Solar Radiation Data to Compute Reference Evapotranspiration in Marmara Region and Reference Evaporation Frequency Analyze

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Ünlükara A., Baran A.

10th International Symposium on Atmospheric Sciences, İstanbul, Turkey, 18 - 21 October 2022, pp.1-10

  • Publication Type: Conference Paper / Full Text
  • City: İstanbul
  • Country: Turkey
  • Page Numbers: pp.1-10
  • Erciyes University Affiliated: Yes


In plant evapotranspiration predictions, the effect of the atmosphere is expressed by reference evapotranspiration (ETo) while plant coefficients are used to express the effect of the plant. Last few decades, the reference evapotranspiration estimation methodology in FAO Irrigation and Drainage Paper No.56 has been accepting as a standard method. In this method, using local Ångström-Prescott (A-P) coefficients were advised but in the case of absence of these coefficients, the calculation procedures are continuing by taking the coefficients as 0.25 and as 0.50. The first purpose of this study was to determine the local A-P coefficients for Marmara Region of Turkey. The second purpose of this study was calculation and comparison of monthly reference evapotranspiration values using local A-P coefficients for the provinces in this region and performing of their frequency analysis at some probabilities (95%, 50%, and 5%).  The long-term climate data required for this study have been obtained from the General Directorate of Turkish State Meteorology Affairs. Although both monthly and annual A-P coefficients of the provinces in the Region were determined, only annual A-P coefficients of Kırklareli and Balıkesir provinces could be determined due to insufficient data. Monthly ETo1 series based on advised A-P coefficients, ETo2 (control) series based on measured solar radiation data (Rs) in the Region and ETo3 series based on local A-P coefficients were obtained and compared. According to ETo2 series, ETo3 series gave lower mean absolute errors than ETo1. This result mean that more sensitive ETo estimations could be made by local A-P coefficients. As minimum and maximum mean total annual ETo values varied between 808.5 and 1185.9 mm for Kocaeli and Balıkesir, respectively. Respective mean total annual evapotranspiration values were found as 965.1, 959.2, 1052.4, 840.5, 952.5, 957.8, 876.6, 858.7 and 903 mm for Bilecik, Bursa, Çanakkale, Edirne, İstanbul, Kırklareli, Sakarya, Tekirdağ and Yalova. It was concluded that better estimation of crop evapotranspiration would be made by ETo values calculated by using local A-P coefficients.