1978-2017年西藏高原冻融指数时空变化特征

Spatiotemporal variations in freezing and thawing indices on the Tibetan Plateau during 1978-2017

西藏高原是我国面积最大的高寒冻土区,研究土壤的冻融变化可为该区生态环境变化及评估提供依据。本文基于西藏高原气象站1978-2017年日均气温数据,计算了空气的冻结和融化指数并分析了其时空变化特征,探讨了主要的影响因子。分析结果表明:由34个气象站点代表的近40年西藏高原冻结指数范围在386.8~886.1℃·d,融化指数范围在1960.3~2521.5℃·d;冻结指数与融化指数都随时间波动变化,但趋势相反:其中冻结指数倾向率为-9.2℃·d·a^(-1),呈下降趋势;融化指数倾向率为11.1℃·d·a^(-1),呈上升趋势。冻融指数的变化趋势表明西藏高原具有暖化的特点。冻结指数均值的空间分布特征表现出自东南向西北递增的规律,而融化指数则在中南部和东部出现高值中心;西藏高原西北地区冻结指数下降速率较东南地区更快,融化指数则在西藏高原大部分区域内呈现快速上升的变化趋势。西藏高原冻融指数受经纬度、海拔和社会经济因素的综合影响,但海拔是影响冻融指数变化的主导因子。

The Tibetan Plateau is the largest expanse of alpine frozen soil in China.The study of freezing and thawing indices can provide some implications for ecological environmental evaluation.Based on the daily air temperature data obtained from 34 meteorological stations,freezing and thawing indices and their spatiotemporal variation trends from 1978 to 2017 on the Tibetan Plateau were calculated and analyzed,and some key factors that may affect these indices are discussed.The results showed that during 1978–2017,the freezing index of the Tibetan Plateau ranged from 386.8 to 886.1℃·d,and the thawing index ranged from 1960.3 to 2521.5℃·d;the temporal variation trends of the two indices were nearly negatively correlated,and significant downward(-9.2℃·d·a^(-1))and upward trends(11.1℃·d·a^(-1))were observed for the time series of the freezing index and thawing index,respectively.The spatial distribution of the mean value of the freezing index showed an increase from southeast to northwest,whereas the thawing index was high in the south-central and eastern areas.The rate of decline of the freezing index in the northwest of the Tibetan Plateau was faster than in the southeast,whereas the thawing index showed a rapid upward trend in most areas on the Tibetan Plateau.Freezing and thawing indices were affected by the latitude,longitude,altitude,and some socio-economic factors;however,altitude was the dominant factor.