Response Of Changes In Soil Freeze/Thaw State To Climate Change In Northeast China

Soil freeze-thaw change is an important factor in the study of permafrost and play a key role in climate change,which will have an important impact on ecosystem,hydrological process and infrastructure.In permafrost regions,snow cover has a great impact on soil temperature,soil freeze-thaw process,cold season hydrological cycle,hot-quality and carbon exchange between atmosphere and ground.Northeast China is one of the main regions of permafrost distribution,and the distribution of snow cover is also very extensive.The freeze-thaw state of soil will be affected by climatic characteristics and it changed dramatically.Therefore,it is particularly important to analyze the freeze-thaw state of soil in Northeast China and study the relationship between its change and climate.This paper,by using the ground stations in Northeast China in recent 50 years of observation data and remote sensing data.Through linear regression analysis,Mann-Kendall method,spatial analysis.Discuss temporal variation characteristics of Northeast China area elements such as temperature,precipitation,snowfall,snow cover,and the relationship between soil temperature and the maximum freezing depth and climate change and vegetation.The main results are as follows:(1)The air temperature,snowfall,snow cover index,maximum snow cover thickness and soil temperature showed a trend of increase in nearly 50 years in Northeast China,the air temperature and soil temperature heating rate is about 0.3 ?/10 a.Snow cover index and maximum snow cover thickness rising rates were 6.5 cm·d/a and 0.8 cm/a,respectively,and the seasonal maximum freezing depth is gradually reduced at a rate of 0.02 m/10 a.Precipitation fluctuates greatly,but the trend is not obvious.(2)In spatial,the standard climatological normals of air temperature,precipitation and soil temperature increased from north to south,while the values of snowfall,snow cover index,maximum snow cover thickness and seasonal maximum freezing depth decreased from north to south.The change rate of seasonal maximum freezing depth was significantly reduced,the change rate of precipitation did not reach above the significant level of 95%,the other climatic elements show a significant increase.The maximum change rate of temperature station is 0.6 ?/10 a,the 40 cm soil temperature change rate is 0.78 ?/10 a,it is faster than the air temperature.(3)The analysis results of the correlation coefficients of various elements in spatial distribution show that: the surface temperature at 0 cm and the soil temperature at 40 cm have a significant positive correlation with air temperature,and the seasonal maximum freezing depth has a significant negative correlation with air temperature.Precipitation change has a weak impact on the surface temperature at 0 cm,showing a significant negative correlation.The snow cover index and maximum snow cover thickness have a positive influence on soil temperature at 40 cm,and have a significantly negatively correlated with surface temperature at 0 cm and seasonal maximum freezing depth.The correlation coefficient reflects that the surface temperature at 0 cm,soil temperature at 40 cm and maximum freezing depth are mainly influenced by the double influences of air temperature and snow cover,followed by the changes of snowfall,and the changes of snowfall have little influence on the soil temperature at a certain depth.(4)From 1982 to 2014,the spatial distribution of the beginning and ending time of vegetation growing season in northeast China presented an opposite phenomenon.The start time(SOS)and the end time(EOS)of the growing season were earlier in the Xing'an Mountains regions.In the Inner Mongolia plateau and Changbai Mountain regions,the start time(SOS)was earlier and the end time(EOS)was later.So,this regions have the longest growing season length(LOS).In the central plains of northeast China,the start time(SOS)was later and the end time(EOS)was earlier,and have a shorter length of growing season(LOS).The trend of vegetation growing season change shows that in the Xing'an Mountains and Changbai Mountain regions,the start time(SOS)of growing season was advanced,and the end time(EOS)of growing season was delayed.In the central plains of northeast China,the start time(SOS)of growing season was delayed,and the end time(EOS)of growing season was advanced.