| For arid regions in western China,runoff produced by snow and ice is an important part of local water resources.Changes in spatial and temporal characteristics of snow cover would affect the total water resources volume and the annual runoff of the rivers in the snow covered regions.It would also affect to some degree the management and utilize of local water resources,even leading to droughts and floods frequently.Supported by the "One Hundred Talents Programme" of the Chinese Academy of Sciences,under the background of global warming,spatial and temporal characteristics of snow cover between 2002 and 2012 in the Tizinafu watershed of western Kunlun Mountains were analyzed using MODIS daily snow cover products.The main contents and results of the research are presented as follows:(1)Cloud mitigation of MODIS daily snow cover products:MODIS Terra daily snow cover product MOD10A1 and Aqua daily snow cover product MYD10A1 were combined to obtain a new product MOYD10A1,then a 7-day temporal filter was employed to the MOYD10A1 to further reduce the cloud.Results show that the declouded data effectively reduced the cloud cover,at the same time maintained the daily time resolution of the snow cover product MOD10A1.(2)Study of the temporal characteristics of snow cover:based on the snow cover percentage(SCP),the temporal characteristics of snow cover in Tizinafu watershed in different time spans were analyzed.Results are shown as follows.The regular pattern of snow cover variation in a year is obvious,snow generally starts melting in March and the SCP reaches the minimum in early August in the watershed,then it starts to accumulate in September until SCP rises to the maximum in middle October.SCPs in five natural vertical zones increase consistently with the rise of elevation.SCP is lower in areas with slope less than 10°,compared with the other slope bands,and so is the case with the aspect facing south.For the SCPs between 10%and 80%,they exhibit a linear relationship with elevation in all the months during snowmelt season,from March to July,increasing with the rising of the elevation.SCP increases with slopes less than 12°,and then stays relatively level.The total SCP in Tizinafu watershed shows a slight downward trend,with the linear trend rate less than zero,while the downward trend is not significant.(3)Study of the spatial characteristics of snow cover:based on the snow cover duration(SCD),the spatial characteristics of snow cover in Tizinafu watershed in were analyzed.Results are shown as follows.The mean SCD in a hydrological year and in the snowmelt season share a similar spatial pattern to the DEM of the watershed.The standard deviations of SCD in the hydrological years and in the snowmelt season show that the variation of SCD occurred in the narrow bands next to the areas of the highest SCD.The CV of SCD in the hydrological years and in the snowmelt season exhibits an opposite spatial pattern of that of mean SCD.SCDs exhibit a linear relationship with elevation in all the months during snowmelt season,from March to July,increasing with the rising of the elevation.The mean annual SCD exhibits an S-shape pattern with elevation.Overall,the elevation of seasonal snowline and SCP share an opposite annual pattern.The elevations of snowline in March and April are the lowest,all under the value of 4500 meters,while the elevations of snowline in August are the highest,reaching to 5206 meters.From March to August,the seasonal snowline at various locations exhibits the same trend of moving to the higher elevations to the southern region of the Tizinafu watershed.The part of Tibet highway in the Tizinafu watershed shares the same pattern with the annual varation of total SCP.There are three sections of red color roads with SCD above 180 days in hydrological year 2005 and 2010.The annual runoff of the Jiangka hydrological station in these two hydrological years are also the highest,during which periods the Tibet highway were the most seriously affected. |
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