Changes of the First Frost Dates,Last Frost Dates and Duration of Frost-free Season in Xinjiang during the Period of 1960-2011

In this paper,the first frost date,last frost date and duration of frost-free season as well as their change trends were analyzed using the linear trend estimation,anomaly analysis and five-year moving average based on the daily minimum temperature data observed by 51 meteorological stations in Xinjiang during the period from 1960 to 2011.The results showed that the average first frost date was postponed by 11 days,the average last frost date was moved up by 7 days,and the duration of frost-free season was extended by 17 days.The first frost dates,last frost dates and durations of frost-free season in north Xinjiang,south Xinjiang and the Tianshan Mountains were consistent with those in whole Xinjiang,but the change extent was not different.Their variation was the most significant in the Tianshan Mountains,and then in north Xinjiang and south Xinjiang.The first frost date,last frost date and duration of frost-free season were closely related to the geographical and temperature factors.The first frost date occurred earlier,the last frost date later,and the duration of frost-free season became shorter along with the increase of latitude and altitude.Along with the temperature increasing,however,the first frost date became later,the last frost date earlier,and the duration of frost-free season longer.The effect of minimum temperature was higher than that of average temperature and maximum temperature.