ABSTRACT
Determining the evapotranspiration (ET) is the base of many disciplines including the irrigation system design, irrigation scheduling and hydrologic and drainage studies [12]. Perfect determination of ET is a big challenge for investigators especially in arid and hyper-arid regions. Actual crop ET is computed by multiplying reference ET by the crop factor. Reference ET is the summation of evaporation and transpiration produced by a reference crop in specific growth conditions (height, coverage and health). ET value depends on two main factors: the selected reference crop and the climatic data [4]. This chapter discusses the possibility of using the weather data recorded at these stations instead of reference agro-climatic data. Hence, the objective of this chapter is to estimate the ET values for the RWS [Reference weather station] and the NRWS [non reference weather station] at Riyadh – Saudi Arabia; and to compare these ET values with the reference evapotranspiration based on lysimeter observations for reference conditions.
