中国东北兴安岭地区年冻融频次的分布规律

Freeze-thaw cycle is one of the important factors affecting rock strength and environment change in cold region engineering. Annual freeze-thaw frequency， namely the annual accumulated amount of freeze-thaw cycle， can directly determine the impact of freeze-thaw cycle on cold region engineering and environment. Thus， it has a great significance to investigate annual freeze-thaw frequency in cold region. Xing’anling （Khingan） region has the largest intact primeval forest in China， with a forest coverage rate of 80.95%. The region covers northern part of Heilongjiang Province and northeast part of Inner Mongolia Autonomous Region. It belongs to the temperate continental monsoon climate， and due to the high latitude， there is seasonally frozen soil， island permafrost and discontinuous permafrost. In this paper， Xing’anling region of Northeast China is taken as the research object， and surface temperature data of 18 meteorological stations in Xing’anling region in the past 30 years from 1990 to 2017 are selected for collation， and annual freeze-thaw frequency of each station is obtained. Then， the variation of annual freeze-thaw frequency of each station is studied and analyzed in spatial distribution and time series. The results show that annual freeze-thaw frequency increases with the increase of latitude， decreases with the increase of longitude， and increases with the increase of altitude in Xing’anling region of Northeast China， and all have good linear trend. In the long-term dimension， annual freeze-thaw frequency showed an obvious downward trend from 1990 to 2017， and a sudden change occurred around 2004. Further analysis shows that among the three factors affecting the spatial distribution of annual freeze-thaw frequency， latitude and longitude have a greater influence， while altitude has a relatively small influence. There was a good negative correlation between annual freeze-thaw frequency and NDVI in Xing’anling region of Northeast China， indicating that annual freeze-thaw frequency was related to local vegetation coverage to some extent， and decreased with the increase of vegetation coverage.

Keywords： annual freeze-thaw frequency ; Xing’anling （Khingan） ; Northeast China ; latitude ; longitude ; altitude