Spatio-temporal variations of winter wheat water requirement and climatic causes in Huang-Huai-Hai Farming Region

Information on crop water requirement and the changes in this factor in time and space are critical for irrigation schemes, water resources planning and decision-making. Based on observed daily meteorological data in 50 weather stations in 7 sub-zones of Huang-Huai-Hai Farming Region (HFR) in 1960—2009, winter wheat water requirement and irrigation amount were simulated using the modified SIMETAW model. Results showed that winter wheat water requirement decreased from 1960 to 2009, with a significant decrease of 9.21~18.90 mm from 1970 to 1999. Winter wheat perennial average water requirement was 452.4 mm, coupled rainfall degree for winter wheat growing season was only 0.40. Winter wheat irrigation amount varied among different sub-zones, it increased at the rate of 10.02~13.48 mm per decade in western Henan Province and central Shanxi and Shaanxi Provinces. With regard to spatial distribution, water requirement and irrigation amount during winter wheat growing season were higher in the peripheral than in the central regions. Both water requirement and irrigation amount were highest in the west Henan Province with values of 457.32 mm and 335.33 mm. However, winter wheat water requirement and irrigation amount were lowest in the lower Haihe Plain with values of 363.24 and 247.51 mm. While temperature significantly increased, wind speed, humidity and solar radiation significantly decreased and also with an insignificant decrease in precipitation from 1960 to 2009. The negative trend in winter wheat water requirement in HFR was mainly attributed to declining solar radiation, which was in turn driven by some other climatic factors. Correlation analysis showed that temperature, sunshine hour and wind speed were positively correlated with winter wheat water requirement, while relative humidity was negatively correlated with it.