Changes Of Soil Temperature In High Latitudes Of Eurasia And Its Response To Climate

Soil temperature is a comprehensive product of heat and mass exchange between the atmosphere and the land surface.Soil temperature is a sensitive climate integrator and indicator,and plays an important role in soil physical and microbial processes.It has great influence on the ecosystem,plant growth and vegetation,greenhouse gases fluxes,and agriculture.Therefore,understanding the soil temperature and its relationship with environmental factors has received substantial attention from scientific community worldwide.However,limited observational data in both spatial and temporal coverage have long been the restrictions for in deep investigation on soil temperatures in long-term time series at local and regional scales.It was also difficult to investigate,effects of changes in temperature,precipitation,snow and other climate variables on soil temperature without reliable soil temperature data and information.The core scientific question of this research is to investigate spatial and temporal changes in soil temperatures and their responses to climate change in high latitudes of Eurasia from 1963 through 2012 using data and information from 239 ground-based observations.More specifically,we will study:(1)Spatial and temporal characteristics and changes of climatic variables such as mean annual air temperature,precipitation,snowfall,and snow cover;(2)Spatial and temporal characteristics and changes of soil temperatures at 20 cm,40cm,80 cm,160cm,and 320 cm depths;(3)Responses of spatial and temporal changes in soil temperatures to climate change.The main research conclusions are:(1)Climate changeChanges in air temperature mainly occurred in winter,while changes in precipitation mainly occurred in summer.There is a general negative correlation between mean annual air temperature and annual precipitation,i.e.,there is more precipitation in cold years while less precipitation in warm years.The annual average temperature in high latitudes of Eurasia from 1963 to 2012 increased at a rate of 0.38?/10 years,showing significant latitudinal gradient and longitudinal gradient.Air temperature thawing index increased at a rate of 62.8?·d/10 years,while air temperature freezing index decreased at a rate of 51.6?·d/10 years.In terms of spatial distribution,thawing index is opposite to the freezing index,and the thawing index is increasing with latitude,while the freezing index is decreasing with latitude,both indicating climate warming.Annual precipitation(both liquid and soil precipitation)and annual rainfall(liquid precipitation only)increased,respectively about 7.9mm /10 years and 8.6mm/10 years,while annual snowfall has no significant change trend.Average snow depth,maximum snow depth,and snow cover index were increased about 0.4cm/10 years,1.2cm/10 years,139.3cm·day/10 years,respectively.(2)Changes in soil temperaturesThe annual average soil temperature increased about 0.27?/10 years at 20 cm,0.35?/10 years at 40 cm,0.28?/10 years at 80 cm,0.28?/10 years at 160 cm,and0.27?/10 years at 320 cm depths.Spatial distribution showing significant latitudinal gradient and longitudinal gradient respectively.The thawing index of 20 cm depth soil temperature increased at a rate of 73.4?·d/10 years,while the freezing index decreased at a rate of 23.2?·d/10 years,both indicating soil temperatures were increasing.Spatially,distribution of soil temperature thawing index is opposite to that of soil temperature freezing index.(3)Response of soil temperatures to climate changeThe annual average soil temperatures at each depth was decreasing with latitude.It was positively correlated with air temperature,annual precipitation,annual rainfall,average snow depth,and snow cover index.Comprehensive analysis of the relationship between soil temperature and climatic elements at various depths shows that air temperature is the most important factor affecting soil temperature,and the difference between soil temperature and air temperature is controlled by many factors,but the main reason for its temporal and spatial changes is the seasonal accumulation in winter.The difference in snow cover thickness results in different changes in the thermal insulation effect of snow;the difference in near-surface soil moisture caused by the spatial and temporal differences in summer rainfall is also one of the main factors leading to changes in the land-temperature difference.These research results are of great significance to hydrology,ecosystems,and cryosphere.In addition to the analyzed climatic elements,soil temperature is also affected by complex topography,vegetation distribution,and landform features.It is required for further studies and investigation with newer data and information.