-spot, as well as the main water source for a population of about 35,000 inhabitants, so far little attention has been paid to groundwater estimation, mainly due to lack of data. In this context, this work aims to improve knowledge on groundwater recharge at the annual scale in this case-study area. In particular, the main objectives of this study are: (1) to quantify the influence of the DEM resolution on groundwater resource estimation and (2) to investigate the influence of the method used for evapotranspiration assessment on the model’s results. More specifically, groundwater and surface flows are evaluated by considering different DEM resolutions (i.e., 20, 60, 100, 300, 500 m) and three different theoretical approaches for evapotranspiration calculation (i.e., the Turc method, a modified-Turc method, and the Budyko model).

Assessment of reference evapotranspiration estimation methods in controlled greenhouse conditions

Precise estimation of reference evapotranspiration (ETo) is one of the most influential factors in proper irrigation scheduling and water resources management. Over the years, various methods and formula have been developed to estimate ETo based on several required variables and assumptions. Accuracy and performance of different ETo estimation equations applied for open field differ from those under controlled greenhouse conditions. Considering the microclimate condition of greenhouses, local calibration is required to choose the best and the most accurate method. This study aimed to investigate the performance of different ETo simulation models including one combination, one temperature-based and seven radiation-based methods under the greenhouse conditions. First, computational methods were calibrated by regression analysis. Then, the accuracy of ETo simulation models was compared with that of micro-lysimeter measurements. Statistical indices including coefficient of determination (R2), mean bias error (MBE), root mean square error (RMSE), relative root mean square error (RRMSE) and index of agreement (d) were used for validation and verification. Finally, the general ranking among the models was conducted using the standardized Ranking Performance Index (sPRI). According to the results, Penman–Monteith method with a fixed aerodynamic resistance of 53 s m−1 (with 0.98, − 0.01 mm day−1, 0.07 mm day−1, 0.80% and 0.99 for R2, MBE, RMSE, RRMSE and d statistical indices, respectively) was the best and the most precise method for estimating ETo under greenhouse conditions. Turc method, with a cumulative difference of 24.01 mm during the whole simulation period (73 days), underestimated ETo the most under the same conditions.

Assessment of empirical methods for estimation of reference evapotranspiration in the Brazilian Savannah

Evapotranspiration can be sufficiently estimated when meteorological data are available to implement robust models such as Penman-Monteith (PM). However, due to data scarcity, alternative approaches are necessary. In this context, this study aims to compare the reference evapotranspiration (ETo) obtained from the PM standard method with eight empirical equations to identify the simplest method that can be alternative to the reference method (Penman Monteith method) for ten places in state of Goiás (located in west-central Brazil, Brazilian Savanna). To estimate the ETo, air temperature and relative humidity air, wind speed, sunshine and solar radiation data, which were obtained from the data platform National Institute of Meteorology and the Meteorological and Hydrological System of the State of Goiás, were used. For comparison of empirical methods with PM standard method, we used the following statistical indicators: slope and intercept coefficients (β0 and β1) of regressions equations, the coefficient of determination (r²), Pearson's correlation (r), mean bias error (MBE), root mean square error (RMSE) concordance index refined (dr) and performance index (Pi). Our results indicated that the Turc method is the best option for the state of Goiás when meteorological data are not suffeciently available to use the standard PM method. On the other hand, the method of Romanenko did not present acceptable performance in nine of the ten studied localities. Therefore, its use is advised only in the municipality of the Itumbiara. Among evaluated methods the Hargreaves-Samani method is the best alternative, when there is only air temperature data.

Hydrological modeling of floods in the Wadi Bechar watershed and evaluation of the climate impact in arid zones (southwest of Algeria)

Precise knowledge regarding the quantities of water available in the Wadi Bechar watershed and better management of this resource is necessary to initiate the transformation of rainfall data into hydrometric data (simulated flow); this is the main objective of the hydrological rainfall–runoff modeling. The primary focus of this paper is the rainfall–runoff modeling on an annual and monthly scale in the Wadi Bechar watershed which covers an area of 6858 km2. We employ the rural engineering model (GR) for annual timestep GR1A and for the monthly timestep GR2M. The input parameters are precipitation (P) and evapotranspiration (ETP) calculated by the Turc method; the output parameter is elapsed water slide (Q). The results obtained indicate that the model takes into account the different atmospheric and underground exchanges, as well as the capacities of the production tank and routing tank. With this work, the contribution of precipitation to flows downstream of the watershed can be evaluated and quantified. On an annual scale, the potential evapotranspiration modulator coefficient X is equal to 2.20 > 1. This indicates that the water from the Wadi Bechar watershed seeps into the ground or into the adjacent watersheds of Wadi Zousfana and Wadi Guir. On a monthly scale, we calibrate and cross-validate the model with the selected input data, determining the model parameter sets that best reflect the transformation of rainfall into flow. The calibration was done with several passages in computer. The value of the capacity of the estimated production tank X1 is equal to 4.74 mm, which reflects the production function, and subsequently indicates the rainfall capacity transformed into a water flow available for runoff at the Wadi Bechar watershed scale. The value of the estimated underground exchange coefficient parameter X2 is equal to 0.02; it reflects the transfer function, which indicates the movement of this surface flow toward the watershed outlet.

Analysis and Calibration of Empirical Relationships for Estimating Evapotranspiration in Qatar: Case Study

AbstractKnowledge of evapotranspiration (ETo), which is the process of water loss from vegetated soils due to evaporation and transpiration, is important in real-time irrigation management and water-resource allocation, particularly in water-scarce regions. In this study, several methods used in estimating evapotranspiration, including the Blaney-Criddle, Hargreaves-Samani, Jensen-Haise, Linacre, and Turc methods were calibrated and validated against the Penman-Monteith model, which is considered as the standard method of estimating evapotranspiration. The paper utilizes data from the Doha International Airport meteorological station over a period of 30 years (January 1985–December 2014). ETo values were estimated using the different methods. These values were then compared to those obtained by the Penman-Monteith method. Using appropriate indicators, the Turc method was found to be the best for estimating ETo over Doha (R2=0.9519, RMSE=1.4511 mm day−1, and MAE=1.1633 mm day−1). The Turc method comes in...

Karst spring catchment: an example from Dinaric karst

Definition of karst spring catchment or basin area and boundaries belongs to one of the greatest prob- lems of karst hydrology and hydrogeology, not adequately solved until now. This paper tries to address main problems in defining this crucial parameter. The theoretical aspect of this issue is discussed in the first two chapters. We have presented the example of the catchment area and bound- aries definition for the karst spring Zrnovnica catchment in Dinaric karst. Topographic catchment area of the Zrnov- nica Spring is 8.4 km 2 . The significant discrepancy in size of the hydrological-hydrogeological and topographical catchment is very common characteristic for the springs located in the karst areas. In the case of the Zrnovnica Spring, the hydrogeological catchment is at least seven times larger than topographic. Two following simple hydrological methods are used in order to calculate its hydrologic-hydrogeologic catchment: (1) the relationship between mean annual discharges and annual rainfall falling on the catchment, and (2) the Turc method. It is estimated that hydrogeologic catchment area of the Zrnovnica karst spring is much larger and very probably ranges between 60 and 80 km 2 . These values represent first rough assessment, which should be confirmed by more detailed interdisci- plinary investigations. According to the performed tracing tests, it seems that the catchment spreads on the north-east from the topographic catchment and that the Zrnovnica Spring karst aquifer is fed by groundwater overflow from the neighbouring more abundant karts spring Jadro.

Comparison of the values of potential evapotranspiration estimated through different methods and their relationship

In the present study, six empirical methods, namely, Modified Penman, Blaney Criddle, Christiansen, Thornthwaite, Open pan, Turc and FAO penman method are computed using the daily weather data for the period 1981-2012 (32 years) was collected for three stations in Chhattisgarh state representing 3 agroclimatic zones. It is found that FAO Penman method is the best method for estimating potential evapotranspiration. The comparison of ETo estimates was done based on the weekly averages of PET using correlation co-efficients and regression methods through different methods. At Ambikapur the highest correlation co-efficient between FAO Penman and Modified Penman method 0.998 and lowest in between Christiansen and Blaney criddle method 0.918. At Jagdalpur and Raipur also having the highest correlation co-efficient between FAO penman and Modified penman method 0.999 and lowest correlation co-efficient in between Christiansen and Turc method 0.85 or 0.84. Regarding regression with Open pan evaporation, highest R 2 values are with Modified Penman and Christiansen methods at Ambikapur while at Jagdalpur and Raipur highest R 2 was with Christiansen method. Thus, the open pan evaporation can be estimated by Christiansen method.

COMPARATIVE EVALUATION OF DIFFERENT POTENTIAL EVAPOTRANSPIRATION ESTIMATION APPROACHES

Accurate estimation of potential evapotranspiration is necessary step in water resources management. Recently, the FAO-56 version of Penman-Monteith equation has been established as a standard for calculating reference evapotranspiration (ET0). Still there are different approaches (requiring less data) which estimate ET0 closely to Penman-Monteith method for different climatological conditions. Performance Evaluation of all the approaches on the same basis is prerequisite for selecting an alternative approach in accordance with available data. Therefore, two most popular temperature-based approaches (Hargreaves and Thornthwaite) and two radiation based approaches (Priestley-Taylor and Turc) were used to estimate monthly potential evapotranspiration (ET0) at Pantnagar (Uttarakhand), India. Further, the performance of all these methods were evaluated by regression and error analysis between standard ET0 derived using FAO-56 Penman-Monteith method and ET0 values estimated using all the four methods, on monthly and seasonal basis. On monthly basis Turc method performed best with lowest RMSE (0.562), ARE (0.137), AAD (0.448) and high coefficient of determination (0.792). On seasonal basis, the Priestley-Taylor methodwas found to be the best for Rabiseasonwith lowest error values and minimum seasonal over/under ET0 predication rate with respect to standard ET0.Turc method holds second rank in Rabi season. However in Kharif season Truc method performed better than any other method with lowest error terms and lowest seasonal over/under predication rate. In summer season all the methods performed poorly compared to other two seasons but Hargreaves method performed better than other methods. Though the performance and accuracy of FAO-56 Penman-Monteith method can never be debated in theoretical or practical applications yet the comparative evaluation performed in this paper can be used as guideline for selection of alternative or less data dependent methods in case of non-availability of data.

Rainfall Distribution Functions for Irrigation Scheduling: Calculation Procedures Following Site of Olive (<i>Olea europaea</i> L.) Cultivation and Growing Periods

In Tunisia (36.5oN, 10.2oE, Alt.10 m), rainfall is the major factor govering olive production. Annual and seasonal falls are variable following years and regions, making yields of olive trees fluctuating consistently. Irrigation was applied since the 70th in the intensive olive orchards to improve and stabilize olive production. This study aimed to determine the crop water needs of olive orchards and the rainfall frequencies at which they are covered following age and site of olive production. For this purpose, the rainfall distribution functions were established for different cities of Tunisia (Tunis, Bizerte, Béja, Nabeul, Sidi Bouzid, Gabes and Sousse). For all sites and growing periods, the reference evapotranspiration (ET0) was computed by using several methods. Their performance against the PM-ET0 (Penman-Monteith) estimates was evaluated graphically and statistically for a better adaptation them to the existing environmental conditions, particularly when data are missing to compute ET0-PM. Results show that ET0 estimates strongly correlate with ET0-PM with r values of up to 0.88. Particularly, the methods of Turc and Ivanov appropriately predict the ET0-PM in all climatic regions of Tunisia, constituing an appropriate alternative for determining ET0 when data are missing to compute ET0-PM. However, although the Turc method performs well with all climatic zones of Tunisia, the Ivanov method appears to be more appropriate to the northern areas (Béja and Bizerte), though a poorer agreement was found when using the Eagleman method. Estimates of ET0 by using the Hargreave-Samani (HS) formula for the east-southern area (Gabes, arid climate) show satisfactory agreement with ET0-PM estimates. It appears also that at a given site, the most appropriate method for ET0 estimation at annual scale may be different from that giving the best value of ET0 when considering the growing stages of the olive tree, for example, the method of Turc, although it was appropriate when estimating the annual ET0 value for Sousse, it wasn’t adequate at seasonal scale. In opposite, although the method of BC is suitable for stages 1, 2, 4 and 5 at Sousse, the appropriate method for the overall cycle is that of Turc. This indicates that there is no weather-based evapotranspiration equation that can be expected to predict evapotranspiration perfectly under every climatic situation due to simplification in formulation and errors in data measurement. However, we can say that when data are missing, ET0 can be estimated with a specific formula; that of Turc can be appropriately used for Tunis, Sidi Bouzid, Sousse and Béja at annual scale despite of their appartenance to different climatic regions, while the method of Ivanov is quite valuable for Bizerte and Nabeul. Results show also that values of P-ETc recorded during the irrigation period are negative even for young plantations, with lowest and highest deficits observed at Béja and Gabes cities, respectively. The driest period is that of July-August for all sites with F values exceeding 0.9 in most cases. Only 10% of water needs are supplied by rainfall during this period of fruit development. Therefore, irrigation is needed all time for adult trees even at the rainiest locations. For young plantations, irrigation becomes necessary beginning from the second period of tree development, i.e. April-June for Bizerte, Béja, Nabeul and Tunis and since the early spring period for both young and old plants for Gabes and Sidi-Bouzid. It appears from this analyze based on the seasonal rainfall frequencies and water needs computed with the PM-method, that there is a need for irrigating olive plantations aging more than 5 years in most case studies and especially when olive is cultivated in the western areas of Tunisia. Results indicate also that the use of no adequate method to estimate ET0 allowed overestimating or underestimating of irrigation water needs. So it is desirable to have for Tunisia a method that estimates ET consistently well and future research is needed to reconcile which should be the standard method of calculating the change in the crop coefficient over time. However, despite a quite good performance of the PM-equation in most applications, particularly when it is used for irrigation scheduling purposes, some problems may appear because of lack of local information on Kc-values and determination of the effective rainfall. Additional research is needed on developing crop coefficients that use the Penman-Monteith equation when calculating ET. In conclusion we can say that on the basis of the results produced, we can decide for each region and growing period if complementary irrigation is needed or not. Indicative amounts are given for each case study.

Evaluation and modification of potential evapotranspiration methods in Beijing, China

Abstract: In this study, seven widely used potential evapotranspiration (ETo) methods were evaluated by comparing with the FAO-56 Penman-Monteith method (PM method) to provide useful information for selecting appropriate ETo equations under data-limited condition in Beijing, China. Statistical methods and parameters, namely linear regression, root mean squared error (RMSE) and mean bias error (MBE), were used to evaluate the seven ETo methods. Results showed that ETo estimated using Kimberly–Penman method have fairly close agreement with the PM method (referring to standard ETo), considering the coefficient of determination (R2) of 0.96, RMSE of 0.42 mm/day, and a coefficient of efficiency (E) of 0.96. Locally calibrated Penman and Doorenbos–Pruitt methods also have better agreement with the PM method, correspondingly with R2 of 0.99 and 0.95, RMSEs of 0.24 mm/day and 0.21 mm/day, and coefficients of efficiency of 1.02 and 0.99, respectively. The ETo is the most sensitive to vapor pressure deficit (VPD) and net radiation in the Beijing area. Hence, the VPD-based and VPD-radiation combined ETo methods were developed and calibrated. Results showed that the two developed methods performed well in ETo estimation. By fully considering the data-limit situation, the calibrated Turc method, VPD-based method and VPD-radiation-combined method may be attractive alternatives to the more complex Penman−Monteith method in Beijing. Keywords: potential evapotranspiration, Penman-Monteith method, determination coefficient, coefficient of efficiency, Beijing DOI: 10.3965/j.ijabe.20130604.002 Citation: Liu H J, Li Y, Zhang R H, Huang G H. Evaluation and modification of potential evapotranspiration methods in Beijing, China. Int J Agric & Biol Eng, 2013; 6(4): 9－18.

Comparison of Different Empirical Methods for Estimating Daily Reference Evapotranspiration in Mediterranean Climate

The estimation of reference evapotranspiration (ET0) is very important for the management of water resources and the determination of the water budget, especially under arid conditions. The applicability of simple forms of Penman equations that were recently developed by Valiantzas is investigated in this study. The new empirical equations are applied to daily climatic data from four stations located in the Mediterranean region of Turkey: Adana, Antalya, Isparta, and Mersin. The results are compared with the ET0 values obtained by Food and Agricultural Organization 56 Penman-Monteith and the following empirical equations: Copais, Turc, Hargreaves-Samani, Hargreaves, Ritchie, and Irmak. Root mean square errors, mean absolute errors, and determination coefficient statistics are used for comparison of the empirical models. The results indicate that the Valiantzas equation with full weather data performs better than the other empirical methods at stations in Adana, Antalya, and Isparta. In the Mersin station, however, the Copais equation perform the best out of the nine methods. The worst estimates are generally obtained from the Turc method.

Comparison of different methods to estimate actual evapotranspiration and hydrologic balance

ABSTRACT The aim of this study was the assessment of the utilization of two methods, i.e. the Thornthwaite and the Turc equations, for the analysis of the water balance in an environmentally sensitive area. The hydrologic balance of a basin consisting in two lakes (Zazari and Cheimaditida) in northern Greece, and covering an area of 228 km2 has been estimated. The Thornthwaite method was applied in the study area, for the calculation of the evapotranspiration factor and was compared to the results obtained by the application of the Turc method in the same area. For the development of these equations and the calculation of the evapotranspiration rates, monthly temperature and precipitation values collected from meteorological stations over a period of 30 years were used. The utilization of monthly average temperatures in the Thornthwaite equation resulted to an actual evapotranspiration rate of ET = 412.7 mm (80.23%) for p = 514.4 mm and a runoff rate of Q = 101.7 mm (19.77%). However, the Turc equation ga...

A comparison of models for estimating potential evapotranspiration for Florida land cover types

summary We analyzed observed daily evapotranspiration (DET) at 18 sites having measured DET and ancillary climate data and then used these data to compare the performance of three common methods for estimating potential evapotranspiration (PET): the Turc method (Tc), the Priestley–Taylor method (PT) and the Penman–Monteith method (PM). The sites were distributed throughout the State of Florida and represent a variety of land cover types: open water (3), marshland (4), grassland/pasture (4), citrus (2) and forest (5). Not surprisingly, the highest DET values occurred at the open water sites, ranging from an average of 3.3 mm d � 1 in the winter to 5.3 mm d � 1 in the spring. DET at the marsh sites was also high, ranging from 2.7 mm d � 1 in winter to 4.4 mm d � 1 in summer. The lowest DET occurred in the winter and fall seasons at

Genetic Programming‐Based Empirical Model for Daily Reference Evapotranspiration Estimation

AbstractGenetic programming (GP) is presented as a new tool for the estimation of reference evapotranspiration by using daily atmospheric variables obtained from the California Irrigation Management Information System (CIMIS) database. The variables employed in the model are daily solar radiation, daily mean temperature, average daily relative humidity and wind speed. The results obtained are compared to seven conventional reference evapotranspiration models including: (1) the Penman‐Monteith equation modified by CIMIS, (2) the Penman‐Monteith equation modified by the Food and Agricultural Organization (FAO 56), (3) the Hargreaves‐Samani equation, (4) the solar radiation‐based ET0 equation, (5) the Jensen‐Haise equation, (6) the Jones‐Ritchie equation, and (7) the Turc method. Statistical measures such as average, standard deviation, minimum and maximum values, as well as criteria such as mean square error and determination coefficient are used to measure the performance of the model developed by employing GP. Statistics and scatter plots indicate that the new equation produces quite satisfactorily results and can be used as an alternative to the conventional models.

Comparative study of conventional and artificial neural network-based ETo estimation models

Accurate estimation of reference crop evapotranspiration (ETo) is required for several hydrological studies and thus, in the past, a number of ETo estimation methods have been developed with different degree of complexity and data requirement. The present study was carried out to develop artificial neural network (ANN) based reference crop evapotranspiration models corresponding to the ASCE’s best ranking conventional ETo estimation methods (Jensen et al. ASCE Manual and Rep. on Engrg. Pract. no. 70, 1990). Among the radiation methods, FAO-24 radiation (or Rad) method for arid and Turc method for humid region, and among the temperature methods, FAO-24 Blaney–Criddle (or BC) method were studied. The ANN architectures corresponding to the above three less data-intensive methods were developed for four CIMIS (California Irrigation Management Information System) stations, namely, Davis, Castroville, Mulberry, and West Side Field station. The comprehensive ANN architecture developed by Kumar et al. (J Irrig Drain Eng 128(4):224–233, 2002) corresponding to Penman–Monteith (PM) ETo for Davis was also tried for the other three stations. Daily meteorological data for a period of more than 10 years (01 January 1990 to 30 June 2000) were collected from these stations and were used to train, test, and validate the ANN models. Two learning schemes, namely, standard back-propagation with learning rate of 0.2 and standard back-propagation with momentum having learning rate of 0.2 and momentum term of 0.95 were considered. ETo estimation performance of the ANN models was compared with the FAO-56 PM method. It was found that the ANN models gave better closeness to FAO-56 PM ETo than the best ranking method in each category (radiation and temperature). Thus these models can be used for ETo estimation in agreement with climatic data availability, when not all required climatic variables are observed.

Effect of wind speed on accuracy of Turc method in a humid climate

The Turc method is one of the simplest and most accurate empirical equations used for ETO estimation. The objectives of this study are: first, to investigate the effect of wind speed on accuracy of Turc method; second, to develop the wind speed adjustment factors for the Turc method. The adjusted Turc method provides the quite good agreement with the evapotranspiration obtained by the FAO-56 Penman-Monteith method. It gave reliable estimation at all the locations and it has proven to be the most adjustable to the local climatic conditions. These results recommend the adjusted Turc method for estimating reference evapotranspiration.