Risk Assessment And Regionalization Study On Winter Wheat Drought In North Of China

On the background of irrigation and nonirrigation, making natural moisture deficiency rates calculated basing on the theory of balance of water as axis, and risk assessment techniques and methods as core, the risk levels of effect that drought on yield of winter wheat in semi-humid and semi-drought areas in recent 40 years were studied by two methods from actual yields and productive potentialities respectively. The spatial distribution principles and losses zonation were made by Mapinfo.According to the response yield to water, five types of drought and yield reduction were defined, they are light moderate, heavy, serious heavy and ultra-heavy, and the spatio-temporal distribution of which and the correlativity between them in recent 40 years is analysed. The results indicated: the probability distribution of natural moisture deficiency rates of winter wheat during the growing period could be divided into three types because of their regional difference, which were mainly in the north part, the middle part and the south part respectively in producing area of northern China. In north and middle, the frequency of serious drought was higher, but in south, it was the light drought. The probability distribution of yield reduction could be divided into three types also, of all these types, it was the frequency of light yield reduction was higher, which reflected that irrigation was important to lessen the effect drought on yield. The correlativity indicated: there was no clear coherence between drought types and yield reduction types, and the frequency of drought was more than that of yield reduction, especially heavier drought occurred more frequently than lighter yield reduction.Photosynthesis potential productivity, photo - temperature productivity and climate productive potentialities were calculated using "correcting method step by step". From the balance of water, a new model was used to construct water function. The result indicated that because effective moisture accounts for 20%~30% of the water requirement of winter wheat, and it was important to climatic productive potentialities, the climatic productive potentialities was 20%~30% higher than before accordingly, which would make great sense to evaluate climatic productive potentialities. The high change of preci-pitation made spatio-temporal change of climatic productive potentialities bigger than that of photosynthesis and photo - temperature. The trend of water decreasing from south to north, from east to west in Hebei, Beijing, Tianjin and Shandong, from south to north in Shanxi, Shaanxi and Henan made every index has the same trend almostly.Correlations between actual yields of winter wheat and natural moisture deficiency rates in irrigated areas were established, and because of the differences of sensitivity between them, two types(A and B) indices of natural moisture deficiency rates and the corresponding yield reduction rates of actual yield were confirmed. The results indicated: the yield reduction rates of A type are <9 %,9%~12%,12%~14%,14%~21 % and >2\ %, which were suitable for the east and some areas of midst in Shandong,south near Weihe river in Shanxi and some areas of midst in Hebei; and B type were <9 %,9%~15%,15%~21 %,21 %~40%and >40% respectively, which are suitable for other areas?From the point of view of risk, a index system of risk assessment of winter wheat losses caused by drought was established, including the meanings, token models and estimate methods of risk index of natural water deficiency rate, risk index of yield reduction rate and trending vector coefficient of disaster resistance capability, then on the base of these indices, the comprehensive risk index model of losses caused by drought was established and regionalized. The results indicated: the high risk region included the middle north of Shanxi, some of middle of Shaanxi and some of Hebei in east; the higherrisk region included some of middle of Shaanxi, the Tangshan region and some of west of Hebei; the moderate risk region included the middle of S...