| Since the 20th century,the global temperature has generally increased,and the permafrost on the Qinghai-Tibet Plateau has also undergone significant changes.Permafrost degradation will have a significant impact on the hydrogeological conditions and water and heat exchange processes in the region.Therefore,it is of great significance to study the spatial distribution of permafrost on the Qinghai-Tibet Plateau and the hydrological response caused by permafrost degradation.Based on the extended freezing index model and Kudryavtse method,this paper simulated the distribution of permafrost over the Qinghai-Tibet Plateau from 1961 to 2019 using the measured data from meteorological stations,and analyzed the consistency between the simulation results and the maps compiled by previous authors;based on the Stefan method and Kudryavtse method,the thickness of active permafrost layer and the maximum freezing depth of seasonal frozen soil are simulated and verified by the measured data of boreholes.On this basis,taking the Yellow River source region with obvious permafrost degradation as a typical region,using methods such as base flow segmentation,wavelet analysis,and M-K test to analyze meteorological,hydrological and permafrost elements,and explore the hydrological response of permafrost degradation.The research results show that:the extended freezing index model and Kudryavtse method are in moderate agreement with previous maps,and can better simulate the distribution of permafrost in the Qinghai-Tibet Plateau;The thickness of active permafrost layer calculated by Stefan method and Kudryavtse method has a certain correlation with the borehole data.On the whole,the active layer thickness calculated by Stefan method is closer to the measured data than that by Kudryavtse method.From 1961 to 2019,the permafrost area of the Qinghai-Tibet Plateau decreased from 1.24×10~6km~2 to 0.88×10~6km~2,and the overall degradation rate was 1.01×10~4km~2/a.The changes of permafrost area can be divided into two stages:from 1961 to 2002,the permafrost area was relatively stable;from 2002 to 2019,the permafrost was degraded significantly,and the degradation rate in this stage was 2.22×10~4km~2/a.The annual average value of the maximum freezing depth of seasonal frozen soil is between 100cm and 400cm,and the spatial distribution has obvious latitude zonality and vertical zonality;from 1961 to 2019,there was an overall decreasing trend,and the average annual decreasing rate was between 0.005 m/a and 0.015m/a.The thickness of permafrost active layer is mostly between 0 and 300cm,and it gradually increases from the center of permafrost distribution to the permafrost-seasonal frozen soil contact area;in terms of time,the overall performance was increased year by year,and the average rate of increase for many years was between 0-0.01m/a.The main period time of energy fluctuation of permafrost area in the source region of the Yellow River is the same as that of hydrometeorological elements,which is 46-48 years.During the main cycle,the permafrost in the source region of the Yellow River presents a trend of increase-decrease-increase-decrease-increase,while the change trend of meteorological and hydrological elements was opposite.The permafrost area,annual precipitation,and annual runoff occurred at the same time points,all around 2002.The regression index and permafrost area of the Jimai basin in the source region were positively correlated after 1998.With the degradation of permafrost,the regressive water index decreases,the regressive water rate of basin slows down,and the conversion rate between surface water and groundwater slows down. |
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