| The Tibetan Plateau is one of the main snow-covered areas in Asia.It has a wide distribution of glaciers and snow,and it is the wide stream of major river reservoirs in China and Southeast Asia regions.The snow cover on the Tibetan Plateau not only play an important role on the East Asian monsoon circulation and precipitation but also affects the atmospheric circulation and climate in North America,Europe,and the South Indian Ocean.Understanding the spatial and temporal distribution and variation characteristics of snow cover on the Tibetan Plateau has greater significance for revealing seasonal snow cover,which significantly affect the climate evolution,water resources utilization,ecological environment,and disaster exploration.The present study initially was envisaged to use the higher resolution Landsat-8 OLI data and the meteorological station snow observation data to compare the accuracy of two snow products MODIS V006/005 under different land cover types,altitudes and snow depth conditions.Secondly,using MODIS daily snow products and AMSR-E snow water equivalent products,we generated daily cloudless snow products with a resolution of 500 m in the Tibetan Plateau from the year 2000 to 2016;then we calculated snow parameters in the Tibetan Plateau,including snow covered days(SCD),the snow onset day(SOSD),the snow off day(SOD)and the snow period length(SPL).The temporal and spatial variation characteristics of snow phenology in the Tibetan Plateau and its response to climatic change factors were analyzed.From these finding the main results are summarized as below:1)Divergences and analysis of the snow classification accuracy of MOD10A1 and MYD10A1 two versions V006/005 were performed;the analysis showed that under different altitude conditions,the total volume snow classification accuracy of MODIS V006 was higher than that of V005,which were more accurately reflected the real situation of snow distribution in this area.The overall classification accuracy of MODIS V006 under different land cover type was improved than V005,and the classification accuracy of bare ground and grass underlying surface were more significant;these results were consistent of V006 snow cover products and site snow depth observation results,but was superior to the V005 version,whereas the leakage measurement error also decreased,indicating that the new version of the MODIS day-to-day snow product accuracy had been significantly improved.2)By using day-to-day cloudless snow range products generated by multi-source remote sensing and snow product,the temporal and spatial variation characteristics of snow phenology on the Tibetan Plateau were analyzed.Furthermore,on the surface analysis,the SCD on the Tibetan Plateau showed the significant spatial heterogenetic pattern in the Tibetan Plateau.High altitude mountain SCD is longer,such as the Nyenchen Tanglha Mountains,the Himalayas,the Hengduan Mountains,and the Qilian Mountains,while the Qaidam Basin had lesser snow cover days.The high-altitude mountain start time(SOSD)with concentrated snow accumulation is earlier than the early end time(SOD).The start time of the plateau hinterland is earlier than the late end time,with the decrease of altitude,SOSD is gradually delayed,and SOD is gradually progressive;SPL was at high altitude.In general,the spatial variation of snow phenology was extremely uneven throughout the plateau,they had the obviously different spatial pattern.3)The meteorological data were obtained from the ground stations,the temporal and spatial changes of temperature and precipitation over the past 16 years on the Tibetan Plateau were assessed.These results showed that the spatial distribution of the average temperature in the plateau was roughly divided into two parts;the north and the south,it was colder in the north and warmer in the south respectively.The average minimum temperature in the year 2000 to 2016 was at-30.8℃,whereas,the average minimum temperature in 2010-2016 was recorded-25.7℃,the average minimum temperature showed a clear rising trend,as he hot center appeared,the cold center disappeared so that the warming trend was obvious.The annual precipitation on the Tibetan Plateau decreasing from the southeast to the northwest,and the precipitation in the southern region was significantly more than others.The relative rainy year was 2016,whereas the lower rainy year were 2006,2014 and 2015.Taken together,we can see most of the areas with significant temperature changed as a result of an upward trend,and this growth range was mainly concentrated in the middle of the Tibetan Plateau.There were also a small number of descending areas located in the Qilian Mountains in the northern parts of the plateau.The temporal and spatial changes of temperature and precipitation over the Tibetan Plateau were found more complex.The significantly augmented areas are mainly distributed in the eastern part of Tanggula Mountain,Qinghai Lake area,the Yangtze River source area,and the northern Tibet Plateau,while the northwestern Sichuan and the Yarlung Zangbo River show a significant decreasing tendency.4)Climate change had an important impact on the snowy phenology of the Tibetan Plateau.Snow phenology in most part of the Tibetan Plateau has feedback on temperature,as the temperature rose,the snow cover days decreased,the snow start date delayed,the snow end date advanced,and the snow cover period decreased.Snow phenology of Plateau is more sensitive to changes in precipitation.The SCD in most of the plateau has a significant relationship with the precipitation of the cold season.By increasing precipitation,the SCD increased significantly.The increase in precipitation contributes to the advancement of SOSD,the delay of SOD,and the extension of SPL. |
