Spatiotemporal Dynamics Of Snow Cover And Influencing Factors In The High Mountain Asia

As a high-altitude region with the Tibetan Plateau as the core and some surrounding mountain systems,High Mountain Asia located in the central part of Asia has the most abundant ice and snow storage except for the two poles,and is the birthplace of many international rivers.The study on the spatial and temporal dynamics of snow accumulation and its influencing factors in the High Mountain Asia can provide scientific basis for global climate change research,regional water resources management and sustainable economic and social development,which is consistent with China’s "One Belt,One Road" initiative.In this study,High Mountain Asia with elevation over 1500 m was used as the research area and daily MODIS snow products,SRTM digital elevation model data and ERA5 meteorological reanalysis data are used.Firstly,the daily cloud-removed FSC data in the study area are produced based on the developed cubic spline interpolation algorithm.On this basis,the Snow cover days（SCD）,seasonal snowline altitude,Snow Onset Date（SOD）,snow end date（SED）and snow duration days（SDDs）for each hydrological year（from September 1 to August 31）are extracted.Finally,the spatiotemporal dynamics of snow cover and its influencing factors in the High Mountain Asia are investigated combining various topographic and meteorological factors,and the main findings are summarized as follows:（1）On the whole,there is a spatial distribution pattern of more snow cover in the surrounding mountains and less snow cover in the central hinterland of High Mountain Asia,and the snow cover rate in the high altitude areas is higher.During the past 20 years,the snow cover in the study area shows a decreasing trend in all seasons except for a slight increase in winter.The spatial distribution of SCD in High Mountain Asia shows great spatial heterogeneity,and SCD is generally higher in the high altitude areas.The areas with SCD decreasing trend accounted for 33.02% of the total area of the study area（7.41% was a significant decrease）.The areas with an increasing SCD accounted for 31.14% of the total area of the study area（6.52% was a significant increase）.The spatial distribution of the snowline altitude in High Mountain Asia shows a strong spatial heterogeneity: it gradually decreases in a ring from the interior of the Tibetan Plateau to the periphery;The snowline is lower and the contour line is more dense in the western mountainous area.However,the snowline altitude in the inner region of the Tibetan Plateau is high and the distribution of isoline is relatively sparse,and the change is relatively moderate.（2）The spatial variation of snow phenology in High Mountain Asia is very uneven.SOD and SED are earlier and later respectively in the high mountain areas with concentrated distribution of snow cover,and SDDs is more persistent.However,SOD,SED and SDDs in Tibet Autonomous Region and western Sichuan province are later,earlier and shorter,respectively.SOD gradually delayed,SED gradually advanced and SDDs is getting shorter with the decreasing of altitude.During the 20 years,9.6% of SOD in High Mountain Asia showed an obvious trend of advance,and 10.4% of SOD in High Mountain Asia showed an obvious trend of delay.In 15.9% of the regions,SED was significantly advanced,while in 8.9%of the regions,SED was significantly delayed.SDDs in most regions showed no significant trend of change and was relatively stable.（3）Altitude,slope and aspect have important effects on the dynamic change of snow cover.The higher the altitude and slope,the higher the snow cover rate,the earlier SOD,the later SED,and the more durable SDDs are.In the non-monsoon affected area,the snow cover rate of the northern slope is greater than that of the southern slope,while the snowline altitude is significantly lower than that of the southern slope.In general,there is a significant correlation between snow cover and climatic factors in High Mountain Asia.SOD,SED and SDDs in different regions are greatly affected by precipitation,temperature and solar radiation,showing different spatial pattern characteristics.