Abstract: Based on daily ice data of five meteorological stations in Shiyang River Basin,Gansu Province,China during 1960-2014,this paper analyzed the temporal and spatial distribution and extreme changes characteristics of ice days,and the relationship between ice days and atmospheric circulation by using linear trend coefficient method,Morlet wavelet analysis method,accumulative anomaly,signal-to-noise ratio method and correlation coefficient method. Results show that:spatial distribution of ice days in Shiyang River Basin was regionally obvious due to the altitude,topography and vegetation cover;ice days overall increased gradually from north to south(except Liangzhou),with the most appeared in Tianzhu(220.8 d) of southern mountains area,accounting for 60.5% of the annual total days,and the least appeared in Liangzhou(155.8 d) of oasis plain area,accounting for 42.7% of the annual total days. Annual and decadal changes of ice days all appeared decreasing trends,and were the most significant in Minqin and Liangzhou with decreasing rates being -4.458 d·(10 a)^-1 and -3.300 d·(10 a)^-1,respectively. Ice days occurred mainly from Nov. to Mar. next year,accounting for 68.7% to 91.4% of the annual ice days,and ice appeared every day in Dec. and Jan.. Ice starting date overall had a delay trend,and ice ending date had an advanced trend(except Gulang). Ice starting and ending date differed in places,with the earliest ice first date appeared in Tianzhu(August 15,2003),the latest ice first date appeared in Liangzhou(November 1,2009),the earliest ice ending date appeared in Minqin(April 9,1969),and the latest ice ending date appeared in Tianzhu(June 26,1986). Ice periods also differed in places,with the average ice periods ranging from 189.4 to 264.2 d,the longest ice period appeared in Tianzhu(307 d),and the shortest ice period appeared in Liangzhou(162 d). Time series of annual ice days had 6 years and 8-9 years quasi-periodic variation. Annual ice days in Minqin and Liangzhou both had abrupt changes in 1995,and ice days in Yongchang,Gulang and Tianzhu appeared transition years,but no mutation. Significant positive correlation was found between ice days and circulation characteristics including vortex area index and intensity index of Asia and northern hemisphere polar,and cold air;and significant negative correlation between ice days and circulation characteristics including Tibet plateau and East Asian Trough strength. In this paper,change rule of ice days as well as the relation with atmospheric circulation characteristics were analyzed and summarized in Shiyang River Basin,and these conclusions can not only be used for project design such as water conservancy,electric power,transportation,construction,disaster prevention and mitigation,and economic development,but also provide reference for study of climate change and ice forecast in Shiyang River Basin.

Key words: ice days, circulation characteristics, Shiyang River Basin