scholarly journals Correcting Thornthwaite potential evapotranspiration using a global grid of local coefficients to support temperature-based estimations of reference evapotranspiration and aridity indices

2021 ◽  
Author(s):  
Vassilis Aschonitis ◽  
Dimos Touloumidis ◽  
Marie-Claire ten Veldhuis ◽  
Miriam Coenders-Gerrits
Keyword(s):  
Reference Evapotranspiration ◽  
Potential Evapotranspiration ◽  
Correction Coefficient ◽  
Climatic Data ◽  
Validation Data ◽  
Global Database ◽  
Local Coefficients ◽  
Local Correction ◽  
Aridity Indices ◽  
Data Requirements

Abstract. Thornthwaite’s formula is globally an optimum candidate for large scale applications of potential evapotranspiration and aridity assessment at different climates and landscapes since it has the lower data requirements compared to other methods and especially from the ASCE-standardized reference evapotranspiration (former FAO-56), which is the most data demanding method and is commonly used as benchmark method. The aim of the study is to develop a global database of local coefficients for correcting the formula of monthly Thornthwaite potential evapotranspiration (Ep) using as benchmark the ASCE-standardized reference evapotranspiration method (Er). The validity of the database will be verified by testing the hypothesis that a local correction coefficient, which integrates the local mean effect of wind speed, humidity and solar radiation, can improve the performance of the original Thornthwaite formula. The database of local correction coefficients was developed using global gridded temperature and Er data of the period 1950–2000 at 30 arc-sec resolution (~1 km at equator) from freely available climate geodatabases. The correction coefficients were produced as partial weighted averages of monthly Er / Ep ratios by setting the ratios’ weight according to the monthly Er magnitude and by excluding colder months with monthly values of Er or Ep < 45 mm month−1 because their ratio becomes highly unstable for low temperatures. The validation of the correction coefficients was made using raw data from 525 stations of Europe, California-USA and Australia including data up to 2020. The validation procedure showed that the corrected Thornthwaite formula Eps using local coefficients led to a reduction of RMSE from 37.2 to 30.0 mm m−1 for monthly and from 388.8 to 174.8 mm y−1 for annual step estimations compared to Ep using as benchmark the values of Er method. The corrected Eps and the original Ep Thornthwaite formulas were also evaluated by their use in Thornthwaite and UNEP (United Nations Environment Program) aridity indices using as benchmark the respective indices estimated by Er. The analysis was made using the validation data of the stations and the results showed that the correction of Thornthwaite formula using local coefficients increased the accuracy of detecting identical aridity classes with Er from 63 % to 76 % for the case of Thornthwaite classification, and from 76 % to 93 % for the case of UNEP classification. The performance of both aridity indices using the corrected formula was extremely improved in the case of non-humid classes. The global database of local correction factors can support applications of reference evapotranspiration and aridity indices assessment with the minimum data requirements (i.e. temperature) for locations where climatic data are limited. The global grids of local correction coefficients for Thornthwaite formula produced in this study are archived in PANGAEA database andcan be assessed using the following link: https://doi.pangaea.de/10.1594/PANGAEA.932638 (Aschonitis et al., 2021).

scholarly journals Comparative evaluation of different reference evapotranspiration models

2017 ◽  
Vol 9 (1) ◽  
pp. 609-613
Author(s):  
C. K. Arya ◽  
R. C. Purohit ◽  
L. K. Dashora ◽  
P. K. Singh ◽  
Mahesh Kothari ◽  
...  
Keyword(s):  
Water Resource Management ◽  
Meteorological Parameters ◽  
Reference Evapotranspiration ◽  
Potential Evapotranspiration ◽  
Accurate Estimation ◽  
Climatic Data ◽  
Pan Evaporation ◽  
Alternative Method ◽  
Monteith Equation

The study was carried out to select best alternative method for the estimation of reference evapotranspi-ration (ET0). Accurate estimation of potential evapotranspiration is a necessary step in water resource management. Recently, the FAO-56 version of Penman-Monteith equation has been established as a standard for calculating ref-erence evapotranspiration (ET0) which requires measurement of a number of meteorological parameters namely, air temperature, relative humidity, solar radiation, and wind speed which may not be available in most of the meteoro-logical stations. Still there are different approaches (requiring less data) which estimate ET0 closely to Penman- Monteith (P-M) method for different climatological conditions. The present study is based on analysis of long term of 13 years (2000 to 2012) climatic data to calculate monthly reference evapotranspiration for Capsicum production (September–March) and also to compare the performance of evapotranspiration equations for Jhalawar district of Rajasthan with the standard FAO-56 Penman-Monteith method on the basis of the least root mean square error (RMSE) analysis. Hargreaves method and Pan evaporation (E-Pan) method overestimated the values of ETo when compared with FAO-56 Penman-Monteith method. On the basis of lowest value of RMSE, Pan evaporation method is found best alternative method to FAO-56 Penman-Monteith method in the study area.

scholarly journals COMPARAÇÃO ENTRE MÉTODOS DE ESTIMATIVA DA EVAPOTRANSPIRAÇÃO DE REFERÊNCIA PARA O MUNICÍPIO DE PETROLINA, PE

Irriga ◽  
2017 ◽  
Vol 1 (1) ◽  
pp. 31-39 ◽  
Author(s):  
Roberta Daniela Silva Santos ◽  
Marcello Henryque Costa de Souza ◽  
Regiane De Carvalho Bispo ◽  
Kevim Muniz Ventura ◽  
Luis Henrique Bassoi
Keyword(s):  
Reference Evapotranspiration ◽  
Estimation Method ◽  
Arid Climate ◽  
Estimation Methods ◽  
Coefficient Of Determination ◽  
Climatic Data ◽  
Test Field ◽  
Rating Method ◽  
And Performance ◽  
Semi Arid

COMPARAÇÃO ENTRE MÉTODOS DE ESTIMATIVA DA EVAPOTRANSPIRAÇÃO DE REFERÊNCIA PARA O MUNICÍPIO DE PETROLINA, PE  ROBERTA DANIELA DA SILVA SANTOS1; MARCELLO HENRYQUE COSTA DE SOUZA1; REGIANE DE CARVALHO BISPO1; KEVIM MUNIZ VENTURA1 E LUÍS HENRIQUE BASSOI2 1Programa de Pós-Graduação em Irrigação e Drenagem, Universidade Estadual Paulista “Júlio de Mesquita Filho”- UNESP/FCA, Rua Dr. José Barbosa de Barros, 1780, Botucatu, SP, [email protected], [email protected], [email protected], [email protected] Embrapa Instrumentação, São Carlos, SP, [email protected]  1 RESUMO O conhecimento da evapotranspiração é vital na determinação das necessidades hídricas de uma cultura. Diante disso, o objetivo deste trabalho foi comparar o desempenho de sete métodos de estimativa da evapotranspiração de referência em relação ao método de Penman-Monteith, adotado como padrão, para o município de Petrolina, PE. Foram utilizados dados climáticos diários de 2004 a 2015, para estimar da ET0, obtidos na estação meteorológica automática do Campo Experimental de Bebedouro da Embrapa Semiárido, Petrolina, PE. Os indicadores estatísticos utilizados na avaliação foram: coeficiente de determinação (r²); coeficiente de correlação (r); índice de concordância (d) e índice de desempenho (c). Os valores do r² mostraram que o método de estimativa que melhor se ajustou ao método de Penman-Monteith foi o de Ivanov (0,73); seguido pelos métodos de Jensen-Haise (0,64); Makkink e Priestley-Taylor (0,63); Villa Nova (0,62); Hargreaves e Samani (0,53) e Hamon (0,45). No entanto, com relação ao do índice “c”, Hamon foi classificado com “péssimo”; Makkink como “mau”; Hargreaves e Samani e Villa Nova como “sofrível”; Ivanov e Priestley-Taylor como “mediano”; e Jensen-Haise como “bom”. Esse último método foi considerado como o de melhor classificação de desempenho. Palavras-chave: Penman-Monteith, correlação, semiárido.  SANTOS, R. D. S.; SOUZA, M. H. C.; BISPO, R. de C.; VENTURA, K. M.; BASSOI, L. H.METHOD-COMPARISON STUDY TO ESTIMATE THE REFERENCE EVAPOTRANSPIRATION IN PETROLINA, PE  2 ABSTRACT The knowledge on evapotranspiration is vital in determining the water requirements of a crop. Therefore, this paper aims to compare the performance of seven of estimation methods for the reference evapotranspiration in relation to the Penman-Monteith method, adopted as standard, for the municipality of Petrolina, state of Pernambuco, Brazil. We used daily climatic data from 2004 to 2015 to estimate the ET0 coefficient, obtained in the automatic weather station of the Test Field in Bebedouro, Embrapa in the Semi-arid climate. The statistical indicators used in the evaluation were: coefficient of determination (r²), correlation coefficient (r), agreement index (d) and performance index (c). The r2 values showed that the estimation method that best fitted to the Penman-Monteith method was Ivanov's (0.73), followed by Jensen-Haise (0.64), Makkink and Priestley-Taylor (0.63), Villa Nova (0.62), Hargreaves and Samani (0.53) and Hamon (0.45) methods. However, in relation to the index "c", Hamon was classified as "very poor"; Makkink as "poor"; Hargreaves and Samani and Villa Nova as "tolerable"; Ivanov and Priestley-Taylor as "medium"; and Jensen-Haise as "good". The last one was considered as the best performance rating method. Keywords: Penman-Monteith, correlation, semi-arid climate.

scholarly journals Comparative evaluation of 24 reference evapotranspiration equations applied on an evergreen-broadleaved forest

2017 ◽  
Vol 49 (4) ◽  
pp. 1028-1041 ◽  
Author(s):  
Athanassios Bourletsikas ◽  
Ioannis Argyrokastritis ◽  
Nikolaos Proutsos
Keyword(s):  
Goodness Of Fit ◽  
Hydrological Cycle ◽  
Reference Evapotranspiration ◽  
Potential Evapotranspiration ◽  
Efficiency Index ◽  
Daily Basis ◽  
Forest Environment ◽  
Statistical Parameters ◽  
Model Efficiency

Abstract Reference evapotranspiration (ET0) is a major component of the hydrological cycle. Its use is essential both for the hydrological rainfall–runoff assessment models and determination of water requirements in agricultural and forest ecosystems. This study investigates the performance of 24 different methods, which produce ET0 or potential evapotranspiration estimates above a grass-covered ground in a Mediterranean forest environment in Greece and compares the derived results with those of the presumed most accurate and scientifically acceptable Penman–Monteith method (ETP-M). Their performance was evaluated on a daily basis for a period of 17 years, using 17 different statistical parameters of goodness of fit. The results showed that some empirical methods could serve as suitable alternatives. More specifically, Copais (ETCOP), Hargreaves original (ETHAR), and Valiantzas2 (ETVA2) methods, exhibited very good values of the model efficiency index, EF (0.934, 0.932, and 0.917, respectively) and the index of agreement, d (0.984, 0.982, and 0.977, respectively). Additionally, the differences of the estimated mean daily value against the respective ETP-M value (rt index) for all methods had a range of −27.8% (Penman – ETPEN) to +59.5% (Romanenko – ETROM), while Copais (ETCOP), Hargreaves–Samani modified1 (ETHS1), and STU (ETSTU) yielded the best values (−0.06%, +0.06%, and 0.22%, respectively).

Estimation of Evapotranspiration using the Modified Hargreaves Equation by Genetic Algorithm

2020 ◽  
Author(s):  
Deokhwan Kim
Keyword(s):  
Genetic Algorithm ◽  
Developing Countries ◽  
Correction Factor ◽  
Historical Data ◽  
Reference Evapotranspiration ◽  
Weather Data ◽  
Correction Coefficient ◽  
Test Bed ◽  
True Value ◽  
Daily Weather Data

&lt;p&gt;In this study, the Hargreaves monthly correction factor is presented to estimate the reference evapotranspiration. For the analysis, I used daily weather data from 1989 to 2018, at 67 meteorological stations located throughout the Korean peninsula.&lt;/p&gt;&lt;p&gt;A large number of more or less empirical methods have been developed over the last 50 years by numerous scientists and specialists worldwide to estimate evapotranspiration from different climatic variables. The FAO Penman-Monteith method is recommended as the sole ETo method for determining reference evapotranspiration. However, the Penman-Monteith method has the disadvantage of inputting a lot of weather data. In addition, there is a lack of meteorological data when using old historical data or as a test bed for developing countries.&lt;/p&gt;&lt;p&gt;In the case of the Hargreaves method, the reference evapotranspiration can be estimated only if the latitude, maximum and minimum temperatures of the meteorological station are known. However, the accuracy of the results is not as good as that of the Penman-monteith method. Thus, using the genetic algorithm method suggested the monthly correction factor of the Hargreaves method each station. The reference evapotranspiration amount calculated by Penman-Monteith was set as the true value, and the learning period of genetic algorithm was set from 1989 to 2013, and the validation period was set from 2014 to 2018.&lt;/p&gt;&lt;p&gt;In order to verify the model efficiency, the root mean square error decreased and the correlation coefficient increased when the monthly correction coefficient was applied to the reference evapotranspiration calculated by the Hargreaves method.&lt;/p&gt;&lt;p&gt;It is very important to estimate the reference evapotranspiration amount in order to develop the water long-term plan.&lt;/p&gt;&lt;p&gt;With the development of measuring equipment and technological capabilities, it is now possible to simulate the state of nature as if it were real, but many problems arise when using historical data or analyzing developing countries.&lt;/p&gt;&lt;p&gt;If the monthly correction coefficient suggested in this study is applied, it is possible to estimate the standard evaporation amount with a more approximate value.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Acknowledgements&lt;/p&gt;&lt;p&gt;&amp;#160;This research is supported by the Research Program (20200041-001) of Korea Institute of Civil Engineering &amp; Building Technology&amp;#160;&lt;/p&gt;

scholarly journals Drought severity and change in Xinjiang, China, over 1961–2013

2016 ◽  
Vol 48 (5) ◽  
pp. 1343-1362 ◽  
Author(s):  
Yi Li ◽  
Chunyan Chen ◽  
Changfeng Sun
Keyword(s):  
Global Warming ◽  
Reference Evapotranspiration ◽  
Standardized Precipitation Index ◽  
Drought Severity ◽  
Climatic Data ◽  
Standardized Precipitation Evapotranspiration Index ◽  
Water Utilization ◽  
Monthly Climatic Data ◽  
Increasing Trends ◽  
Southern Xinjiang

Monthly climatic data from 53 sites across Xinjiang, China, were used to compare drought severity from the widely accepted Standardized Precipitation Index (SPI) with the recently proposed Standardized Precipitation Evapotranspiration Index (SPEI), as well as trends in the data from 1961 to 2013. Monthly Thornthwaite based (ETo.TW) and Penman-Monteith based reference evapotranspiration (ETo.PM) were computed and subsequently used to estimate SPEITW and SPEIPM, respectively. The indices' sensitivity, spatiotemporal distributions and trends were analyzed. The results showed that the TW equation underestimated ETo, which affected the accuracy of the SPEI estimation. Greater consistency was found between SPI and SPEIPM than between SPI and SPEITW at different timescales. SPI and SPEIPM were sensitive to precipitation, but SPEITW and SPEIPM were insensitive to ETo. The scope of spatial SPEIPM was wider than that of SPI at the same timescale. Obvious differences in SPI, SPEITW and SPEIPM existed between northern and southern Xinjiang. SPEIPM was a better indicator of global warming than SPI. Both SPI and SPEIPM had increasing trends, which contradict previously reported trends in global drought. In conclusion, the decrease in drought severity observed over the last 53 years may indicate some relief in the water utilization crisis in Xinjiang, China.

Climatic Parameters Analysis of Koysinjaq Meteorological Station, Kurdistan Region, Northern Iraq

2020 ◽  
Vol 54 (1A) ◽  
pp. 99-109
Author(s):  
Rebwar Dara
Keyword(s):  
Potential Evapotranspiration ◽  
Meteorological Data ◽  
Climatic Conditions ◽  
Annual Rainfall ◽  
Climatic Data ◽  
Water Losses ◽  
Northern Iraq ◽  
Total Potential ◽  
Balance Technique ◽  
Water Surplus

The aim of this study was to analyze the climatic data parameters in an interesting catchment, northern Iraq, the Koysinjaq catchment. The climatic conditions were further utilized in the water balance technique. The investigated periods (2000-2019) of meteorological data were used to assess the climatic and drought conditions in Koysinjaq Basin. In terms of water availability, the mean annual rainfall was 595mm and relative humidity was 50.3%, whereas regarding the water losses elements, the total monthly evaporation is 2058.3 mm, temperature, wind speed and sunshine were 22.3 oC, 2 m/sec, and 7.8 hr/day respectively. Kharrufa method was employed to define potential evapotranspiration, and identify periods of water surplus and deficit. The results indicated that total potential evapotranspiration, water surplus and deficit are 2209.04 mm, 258.2 mm, and 1872.4 mm respectively. Different methods were used for climate classification like Mather, Unep, and Al-Kubaisi, the results of these classifications show that climate is dry-sub humid according to the first classification, semi-arid according to the second classification, and humid to moist according to the third classification.

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