| Based on the observation data collected from 22 weather stations during 1961—2010, the winter wheat water requirement (ETi) was measured, the crop water deficit index (CWDI) of different classes of drought was determined, the frequencies of different classes of drought in Shaanxi were calculated, and the temporal and spatial distribution characteristics of winter wheat water deficit at different growth stages in Shaanxi area were studied. The results indicated that drought occurred frequently during the growth period of winter wheat in Shaanxi area. The occurrence frequencies of drought during wheat growth followed the following order: jointing-booting stage>filling maturation stage>turning green stage>seeding before winter>growing in winter. The occurrence frequency of severe or worse drought at various growth stages of winter wheat showed a decreasing trend from north to south. For inter-decade change characteristics, drought index fluctuation turned an increasing trend, reaching high in 1970s and 1990s and becoming mutated in 1968. |