Abstract: Evapotranspiration and precipitation are two main parameters during the growth period of winter wheat and also important for irrigation planning. Based on the climate data of 48 weather stations throughout the winter wheat areas of Hebei Province from 1965 to 2007 and Penman-Monteith equation recommended by FAO,the Differences between Evapotranspiration and Precipitation (DEP) during the growth period of winter wheat and its temporal-spatial variations and the relationships with meteorological factors were analyzed. The results showed that the DEP were positive during whole winter wheat growth period,which meaning the water deficit of winter wheat growing. The times of the most water deficit was in the middle period of winter wheat growing and had little variation,and the largest region of water deficit was located in the southeastern part of Hebei Province. Water deficit in the medium-term of growth period was most serious and less variable. Under the climate change,the DEP had a declining tendency during the whole growth period,and it declines significantly at 0.01 level of statistical test in the late term,but not significant in other times of growth period,and the changing rate of DEP was little in the whole growing seasons for winter wheat during 1965 to 2007. The main reasons that caused the DEP decline was the reduction of sunshine duration and wind speed in the whole growth period,although minimum temperature had a limited impact. At the same time,the advancement of agrotechniques such as crop variety and management practices also played a role for the variation of DEP.

Key words: Winter wheat, Winter wheat, Differences between Evapotranspiration and Precipitation(DEP), Temporal-spatial variations, Water deficit, Trend analysis