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Kotsopoulos, S., and C. Babajimopoulos. "Analytical Estimation of Modified Penman Equation Parameters." Journal of Irrigation and Drainage Engineering 123, no. 4 (1997): 253–56. http://dx.doi.org/10.1061/(asce)0733-9437(1997)123:4(253).
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Anggraheni, Evi, Faris Zulkarnain, Pranita Giardini, et al. "Assessing the Reliability of Satellite-Derived Evapotranspiration Data Using Numerical Modified Penman Method at Citarum Watershed." Indonesian Journal of Geography 55, no. 2 (2023): 213. http://dx.doi.org/10.22146/ijg.77725.
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Evapotranspiration is an essential part of water availability analysis and crop water needs that are useful to estimate irrigation water demand. Since discharge measurement stations are limited, the analysis of water availability is the most important part of water management planning. Citarum watershed is the biggest watershed in West Java, supplies raw water to Jakarta, the capital city of Indonesia. Modified Penman is the common equation to analyze evapotranspiration, which was developed by Food and Agriculture Organization (FAO) and modified for tropical areas. Evapotranspiration is one term of the water balance equation. To determine water losses, it is necessary to solve this equation. Another source of evapotranspiration data is provided by the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite's standard product, MOD16A2. In order to used the evapotranspiration satelilite data to fullfill the lack of groud station data, the reliability of satelite data is needed. The objective of this study is to compares and analyzes the reliability of satellite evapotranspiration potential images with the numerical Modified Penman method at Citarum Watershed. Modified Penman is one of several methods that calculate the evapotranspiration potential based on climate data. MOD16A2 was used for simulation data, and Modified Penman was used for baseline data. The reliability of the two simulations was analyzed by the skewness percentage of each pixel and period. The distribution of percent skewness indicates the performance of satellite evapotranspiration on the Modified Penman that represents the actual condition. The sensitivity of satellites is greatly affected by local weather conditions.
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Sperna Weiland, F. C., C. Tisseuil, H. H. Dürr, M. Vrac, and L. P. H. van Beek. "Selecting the optimal method to calculate daily global reference potential evaporation from CFSR reanalysis data." Hydrology and Earth System Sciences Discussions 8, no. 4 (2011): 7355–98. http://dx.doi.org/10.5194/hessd-8-7355-2011.
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Abstract. Potential evaporation (PET) is one of the main inputs of hydrological models. Yet, there is limited consensus on which PET equation is most applicable in hydrological climate impact assessments. In this study six different methods to derive global scale reference PET time series from CFSR reanalysis data are compared: Penman-Monteith, Priestley-Taylor and original and modified versions of the Hargreaves and Blaney-Criddle method. The calculated PET time series are (1) evaluated against global monthly Penman-Monteith PET time series calculated from CRU data and (2) tested on their usability for modeling of global discharge cycles. The lowest root mean squared differences and the least significant deviations (95 % significance level) between monthly CFSR derived PET time series and CRU derived PET were obtained for the cell specific modified Blaney-Criddle equation. However, results show that this modified form is likely to be unstable under changing climate conditions and less reliable for the calculation of daily time series. Although often recommended, the Penman-Monteith equation did not outperform the other methods. In arid regions (e.g., Sahara, central Australia, US deserts), the equation resulted in relatively low PET values and, consequently, led to relatively high discharge values for dry basins (e.g., Orange, Murray and Zambezi). Furthermore, the Penman-Monteith equation has a high data demand and the equation is sensitive to input data inaccuracy. Therefore, we preferred the modified form of the Hargreaves equation, which globally gave reference PET values comparable to CRU derived values. Although it is a relative efficient empirical equation, like Blaney-Criddle, the equation considers multiple spatial varying meteorological variables and consequently performs well for different climate conditions. In the modified form of the Hargreaves equation the multiplication factor is uniformly increased from 0.0023 to 0.0031 to overcome the global underestimation of CRU derived PET obtained with the original equation. It should be noted that the bias in PET is not linearly transferred to actual evapotranspiration and runoff, due to limited soil moisture availability and precipitation. The resulting gridded daily PET time series provide a new reference dataset that can be used for future hydrological impact assessments or, more specifically, for the statistical downscaling of daily PET derived from raw GCM data.
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TAHASHILDAR, MOUTUSI, PRADIP K. BORA, LALA I. P. RAY, and VISHRAM RAM. "Crop-coefficients of tomato as derived using monolithic weighing type lysimeter in mid hill region of Meghalaya." MAUSAM 68, no. 4 (2021): 723–32. http://dx.doi.org/10.54302/mausam.v68i4.790.
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Crop coefficients (kc) was determined for tomato (Lycopersicon esculentum Mill.) with the help of UMS-GmBH cylindrical field lysimeter of 30 cm diameter and 120 cm deep and Penman-Monteith FAO-56 model. Eight other models viz. Modified Penman Method, Hargreaves equation, Samani-Hargreaves equation, Thornthwaite equation, Solar Radiation Method, Net Radiation Method, Blaney-Criddle Method and Radiation Method were also used for estimation of ET0 and compared with Penman-Monteith model to find out the accuracy of prediction with limited weather parameters. Scatter plot and paired t-test were used for comparison. Out of all these models, Blaney-Criddle method, Solar and Net Radiation method were found to yield similar results as given by Penman-Monteith model. The values of crop evapo-transpiration (ETc) were varying from 2.54 mm d-1 to 6.70 mm d-1. The crop-coefficients (kc) for three growth stages of tomato viz., initial, mid and maturity were found to be 0.55, 1.07 and 0.78, respectively.
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M. TAHASHILDAR, PRADIP K. BORA, LALA I. P. RAY, and D. THAKURIA. "Comparison of different reference evapotranspiration (ET0) models and determination of crop-coefficients of french bean (Phesiolus vulgaris.) in mid hill region of Meghalaya." Journal of Agrometeorology 19, no. 3 (2017): 233–37. http://dx.doi.org/10.54386/jam.v19i3.645.
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The water requirement and crop evapotranspiration (ETc)is determined using reference evapotranspiration (ET0) and crop-coefficient (kc). Numerous models are available for estimation of ET0,among which Penman-Monteith (FAO-56) model is considered to be the most accurate and universally acceptable. In present study eight models for estimation of ET0viz. Modified Penman method, Hargreaves equation, Samani-Hargreaves equation, Thornthwaite equation, Solar radiation method, Net radiation method, Blaney-Criddle method and Radiation method were compared with Penman-Monteith model to find out the accuracy of prediction with limited weather parameters. Among these, Net radiation and Solar radiation models were found to yield relatively closer values. A field experiment was also conducted withfrench bean (Phesiolus vulgaris.) crop in UMS-GmbH cylindrical field lysimeter of 30 cm diameter and 120 cm deep for determination of crop coefficient taking Penman-Monteith FAO-56 model as the base model for ET0 estimation. The values of ETc as determined in field lysimeter varied from 3.80 mm-d-1 to 5.89 mm-d-1. The kc for initial, mid and maturity were found to be 0.45, 1.01 and 0.39, respectively.
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Osama, Osman Ali. "A Computer program for Calculating Crop Water Requirements." Greener Journal of Agricultural Sciences 3, no. 2 (2013): 150–63. https://doi.org/10.15580/GJAS.2013.2.121712325.
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<strong>A computer program was developed for determination of crop water requirements using local meteorological and research data, and also using Visual Basic 6.0 Programming language. For verification of the model, field trials were carried out during the period December 2007 - July 2008 at four schemes using center-pivot irrigations in the northern parts of Sudan. The program was based on using Penman equation and Penman-Monteith method. Results were comparable to those obtained through traditional time-consuming methods. The program could offer a simple tool for planning crop water requirements for agricultural projects.</strong>
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Mills, T., K. Morgan, L. Parsons, and A. Wheaton. "Measurement and Calculation of Total Plant Water Use of Citrus." HortScience 33, no. 3 (1998): 490d—490. http://dx.doi.org/10.21273/hortsci.33.3.490d.
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This preliminary study serves to parameterize a modified Penman–Monteith equation for young citrus trees. Two-year-old citrus trees (`Hamlin' grafted on Carrizo citrange) were planted individually into 1500-L (1.5-m-diameter) plastic pots in late Oct. 1997. Pots were placed upon industrial scales with a maximum weight capacity of 2270 ± 0.05 kg. Continuous weight measurements were made every minute and average half-hourly values recorded. An automated weather station was located within 10 m of the pots and half hourly values of temperature, humidity, wind speed, rainfall, and net radiation were recorded. Meteorological data, coupled with diurnal measurements of stomatal conductance taken periodically throughout the experimental period and leaf area for each tree allow calcuatiion of total plant water use using a modified Penman–Monteith equation. These calculation may be cross-checked using weight change measurements. Such model parameterization for citrus will aid irrigation management of citrus in the field as it provides a link between the physiological and meteorological aspects which drive plant water use.
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Lhomme, J. P., N. Boudhina, M. M. Masmoudi, and A. Chehbouni. "Estimation of crop water requirements: extending the one-step approach to dual crop coefficients." Hydrology and Earth System Sciences 19, no. 7 (2015): 3287–99. http://dx.doi.org/10.5194/hess-19-3287-2015.
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Abstract. Crop water requirements are commonly estimated with the FAO-56 methodology based upon a two-step approach: first a reference evapotranspiration (ET0) is calculated from weather variables with the Penman–Monteith equation, then ET0 is multiplied by a tabulated crop-specific coefficient (Kc) to determine the water requirement (ETc) of a given crop under standard conditions. This method has been challenged to the benefit of a one-step approach, where crop evapotranspiration is directly calculated from a Penman–Monteith equation, its surface resistance replacing the crop coefficient. Whereas the transformation of the two-step approach into a one-step approach has been well documented when a single crop coefficient (Kc) is used, the case of dual crop coefficients (Kcb for the crop and Ke for the soil) has not been treated yet. The present paper examines this specific case. Using a full two-layer model as a reference, it is shown that the FAO-56 dual crop coefficient approach can be translated into a one-step approach based upon a modified combination equation. This equation has the basic form of the Penman–Monteith equation but its surface resistance is calculated as the parallel sum of a foliage resistance (replacing Kcb) and a soil surface resistance (replacing Ke). We also show that the foliage resistance, which depends on leaf stomatal resistance and leaf area, can be inferred from the basal crop coefficient (Kcb) in a way similar to the Matt–Shuttleworth method.
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Lhomme, J. P., N. Boudhina, M. M. Masmoudi, and A. Chehbouni. "Estimation of crop water requirements: extending the one-step approach to dual crop coefficients." Hydrology and Earth System Sciences Discussions 12, no. 5 (2015): 4933–63. http://dx.doi.org/10.5194/hessd-12-4933-2015.
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Abstract. Crop water requirements are commonly estimated with the FAO-56 methodology based upon a "two-step" approach: first a reference evapotranspiration (ET0) is calculated from weather variables with the Penman–Monteith equation; then ET0 is multiplied by a tabulated crop-specific coefficient (Kc) to determine the water requirement (ETc) of a given crop under standard conditions. This method has been challenged to the benefit of a "one-step" approach, where crop evapotranspiration is directly calculated from a Penman–Monteith equation, its surface resistance replacing the crop coefficient. Whereas the transformation of the two-step approach into a one-step approach has been well documented when a single crop coefficient (Kc) is used, the case of dual crop coefficients (Kcb for the crop and Ke for the soil) has not been treated yet. The present paper examines this specific case. Using a full two-layer model as a reference, it is shown that the FAO-56 dual crop coefficient approach can be translated into a one-step approach based upon a modified combination equation. This equation has the basic form of the Penman–Monteith equation, but its surface resistance is calculated as the parallel sum of a foliage resistance (replacing Kcb) and a soil surface resistance (replacing Ke). We also show that the foliage resistance, which depends on leaf stomatal resistance and leaf area, can be inferred from the basal crop coefficient (Kcb) in a way similar to the Matt–Shuttleworth method.
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Braunworth, William S., and Harry J. Mack. "Evaluation of Irrigation Scheduling Methods for Sweet Corn." Journal of the American Society for Horticultural Science 112, no. 1 (1987): 29–32. http://dx.doi.org/10.21273/jashs.112.1.29.
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Abstract Accurate irrigation scheduling for sweet corn can reduce irrigation costs and ensure meeting of yield goals. Three scheduling methods, evaluated in a 2-year study, included: a) irrigation when 46% and 57% of available water was depleted in 1984 and 1985, respectively, as measured by a neutron meter; b) irrigation when 50% of available water was depleted as estimated by the Food and Agriculture Organization modified Penman equation; and c) irrigation at three growth stages. Irrigation water applied for the neutron meter, modified Penman, and growth stage method was 367, 279, and 269 mm, respectively, in 1984 while in 1985 these methods resulted in application of 500, 368, and 366 mm of irrigation water. Yields of total unhusked ears in 1984 for the growth stage and modified Penman methods were significantly lower than the yields of the neutron meter method but were not significantly different from one another. In 1985, there were no significant differences in total unhusked or husked processable ear yields among the three scheduling methods. Quality factors, which included ear length, kernel moisture content, and ear weight did not vary significantly with irrigation scheduling methods. Since total unhusked, husked processable yields, and quality differences were minor, irrigation scheduling by any of these methods would appear to be satisfactory.
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Cobaner, Murat, Hatice Citakoğlu, Tefaruk Haktanir, and Ozgur Kisi. "Modifying Hargreaves–Samani equation with meteorological variables for estimation of reference evapotranspiration in Turkey." Hydrology Research 48, no. 2 (2016): 480–97. http://dx.doi.org/10.2166/nh.2016.217.
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The Food and Agriculture Organization advocates the Penman–Monteith (FAO-56 PM) equation as the standard model for estimation of the reference evapotranspiration (ET0) because it is considered to have better accuracy. However, in regions where meteorological variables such as solar radiation, wind speed, and relative humidity are not gauged, the Hargreaves–Samani (HS) equation is resorted to as an alternative simply because it needs minimum and maximum air temperatures only as the explanatory variables. In this study, first the HS equation is applied to the monthly means of measured temperature data recorded at 275 meteorology stations in Turkey. Next, the coefficients of the HS equation are calibrated using the ET0 values given by the FAO-56 PM equation at all these stations. Next, the HS equation is modified by adding the wind speed as an extra explanatory variable, separately in each one of seven geographical regions of Turkey, which is observed to yield smaller error statistics as compared to the original HS equation. It is concluded that for estimation of the ET0 in regions where meteorological measurements are scarce, the HS equation modified in a similar manner can be used with better precision.
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Usta, Selçuk. "Comparison of the performances of six empirical mass transfer-based reference evapotranspiration estimation models in semi-arid conditions." PeerJ 12 (November 27, 2024): e18549. http://dx.doi.org/10.7717/peerj.18549.
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Background Accurately measured or estimated reference evapotranspiration (ETo) data are needed to properly manage water resources and prioritise their future uses. ETo can be most accurately measured using lysimeter systems. However, high installation and operating costs, as well as difficult and time-consuming measurement processes limit the use of these systems. Therefore, the approach of estimating ETo by empirical models is more preferred and widely used. However, since those models are well in accordance with the climatic and environmental traits of the region in which they were developed, their reliability must be examined if they are utilised in distinctive regions. This study aims to test the usability of mass transfer-based Dalton, Rohwer, Penman, Romanenko, WMO and Mahringer models in Van Lake microclimate conditions and to calibrate them in compatible with local conditions. Methods Firstly, the original equations of these models were tested using 9 years of daily climate data measured between 2012 and 2020. Then, the models were calibrated using the same data and their modified equations were created. The original and modified equations of the models were also tested with the 2021 and 2022 current climate data. Modified equations have been created using the Microsoft Excel program solver add-on, which is based on linear regression. The daily average ETo values estimated using the six mass transfer-based models were compared with the daily average ETo values calculated using the standard FAO-56 PM equation. The statistical approaches of the mean absolute error (MAE), mean absolute percentage error (MAPE), root mean square error (RMSE), Nash–Sutcliffe Efficiency (NSE), and determination coefficient (R2) were used as comparison criterion. Results The best and worst performing models in the original equations were Mahringer (MAE = 0.70 mm day−1, MAPE = 15.86%, RMSE = 0.87 mm day−1, NSE = 0.81, R2 = 0.94) and Penman (MAE = 1.84 mm day−1, MAPE = 33.68%, RMSE = 2.39 mm day−1, NSE = −0.49, R2 = 0.91), respectively, whereas in the modified equations Dalton (MAE = 0.29 mm day−1, MAPE = 7.51%, RMSE = 0.33 mm day−1, NSE = 0.97, R2 = 0.97) and WMO (MAE = 0.36 mm day−1, MAPE = 8.89%, RMSE = 0.43 mm day−1, NSE = 0.95, R2 = 0.97). The RMSE errors of the daily average ETo values estimated using the modified equations were generally below the acceptable error limit (RMSE < 0.50 mm day−1). It has been concluded that the modified equations of the six mass transfer-based models can be used as alternatives to the FAO-56 PM equation under the Van Lake microclimate conditions (NSE > 0.75), while the original equations—except for those of Mahringer (NSE = 0.81), WMO (NSE = 0.79), and Romanenko (NSE = 0.76)—cannot be used.
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Blanco, Flávio F., and Marcos V. Folegatti. "Evaluation of evaporation-measuring equipments for estimating evapotranspiration within a greenhouse." Revista Brasileira de Engenharia Agrícola e Ambiental 8, no. 2-3 (2004): 184–88. http://dx.doi.org/10.1590/s1415-43662004000200004.
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With the objective of evaluating the performance of simple evaporation measuring equipments in estimating the evapotranspiration in greenhouse, an experiment was conducted in Piracicaba, SP, during a tomato-growing season. Daily water evaporation rate from Piche atmometer, modified atmometer and a reduced evaporation pan installed inside the greenhouse and a Class A pan installed outside were compared to the evapotranspiration rates calculated with Penman-Monteith equation. Results showed that atmometers had the best performance in estimating the crop evapotranspiration in greenhouse and could be used advantageously in relation to the evaporation pans.
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Quiñonez-Piñón, M. Rebeca, and Caterina Valeo. "Modelling Canopy Actual Transpiration in the Boreal Forest with Reduced Error Propagation." Atmosphere 11, no. 11 (2020): 1158. http://dx.doi.org/10.3390/atmos11111158.
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The authors have developed a scaling approach to aggregate tree sap flux with reduced error propagation in modeled estimates of actual transpiration () of three boreal species. The approach covers three scales: tree point, single tree trunk, and plot scale. Throughout the development of this approach the error propagated from one scale to the next was reduced by analyzing the main sources of error and exploring how some field and lab techniques, and mathematical modeling can potentially reduce the error on measured or estimated parameters. Field measurements of tree sap flux at the tree point scale are used to obtain canopy transpiration estimates at the plot scale in combination with allometric correlations of sapwood depth (measured microscopically and scaled to plots), sapwood area, and leaf area index. We compared the final estimates to actual evapotranspiration and actual transpiration calculated with the Penman–Monteith equation, and the modified Penman–Monteith equation, respectively, at the plot scale. The scaled canopy transpiration represented a significant fraction of the forest evapotranspiration, which was always greater than 70%. To understand climate change impacts in forested areas, more accurate actual transpiration estimates are necessary. We suggest our model as a suitable approach to obtain reliable estimates in forested areas with low tree diversity.
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Kra, Eric. "FAO-56 Penman-Monteith DailyETofrom Linear Regression Calibrated Hargreaves Equation with Wind Terms in Tropics with Limited Data." International Journal of Agronomy 2014 (2014): 1–9. http://dx.doi.org/10.1155/2014/402809.
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Hargreaves equation (HG), which lacks a wind speed (u2) term, was modified, through a linear regression calibration method, into LHGu which hasu2terms. LHGu is effectively a simplified method for approximating FAO-56 Penman-Monteith equation (FPM) daily reference evapotranspiration (ETo) in tropics with only temperature data. In LHGu, the “0.0023” constant term in HG was calibrated as a shifted power function ofu2, and the calibration constant was parametrized as a quadratic function ofu2. LHGu was developed using simulated constantu2data and historical temperature data for four sites in West Africa: Abidjan, Accra, Daloa, and Lome. LHGu matched FPMETobetter than HG over a wide range ofu2: for Accra, foru2range 0.5–6.0 m/s, the modified coefficient of efficiency,E1, varied narrowly (0.83–0.98) for LHGu but widely (0.14–0.95) for HG optimized foru2=2.0 m/s; the corresponding MBE ranges were −0.05–0.01 mm/d for LHGu and 0.02–0.63 mm/d for HG which cannot respond to varying dailyu2. LHGu is useful for quickly computing practically accurate estimates of FPMETofor varying dailyu2where only temperature data are available.
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Almsaraf, Sabah Anwer Dawood. "Evaluating the Crop Coefficient for Cherries Plants in Michigan State." Journal of Engineering 20, no. 3 (2023): 41–50. http://dx.doi.org/10.31026/j.eng.2014.03.04.
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Crop coefficient for cherries was evaluated by measure the water consumption in Michigan State to find its variation with time as the plant growth. Crop coefficients value (Kc) for cherries were predicated by Michigan State University (MSU) and also by Food and Agriculture Organization (FAO) according to consume of water through the season. In this paper crop coefficients for cherries are modified accordingly to the actual measurements of soil moisture content. Actual evapotranspiration (consumptive use) were measured by the soil moisture readings using Time Domain Reflectometers (TDR), and compared with the actual potential evapotranspiration that calculated by using modified Penman-Monteith equation which depends on metrological station and by using pan evaporation method. Absolut error techniques show that the predicated crop coefficient by MSU should be modified and changed from 1.0 to 1.20 during June, and from 1.02 during July and August to 1.2 to reduce the crop water stress and give better water management and perfect schedule for irrigation process.
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Lujano, Apolinario, Miguel Sanchez-Delgado, and Efrain Lujano. "Improvement of Hargreaves–Samani Reference Evapotranspiration Estimates in the Peruvian Altiplano." Water 15, no. 7 (2023): 1410. http://dx.doi.org/10.3390/w15071410.
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The FAO 56 Penman–Monteith equation (PM) is considered the most accurate method for estimating reference evapotranspiration (ETo). However, PM requires a large amount of data that is not always available. Thus, the objective of this study is to improve the Hargreaves–Samani (HS) reference evapotranspiration estimates in the Peruvian Altiplano (PA) by calibrating the radiation coefficient KRS. The results show modified HS (HSM) ETo estimates at validation after KRS calibration, revealing evident improvements in accuracy with Nash–Sutcliffe efficiency (NSE) between 0.58 and 0.93, percentage bias (PBIAS) between −0.58 and 1.34%, mean absolute error (MAE) between −0.02 and 0.05 mm/d, and root mean square error (RMSE) between 0.14 and 0.25 mm/d. Consequently, the multiple linear regression (MLR) model was used to regionalize the KRS for the PA. It is concluded that, in the absence of meteorological data, the HSM equation can be used with the new values of KRS instead of HS for the PA.
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Gul, Sajid, Jingli Ren, Neal Xiong, and Muhammad Fawad. "An effective evapotranspiration estimation scheme based on statistical indicators for sustainable environments in humid and semi-arid area of Khyber Pakhtunkhwa, Pakistan." Water Supply 22, no. 3 (2021): 2493–517. http://dx.doi.org/10.2166/ws.2021.457.
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Abstract Reference evapotranspiration (ETo) is critical for irrigation design and water management in rainfed and irrigated agriculture. The Penman-Monteith (FAO-56(PM)) equation was demonstrated to be the most reliable and adaptive to a wide range of humid to semi-arid climates. However, it requires several environmental parameters (e.g., wind speed, solar radiation), rarely available in developing countries. Therefore, numerous temperature-based formulas have been designed to address this issue for various environments. Their calibration and validation against the local climate frequently lead to increases in performance. We revised the Hargreaves exponent (EH) and substituted a value of (0.16) for the original value (0.5). The modified Hargreaves formula enhances the ETo predictions with a mean absolute error ranging from (0.791) mm per day for Balakot to (2.36) mm per day in Risalpur, averaging (3.797) mm per day, as compared to the Hargreaves-Samani (16.827) mm per day. In general, all the selected models showed high accuracy. However, the modified Hargreaves equation appeared to give the most promising results. It ranked first in (50%) of the whole area based on the standard error of estimate for estimating ETo in Khyber Pakhtunkhwa. Additional research must be conducted to determine the study's relevance to other regions.
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Kumari, Arti, Ashutosh Upadhyaya, Pawan Jeet, et al. "Estimation of Actual Evapotranspiration and Crop Coefficient of Transplanted Puddled Rice Using a Modified Non-Weighing Paddy Lysimeter." Agronomy 12, no. 11 (2022): 2850. http://dx.doi.org/10.3390/agronomy12112850.
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Lysimetric and eddy covariance techniques are commonly used to directly estimate actual crop evapotranspiration (ETa). However, these technologies are costly, laborious, and require skills which make in situ ET estimation difficult, particularly in developing countries. With this in mind, an attempt was made to determine ETa and stagewise crop coefficient (Kc) values of transplanted puddled rice using a modified non-weighing paddy lysimeter. The results were compared to indirect methods, viz., FAO Penman–Monteith and pan evaporation. Daily ETa ranged from 1.9 to 8.2 mmday−1, with a mean of 4.02 ± 1.35 mmday−1, and their comparison showed that the FAO Penman–Monteith equation performed well for the coefficient of determination (R2 of 0.63), root mean squared error (RMSE = 0.80), and mean absolute percentage error (MAPE = 13.6 %), and was highly correlated with ETa throughout the crop season. However, the pan evaporation approach was underestimated (R2 of 0.24; RMSE = 0.98; MAPE = 22.13%) due to a consistent pan coefficient value (0.71), vegetation role and measurement errors. In addition, actual Kc values were obtained as 1.13 ± 0.13, 1.27 ± 0.2, 1.23 ± 0.16, and 0.93 ± 0.18 for the initial, crop development, mid-season, and end-season stages, respectively. These estimated crop coefficient values were higher than FAO Kc values. Statistical analysis results revealed that the overall stagewise-derived average Kc values were in line with FAO values, but different from the derived pan Kc values, although found insignificant at a 5% significance level. In addition, water productivity and agro-meteorological indices were derived to evaluate the cultivar performance in this experiment. Therefore, such a methodology may be used in the absence of weighing lysimeter-derived Kc values. The derived regional Kc values can be applied to improve irrigation scheduling under similar agro-climatic conditions.
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Patel, J., H. Patel, and C. Bhatt. "Generalized calibration of the Hargreaves equation for evapotranspiration under different climate conditions." Soil and Water Research 9, No. 2 (2014): 83–89. http://dx.doi.org/10.17221/28/2013-swr.
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Accurate estimation of evapotranspiration (ETo) is a key factor in weather-based irrigation scheduling methods. To estimate ETo using the Hargreaves equation, just the data on the minimum and maximum temperature and solar radiation are required. However, this procedure cannot offer consistent accuracy for different climate conditions. To attain the accuracy, calibration of the equation constants (C<sub>H</sub>and E<sub>H</sub>) for different climate conditions have successfully been attempted by many researchers. Because these calibration procedures are lengthy and location-specific, there is a need of a generalized calibration method to make the Hargreaves equation more pertinent and effective. In this paper, fuzzy logic based calibration method for the Hargreaves equation is proposed and validated. The fuzzy inference system is developed to compute appropriate values of the constants C<sub>H</sub>and E<sub>H</sub> on the basis of past data on humidity and wind velocity of a selected location. The underlying relationship between weather conditions and the best values of the constants C<sub>H</sub>and E<sub>H</sub> are used to establish a fuzzy rule base. The performance of the method is checked at eight geographically different locations of India with diverse climate conditions. The Mean Absolute Error (MAE) in ETovalues estimated by the calibrated modified Hargreaves equation and the Penman-Monteith (PM) equation is in the range of 0.3220&ndash;1.0325. It is far more lower than if the error is calculated using the original Hargreaves equation. It confirms the correctness of the calibration method for different climate conditions.
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Kohu, Mojmír, Jaroslav Rožnovský, and Grazyna Knozová. "Comparison of actual evaporation from water surface measured by GGI-3000 evaporimeter with values calculated by the Penman equation." Contributions to Geophysics and Geodesy 44, no. 3 (2014): 231–40. http://dx.doi.org/10.1515/congeo-2015-0003.
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Abstract Information about water evaporation is essential for the calculation of water balance. Evaporation, however, is a very complex physical process and it is therefore difficult to quantify. Evaporation measurements from the weather station network of the Czech Hydrometeorological Institute between 1968 and 2011 were performed using the evaporimeter GGI-3000. Evaporation was calculated using modified standard method based on FAO. The aim of the article was to compare the measured values and calculations. It has been found that the evaporation values from water surface calculated using the empirical equation are usually higher than the measured values by on average 0.8 mm, in extreme cases even 6.9 mm. The measured data shows higher variability than the calculated values, which means that correlations between series are not strong, the correlation coefficient being 0.7. Nevertheless the findings can be used for homogenization of series measured by the GGI-3000 evaporimeter.
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Amazirh, Abdelhakim, Salah Er-Raki, Abdelghani Chehbouni, et al. "Modified Penman–Monteith equation for monitoring evapotranspiration of wheat crop: Relationship between the surface resistance and remotely sensed stress index." Biosystems Engineering 164 (December 2017): 68–84. http://dx.doi.org/10.1016/j.biosystemseng.2017.09.015.
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Wei, Yingnan, Han Ru, Xiaolan Leng, et al. "Better Performance of the Modified CERES-Wheat Model in Simulating Evapotranspiration and Wheat Growth under Water Stress Conditions." Agriculture 12, no. 11 (2022): 1902. http://dx.doi.org/10.3390/agriculture12111902.
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Crop models are important for understanding and regulating agroecosystems. Although the CERES-Wheat model is an important tool for winter wheat research, it has some limitations under water stress conditions. To narrow the gap, this study aimed to improve the performance of the CERES-Wheat model under water stress in arid and semi-arid regions based on the winter wheat experimental data from 2012 to 2014. The Priestley–Taylor (PT) and FAO56 Penman–Monteith (PM) equations were used to calculate the reference crop evapotranspiration and further modified the crop coefficient of the CERES wheat model to improve the simulation accuracy of crop yield and evapotranspiration under water stress conditions. The results showed that: water stress before jointing seriously affected the accuracy of the CERES-Wheat model in simulating biomass and grain yield, so it was necessary to improve the original model. In the original and improved models, the accuracy of the PM equation was lower than that of PT. In addition, the simulation accuracy of the improved model was higher than that of the original model (the average RMAE and RRMSE are less than 30%). In general, among the four scenarios, the PT equation for calculating crop reference evapotranspiration and crop coefficient had the best performance. Water stress occurred at the heading and grain filling stages, and the simulated biomass was in good agreement with the observed results, which better simulated the soil water content under water stress at the later growth stages. Therefore, the change in water stress response function had positive effects on winter wheat growth under simulated water stress conditions. This study provided a reference for applying the CERES-Wheat model in arid and semi-arid areas.
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Rodrigues, Gonçalo C., and Ricardo P. Braga. "Estimation of Reference Evapotranspiration during the Irrigation Season Using Nine Temperature-Based Methods in a Hot-Summer Mediterranean Climate." Agriculture 11, no. 2 (2021): 124. http://dx.doi.org/10.3390/agriculture11020124.
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The FAO-56 Penman–Monteith (PM) equation is regarded as the most accurate equation to estimate reference evapotranspiration (ETo). However, it requires a broad range of data that may not be available or of reasonable quality. In this study, nine temperature-based methods were assessed for ETo estimation during the irrigation at fourteen locations distributed through a hot-summer Mediterranean climate region of Alentejo, Southern Portugal. Additionally, for each location, the Hargreaves–Samani radiation adjustment coefficient (kRs) was calibrated and validated to evaluate the appropriateness of using the standard value, creating a locally adjusted Hargreaves–Samani (HS) equation. The accuracy of each method was evaluated by statistically comparing their results with those obtained by PM. Results show that the calibration of the kRs, a locally adjusted HS method can be used to estimate daily ETo acceptably well, with RMSE lower than 0.88 mm day−1, an estimation error lower than 4% and a R2 higher than 0.69, proving to be the most accurate model for 8 (out of 14) locations. A modified Hargreaves–Samani method also performed acceptably for 4 locations, with a RMSE of 0.72–0.84 mm day−1, a slope varying from 0.95 to 1.01 and a R2 higher than 0.78. One can conclude that, when weather data is missing, a calibrated HS equation is adequate to estimate ETo during the irrigation season.
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Pereira, Vágna Da Costa, Gilberto Chohaku Sediyama, Magna Soelma Beserra De Moura, Thieres George Freire Da Silva, and Luciana Sandra Bastos De Souza. "EFICIÊNCIA DO USO DA ÁGUA EM VIDEIRA ‘SYRAH’ IRRIGADA NO SUBMÉDIO DO VALE SÃO FRANCISCO1." IRRIGA 21, no. 2 (2018): 269. http://dx.doi.org/10.15809/irriga.2016v21n2p269-283.
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EFICIÊNCIA DO USO DA ÁGUA EM VIDEIRA ‘SYRAH’ IRRIGADA NO SUBMÉDIO DO VALE SÃO FRANCISCO1 VÁGNA DA COSTA PEREIRA1; GILBERTO CHOHAKU SEDIYAMA2; MAGNA SOELMA BESERRA DE MOURA3; THIERES GEORGE FREIRE DA SILVA4 E LUCIANA SANDRA BASTOS DE SOUZA51Resultado da Dissertação de Mestrado do primeiro autor2Doutoranda em Meteorologia Agrícola – Departamento de Engenharia Agrícola – Universidade Federal de Viçosa – Campus Viçosa – 36570-900 – Viçosa, Minas Gerais, Brasil, vagna.pereira@ufv.br3Prof. Titular – Departamento de Engenharia Agrícola – Universidade Federal de Viçosa – Campus Viçosa – 36570-900 – Viçosa, Minas Gerais, Brasil, g.sediyama@ufv.br4Pesquisadora – Núcleo Temático de Recursos Naturais – Embrapa Semiárido – 56302-970 – Petrolina, Pernambuco, Brasil, magna.moura@embrapa.br5Prof. Adjunto – Departamento de Ciências Agrárias – Universidade Federal Rural de Pernambuco – Unidade Acadêmica de Serra Talhada – 56909-535 – Serra Talhada, Pernambuco, Brasil, thigeoprofissional@hotmail.com6Prof. Assistente – Departamento de Ciências Agrárias – Universidade Federal Rural de Pernambuco – Unidade Acadêmica de Serra Talhada – 56909-535 – Serra Talhada, Pernambuco, Brasil, sanddrabastos@yahoo.com.br 1 RESUMO O estudo teve como objetivo estimar a eficiência do uso da água (EUA) na videira ‘Syrah’ irrigada no Submédio do Vale São Francisco, com base no rendimento em função da evapotranspiração da cultura e da transpiração máxima. Para isso, a evapotranspiração da cultura foi determinada pelo balanço de energia com base no método da razão de Bowen (ETcBERB), enquanto a transpiração máxima (TR) foi estimada pelo modelo de Penman-Monteith modificado com base no índice de área foliar da cultura. Os dados micrometeorológicos foram monitorados durante um ciclo produtivo por meio de uma estação automática localizada no parreiral. A evapotranspiração de referência (ETo) também foi calculada ao longo do experimento, pelo método de Penman-Monteith parametrizado no boletim 56 da FAO. A ETo e a ETcBERB corresponderam ao valor total de 474,0 e 376,4 mm ciclo-1, com valor médio diário de 3,9 e 3,1 mm, respectivamente. A TR oscilou entre 3,5 e 0,9 mm d-1, com volume total durante o ciclo de 284,4 mm. A EUA, com base no total de água consumida e transpirada, foi de 1,17 kg m-3 e 1,55 kg m-3, respectivamente. O método do BERB e o modelo de Penman-Monteith modificado para plantas isoladas apresentaram resultados confiáveis para estimativa da EUA sob as condições climáticas da região do Submédio do Vale São Francisco. No entanto, torna-se necessário que novos estudos nesse sentido com a cultura da videira para produção de vinhos sejam realizados, principalmente nesta região Semiárida, onde a maioria das pesquisas voltadas para o manejo do vinhedo ainda estão em desenvolvimento. Palavras-chave: semiárido, evapotranspiração, razão de Bowen, transpiração máxima PEREIRA, V. C.; SEDIYAMA, G. C.; MOURA, M. S. B.; SILVA, T. G. F.; SOUZA, L. S. B.WATER USE EFFICIENCY IN IRRIGATED "SYRAH'' GRAPE PLANTATION AT SÃO FRANCISCO RIVER VALLEY 2 ABSTRACT The objective of this work was to evaluate the water use efficiency (WUE) in irrigated ‘Syrah’ grapevine plantation at São Francisco River valley, on the basis of yields as a function of crop evapotranspiration and maximum transpiration. To this end, the crop evapotranspiration was determined by energy balance based on the Bowen ratio method (ETcBERB), while the maximum transpiration (TR) was estimated by the modified Penman-Monteith equation based on the crop leaf area index. The micrometeorological data within the vineyard canopy were monitored using an automatic micrometeorological station, during a productive cycle. The reference evapotranspiration (ETo) was also calculated during that period using the FAO parameterized Penman-Monteith equation. The reference evapotranspiration (ETo) and the crop evapotranspiration determined by BREB method (ETcBERB), during the crop cycle, were 474.0 and 376.4 mm cycle-1, respectively, with a daily average of 3.9 and 3.1 mm. The TR rate ranged between 3.5 and 0.9 mm d-1, with total volume during 284.4 mm cycle -1. The WUE, on the basis of the total water consumed and transpiration, was 1.17 kg m-3 and 1.55 kg m-3, respectively. The BERB method and the Penman-Monteith model modified to isolated plants showed reliable results to estimate the WUE under the climatic conditions of São Francisco River valley. However, new studies on grape culture for wine production are necessary, especially in this semiarid region, where most researches focused on the vineyard management are still in development. Keywords: Bowen ratio. Evapotranspiration. Maximum transpiration. Semiarid.
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Hu, Maochuan, Takahiro Sayama, Sophal TRY, Kaoru Takara, and Kenji Tanaka. "Trend Analysis of Hydroclimatic Variables in the Kamo River Basin, Japan." Water 11, no. 9 (2019): 1782. http://dx.doi.org/10.3390/w11091782.
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Understanding long-term trends in hydrological and climatic variables is of high significance for sustainable water resource management. This study focuses on the annual and seasonal trends in precipitation, temperature, potential evapotranspiration, and river discharge over the Kamo River basin from the hydrological years 1962 to 2017. Homogeneity was examined by Levene’s test. The Mann–Kendall and a modified Mann–Kendall test as well as Sen’s slope estimator were used to analyze significant trends (p < 0.05) in a time series with and without serial correlation and their magnitudes. The results indicate that potential evapotranspiration calculated by the Penman–Monteith equation was highly related to temperature, and significantly increased in the annual and summer series. Annual river discharge significantly decreased by 0.09 m3/s. No significant trend was found at the seasonal scale. Annual, autumn, and winter precipitation at Kumogahata station significantly increased, while no significant trend was found at Kyoto station. Precipitation was least affected by the modified Mann–Kendall test. Other variables were relatively highly autocorrelated. The modified Mann–Kendall test with a full autocorrelation structure improved the accuracy of trend analysis. Furthermore, this study provides information for decision makers to take proactive measures for sustainable water management.
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Saeed Shah, Syed Muhammad, M. El-Morshedy, and Wahidullah Mansoor. "Spatial-Temporal Interpolation of Reference Evapotranspiration for Pakistan." Mathematical Problems in Engineering 2022 (April 28, 2022): 1–18. http://dx.doi.org/10.1155/2022/5488725.
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The unequal water distribution in the universe has resulted in more than 2 billion people living in water-stressed areas. Globally, withdrawals of water resources are still below the critical level. Pakistan is also affected by this serious problem. In the context of environmental evaluation, irrigation scheduling, and water resource management, evapotranspiration predictions are crucial. The evapotranspiration estimation methods may need to be evaluated daily or monthly to understand the climate change effects in the local areas. This paper investigates spatial-temporal interpolation of evapotranspiration data from 41 Pakistani meteorological stations. To estimate evapotranspiration, we have used the average time series data between 2006 and 2015 on temperature, relative humidity, wind speed, and solar radiation. We developed a new modified Hargreaves equation to estimate evapotranspiration and evaluate the performance of different models. We found that our modified Hargreaves model could perform better than the original Hargreaves model. To analyze trends in different seasons, such as rainy, dry, and annual, FAO-56 Penman-Monteith, Blaney-Criddle, and Hargreaves-Samani models are used. We used Ordinary Kriging for Functional Data to map and predict evapotranspiration spatially and temporally in various locations.
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Staats, David, and James E. Klett. "EVALUATION OF WATER CONSERVATION POTENTIAL OF NON-TURF GROUNDCOVERS VS. KENTUCKY BLUEGRASS UNDER INCREASING LEVELS OF DROUGHT STRESS." HortScience 27, no. 6 (1992): 676c—676. http://dx.doi.org/10.21273/hortsci.27.6.676c.
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In June 1991, a two year field study was initiated to examine if three non-turf groundcovers with reputations for using low amounts of water actually use less water than Kentucky bluegrass (KBG). Irrigation treatments were based on percentages of ET (100%, 75%, 50%, 25%, 0%) and calculated by the modified Penman equation. Results from the 1991 season indicate that at the 100% and 75% treatments Potentilla tabernaemontani and Cerastium tomentosum were significantly better than the other species in terms of establishment and vigor but quality declined significantly at rates below 75%. At the 50% rate both KBG and Sedum acre maintained good quality although growth was slow. At the 25% rate, quality of KBG significantly declined while Sedum acre maintained good quality. Quality of Sedum acre declined only slightly at the 0% treatment and would be a good alternative to KBG if water conservation was a high priority in the landscape.
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Staats, David, and James E. Klett. "WATER CONSERVATION POTENTIAL OF NON-TURF GROUND COVERS VERSUS KENTUCKY BLUEGRASS UNDER INCREASING LEVELS OF DROUGHT STRESS." HortScience 28, no. 5 (1993): 536b—536. http://dx.doi.org/10.21273/hortsci.28.5.536b.
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In June 1991, a two yield field study was initiated to determine if three non-turf ground covers actually use less water than Kentucky Bluegrass (KBG). Irrigation treatments were based on percentages of ET (100%, 75%, 50%, 25%, 0%) and calculated by the modified Penman equation. Establishment rates, visual quality, soil moisture and canopy temperature were measured over two seasons. KBG sustained good appearance at irrigation rates as low as 50% ET. Potentilla tabemaemontani required irrigation rates between 50% and 75% of ET. It can be considered a low water user, but not a water conserving alternative to KBG. Cerastium tomentosum sustained good appearance at irrigation rates as low as 25% of ET. It can be considered a water conserving alternative to KBG but visual quality declined during seed formation. Sedum acre maintained good visual quality at irrigation rates as low as 25% of ET and is a water saving alternative to KBG.
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Villagra, M. M., D. Gabriels, H. Verplancke, R. Hartmann, and K. Reichardt. "Estimating crop coefficients for corn during an evapotranspiration experiment on an oxisol in Brazil." Scientia Agricola 51, no. 2 (1994): 270–78. http://dx.doi.org/10.1590/s0103-90161994000200012.
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Soil water balance components were measured during two periods (from 1989 to 1991) on a Dark Red Latosol (oxisol) in Piracicaba,SP, Brazil. The change in soil water storage and the soil water fluxes at the lower limit of the rooting zone were calculated for a transect of 25 observation plots. Hydraulic head gradients were determined by tensiometer measurements. Soil water flux densities were estimated through Darcy's equation. The actual evapotranspiration of the crops and weeds and the actual evaporation of bare soil were obtained from the water balance equation and this for two periods under different crop rotations. For the first period the sequence was bare soil-corn-weeds and for the second period it was stubble mulch-weeds-corn. For assessing the crop coefficients the potential evapotranspiration was calculated according to two different methods. The first method was based on the modified Penman equation with grass as a reference crop, to obtain this way reference coefficients, and the second method was based on the pan "A" evaporation data in order to obtain pan coefficients. These coefficients were compared with the tabulated crop coefficients. In general when there was no shortage of water during the corn growth, the crop coefficients k c"A" and k c ref were very close to the k c values.
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Marquez-Alvarez, Tariacuri, Joel Hernandez Bedolla, Jesus Pardo-Loaiza, Benjamín Lara-Ledesma, and Constantino Domínguez-Sánchez. "Multi Standardized Precipitation Evapotranspiration Index (Multi-SPEI-ETo): Evaluation of 40 Empirical Methods and Their Influence in SPEI." Agriculture 15, no. 7 (2025): 703. https://doi.org/10.3390/agriculture15070703.
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Reference evapotranspiration (ETo) refers to the combined processes of evaporation and transpiration, which are relevant for hydrology, climate change research, and irrigation system design. The ETo is considered for different climatological studies, agriculture-focused studies, drought indices and climate change as well. From the ETo, water needs can be obtained, and along with precipitation, it is important to determine water availability and drought indices like the Standardized Precipitation Evapotranspiration Index (SPEI). Currently, there are different methods to estimate the ETo based on various climatic variables, which have been proposed for different climates and applied in different regions worldwide. The method standardized by most studies for determining the ETo is the “modified Penman–Monteith” method by the Food and Agriculture Organization (FAO). This method is versatile as it considers different climatic conditions and global latitudes. Due to limited climate data in developing countries like Mexico, alternative methods are used. The present study analyzed 40 comparative methods for determining ETo and their influence on SPEI. The best methods for the study area were chosen, including Hansen, Hargreaves and Samani, and Trajkovic, as they are the best based on the available information in Mexico. Additionally, each equation was adjusted to reduce errors and achieve closer approximations to actual ETo values to obtain the most accurate values possible. The influence on SPEI calculation indicates overestimations in temperature-based methods and underestimations in radiation and mass-transfer-based methods. The SPEI calculation showed fewer errors when using the modified HANSEN equations. In the absence of information, Allen’s temperature-based method is recommended.
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Santos, Antonio Odair, Homero Bergamaschi, Luiz Mauro G. Rosa, and João Ito Bergonci. "Calibrated heat-pulse method for the assessment of maize water uptake." Scientia Agricola 57, no. 1 (2000): 27–31. http://dx.doi.org/10.1590/s0103-90162000000100006.
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Plant water requirements are important aspects of crop production to be determined in the field, in order to judiciously manage crop water usage. Water uptake by field grown maize (Zea mays L.), under well-watered conditions was verified with the heat-pulse system. The temperature difference between two radially inserted thermocouples, one 9 mm above and the other 4 mm below a heater piercing the maize stem, was measured every 0.3 seconds following emission of a heat-pulse. Comparisons of the heat-pulse system outputs, lysimetric measurement and transpiration model estimates were monitored on an hourly and daily basis. At normal and low atmospheric demand daily and hourly values of heat-pulse outputs and lysimetric measurement showed good agreement. Hourly agreement of a modified Penman-Monteith energy balance equation estimate and heat-pulse outputs showed accordance between measurement of sap flow and the plant water-loss theory. Study of the relationship between maize canopy water loss rate and heat velocity in the stem showed that these two parameters were proportional and a calibration factor of 1.51 for full soil foliage coverage was verified.
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SAMBASIVARAO, A., and VK VAMADEVAN. "Evaporation rates from different pans under humid tropical conditions." MAUSAM 37, no. 3 (1986): 325–28. http://dx.doi.org/10.54302/mausam.v37i3.2378.
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Under humid tropical conditions, the relative evaporation .rates from Class A open pan, G.G.I. 3000 and Colorado sunken pans were studied.. The recorded evaporation values were compared with evaporation estimated with a modified Penman equation. The Inter relationship between evaporation values and the influence of weather parameters on evaporation were also studied using statistical correlations.
 About 88-93 per cent of insolation was absorbed from the pan surfaces for evaporation. The seasonal variation of evaporation was between 4 and 10. mm/day and the variation In evaporation due to type of pan used was up to 3 mm/day. The estimated evaporation values were within +-2.0 mm/day from the measured values. The evaporation values from the sunken pans were higher than from Class A by 1-3 mm/day and they were also closely correlated. The aerodynamic parameters were closely correlated with evaporation from Class A than from the sunken pans. The high soil thermal regime the area during October to May has increased the evaporation from the sunken pans.
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Yang, Xiaoping, Nina Ma, Jufeng Dong, et al. "Recharge to the Inter-Dune Lakes and Holocene Climatic Changes in the Badain Jaran Desert, Western China." Quaternary Research 73, no. 1 (2010): 10–19. http://dx.doi.org/10.1016/j.yqres.2009.10.009.
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We present new estimates on evaporation and groundwater recharge in the Badain Jaran Desert, western Inner Mongolia of northwestern China, based on a modified Penman Equation suitable for lakes in China. Geochemical data and water balance calculations suggest that local rainfall makes a significant contribution to groundwater recharge and that past lake-level variations in this desert environment should reflect palaeoclimatic changes. The chronology of lake-level change, established by radiocarbon and U-series disequilibrium dating methods, indicates high lake levels and a wetter climate beginning at ca. 10 ka and lasting until the late mid-Holocene in the Badain Jaran Desert. The greatest extension of lakes in the inter-dune depressions indicates that the water availability was greatest during the mid-Holocene. Relicts of Neolithic tools and pottery of Qijia Culture (2400–1900 BC) suggest relatively intensive human activity in the Badain Jaran Desert during the early and middle Holocene, supporting our interpretation of a less harsh environment. Wetter climates during the Holocene were likely triggered by an intensified East Asian summer monsoon associated with strong insolation.
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Staats, David, and James E. Klett. "Water Conservation Potential and Quality of Non-turf Groundcovers versus Kentucky Bluegrass under Increasing Levels of Drought Stress." Journal of Environmental Horticulture 13, no. 4 (1995): 181–85. http://dx.doi.org/10.24266/0738-2898-13.4.181.
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Abstract In June 1991, a 2-year field study was initiated to examine if three non-turf groundcovers require less irrigation than Kentucky bluegrass (KBG). Irrigation treatments were based on decreasing percentage of évapotranspiration (ET) (100%, 75%, 50%, 25% and 0%). ET was estimated by the modified Penman equation using alfalfa as a reference crop. Plants receiving the 0% irrigation treatment were not irrigated and relied on precipitation for survival. The groundcovers studied were Kentucky bluegrass ‘Challenger’ (Poa pratensis L.), creeping potentilla (Potentilla tabernaemontani Asch.), goldmoss (Sedum acre L.) and snow-in-summer (Cerastium tomentosum L.). Data were collected on visual ratings, growth, soil moisture and canopy temperature. Optimum irrigation for KBG was 50% ET. Cerastium required irrigation at 50%-75% of estimated ET during the initial season (1991) for optimum appearance and growth. During 1992, the plants were better established and 25% ET was optimum. Potentilla required irrigation at the 75% ET rate for optimum visual quality. Sedum maintained a good aesthetic appearance at irrigation rates as low as 25% ET and could be considered as a water-conserving alternative to KBG
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Ghasemi-Saadatabadi, Fatemeh, Shahrokh Zand-Parsa, Mahdi Gheysari, Ali Reza Sepaskhah, Mehdi Mahbod, and Gerrit Hoogenboom. "Improving prediction accuracy of CSM-CERES-Wheat model for water and nitrogen response using a modified Penman-Monteith equation in a semi-arid region." Field Crops Research 312 (May 2024): 109381. http://dx.doi.org/10.1016/j.fcr.2024.109381.
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Whitley, Rhys, Belinda Medlyn, Melanie Zeppel, Catriona Macinnis-Ng, and Derek Eamus. "Comparing the Penman–Monteith equation and a modified Jarvis–Stewart model with an artificial neural network to estimate stand-scale transpiration and canopy conductance." Journal of Hydrology 373, no. 1-2 (2009): 256–66. http://dx.doi.org/10.1016/j.jhydrol.2009.04.036.
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SARMA, AALN, VVIZAYA BHASKAR, and CM SASTRY. "Potential Evapotranspiration over India - An estimate of Green Water flow." MAUSAM 65, no. 3 (2014): 365–78. http://dx.doi.org/10.54302/mausam.v65i3.1042.
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The spatial distribution of Potential Evapotranspiration (PET) is studied by selecting stations that are drawn from the Koppen Climate spectrum of India that spread the length and breadth of the country using the modified Penman potential evapotranspiration equation. Annual and seasonal PET trends are reported. Variation of mean seasonal PET for the country as whole for all the four meteorological seasons and its rate of change are graphically shown. Anomalies in the annual and seasonal PET for the epoch of 1961-1995 with reference to the base period 1931-1960 are brought out. Distribution of climatic types over India according to Koppens climate classification for the period 1951-1980 are presented along with the changes that occurred compared to earlier report. Koppen climate types are characterized in terms of PET to P ratio expressed in percentage. Significant decreasing, increasing and no trend are noticed in annual PET both in space and time. Annual PET for the country as a whole is increased in the latter half of the 20th century. The mean seasonal potential evapotranspiration to precipitation ratio is found to be increased from tropical monsoon climates to dry climate types.
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Gutiérrez, Marco V., and Frederick C. Meinzer. "Estimating Water Use and Irrigation Requirements of Coffee in Hawaii." Journal of the American Society for Horticultural Science 119, no. 3 (1994): 652–57. http://dx.doi.org/10.21273/jashs.119.3.652.
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Crop evapotranspiration (ETc) was measured as evaporative heat flux from drip-irrigated coffee (Coffea arabica L. cv. Yellow Catuai) fields at different stages of canopy development using the Bowen ratio-energy balance technique. Irrigation requirements were determined by comparing the ETc values obtained against reference values (ET0) derived from a modified Penman equation, and expressed as the ETc/ET0 ratio, or crop coefficient (Kc). In 1991, the average Kc was 0.75 to 0.79 for fields containing 2- to 4-year-old plantings. This ratio was 0.58 for a field containing a 1-year-old planting. Crop coefficient was 30% lower in 1992 due to higher ET0 values and lower stomatal conductance. Measurements made between July and August and again between September and November 1991 suggested that Kc may vary seasonally. Crop transpiration (T), determined with the stem heat balance technique, comprised from 40% to 95% of ETc as the leaf area index increased from 1.4 to 6.7. Behavior of Kc and T during a 25-day soil drying-reirrigation cycle indicated that the crop was able to maintain relatively high levels of gas-exchange activity during periods of severe water deficit.
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Levitt, D. G., J. R. Simpson, and J. L. Tipton. "Water Use of Two Landscape Tree Species in Tucson, Arizona." Journal of the American Society for Horticultural Science 120, no. 3 (1995): 409–16. http://dx.doi.org/10.21273/jashs.120.3.409.
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Although water conservation programs in the arid southwestern United States have prompted prudent landscaping practices such as planting low water use trees, there is little data on the actual water use of most species. The purpose of this study was to determine the actual water use of two common landscape tree species in Tucson, Ariz., and water use coefficients for two tree species based on the crop coefficient concept. Water use of oak (Quercus virginiana `Heritage') and mesquite (Prosopis alba `Colorado') trees in containers was measured from July to October 1991 using a precision balance. Water-use coefficients for each tree species were calculated as the ratio of measured water use per total leaf area or per projected canopy area to reference evapotranspiration obtained from a modified FAO Penman equation. After accounting for tree growth, water-use coefficients on a total leaf area basis were 0.5 and 1.0 for oak and mesquite, respectively, and on a projected canopy area basis were 1.4 and 1.6 for oaks and mesquites, respectively. These coefficients indicate that mesquites (normally considered xeric trees) use more water than oaks (normally considered mesic trees) under nonlimiting conditions.
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Villaroman, Cresan Joy, Armando Espino, Jeffrey Lavarias, and Victorino Taylan. "Atmometer – based irrigation scheduling system for drip – irrigated onion (Allium cepa L.)." MATEC Web of Conferences 192 (2018): 03039. http://dx.doi.org/10.1051/matecconf/201819203039.
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This study was conducted to develop an atmometer-based irrigation scheduling system for drip-irrigated onion production. The study was conducted at San Agustin, San Jose City Nueva Ecija from November 2016 – March 2017. Three treatments composing of three replicates were considered in the research. Treatments 1 and 2 were based on the recorded atmometer readings with an irrigation interval of two days and five days respectively. Treatment 3 is a soil moisture-based irrigation scheduling with a management allowed deficit of 50 %. Calibration curved was obtained by comparing the atmometer readings with the estimated evapotranspiration using Modified Penman-Monteith equation. It was used in computing the crop water requirement for Treatments 1 and 2. The important parameters that used to answer the objective of the study such as plant height, crop yield, bulb weight, bulb diameter, water use and water productivity, were acquired during and after crop production. The statistical analysis used in the study was Analysis of Variance for Complete Randomized Design and paired T-test. Based on the result, Treatment 1 was highly useful in increasing water productivity without sacrificing the crop qualities.
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Uzunlar, Ali, and Muhammet Omer Dis. "Novel Approaches for the Empirical Assessment of Evapotranspiration over the Mediterranean Region." Water 16, no. 3 (2024): 507. http://dx.doi.org/10.3390/w16030507.
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The hydrological cycle should be scrutinized and investigated under recent climate change scenarios to ensure global water management and to increase its utilization. Although the FAO proposed the use of the Penman–Monteith (PM) equation worldwide to predict evapotranspiration (ET), which is one of the most crucial components of the hydrological cycle, its complexity and time-consuming nature, have led researchers to examine alternative methods. In this study, the performances of numerous temperature-driven ET methods were examined relative to the PM using daily climatic parameters from central stations in 11 districts of the Kahramanmaras province. Owing to its geographical location and other influencing factors, the city has a degraded Mediterranean climate with varying elevation gradients, while its meteorological patterns (i.e., temperature and precipitation) deviate from those of the main Mediterranean climate. A separate evaluation was performed via ten different statistical metrics, and spatiotemporal ET variability was reported for the districts. This study revealed that factors such as altitude, terrain features, slope, aspect geography, solar radiation, and climatic conditions significantly impact capturing reference values, in addition to temperature. Moreover, an assessment was conducted in the region to evaluate the effect of modified ET formulae on simulations. It can be drawn as a general conclusion that the Hargreaves–Samani and modified Blaney–Criddle techniques can be utilized as alternatives to PM in estimating ET, while the Schendel method exhibited the lowest performance throughout Kahramanmaras.
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Peng, Xiongbiao, Xuanang Liu, Yunfei Wang, and Huanjie Cai. "Evapotranspiration Partitioning and Estimation Based on Crop Coefficients of Winter Wheat Cropland in the Guanzhong Plain, China." Agronomy 13, no. 12 (2023): 2982. http://dx.doi.org/10.3390/agronomy13122982.
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Accurate estimation and effective portioning of actual evapotranspiration (ETa) into soil evaporation (E) and plant transpiration (T) are important for increasing water use efficiency (WUE) and optimizing irrigation schedules in croplands. In this study, E/T partitioning was performed on ETa rates measured using the eddy covariance (EC) technique in three winter wheat growing seasons from October 2020 to June 2023. The variation in the crop coefficients (Kc, α, and KHc) were quantified by combining the ETa and reference evapotranspiration rates using the Penman–Monteith, Priestley–Taylor, and Hargreaves equations. In addition, the application of models based on the modified crop coefficient (Kc, α, and KHc) was proposed to estimate the ETa rates. According to the obtained results, the average cumulative ETa, T, and E rates in the three winter wheat growth seasons were 471.4, 265.2, and 206.3 mm, respectively. The average T/ETa ratio ranged from 0.16 to 0.72 at the different winter wheat growth stages. Vapor pressure deficit (VPD) affected the ETa rates at a threshold of 1.27 KPa. The average Kc, α, and KHc values in the middle stage were 1.34, 1.54, and 1.21, respectively. The measured ETa rates and ETa rates estimated using the adjusted Kc, α, and KHc showed regression slope coefficients of 0.96, 0.99, and 0.96, and coefficients of determination (R2) of 0.92, 0.93, and 0.90, respectively. Therefore, the Priestley–Taylor-equation-based adjusted crop coefficient is recommended. The adjusted crop-coefficient-based models can be used as valuable tools for local policymakers to effectively improve water use.
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Zhang, Xiaolong, Bing Shen, Lingmei Huang, Changsen Zhao, Jiqiang Lyu, and Quan Quan. "Complementary relationship estimation of actual evapotranspiration in extreme cold and arid areas: a case study of the Hotan River Basin, northwest China." Hydrology Research 49, no. 5 (2017): 1540–58. http://dx.doi.org/10.2166/nh.2017.104.
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Abstract Application of complementary relationship (CR) approaches using only routine meteorological data is a very convenient method of estimating actual evapotranspiration (ETa). Reanalysis datasets and remote sensing data provide good tools to overcome the difficulties in obtaining observation data. This study of the Hotan River Basin (HRB) in northwest China serves as a prime example for estimation of ETa during 2006–2014 by using the modified generalized CR. Based on comparison and analysis, the maximum potential evaporation calculated by the Penman-based equation was adopted. The estimated ETa rates were verified using a regional water balance method at annual time scales because of the limited available data. The calibration parameter was calibrated based on the elevation and underlying surface types. The mean annual ETa ranged from 2.3 mm to 800 mm during 2006–2014. ETa rates in the plains regions were higher than those in the mountainous regions. Most of ETa was concentrated in the months of May to September. A water deficit occurred in the middle and lower regions, while a water surplus occurred in the upper regions. This study not only provided a new concept for calibration, but also a potential solution for different underlying surfaces and time scales.
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Oribi, Mustafa, and Asraa Abdulkareem. "Scenarios to reduce evaporation from class A evaporation pan by using windbreaks." Przegląd Naukowy Inżynieria i Kształtowanie Środowiska 29, no. 3 (2020): 343–54. http://dx.doi.org/10.22630/pniks.2020.29.3.29.
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Evaporation from reservoirs and lakes is an important processes frequently occurring in dry, hot regions such as Iraq. In order to preserve the environment and to reduce the amount of evaporation from open water bodies in this study, simulation was performed to reduce evaporation from evaporation basin class A by using windbreaks natural (Conocarpus trees). Three basic scenarios were made that depended on the values of the atmospheric elements affecting the evaporation process in summer according to the modified Penman equation for the conditions of Iraq, the climate factors are temperature, solar radiation, wind speed, dew point, and the effect of the number of windbreaks and their height was also introduced in sub- scenario. Experiments have shown that the best sub-scenario for all basic scenarios is when the windbreaks are placed in a direct direction to the wind blowing on the evaporation basin in the form of three rows, each row contains three trees where the windbreaks are in case cross and the height of the trees is 100 cm and the distance between each tree and another, and between each row and row 15 × 15 cm, the results of this subscenario recorded the highest rate of evaporation reduction up to 35% of its original value before using windbreaks.
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Wang, Wei-guang, Shan Zou, Zhao-hui Luo, Wei Zhang, Dan Chen, and Jun Kong. "Prediction of the Reference Evapotranspiration Using a Chaotic Approach." Scientific World Journal 2014 (2014): 1–13. http://dx.doi.org/10.1155/2014/347625.
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Evapotranspiration is one of the most important hydrological variables in the context of water resources management. An attempt was made to understand and predict the dynamics of reference evapotranspiration from a nonlinear dynamical perspective in this study. The reference evapotranspiration data was calculated using the FAO Penman-Monteith equation with the observed daily meteorological data for the period 1966–2005 at four meteorological stations (i.e., Baotou, Zhangbei, Kaifeng, and Shaoguan) representing a wide range of climatic conditions of China. The correlation dimension method was employed to investigate the chaotic behavior of the reference evapotranspiration series. The existence of chaos in the reference evapotranspiration series at the four different locations was proved by the finite and low correlation dimension. A local approximation approach was employed to forecast the daily reference evapotranspiration series. Low root mean square error (RSME) and mean absolute error (MAE) (for all locations lower than 0.31 and 0.24, resp.), high correlation coefficient (CC), and modified coefficient of efficiency (for all locations larger than 0.97 and 0.8, resp.) indicate that the predicted reference evapotranspiration agrees well with the observed one. The encouraging results indicate the suitableness of chaotic approach for understanding and predicting the dynamics of the reference evapotranspiration.
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BOHAİENKO, Vsevolod, Tetiana MATİASH, and Mykhailo ROMASHCHENKO. "Simulation of irrigation in southern Ukraine incorporating soil moisture state in evapotranspiration assessments." EURASIAN JOURNAL OF SOIL SCIENCE (EJSS) 12, no. 3 (2023): 267–76. http://dx.doi.org/10.18393/ejss.1277096.
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The paper studies the accuracy of modeling moisture transport under the conditions of sprinkler irrigation using evapotranspiration assessment methods that take into account the soil moisture conditions. Appropriate modifications of the Penman-Monteith and the Priestley-Taylor models are considered. Moisture transport modeling is performed using the Richards equation in its integer- and fractional-order forms. Parameters identification is performed by the particle swarm optimization algorithm based on the readings of suction pressure sensors. Results for the two periods of 11 and 50 days demonstrate the possibility of up to ~20% increase in the simulation accuracy by using a modified Priestley-Taylor model when the maintained range of moisture content in the root layer is 70%-100% of field capacity. When irrigation maintained the range of 80%-100% of field capacity, moisture content consideration within evapotranspiration assessment models did not enhance simulation accuracy. This confirms the independence of evapotranspiration from soil moisture content at its levels above 80% of field capacity as in this case actual evapotranspiration reaches a level close to the potential one. Scenario modeling of the entire growing season with the subsequent estimation of crop (maize) yield showed that irrigation regimes generated using evapotranspiration models, which take into account soil moisture data, potentially provide higher yields at lower water supply.
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A. S. RAO and SURENDRA POONIA. "Climate change impact on crop water requirements in arid Rajasthan." Journal of Agrometeorology 13, no. 1 (2011): 17–24. http://dx.doi.org/10.54386/jam.v13i1.1328.
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The impact of projected climate change by 21st century on water requirements of rainfed monsoon and irrigated winter crops of arid Rajasthan has been studied. Crop water requirements were estimated from daily potential evapotranspiration at ambient and projected air temperature by 2020, 2050, 2080 and 2100 using modified Penman-Monteith equation and then by multiplying with crop coefficients. Crop water requirements in the region varied from 308 to 411 mm for pearl millet, 244 to 332 mm for clusterbean, 217 to 296 mm for green gram, 189 to 260 mm for moth bean, 173 to 288 mm for wheat and 209 to 343 mm for mustard. Further, due to global warming, if the projected temperatures rises by 40C, by the end of 21st century, water requirement in arid Rajasthan increases from the current level, by 12.9% for pearl millet and clusterbean, 12.8% for green gram, 13.2% for moth bean, 17.1% for wheat and 19.9% for mustard. The increased crop water requirements in the region, resulted in reduction in crop growing period by 5 days for long duration crops, but the crop acreage where rainfall satisfies crop water requirements, reduced by 23.3% in pearl millet, 15.2% in clusterbean, 6.7% in green gram, 13% in moth bean. The study reveals that the impact will be more severe on rabi crops than kharif crops, the rabi crops being dependent on depleting ground water resources in the region.
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Zhang, Yongqiang, Francis H. S. Chiew, Lu Zhang, and Hongxia Li. "Use of Remotely Sensed Actual Evapotranspiration to Improve Rainfall–Runoff Modeling in Southeast Australia." Journal of Hydrometeorology 10, no. 4 (2009): 969–80. http://dx.doi.org/10.1175/2009jhm1061.1.
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Abstract This paper explores the use of the Moderate Resolution Imaging Spectroradiometer (MODIS), mounted on the polar-orbiting Terra satellite, to determine leaf area index (LAI), and use actual evapotranspiration estimated using MODIS LAI data combined with the Penman–Monteith equation [remote sensing evapotranspiration (ERS)] in a lumped conceptual daily rainfall–runoff model. The model is a simplified version of the HYDROLOG (SIMHYD) model, which is used to estimate runoff in ungauged catchments. Two applications were explored: (i) the calibration of SIMHYD against both the observed streamflow and ERS, and (ii) the modification of SIMHYD to use MODIS LAI data directly. Data from 2001 to 2005 from 120 catchments in southeast Australia were used for the study. To assess the modeling results for ungauged catchments, optimized parameter values from the geographically nearest gauged catchment were used to model runoff in the ungauged catchment. The results indicate that the SIMHYD calibration against both the observed streamflow and ERS produced better simulations of daily and monthly runoff in ungauged catchments compared to the SIMHYD calibration against only the observed streamflow data, despite the modeling results being assessed solely against the observed streamflow data. The runoff simulations were even better for the modified SIMHYD model that used the MODIS LAI directly. It is likely that the use of other remotely sensed data (such as soil moisture) and smarter modification of rainfall–runoff models to use remotely sensed data directly can further improve the prediction of runoff in ungauged catchments.
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Fischer, T., M. Veste, O. Bens, and R. F. Hüttl. "Dew formation on the surface of biological soil crusts in central European sand ecosystems." Biogeosciences Discussions 9, no. 7 (2012): 8075–92. http://dx.doi.org/10.5194/bgd-9-8075-2012.
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Abstract. Dew formation was investigated in three developmental stages of biological soil crusts (BSC), which were collected along a catena of an inland dune and in the initial substrate. The Penman equation, which was developed for saturated surfaces, was modified for unsaturated surfaces and used for prediction of dewfall rates. The levels of surface saturation required for this approach were predicted using the water retention functions and the thicknesses of the BSCs. During a single event, dewfall increased with crust development from 0.08 kg m−2 for the initial substrate to 0.10, 0.20 and 0.25 kg m−2 for crusts stages 1 to 3, respectively, which was well reflected by the model response. The suggested mechanism of dew formation involves a delay in water saturation in near-surface soil pores and EPS where the crusts were thicker and where the water capacity was high, resulting in elevated vapor flux towards the surface. The results also indicate that the amount of dewfall was too low to observe water flow into deeper soil. Analysis of the soil water retention curves revealed that, despite the sandy mineral matrix, moist crusts with clogged by swollen EPS pores exhibited a clay-like behavior. It is hypothesized that BSCs gain double benefit from suppressing their competitors by runoff generation and from improving their water supply by dew collection. Despite higher amounts of dew, the water availability to the crust community decreases with crust development, which may be compensated by ecophysiological adaptation of crust organisms, and which may further suppress higher vegetation or mosses.