Research On Evaluate The Yield Loss Of Winter Wheat Caused By Drought In North China

Natural disasters occurred frequently in China, and in North China, drought is the main agro-disaster during winter wheat growth periods, which seriously influence the growth and yield of winter wheat. In this study, we take Hebei, Henan, and Shandong Province as research regions. We get the meteorological and winter wheat yield data of 41 sites from the three provinces. Then we analysis the drought's law, time-space variation, intensity by the index of precipitation anomaly using stat. analytical method. Choose the negative precipitation anomaly of the whole growth period and each growth stage of winter wheat as evaluation index, as while as yield reducation rate. Assess the drought yield loss of winter wheat quantificationally in North China from 1981 to 2005. Analysis the drought yield loss grade in each growth stage, and the impact on winter wheat. Then establish the yield loss assessment model based on the rainfall in the whole and every growth period. At last found regression model of drought yield loss on winter wheat by taking negative precipitation anomaly in the whole and every growth period as variable. In order to actualize the quantificational evaluate on winter wheat yield loss caused by drought. The main conclusions are as follows:1. In the nearly 25 years, the drought in North China shows ascend tend. And the frequency and grade of drought is obviously higher in 1990s than that of 1980s', that the frequency is about 60%-70%, some sites even achieved to 80%.The grade changed too, in 1980s, light drought happened most, but in 1990s, mid drought happened most. In 1990s, the light drought happended once every six years , mid drought happended once every four years, and the most serious drought happened once every 25 years.2. Drought happened in jointing and heading-blooming stage with more frequency than other stages, wich happended 6.4 times in ten years on average. Next is drought before seeding, which happended about 6 times in 10years. Drought happended in the whole growth period has the lowest frequency, which happeneded about 5.2 times in 10years. According to the drought distribution in regions, Jointing stage drought has the most frequency in Hebei province, 16 times in 25 years; jointing and heading-blooming stage drought have the most frequency in Henan, about 17 in 25 years; and in Shandong, the most frequency drought is in heading-blooming stage, about 15 times in 25 years.3. The precipitation anomaly in the whole growth period has the most corelationship with the relative meteorological yield, according to the correlation analysis between the yield and drought in every growth stage of winter wheat,. In the mid and west part of North China, the precipitation anomaly before seeding and seeding to jointing stage also impact the yield of winter wheat; in the east part of North China, the rainfall in jointing and grain-filling stage is related to yield too. But the influence of rainfall in heading-blooming stage on yield is not significant in all sites.4. Using regression analysis, we have found the drought assessment index and equation based on yield reduction, negative precipitation anomaly and the corresponding drought grade. And then set up the agro-drought grade of winter wheat. That is: for the whole growth period, when negative precipitation anomaly<15%,15%~35%,35%~55%,≥55%, the drought grade is light, mid, serious and most serious, the corresponding yield reduction rate is <10%,10%~20%,20%~30%,≥30%; before seeding, when the index<65% or≥65%, light or mid drought happened, the corresponding yield reduction is <10% or 10%~20%; in seeding to establishment period,the index is <45%,45%~90%,≥90%, the drought grade is light, mid, and serious, yield reduction is <10%,10%~20%,20%~30%; in jointing stage when the index <40%,40%~75%,≥75%, drought grade is light, mid, and serious, yield reduction is s light, mid, and serious; in grain-filling stage, when the index <50% or≥50%, drought grade is light or mid, yield reduction is <10%,10%~20%.Choose the precipitation anomaly in every growth stage as index, considering the precipitation in which stage to establish a multi-regression model for drought assessment of winter wheat in Nangong site. The assessment result is accord with the fact after test.