Effects Of Climate Change On Permafrost And Hydrological Processes In Northeast China

Under the background of global warming,the permafrost environment in northeast China has undergone significant changes,such as the increase of ground temperature,the deepening of active layer,the decrease of permafrost area and the northward movement of the south boundary,etc.,and the permafrost changes also have a corresponding impact on the hydrological process in the cold region.At the same time,permafrost,through the state of the soil and the water cycle,in turn affects the land~gas exchange,ecological and hydrological processes,engineering construction in the cold region and human activities.Therefore,it is particularly important to study permafrost changes and hydrological responses of permafrost under climate change.Supported by meteorological data from 1960 to 2012,this paper constructed the background of climate change in northeast China.Then,ArcGIS spatial analysis,raster calculator,model builder and other tools were used to simulate the distribution of frozen soil in northeast China with the frozen number model,and analyze its spatial and temporal changes.At the same time,temperature data and freeze-thaw index calculation formula were used to analyze the change characteristics of freeze-thaw index.The runoff,evapotranspiration and freeze-thaw process of two small basins in northeast China were simulated by SHAWDHM,a distributed hydrological model coupled with frozen soil module.Finally,the model precision is evaluated by using Nash ratio coefficient and runoff data measured by hydrological station.The results show that the warming trend is obvious in northeast China from 1960 to 2012,the temperature rising rate is 0.36?/10 a,significantly higher than the national average heating rate(0.22?/10 a),and the winter heating rate is highest,increase in Lesser hinggan mountains area is the largest space;During the 53-year period,the precipitation showed a slight increase in fluctuation,and the seasonal difference was obvious.The precipitation increased in spring and winter,and decreased in summer and autumn.The actual evapotranspiration increased significantly in spring and summer,followed by autumn,and decreased in winter,the northern part of the greater hinggan mountains,the lesser hinggan mountains and the sanjiang plain are the regions with the largest increase.In this context of climate change,the permafrost in northeast China experienced a decrease-increase-decrease from 1960 to 2012.By 2012,the permafrost area had decreased to 0.36×10~6km~2,and the degradation rate was about 3%/10a.According to NSE Nash ratio coefficient accuracy evaluation results,SHAWDHM model simulation accuracy is above 0.6,the results are reliable;The results of model simulation show that the maximum melting depth of Tahe river and Honghuaerji river basin shows an upward trend from 1960 to 2012,and the end time of melting has been delayed and slowed down for many years.The permafrost degradation in Honghuaerji river basin in the south is more significant and serious.