Estimating the Winter Wheat Water Requirement under Climate Change Scenarios in Gorgan Plain

Climate change through increased water demand, especially in agricultural sector, is the main challenge facing water resources management. Wheat is one of the staple and strategic crop throughout the world, particularly in Iran. In this study, historical observations from 1985-2005 were used to simulate the effects of climate change on the winter wheat water requirement across Gorgan plain. SDSM4.2 and CanESM2 models were used to downscale winter wheat water requirement under three concentration pathway scenarios; RCP2.6, RCP4.5, and RCP8.5 in four periods (2020-2039, 2040-2059, 2060-2070, and 2080-2099). The Hargreaves-Samani (HS) model with less input variables in comparison with FAO-Penman-Monteith (PMF-56), was used for downscaling water requirement. The results of RCP2.6 scenario showed that the maximum and minimum annual water requirement of winter wheat are 403 and 286 mm in 2040-2059 and 2020-2039 periods, respectively. These values for RCP4.5 scenario were predicted to be 361 and 336 mm in 2020-2039 and 2040-2059 periods, respectively. For RCP8.5 scenario, they were predicted to be 336 and 199 mm in 2020-2039 and 2060-2079 periods, respectively. The growing period will be reduced in all three proposed scenarios and the reduction rate in RCP8.5 scenario is more than that in RCP4.5 scenario. According to the results, climate change is generally expected to reduce agricultural water consumption in Gorgan plain by reducing the cumulative winter wheat water requirement.