2007-2011年西藏纳木错流域积雪时空变化及其影响因素分析

通过2007-2011年纳木错站人工积雪观测资料，对西藏纳木错流域MODIS两种积雪产品(MOD10A1和MOD10A2)进行了精度验证，分析了纳木错流域积雪累积和消融的空间差异，以及流域积雪覆盖率的时空变化；利用纳木错站人工积雪观测资料及自动气象站资料，分析了纳木错流域积雪要素(积雪深度、雪水当量、积雪密度)的时间变化及其与气候参数(气温、降水量、风速等)的关系.结果表明：纳木错流域MOD10A2数据的积雪识别精度(67.1%)高于MOD10A1(42.2%)，总识别精度(73.0%)略低于MOD10A1数据(78.4%).纳木错流域积雪累积和消融存在空间差异，积雪在流域南部的念青唐古拉山脉最先累积，之后为流域东部，最后为流域西部；积雪消融的空间变化则相反.由此导致流域积雪日数南部最大、东部次之、西部及西北部最小.纳木错流域各积雪要素的年内变化存在双峰值特征，峰值分别出现在10-11月和1月，积雪在10-11月受降水和气温共同作用，12月至次年3月主要受气温影响.纳木错流域的平均积雪覆盖率为21.9%，受湖泊效应影响区域(主要为东部地区)达到50.6%，而其他区域仅为18.3%.同时，受湖泊效应影响，纳木错平均积雪深度、积雪水当量均显著大于周边地区.

Temporal and Spatial Variations of Snow Cover and Its Effect Factors in the Nam Co Basin,Tibetan Plateau, 2007-2011

Snow over the Tibetan Plateau (TP) is an essential water source of major Asian rivers and greatly influences water availability in the downstream areas. The Nam Co basin is one of the most characteristic lake basins in TP, where the snow accumulation and its spatial pattern is an important indicator of the local climate and plays a crucial role in hydrological cycle. In this paper, the accuracies of two kinds of MODIS snow products were verified by in situ data, firstly. Furthermore, based on the MODIS data, the spatial changes of accumulation and ablation of snow cover, as well as snow cover days (SCD) and snow cover area (SCA), in Nam Co basin were analyzed. Combined the observed data with automatic weather data, the temporal variation of snow cover elements in Nam Co basin, such as snow depth (SD), snow water equivalent (SWE), snow density and SCD, were discussed. Finally, the relationships between snow cover elements and climate factors, such as temperature, precipitation and wind speed, were also discussed. The result shows: (1) the snow identification accuracy of MOD10A2 is higher than that of MOD10A1.However, its total identification accuracy is lower than that of MOD10A1; (2) there are spatial variations of accumulation and ablation of snow cover in Nam Co basin. The trend for the snow cover accumulation in the Nam Co basin is obviously clear, increasing from southeast to northwest of the basin, but the snow cover ablation has an opposite trend. Hence, the SCD in the south part of Nam Co basin is the maximum and that of the west part is the minimum; (3) the temporal variation of snow cover elements presents double peaks, generally in October and November or January. All kinds of snow cover elements are strongly influenced by temperature and precipitation from October to November, while from December to March, they are influenced by temperature. The average annual snow cover ratio is 21.9% of the total basin, with 50.6% in the east (due to the lake effect) and only 18.3% in other area of the basin. Lake effect has a distinct impact on the Nam Co basin, resulting in the mean SD and SWE all higher than those in the surrounding stations, such as Damxung, Nagchu and Baingoin.