Characteristics of heat resources in winter wheat growing seasons and its impacts in Guanzhong area over last 40 years

Based on the observed data of 10 conventional meteorological stations in Guanzhong area from 1971 to2010 and investigated data of winter wheat growth periods from 1986 to 2010,heat resources changes in the winter wheat growth period and their variation effects were analyzed by using mathematical statistic method. The results show that heat resources increasing trend was evident in the recent 40 years,although the serious inter-annual fluctuation existed,warming trend increased sharply in 1990s. The beginning date of 0℃ was obviously advanced,it's terminal date was delayed and overwintering period was delayed correspondingly. The terminal date of 14℃ advanced and the terminal date of 18℃ postponed since 1980s,the suitable stage of winter wheat planting was extended. There was a very obvious ascending trend for the accumulated temperature above 0℃ and continuous days,the winter negative accumulated temperature and overwintering period was decreasing. The total accumulated temperature above 0℃ in growth period of winter wheat increased by 180( ℃ ·d) ·10a-1during1986-2010. The days of the growth period of winter wheat decreased by 6d·10a-1. The suitable sowing time was Sep 28th to Oct 11th which the accumulated temperature above 0℃ before wintering of wheat from 500℃ ·d to 700℃ ·d at 80% of guarantee rate. The optimum sowing time should delayed 3 ~ 5 days than regular time with heat resources increasing,which help to prevent prosperous grow before winter. The sowing time was influenced by several factors,so the practical sowing time should work out according to local conditions to raise the utilization rate of heat resources.