Changes in Climatic Variables and Their Effect on Wheat Water Requirement in Urmia Lake Basin

Climate change and low water use efficiency are the main reasons for reducing the water entering the Urmia Lake. Therefore, water use management via irrigation scheduling can be an effective strategy to restore this lake. This research was conducted to investigate the effect of climatic variables on water requirements, identify water-sensitive growth stages, and prepare irrigation scheduling guidelines for wheat, which is one of the main crops in the studied region. For this purpose, crop Evapotranspiration (ETc) and Net Irrigation Requirement (NIR) of wheat growth stages were estimated by computing the daily soil water balance of the root zone for a period of 32 years (1985-1986 to 2016-2017). Dividing wheat growth period into nine phenological stages was performed using Growing Degree Days (GDDs) and Zadoks scale. These stages included intervals of [Sowing-Emergence (StE)], [Emergence-Trifoliate (EtT)], [Trifoliate-Double ridge (TtD)], [Double ridge-Jointing (DtJ)], [Jointing-Booting (JtB)], [Booting-Heading (BtH)], [Heading-Anthesis (HtA)], [Anthesis-Maturity (AtM)] and [Maturity-Harvesting (MtHa)], whose mean ETe was estimated to be 2.30, 1.33, 1.03, 3.63, 4.69, 5.13, 6.53, 7.09 and 1.35 mm d(-1), respectively. The mean ETC, Effective Precipitation (Eff. P) and NIR of wheat during its growth period were estimated to be 774, 349, and 425 mm, respectively. Results showed that wheat sensitivity to water stress is high from booting to maturity, is low from sowing to double ridge and from maturity to harvesting, and is moderate in other stages. Therefore, increasing the irrigation interval in the first three stages of growth and eliminating the end-stage irrigation are recommended for water saving.