scholarly journals High-resolution global grids of revised Priestley–Taylor and Hargreaves–Samani coefficients for assessing ASCE-standardized reference crop evapotranspiration and solar radiation

2017 ◽  
Vol 9 (2) ◽  
pp. 615-638 ◽  
Author(s):  
Vassilis G. Aschonitis ◽  
Dimitris Papamichail ◽  
Kleoniki Demertzi ◽  
Nicolo Colombani ◽  
Micol Mastrocicco ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Climatic Data ◽  
Climatic Zones ◽  
Reference Crop Evapotranspiration ◽  
Weighted Averages ◽  
The Usa ◽  
Validation Procedure ◽  
The Mean ◽  
American Society ◽  
Reference Crop

Abstract. The objective of the study is to provide global grids (0.5°) of revised annual coefficients for the Priestley–Taylor (P-T) and Hargreaves–Samani (H-S) evapotranspiration methods after calibration based on the ASCE (American Society of Civil Engineers)-standardized Penman–Monteith method (the ASCE method includes two reference crops: short-clipped grass and tall alfalfa). The analysis also includes the development of a global grid of revised annual coefficients for solar radiation (Rs) estimations using the respective Rs formula of H-S. The analysis was based on global gridded climatic data of the period 1950–2000. The method for deriving annual coefficients of the P-T and H-S methods was based on partial weighted averages (PWAs) of their mean monthly values. This method estimates the annual values considering the amplitude of the parameter under investigation (ETo and Rs) giving more weight to the monthly coefficients of the months with higher ETo values (or Rs values for the case of the H-S radiation formula). The method also eliminates the effect of unreasonably high or low monthly coefficients that may occur during periods where ETo and Rs fall below a specific threshold. The new coefficients were validated based on data from 140 stations located in various climatic zones of the USA and Australia with expanded observations up to 2016. The validation procedure for ETo estimations of the short reference crop showed that the P-T and H-S methods with the new revised coefficients outperformed the standard methods reducing the estimated root mean square error (RMSE) in ETo values by 40 and 25 %, respectively. The estimations of Rs using the H-S formula with revised coefficients reduced the RMSE by 28 % in comparison to the standard H-S formula. Finally, a raster database was built consisting of (a) global maps for the mean monthly ETo values estimated by ASCE-standardized method for both reference crops, (b) global maps for the revised annual coefficients of the P-T and H-S evapotranspiration methods for both reference crops and a global map for the revised annual coefficient of the H-S radiation formula and (c) global maps that indicate the optimum locations for using the standard P-T and H-S methods and their possible annual errors based on reference values. The database can support estimations of ETo and solar radiation for locations where climatic data are limited and it can support studies which require such estimations on larger scales (e.g. country, continent, world). The datasets produced in this study are archived in the PANGAEA database (https://doi.org/10.1594/PANGAEA.868808) and in the ESRN database (http://www.esrn-database.org or http://esrn-database.weebly.com).

scholarly journals High resolution global grids of revised Priestley-Taylor and Hargreaves-Samani coefficients for assessing ASCE-standardized reference crop evapotranspiration and solar radiation

2016 ◽  
Author(s):  
Vassilis G. Aschonitis ◽  
Dimitris Papamichail ◽  
Kleoniki Demertzi ◽  
Nicolo Colombani ◽  
Micol Mastrocicco ◽  
...  
Keyword(s):  
High Resolution ◽  
Solar Radiation ◽  
Climatic Data ◽  
Climatic Zones ◽  
Reference Crop Evapotranspiration ◽  
Weighted Averages ◽  
Validation Procedure ◽  
The Given ◽  
Reference Crop ◽  
Statistical Criteria

Abstract. The objective of the study is to provide high resolution global grids of revised annual coefficients for the Priestley-Taylor (P-T) and Hargreaves-Samani (H-S) evapotranspiration methods after calibration based on ASCE-standardized Penman-Monteith method (ASCE method includes two reference crops: short clipped grass and tall alfalfa). The analysis also includes the derivation of global grids of revised annual coefficients for solar radiation Rs estimations using the respective Rs formula of H-S. The analysis was based on global gridded climatic data of the period 1950–2000. The method for deriving annual coefficients of P-T and H-S methods was based on partial weighted averages (p.w.a.) of their mean monthly values, which eliminate the effect of monthly coefficients that occur during periods where ETo and Rs fall below a specific threshold. Five resolution global grids (30 arc-sec, 2.5, 5, 10 arc-min and 0.5 deg) of annual coefficients for each method were developed. The new coefficients were validated based on data from 140 stations located at various climatic zones of USA and Australia with expanded observations up to 2016. Nine statistical criteria including Taylor diagrams were used in the validation procedure. The validation procedure for ETo estimations of short reference crop showed that the P-T and H-S methods with the new revised coefficients outperformed in comparison to the typical methods reducing the ETo RMSE of estimated values by 39 % and 36 %, respectively. The estimations of Rs using the H-S formula with revised coefficients reduced the RMSE by 30% in comparison to the typical H-S radiation formula (the given results are based on the finer resolution grid). All the statistical criteria indicated better performance of the revised coefficients of all resolutions versus the typical coefficients used in the original methods. Finally, a raster database was built consisting of: a) global maps of revised annual coefficients for the ETo methods of P-T and H-S for both reference crops and the Rs H-S formula, b) global maps which indicate the optimum locations for using the original P-T and H-S methods and their expected error based on reference values. The provision of the database aims to improve ETo and Rs estimations which are used in hydrologic/climatic applications when climatic data are limited. The datasets produced in this study are archived in PANGAEA database (doi:10.1594/PANGAEA.868808, doi:10.1594/PANGAEA.868808) and in ESRN-database (http://www.esrn-database.org or http://esrn-database.weebly.com/).

scholarly journals Impacts of Climatic Change on Reference Crop Evapotranspiration across Different Climatic Zones of Ningxia at Multi-Time Scales from 1957 to 2018

2020 ◽  
Vol 2020 ◽  
pp. 1-23
Author(s):  
Ziyang Zhao ◽  
Hongrui Wang ◽  
Cheng Wang ◽  
Wangcheng Li ◽  
Hao Chen ◽  
...  
Keyword(s):  
Water Management ◽  
Time Scales ◽  
Air Temperature ◽  
Climatic Factors ◽  
Crop Evapotranspiration ◽  
Climatic Zones ◽  
Reference Crop Evapotranspiration ◽  
Short Period ◽  
The Impact ◽  
Reference Crop

The impact of global climate change on agroecosystems is growing, affecting reference crop evapotranspiration (ET0) and subsequent agricultural water management. In this study, the climate factors temporal trends, the spatiotemporal variation, and the climate driving factors of ET0 at different time scales were evaluated across the Northern Yellow River Irrigation Area (NYR), Central Arid Zone (CAZ), and Southern Mountain Area (SMA) of Ningxia based on 20 climatic stations’ daily data from 1957 to 2018. The results showed that the Tmean (daily mean air temperature), Tmax (daily maximum air temperature), and Tmin (daily minimum air temperature) all had increased significantly over the past 62 years, whilst RH (relative humidity), U2 (wind speed at 2 m height), and SD (sunshine duration) had significantly decreasing trends across all climatic zones. At monthly scale, the ET0 was mainly concentrated from April to September. And at annual and seasonal scales, the overall increasing trends were more pronounced in NX, NYR, and SMA, while CAZ was the opposite. For the spatial distribution, ET0 presented a trend of rising first and then falling at all time scales. The abrupt change point for climatic factors and ET0 series was obtained at approximately 1990 across all climatic zones, and the ET0 had a long period of 25a and a short period of 10a at annual scale, while it was 15a and 5a at seasonal scale. RH and Tmax were the most sensitive climatic factors at the annual and seasonal scales, while the largest contribution rates were Tmax and SD. This study not only is important for the understanding of ET0 changes but also provides the preliminary and elementary reference for agriculture water management in Ningxia.

Performance of Modified Temperature-Based Reference Crop Evapotranspiration Models Across Different Agro-Climatic Zones in Karnataka State, India

2020 ◽  
Author(s):  
Niranjan Siddalingamurthy ◽  
Lakshman Nandagiri
Keyword(s):  
Effective Temperature ◽  
Alternative Methods ◽  
Model Parameters ◽  
Crop Evapotranspiration ◽  
Local Calibration ◽  
Climatic Zones ◽  
Reference Crop Evapotranspiration ◽  
Mean Temperature ◽  
Karnataka State ◽  
Reference Crop

<p>Reference crop evapotranspiration (ET<sub>0</sub>) forms an essential forcing variable in hydrological, agricultural, irrigation and climate models. Among several available methods for ET<sub>0 </sub>estimation using regularly recorded climate data, the Food and Agriculture Organization (FAO) Penman-Monteith (PM) equation is popular among researchers due to its accuracy across different environments. However, routine use of the FAO-PM equation is hampered in data-scarce situations because of the requirement of input data pertaining to a large number of climate variables. Therefore, simpler alternative methods for ET<sub>0</sub> estimation such as the Blaney-Criddle (BC) and Hargreaves (HG) have been proposed by previous researchers. However, for routine use of these empirical equations, local calibration of the model parameters may be desirable. Also, a few previous attempts have been made to replace the daily mean temperature with an effective temperature calculated as a weighted average of daily maximum and minimum temperatures.  Therefore, the present study was taken up to evaluate the effect of two aspects on the accuracies of the BC and HG models 1) replacing mean temperature with effective temperature defined using different parameterizations 2) local calibration of parameters. For this purpose, climate records for the historical period 2006-2016 of 67 stations located across ten agro-climatic zones of Karnataka State, India were used and the analysis was carried out using a monthly time step. Since measured ET<sub>0 </sub>data was unavailable, calibration was performed using PM ET<sub>0 </sub>estimates and performance was evaluated using various statistical measures. Overall results showed that the BC equation with mean temperature yielded better results than the ones with effective temperature with calibrated parameters. However, the HG method showed an improvement with the use of effective temperature. Information on the spatial distribution of calibrated parameters was derived which will prove useful to practitioners who wish to derive ET<sub>0</sub> estimates with only temperature inputs.</p>

scholarly journals Time Series and Empirical Orthogonal Transformation Using Meteorological Parameters across the Climatic Zones in Nigeria

2019 ◽  
pp. 257-272
Author(s):  
D. O. Akpootu ◽  
B. I. Tijjani ◽  
U. M. Gana
Keyword(s):  
Time Series ◽  
Relative Humidity ◽  
Solar Radiation ◽  
Meteorological Parameters ◽  
Orthogonal Transformation ◽  
Global Solar Radiation ◽  
Climatic Zones ◽  
Sunshine Hours ◽  
Dry Seasons ◽  
The Mean

Time series and empirical orthogonal transformation analysis was carried out for four (4) selected tropical sites, which are situated across the four different climatic zones, viz. Sahelian, Midland, Guinea savannah and Coastal region in Nigeria using measured monthly average daily global solar radiation, maximum and minimum temperatures, sunshine hours, rainfall, wind speed, cloud cover and relative humidity meteorological data during the period of thirty one years (1980-2010). Seasonal Auto Regressive Integrated Moving Average (ARIMA) models were developed along with their respective statistical indicators of coefficient of determination (R2), Root Mean Square Error (RMSE), Mean Absolute Percentage Error (MAPE) and Mean Absolute Error (MAE). The results indicated that the models were found suitable for one step ahead global solar radiation forecast for the studied locations. Furthermore, the results of the time series analysis revealed that the model type for all the meteorological parameters show a combination of simple seasonal with one or more of either ARIMA, winter’s additive and winter’s multiplicative with the level been more significant as compared to the trend and seasonal variations for the exponential smoothing model parameters in all the locations. The results of the correlation matrix revealed that the global solar radiation is more correlated to the mean temperature except for Akure where it is more correlated to the sunshine hours; the mean temperature is more correlated to the global solar radiation; the rainfall is more correlated to the relative humidity and the relative humidity is more correlated to the rainfall in all the locations. The results of the component matrix revealed that three seasons are identified in Nguru located in the Sahelian region namely, the rainy, the cool dry (harmattan) and the hot dry seasons while in Zaria, Makurdi and Akure located in the Midland, Guinea savannah and Coastal zones two distinct seasons are identified namely, the rainy and dry seasons.

scholarly journals Reference crop evapotranspiration derived from geo-stationary satellite imagery – a case study for the Fogera flood plain, NW-Ethiopia and the Jordan Valley, Jordan

2010 ◽  
Vol 7 (4) ◽  
pp. 4925-4956 ◽  
Author(s):  
H. A. R. de Bruin ◽  
I. F. Trigo ◽  
M. A. Jitan ◽  
N. Temesgen Enku ◽  
C. van der Tol ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Satellite Imagery ◽  
Air Temperature ◽  
Land Surface ◽  
Crop Evapotranspiration ◽  
Jordan Valley ◽  
Data Set ◽  
Reference Crop Evapotranspiration ◽  
First Results ◽  
Reference Crop

Abstract. First results are shown of a project aiming to estimate daily values of reference crop evapotranspiration ET0 from geo-stationary satellite imagery. In particular, for Woreta, a site in the Ethiopian highland at an elevation of about 1800 m, we tested a radiation-temperature based approximate formula proposed by Makkink (MAK) adopting ET0 evaluated with the version of the Penman-Monteith equation described in the FAO Irrigation and Drainage paper 56 as the most accurate estimate. More precisely we used the latter with measured daily solar radiation as input (denoted by PMFAO-Rs). Our data set for Woreta concerns a period where the surface was fully covered with short green non-stressed vegetation. Our project was carried out in the context of the Satellite Application Facility on Land Surface Analysis (LANDSAF) facility. Among others, the scope of LANDSAF is to increase benefit from the EUMETSAT Satellite Meteosat Second Generation (MSG). In this study we applied daily values of downward solar radiation at the surface obtained from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) radiometer. In addition, air temperature at 2 m was obtained from 3-hourly forecasts provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). Both MAK and PMFAO-Rs contain the psychrometric "constant", which is proportional to air pressure, which, in turn, decreases with elevation. In order to test elevation effects we tested MAK and its LANDSAF input data for 2 sites in the Jordan Valley located about 250 m b.s.l. Except for a small underestimation of air temperature at the Ethiopian site at 1800 m, the first results of our LANDSAF-ET0 project are promising. If our approach to derive ET0 proves successfully, then the LANDSAF will be able to initiate nearly real time free distribution of ET0 for the full MSG disk.

scholarly journals Estimating reference crop evapotranspiration with elevation based on an improved HS model

2018 ◽  
Vol 50 (1) ◽  
pp. 187-199 ◽  
Author(s):  
Pengcheng Tang ◽  
Bing Xu ◽  
Zhanyi Gao ◽  
Heping Li ◽  
Xiaoyu Gao ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Meteorological Data ◽  
High Elevation ◽  
Crop Evapotranspiration ◽  
Low Oxygen ◽  
Reference Crop Evapotranspiration ◽  
Improved Model ◽  
Short Time ◽  
Reference Crop ◽  
Different Time Scales

Abstract Estimation of ET0 in high-elevation (above sea level, ASL) areas of Tibet presents unique challenges: scarcity of monitoring stations, short-time coverage of meteorological data, low-oxygen and low-pressure environment, and strong solar radiation. In this study, altitude factors and modified temperature constants are utilized to improve the Hargreaves (HS) model based on 30-year daily meteorological data from 20 typical sites in Tibet. The improved model, Hargreaves-Elevation (HS-E) improved model, could provide better results at different time scales. Negative ET0 values were unavoidable in the HS model when applied to high-elevation areas. However, the HS-E model solved this problem and improved the accuracy of estimated ET0. In particular, the HS-E model performs better when the time scale becomes larger. Therefore, the HS-E model is highly recommended to estimate ET0 in high-elevation areas where the meteorological data are scarce, for example, in Tibet above 2,000 m.

scholarly journals Performance evaluation of solar radiation equations for estimating reference evapotranspiration (ETo) in a humid tropical environment

2019 ◽  
Vol 42 (1) ◽  
pp. 124-135
Author(s):  
Emeka Ndulue ◽  
Ikenna Onyekwelu ◽  
Kingsley Nnaemeka Ogbu ◽  
Vintus Ogwo
Keyword(s):  
Solar Radiation ◽  
Reference Evapotranspiration ◽  
Meteorological Data ◽  
Accurate Estimate ◽  
Tropical Environment ◽  
Crop Evapotranspiration ◽  
Reference Crop Evapotranspiration ◽  
Field Crops ◽  
Essential Input ◽  
Reference Crop

Abstract Solar radiation (Rs) is an essential input for estimating reference crop evapotranspiration, ETo. An accurate estimate of ETo is the first step involved in determining water demand of field crops. The objective of this study was to assess the accuracy of fifteen empirical solar radiations (Rs) models and determine its effects on ETo estimates for three sites in humid tropical environment (Abakaliki, Nsukka, and Awka). Meteorological data from the archives of NASA (from 1983 to 2005) was used to derive empirical constants (calibration) for the different models at each location while data from 2006 to 2015 was used for validation. The results showed an overall improvement when comparing measured Rs with Rs determined using original constants and Rs using the new constants. After calibration, the Swartman–Ogunlade (R2 = 0.97) and Chen 2 models (RMSE = 0.665 MJ∙m−2∙day−1) performed best while Chen 1 (R2 = 0.66) and Bristow–Campbell models (RMSE = 1.58 MJ∙m−2∙day−1) performed least in estimating Rs in Abakaliki. At the Nsukka station, Swartman–Ogunlade (R2 = 0.96) and Adeala models (RMSE = 0.785 MJ∙m−2∙day−1) performed best while Hargreaves–Samani (R2 = 0.64) and Chen 1 models (RMSE = 1.96 MJ∙m−2∙day−1) performed least in estimating Rs. Chen 2 (R2 = 0.98) and Swartman–Ogunlade models (RMSE = 0.43 MJ∙m−2∙day−1) performed best while Hargreaves–Samani (R2 = 0.68) and Chen 1 models (RMSE = 1.64 MJ∙m−2∙day−1) performed least in estimating Rs in Awka. For estimating ETo, Adeala (R2 =0.98) and Swartman–Ogunlade models (RMSE = 0.064 MJ∙m−2∙day−1) performed best at the Awka station and Swartman–Ogunlade (R2 = 0.98) and Chen 2 models (RMSE = 0.43 MJ∙m−2∙day−1) performed best at Abakaliki while Angstrom–Prescott–Page (R2 = 0.96) and El-Sebaii models (RMSE = 0.0908 mm∙day−1) performed best at the Nsukka station.

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