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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Adaramola M. S. 2012. Estimating global solar radiation using common meteorological data in Akure Nigeria. Renewble Energy. Vol. 47 p. 38–44.
Adeala A.A. Huan Z. Enweremadu C.C. 2015. Evaluation of global solar radiation using multiple weather parameters as predictors for South Africa provinces. Thermal Science. Vol. 19. Supl. 2 p. S495–S509.
Adeboye O.B. Osunbitan J.A. Adekalu K.O. Okunade D.A. 2009. Evaluation of FAO-56 Penman–Monteith and temperature-based models in estimating reference evapotranspiration using complete and limited data application to Nigeria. Agricultural Engineering International: The CIGR Ejournal. Vol. 11(1291) p. 1–25.
Adekunle A.A. Badejo A.A. Opafola O.T. Bada B.S. Nkeshita F.C. 2017. Estimation of water requirements of selected field crops in South-West and South-East Nigeria. Journal of Agriculture and Sustainability. Vol. 10(2) p. 172–186.
Akpabio L.E. Etuk S.E. 2003. Relationship between global solar radiation and sunshine duration for Onne Nigeria. International Journal of Sustainable and Green Energy. Vol. 27 p. 161–167.
Akpabio L.E. Udo S.O. Etuk E. 2005. Modeling global solar radiation for a tropical location: Onne Nigeria. Turkish Journal of Physics. Vol. 29. Iss. 1 p. 63–68.
Aladenola O.O. Madramootoo Ch.A. 2014. Evaluation of solar radiation estimation methods for reference evapotranspiration estimation in Canada. Theoretical and Applied Climatology. Vol. 118. Iss. 3 p. 377–385.
Allen R.G. 1996. Assessing integrity of weather data for reference evapotranspiration estimation. Journal of Irrigation and Drainage Engineering. Vol. 122. Iss. 2 p. 97–106.
Allen R.G. Pereira L.S. Raes D. Smith M. 1998. Crop evapotranspiration-guidelines for computing crop water requirements. FAO Irrigation and Drainage Paper. No. 56. Rome. United Nations Food and Agriculture Organization pp. 300.
Almorox J. Hontoria C. 2004. Global solar radiation estimation using sunshine duration in Spain. Energy Conversion and Management. Vol. 45 p. 1529–1535.
Angstrom A. 1924. Solar and terrestrial radiation. Quarterly Journal of the Royal Meteorological Society. Vol. 50 p. 121–125.
Ayodele T.R. Ogunjuyigbe A.S.O. 2016. Performance assessment of empirical models for prediction of daily and monthly average global solar radiation: The case study of Ibadan Nigeria. International Journal of Ambient Energy. Vol. 38(8) p. 803–813.
Besharat F. Dehghan A.A. Faghih A.R. 2013. Empirical models for estimating global solar radiation: A review and case study. Renewable and Sustainable Energy Reviews. Vol. 21 p. 798–821.
Bristow K.L. Campbell G.S. 1984. On the relationship between incoming solar radiation and daily maximum and minimum temperature. Agricultural and Forest Meteorology. Vol. 31. Iss. 2 p. 59–166.
Chen R. Ersi K. Yang J. Lu S. Zhao W. 2004. Validation of five global radiation models with measured daily data in China. Energy Conversion and Management. Vol. 45 p. 1759–1769.
Chineke T.C. 2008. Equations for estimating global solar radiation in data sparse regions. Renewable Energy. Vol. 33(4) p. 827–831.
Davies J.A. 1966. The assessment of evapotranspiration for Nigeria. Geografiska Annaler. Ser. A. Physical Geography. Vol. 48(3) p. 139–156.
De Medeiros F.J. Santos e Silva C.M. Bezerra B.G. 2017. Calibration of Ångström-Prescott equation to estimate daily solar radiation on Rio Grande do Norte State. Revista Brasileira de Meteorologia. Vol. 32(3) p. 409–461.
Djaman K. O’Neill M. Diop L. 2018. Evaluation of the Penman-Monteith and other 34 reference evapotranspiration equations under limited data in a semiarid dry climate. Theoretical and Applied Climatology. Vol. 133 p. 1–9.
Dogniaux R. Lemoine M. 1983. Classification of radiation sites in terms of different indices of atmospheric transparency. In: Solar radiation data. Solar energy research and development in the European Community. Ser. F. Vol. 2. Dordrecht Holland. Reidel p. 94–107.
Echiegu E.A. Ede N.C. Ezenne G.I. 2016. Optimization of Blaney-Morin-Nigeria (BMN) model for estimating evapotranspiration in Enugu Nigeria. African Journal of Agricultural Research. Vol. 11(20) p. 1842–1848.
Egbodion J. Ahmadu J. 2015. Production cost efficiency and profitability of Abakaliki rice in Ihialia Local Government Area of Anambra State Nigeria. Journal of Applied Sciences and Environmental Management. Vol. 19(2) p. 327–333.
Egeonu D.I. Njoku H.O. Okolo P.N. Enibe S.O. 2015. Comparative assessment of temperature based ANN and Angstrom type models for predicting global solar radiation [online]. In: The Second International Afro-European Conference for Industrial Advancement. Eds. A. Abraham P. Krömer V. Snasel. Advances in Intelligent Systems and Computing. Vol. 334. Cham. Springer p. 109–122. [Access 10.10.2018]. Available at: https://link.springer.com/chapter/10.1007/978-3-319-13572-4_9
Ejieji C.J. 2011. Performance of three empirical reference evapotranspiration models under three sky conditions using two solar radiation estimation methods at Ilorin Nigeria. Agricultural Engineering International: CIGR Journal. Vol. 13(3) p. 1–14.
El-Sebaii A.A. Al-Ghamdi A.A. Al-Hazmi F.S Faidah A. 2009. Estimation of global solar radiation on horizontal surfaces in Jeddah Saudi Arabia. Energy Policy. Vol. 37 p. 3645–3649.
Elagib N. Mansell M.G. 2000. New approaches for estimating global solar radiation across Sudan. Energy Conversion Management. Vol. 21 p. 271–287.
Estévez J. Padilla F.L. M. Gavilán P. 2012. Evaluation and regional calibration of solar radiation prediction models in southern Spain. Journal of Irrigation and Drainage Engineering. Vol. 138(10) p. 868–879.
Ezekwe C.I. Ezeifo C.C.O. 1981. Measured solar radiation in a Nigerian environment compared with predicted data. Solar Energy. Vol. 26 p. 181–186.
Glower J. McGulloch J.S.G. 1958. The empirical relation between solar radiation and hours of sunshine. Quarterly Journal of the Royal Meteorological Society. Vol. 84 p. 172.
Gobin A. 2000. Participatory and spatial modeling methods for land resources analysis. Unpublished Ph.D. Dissertation. Leuven. Katholieke Universiteit pp. 328.
Hargreaves G.H. Samani Z.A. 1985. Reference crop evapotranspiration from temperature. Applied Engineering in Agriculture. Vol. 1(2) p. 96–99.
Hassan G.E. Youssef M.E. Mohamed Z.E. Ali M.A. Hanafy A.A. 2016. New temperature-based models for predicting global solar radiation. Applied Energy. Vol. 179 p. 437–450.
Kosa P. 2011. The effect of temperature on actual evapotranspiration based on Landsat 5 TM Satellite Imagery. In: Evapotranspiration [online]. Ed. L. Labedzki. London. InTech. ISBN 978-953-307-251-7. [Access 20.10.2018]. Available at: http://www.intechopen.com/books/evapotranspiration/the-effect-of-temperature-on-actualevapotranspiration-based-on-landsat-5-tm-satellite-imagery
Koudahe K. Djaman K. Adewumi J.K. 2018. Evaluation of the Penman–Monteith reference evapotranspiration under limited data and its sensitivity to key climatic variables under humid and semiarid conditions. Modeling Earth Systems and Environment. Vol. 4(3) p. 1239–1257.
Liu X. Mei X. Li Y. Zhang Y. Wang Q. Jensen J.R. Porter J.R. 2009. Calibration of the Ångström-Prescott coefficients (a b) under different time scales and their impacts in estimating global solar radiation in the Yellow River basin. Agricultural and Forest Meteorology. Vol. 149(3–4) p. 697–710.
López-Urrea R. de Santa Olalla M.F. Fabeiro C. Moratalla A. 2006. Testing evapotranspiration equations using lysimeter observations in a semiarid climate. Agricultural Water Management. Vol. 85(1–2) p. 15–26.
Martel M. Glenn A. Wilson H. Krobel R. 2018. Simulation of actual evapotranspiration from agricultural landscapes in the Canadian Prairies. Journal of Hydrology: Regional Studies. Vol. 15 p. 105–118.
Moriasi D.N. Arnold J.G. van Liew M.W. Bingner R.L. Harmel R.D. Veith T.L. 2007. Model evaluation guidelines for systematic quantification of accuracy in watershed simulations. Transactions of the ASABE. Vol. 50(3) p. 885–900.
Mousavi R. Sabziparvar A.A. Marofi S. Pak N.A.E. Heydari M. 2015. Calibration of the Angström–Prescott solar radiation model for accurate estimation of reference evapotranspiration in the absence of observed solar radiation. Theoretical and Applied Climatology. Vol. 119(1–2) p. 43–54.
NASA 2016. National Aeronautics Space Administration Prediction of Worldwide Energy Resource (POWER) [online]. [Access 15.10.2016]. Available at: https://power.larc.nasa.gov/data-access-viewer/
Ndulue E.L. Ezenne G.I. Mbajiorgu C.C. Ogwo V. Ogbu K.N. 2018. Hydrological modeling of upper Ebonyi watershed using the SWAT model. International Journal of Hydrology Science and Technology. Vol. 8(2) p. 120–133.
Nistor M. Cheval S. Gualtieri A.F. Dumitrescu A. Boţan V.E. Berni A. Hognogi G. Irimuş I.A. Porumb-Ghiurco C.G. 2017. Crop evapotranspiration assessment under climate change in the Pannonian basin during 1991–2050. Meteorological Applications. Vol. 24 p. 84–91.
Nwokolo S.C. 2017. A comprehensive review of empirical models for estimating global solar radiation in Africa. Renewable and Sustainable Energy Reviews. Vol. 78 p. 955–995.
Ogelman H. Ecevit A. Tasdemiroglu E. 1984. A new method for estimating solar radiation from bright sunshine data. Solar Energy. Vol. 33 p. 619–625.
Ogolo E.O. 2014. The comparative analysis of performance evaluation of recalibrated reference evapotranspiration models for different regional climatic conditions in Nigeria. Ife Journal of Science. Vol. 16(2) p. 1–20.
Okundamiya M.S. Emagbetere J.O. Ogujor E.A. 2016. Evaluation of various global solar radiation models for Nigeria. International Journal of Green Energy. Vol. 13(5) p. 505–512.
Onwubuya E.A. Okporie E.O. Nenna M.G. 2009. Nsukka yellow pepper processing and preservation techniques among women in Enugu State. African Journal of Agricultural Research. Vol. 4(9) p. 859–863.
Page I.K. 1961. The estimation of monthly mean values of daily total shortwave radiation in vertical and inclined surfaces from sunshine records for latitude 40°N – 40°S. In: Proceedings of the UN Conference on new Source of Energy. Paper No. 598 p. 378–390.
Prescott J.A. 1940. Evaporation from water surface in relation to solar radiation. Transactions of the Royal Society of South Australia. Vol. 64 p. 114–118.
Schneider K. Ketzer B. Breuer L. Vaché K.B. Bernhofer C. Frede H.G. 2007. Evaluation of evapotranspiration methods for model validation in a semi-arid watershed in northern China. Advances in Geosciences. Vol. 11 p. 37–42.
Sentelhas P.C. Gillespie T.J. Santos E.A. 2010. Evaluation of FAO Penman-Monteith and alternative methods for estimating reference evapotranspiration with missing data in Southern Ontario Canada. Agricultural Water Management. Vol. 97(5) p. 635–644.
Swartman R.K. Ogunlade O. 1967. Solar radiation estimates from common parameters. Solar Energy. Vol. 11(3–4) p. 170–172.
Tabari H. Talaee P.H. Willems P. Martines Ch. 2016. Validation and calibration of solar radiation equations for estimating daily reference evapotranspiration at cool. Hydrological Sciences Journal. Vol. p. 37–41.
Thornton P.E. Running S.W. 1999. An improved algorithm for estimating incident daily solar radiation from measurements of temperature humidity and precipitation. Agricultural and Forest Meteorology. Vol. 93(4) p. 211–228.
Toğrul I.T. Toğrul H. 2002. Global solar radiation over Turkey: Comparison of predicted and measured data. Renewable Energy. Vol. 25(1) p. 55–67.
Vozhehova R.A. Lavrynenko Y.O. Kokovikhin S.V. Lykhovyd P.V. Biliaieva I.M. Drobitko A.V. Nesterchuk V.V. 2018. Assessment of the CROPWAT 8.0 software reliability for evapotranspiration and crop water requirements calculations. Journal of Water and Land Development. No. 39 p. 147–152. DOI 10.2478/jwld-2018-0070.
Wang K. Ma Q. Li Z. Wang J. 2015. Decadal variability of surface incident solar radiation over China: Observations satellite retrievals and reanalyses. Journal of Geophysical. Research: Atmosphere. Vol. 120 p. 6500–6514.
WMO 1987. Guidelines on the quality control of data from the world radiometric network. World climate programme. WCDP-3. Prepared by the World Radiation Data Centre Voeikov Main Geophysical Observatory USSR State Committee for Hydrometeorology. Leningrad. World Meteorological Organization pp. 30.
Wu B. Liu S. Zhu W. Yan N. Xing Q. Tan S. 2017. An improved approach for estimating daily net radiation over the Heihe River Basin. Sensors (Basel). Vol. 17(1): 86.
Xu J. Peng S. Luo Y. Zheng W. 2008. Influence of Angstrom’s Coefficients on estimate of solar radiation and reference evapotranspiration by Penman-Monteith equation. Proceeding of 16th IAHR-APD Congress and 3rd Symposium of IAHR-ISHS. Advances in Water Resources and Hydraulic Engineering p. 339–344.
Zhang Q. Cui N. Feng Y. Jia Y. Li Z. Gong D. 2018. Comparative analysis of global solar radiation models in different regions of China. Advances in Meteorology. Vol. 2018. Art. ID 3894831 p. 1–21.