| Lhasa River basin is located in the south-central of Tibetan Plateau, originated insouth of Tanggula, flowing through Lhasa, and finally import the Brahmaputra River,the vegetation types in the basin is relatively abundant, the downstream river valley isbroad, which is a major farming area of Tibet, as in the Lhasa area, the life andeconomic of people’s development provides an important material support. Accordingto the climate change analysis of snow changes in Lhasa River basin, to improve allthe snow area’s spatial data construction provides a significance of simulating climatecondition, flood warning system, river runoff simulation, etc. as well as providereferences for the strategic protection of water resources, at the same time canpromote the existing business of the Tibetan plateau snow remote sensing monitoringtechnology.Based on MODIS Date from2000to2011, combined with the DEM data, thepaper analyze the spatial and temporal variation and key factors along with the changeof different terrain analysis of snow for nearly a decade of Lhasa River basin. Inaddition, the using of three meteorological site temperature precipitation data analysisof Lhasa basin climate trends nearly30years, and correlation between meteorologicalfactors and snow.Main conclusions are as follows:(1) The10years of snow area in Lhasa river basin from2000to2011,presenting the downward trend, but the decline is not large, the average annual snowarea fluctuate between5000km2~8000km2, which is in a relatively stable state. Interms of distribution, Lhasa basin growth mainly concentrated in the October to thefollowing June, while July and August show a minimum rend. The four seasons ofsnow cover area have a bigger difference, spring and winter is larger, accounted for34%and31%of the basin area, autumn accounts for28%of the basin area, whilesummer snow area is the smallest, accounted for7%. About the change trend ofarea in four seasons, there’s no big difference in the winter and summer, while during the spring and autumn, the snow area showed a trend of decrease.(2) According to the change of snow frequency, we have a spatial variationanalysis of snow cover in Lhasabasin. High frequency of snow cover area mainlydistributed in tall mountain ridge area, including nyenchen tanglha range of riverbasin in northwest and eastern basin of Nagqu County, Lhari County. Lowfrequencies of snow cover area distributed in valley and river valley basin, widelydistributed along the Lhasa River Basin and main tributary valley regions. The snowcover frequency centered in Nagqu County, Lhari County and Maizhokunggar County,these areas are seasonal snow.(3) The snow frequency in Lhasa River basin showed a significant negativecorrelation with altitude, the higher the altitude, the less frequency of snow cover. Thefrequency curve of average snow is presented along with the change of slope type"twin peaks", the two slope of snow cover and total time in7°~20°,50°~80°islonger, the slope of0°~7°,30°~35°. Fewer snow cover to the distribution of thepartial average snow in North Slope and partial frequency is higher, the value of southslope is low. Average snow frequency values in different topography on thedistribution is still spring> winter> autumn> summer, the terrain, having obviousdifferences due to terrain.(4) The change trend of temperature and four seasons in Lhasa River basinnearly30years turn out the upward trend, the increasing rate of annual averagetemperature is0.376℃/10a. Of four seasons, the temperature of spring rises fastest,while summer is lowest. The change of precipitation in Lhasa River for nearly30years also present a rising trend, increasing at a rate of about37.646mm/10a, whichrises significantly, but the changes of four seasons in precipitation is relativelycomplex, the average precipitation in spring and summer is respectively by10.514mm/10a and2.655mm/10a, while in the autumn and winter the rate fell with0.399mm/10a and0.399mm/10a, the decline of which is smaller.(5) Lhasa River basin for nearly10years of average annual snow area present0.719negative correlation with annual average temperature, while snow cover reduceas temperatures rise. Average annual snow area and annual rainfall turn out0.01levelpositive correlation, the correlation coefficient is0.797, the snow area increase withrainfall, and the effects of rainfall on snow area is very significant. During the fourseasons, the temperature of spring and autumn for the quarter affected by the snowarea of river basin is large, and the precipitation in winter and summer season of snow area has relatively significant correlation. |
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