Study on water deficit trend in the recent 30 years in Wuqiao County, Hebei Province

Water is in severe shortage in Heilonggang region, a region where insufficient and uneven precipitation are the main limiting factors to stable production of winter wheat. Thus to lay the theoretical basis for stable winter wheat production in the region under optimal irrigation, a study was conducted on the trends in water deficit in recent 30 years in Wuqiao County, Heibei Province. Based on observed daily meteorological data in Wuqiao County, we analyzed the dynamics of precipitation, crop water requirement, crop water consumption intensity and crop water deficit index (CWDI) for the whole growth period and the individual growth stages of winter wheat from 1981 to 2013 using SIMETAW model. To calculate the coefficient of variation of winter wheat yield reduction in different precipitation years, we divided winter wheat yield into trend yield and meteorological yield using linear moving average. The results of the study showed that CWDI and crop water requirement for the whole growth period of winter wheat gradually increased with time. The probability of the occurrence of drought in the whole growth period of winter wheat was 93.75% in the analyzed 32 years. Of this, the probability of both moderate drought and severe drought was 65.52%. Precipitation decreased in the middle stages of winter wheat growth while it increased in the late stages of winter wheat growth. The trend in daily crop water consumption intensity was the reverse of that of precipitation. The trends in both precipitation and crop water consumption intensity resulted in higher CWDI during greening to jointing and then jointing to flowering stages than in the other growth stages of winter wheat. The absolute value of coefficient of variation of yield reduction of winter wheat was highest (154.241) for dry years, lowest (1.999) for humid years and average (24.776) for normal years. Timing irrigation at jointing through flowering stage was critical for ensuring a stable increase in winter wheat production. Thus to ensure stable yield production in the study area, an adequately irrigation at the beginning of jointing stage or twice irrigations at the early and late jointing stage of winter wheat were required.