Spatial-temporal Evolution Characteristics And Scenario Simulation Of Snow And Ice Cover In The Tianshan Mountains

With the increasingly severe situation of climate warming,global glaciers are retreating rapidly,and snow and ice areas are melting at an accelerated rate.As a sensitive indicator of climate change,snow and ice can not only reflect the relationship between regional and global climate but also reflect local weather characteristics well.Moreover,large-scale snow and ice changes can significantly impact weather,the ecological environment,and water resources utilization.The Tianshan Mountains,known as the "wet island" of Xinjiang,is not only one of the largest modern glacier areas in China,which has given birth to several glaciers but also critical snow and ice distribution area in the arid region of northwest China.Its snow and ice changes have a decisive role in forming the unique ecological environment pattern of Xinjiang Mountains-Oasis-Desert.For the arid region,snow and ice are essential natural resources.Its seasonal snow and ice meltwater is not only a source of recharge for the runoff of many rivers but also a vital freshwater resource for the production and living of residents,which can be said to be the reservoir of freshwater resources and life support place in the arid region.For the southern region of Xinjiang,the snow and ice meltwater from the Tianshan Mountains plays a crucial role in the development of its agricultural production.It has the reputation of being the "Water Tower of South Xinjiang",which can be said to be the lifeline for the survival and development of oasis agricultural civilization in the arid zone of southern Xinjiang.Therefore,this study selects the Tianshan Mountains as the study area and uses the Google Earth Engine(GEE)remote sensing data processing cloud platform to investigate the spatial and temporal evolution characteristics of snow and ice cover in typical years based on multi-source remote sensing data.Meanwhile,we extract several snow parameters such as the Normalized Difference Snow Index(NDSI),Fractional Snow Cover(FSC),Snow Cover Area(SCA),and snow line(SL).Furthermore,we analyze the spatial distribution pattern and interannual variation trend of multi-year snow and ice cover in the Tianshan region to grasp the pattern of multi-year spatial and temporal variation of snow and ice cover.Finally,a scenario simulation of the spatial distribution of snow cover area(SCA)in the Tianshan Mountains in the next 30 years is conducted to explore its future development and change trend.It is of great practical value and research significance for the sustainable utilization of snow and ice meltwater resources,climate and environmental changes,and snow disaster prediction and warning in the arid regions of northwest China,especially in the arid areas of southern Xinjiang.The main findings of this study are as follows:(1)By selecting 2018 as a typical year to carry out a study on the spatial and temporal evolution characteristics of intra-annual snow and ice cover in the Tianshan Mountains,it was found that the NDSI high-value areas were mainly in the Central Tianshan Mountains,including the areas of Tomur Peak,Khan Tengri Peak,and Borokonu Mountains.For the entire Tianshan Mountains,snow cover was present throughout 2018,with Snow Cover Area(SCA)reaching a maximum in January-February and a minimum in July-August.At the same time,the spatial distribution of snow cover in the Central Tianshan District > East Tianshan District > West Tianshan District,and permanent snow and ice dominated in the Central Tianshan District,both permanent and seasonal snow and ice in the East Tianshan District,while seasonal snow and ice dominated in the West Tianshan District.In addition,the study also found that when the elevation is the same,the snow line on the south slope will be higher than the snow line on the north slope,with an instantaneous snow line level of 1150 m and a snow line level of 5250 m at the end of snowmelt in the Tianshan Mountains in 2018.(2)By plotting the interannual variation curve of Snow Cover Area(SCA)in the Tianshan Mountains for thirty years,we found that the multi-year average snow cover area(SCA)showed a decreasing trend,and there was a certain periodicity of interannual fluctuation.At the same time,the overall trend of snow cover areas in the Tianshan Mountains during the thirty years was expanding,and the snow-free areas were shrinking.Most of the snow cover areas were seasonal snow cover areas,while a few of them were permanent snow cover areas.In addition,both snow cover areas and seasonal snow cover areas showed expansion.However,permanent snow cover areas were shrinking,indicating that multi-year snow and ice changes in the Tianshan Mountains were dominated by seasonal snow and ice,and permanent snow and ice areas were melting and gradually transforming into seasonal snow and ice areas.(3)Based on the spatial distribution pattern of snow cover area(SCA)in the Tianshan Mountains in the past 30 years,we explored to simulate the spatial distribution of snow cover area(SCA)in the next 30 years using CA-Markov model.It was found that for the development of snow cover changes in the next 10-30 years,state transition mainly occured in the trace and small amount of snow cover areas,while no major changes occured in the medium and large amount of snow cover areas.