Study On The Permafrost Change In The Qinghai Tibet Plateau And Its Influence On The Runoff Process Of The Yangtze River Source

Climate warming has intensified since the 20th century.As an important part of the cryosphere,the Qinghai Tibet Plateau has shown the response of Permafrost shrinking,thickness thinning and active layer thickness increasing.Therefore,the Yangtze River source permafrost in the hinterland of the plateau has been regarded as an indicator of climate change,and accurate permafrost mapping has been carried out to analyze the change of frozen soil and its hydrological response,so as to understand the hydrological status of frozen soil in the cold region The response mechanism is of great significance.In the past,the mapping work of permafrost depends on the actual survey,which is limited to human and material resources and regional conditions.In this paper,based on the computer technology,meteorological data and remote sensingdata,a more accurate and convenient study on the permafrost of the Qinghai Tibet Plateau is carried out.Three models,i.e.Freezing index model,The temperature at the top of permafrost(TTOP)model and Mean annual ground temperature(MAGT),are selected to simulate the temporal and spatial changes of Permafrost Distribution in the Qinghai Tibet Plateau,and are compared with the previous work maps;Stefan formula is used to simulate the temporal and spatial variation of the maximum thickness of seasonally frozen ground(MTSFG),which provides more accurate construction parameters for engineering construction;the drilling data is used to simulate and verify the thickness and ice content of permafrost.The development and preservation of permafrost is the basis of maintaining the water balance in permafrost area.As an aquiclude,permafrost plays an important role in the regional division of hydrogeological conditions and the runoff distribution as a special underlying surface.In order to explore the influence of permafrost changes on runoff process,this paper uses daily flow data to analyze the source of the Yangtze River in typical hydrological areas.The base flow calculated through modified Kaliner-Abarleyang method,analyzes the relationship between the recession index,and the proportion of permafrost,uses wavelet analysis method to analyze the periodic characteristics of climatic and hydrological elements,and uses cumulative anomaly curve and M-K test method to detect the mutation.The results show that:from 1961 to 2018,the permafrost in the Qinghai Tibet Plateau is in a state of fluctuating degradation,with the area reduced from146.38×10⁴km² to 107.68×10⁴km²;the three models can better simulate the distribution of permafrost,and the TTOP model is the best.The thickness of permafrost active layer is 0-3m,and the maximum thickness of seasonally frozen ground is 50cm-300cm.With the increase of air temperature,the average thickness of active layer increases 0-0.75cm every year,and the maximum freezing depth decreases 3.334cm every year.The total ice content of permafrost in Qinghai Tibet Plateau is 1.272×10¹³m³,and the water release in the past 20 years is 3.708×10¹²m³.Since 1988,the degradation of permafrost in the Yangtze River source has accelerated,and the negative correlation coefficient between permafrost area and recession index is 0.91.The main cycle time of runoff,precipitation,evapotranspiration,annual maximum temperature and annual minimum temperature in the Yangtze River source is about 30 years and the variation time is about2004.The main cycle of annual maximum temperature and active layer thickness is smaller and the mutation year is earlier than other factors.This study provides a good value for the study of permafrost change and hydrological cycle.