Characteristics of Frost Days and Accumulated Temperature in Eastern Gansu Over the Last 40 Years

Using daily air temperature and ground temperature data for 15 meteorological stations in eastern Gansu Province from 1971-2010 we conducted correlation analyses,determined the rate of climate tendency and moving t-test,and applied GIS spatial analysis techniques and mathematical statistics theory.Agro-climatic resources of the first frost date,the last frost date,the frost-free period and ≥0℃,≥10℃,and 0℃ accumulated temperature and number of days were quantitatively analyzed.Variations in temporal and spatial characteristics and the relationship between frost days and accumulated temperature were illuminated.Our goals were to fully understand and use the local agro-climatic resources,and guide the adjustment of local cropping systems,agricultural production and activities.The results showed that the first frost date and frost-free period were negatively correlated with elevation and latitude,and positively correlated with longitude.The last frost date was positively correlated with latitude and altitude and negatively with longitude.The first frost date was earlier,the last frost date was late and the frost-free period was shorter in western and northern parts;this pattern was reversed in the east and south.The first frost day was earlier,the last frost day was late and the frost-free period was shorter in the 1970s and 1980s,but the changes were reversed in the 1990s.The first frost date was pushed back,the last frost date advanced and the frost-free period extended in most parts,especially in the south-central towns of Zhenyuan and Chongxin.A significant upward trend of accumulated temperature was shown in this region:higher values are located in the central region and lower values in the western and northern region.The average annual maximum of accumulated temperature,the average annual latest first frost date,the earliest last frost date and the longest frost-free period were all located in southern region(Jingchuan and Chongxin),while the average annual minimum accumulated temperature,average annual earliest first frost date,latest last frost date,and shortest frost-free period occurred in the western and northern regions(Jingning,Huating and Huachi).