Abstract

Reference evapotranspiration ( ETo ) is a vital factor in water resources managing and planning. Various estimation methods have been developed for different climatic regions and according to the available data. Therefore, the reliability of such methods depends upon climatic conditions. The present investigation evaluates four temperature based methods: FAO Blaney-Criddle (BC), Turc, Jensen-Haise (JH) and Hargreaves (HG), and two radiation based methods: FAO-radiation (FAO-rad) and Priestley-Taylor (PT) in comparison with the FAO-PM method under arid conditions of Libya. In order to select the best ETo method, the percentage error of estimate ( PE ), the root mean square error ( RMSE ), and mean bias error ( MBE ) were calculated. The obtained ETo values (FAO-PM and the average of best-estimated monthly ETo ) were utilized to generate spatial distribution maps of ETo with the aid of Kriging technique. Statistical analysis of the obtained results revealed that, Turc equation fitted well for the northern part of the study area, which include Nalut, Zuara, Mosrata, Sirt, Shahat, Derna, Tubruk, Hon, Galo and Gagbub. While for southern zone, HG equation performed better for Opari and Tazirbu, BC equation for Kufra and Ghadames, FAO-Rad equation for Sebha; and JH equation for Ghat.

Highlights

  • Reference evapotranspiration (ETo) is the synchronized transpiration and evaporation processes in a soil–plant system (Tabari et al, 2011)

  • In case of limited data required for Penman-Monteith method (P-M) method, especially in the developing countries, significant attention has been paid to the evaluation of simple ETo methods and their application

  • The obtained values from the six simple ETo method were compared with that values of P-M method

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Summary

Introduction

Reference evapotranspiration (ETo) is the synchronized transpiration and evaporation processes in a soil–plant system (Tabari et al, 2011). For many regions and climatic conditions, the Penman-Monteith method (P-M) has proved to be the best method and gives consistent ETo values (Allen et al 2005, 2006) It is widely applied in various fields, among which are agronomy and irrigation management (Alexandris et al 2006; Landeras et al, 2008; Du, et al, 2010; Hassanli, et al, 2010; Sentelhas et al 2010). The main limitation of the P-M method is the necessity for various weather data parameters (i.e., air temperature, humidity, wind speed, and solar radiation) which might be not available Such limitation may exist in developing countries (Droogers and Allen, 2002; Gocic and Trajkovic 2010; Maeda et al 2011; Tabari et al 2011). Maps representing the distribution of the ETo values and their relation to elevation above sea level is performed

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