近47年羌塘自然保护区积雪对气候变化的响应

积雪是气候系统中最活跃的环境影响因素之一,其动态变化对全球及区域气候的变化都有重要影响。本研究利用羌塘自然保护区近47年(1971—2017年)5个气象站逐日积雪、气温、降水、风速等资料,采用趋势分析、Mann-Kendall法等方法,分析了气候变暖背景下近47年羌塘自然保护区积雪日数和雪深的时空变化特征,以及与气候要素的关系。结果表明：自然保护区各站积雪日数为18.4~67.0天,总体上呈自西向东递增的分布态势；随海拔升高,积雪日数增多、积雪初日提早、终日推迟、持续日数延长。近47年保护区年积雪日数明显减少,平均每10年减少3.8天,主要表现在秋季和春季；年最大积雪深度平均每10年减小0.53 cm；积雪初日以11.3 d/10a的速率显著推迟,终日每10年提早11.0天,而积雪持续日数每10年减少23.3天,特别是1991—2017年这种变化态势更突出。M-K检测显示,除冬季外,季积雪日数由多变少的突变时间均发生在21世纪前10年,2001年是积雪初日、终日和持续日数的突变点。气温显著升高、空气相对湿度明显减小是积雪日数减少的主要原因,积雪初日推迟、终日提早不仅与气温显著升高有关,还与风速变小密不可分。

Response of Snow Cover to Climate Change in Chang Tang Nature Reserve in 1971-2017

Snow cover is one of the most active natural components in climatic system, and its variability has a major impact on global and regional climate change. Based on the daily data of snow cover, temperature, precipitation and wind speed at five meteorological stations in Chang Tang Nature Reserve of Tibet (CTNRT) from 1971 to 2017, the spatial-temporal evolution characteristics of snow cover days and snow depth were analyzed by using the methods of trend analysis and Mann-Kendall test analysis. Also, the correlation between the change of snow cover and climatic factors was discussed. The results showed that: the annual snow cover days of each station were 18.4- 67.0 in CTNRT, and the distribution increased from the west to the east. Meanwhile, with the increase of altitude, the snow cover days increased, the beginning day of snow cover was earlier, the terminal day of snow cover was delayed, and the duration of snow cover was prolonged. During 1971 to 2017, the annual snow cover days exhibited a significantly decreasing trend with a rate of 3.8 d/10 a, especially in autumn and spring. The annual maximum snow depth showed a decreasing trend with a rate of 0.53 cm/10 a. Additionally, the beginning day of snow cover was postponed with a rate of 11.3 d/10 a, the terminal day of snow cover was earlier with a rate of 11.0 d/10 a, the duration of snow cover was decreased with a rate of 23.3 d/10 a, in recent 27 years (1991-2017), this trend of change was even more obvious. According to the Mann-Kendall test, except in winter, the abrupt change of the seasonal snow cover days occurred in the first decade of the 21st century, the climate mutation point of the beginning day, terminal day and duration of snow cover all occurred in 2001. In conclusion, the decrease of snow cover days is mainly caused by the significant increase of mean temperature and the decrease of relative humidity, and the postponed beginning day and the earlier terminal day are not only related to the significant increase of temperature, but also closely related to the decrease of wind speed.