Abstract: Spring frost is one of the serious agricultural natural disasters in northern China, which has new characteristics under the background of climate change. Based on the daily minimum air temperature data at 19 weather stations of Ningxia from 1961 to 2016, the temporal and spatial change characteristics and periodicity of the minimum air temperature and frost days during the spring frost stage were analyzed by using Mann-Kendall test, Sen’s slope, linear regression and wavelet analysis methods. The results show that the average value of the minimum air temperature and frost days during the spring frost stage was 0.59 ℃ and 3.9 d in Ningxia, respectively, and the minimum air temperature increased significantly, while the frost days decreased distinctly from 1961 to 2016, their Sen’s slopes were 0.005 ℃·a-1 and -0.05 d·a-1, respectively. The frost days were remarkably negative correlated with the minimum temperature during the spring frost stage, and their spatial distribution was opposite. The minimum temperature was higher in central Ningxia and lower in southern Ningxia, while the frost days was more in the south and less in the central. The minimum temperature showed an significant increasing trend at 74% weather stations of Ningxia, while the frost days appeared an significant decreasing trend at 53% stations during the spring frost stage from 1961 to 2016, and the change trends of them at same station weren’t exactly opposite, but Sen’s slopes of them were smaller. The periodic characteristics of the minimum temperature were similar to frost days during the spring frost stage, and the periods with 20-25 a and around 10 a were obvious and stable from 1961 to 2016, but the oscillation was sharp before 1967, then that tended to be flat after 1967, which indicated that the frost days during the spring frost stage were possible to decrease slowly in Ningxia in the future.

Key words: spring frost days, spring frost stage, minimum air temperature, temporal and spatial change characteristics, Ningxia

摘要： 基于宁夏1961—2016年19个气象站点最低气温逐日观测资料，研究春霜冻期最低气温和霜冻日数的时空变化和周期特征。结果表明：近56 a，宁夏全区春霜冻期最低气温平均为0.59 ℃，且呈显著升高趋势，而春霜冻日数平均为3.9 d，呈显著减少趋势。春霜冻期最低气温和霜冻日数呈极显著负相关关系，且两者在空间上呈现反向分布，其中宁夏中部为最低气温高值区，南部为低值区，而霜冻日数正好相反。全区74%的站点最低气温显著上升，53%的站点霜冻日数显著下降，同一站点两者表现趋势并不完全相反，但Sen斜率均较小。最低气温和霜冻日数的周期性特征明显且相似，20~25 a和10 a左右的周期稳定，且1967年以前两者振荡最为剧烈，而后趋于平缓，表明未来宁夏春霜冻日数可能持续平缓下降。

关键词: 春霜冻日数, 春霜冻期, 最低气温, 时空变化, 宁夏