2001—2019年横断山区积雪时空变化及其影响因素分析

基于MOD10A2积雪产品提取横断山区积雪日数及积雪覆盖率等信息，结合横断山区129个地面气象站点的气象数据，采用趋势分析、相关分析及随机森林回归模型等方法分析了横断山区积雪时空分布特征及其影响因素。结果表明：年平均积雪覆盖率的年际变化呈不显著的下降趋势；年内变化呈“单峰”型曲线，其中3月积雪覆盖率最大，为55.04%。海拔3 000 m以上的积雪覆盖率较为稳定，海拔1 000~3 000 m之间的积雪覆盖率波动较大。受暖湿气流和地形影响，阴坡积雪覆盖率大于阳坡。横断山区积雪日数的分布具有纬度地带性，北部山区积雪分布广泛且积雪日数高，南部云贵高原积雪日数低。年均积雪日数介于55.16~79.47 d，积雪日数在28.46%的地区呈减少趋势，在21.66%的地区呈增加趋势，其中呈显著减少和显著增加的地区分别为2.65%和0.68%。中部康定市、九龙县及其周边地区减少趋势明显，北部杂多县—若尔盖县一线的高海拔山地增加趋势明显。积雪日数整体上与降水量、相对湿度呈正相关，与风速、气温和日照时数呈负相关。与降水量呈显著正相关的地区主要分布在西北部杂多县、称多县；与风速呈显著负相关的地区主要分布在西北部称多县、中部康定市；与气温呈显著负相关的地区主要分布在中部九龙县、西北部称多县；与相对湿度呈显著正相关的地区主要分布在北部杂多县—石渠县一线；与日照时数呈显著负相关的地区主要分布在东北部玛曲县、西北部称多县。积雪日数受气温和高程的影响最大，而日照时数和风速为次要因素。

Analysis on spatial-temporal variation of snow cover and its influencing factors in the Hengduan Mountains from 2001 to 2019

This study extracted the snow cover fraction （SCF） and snow cover days （SCD） in the Hengduan Mountains by using the snow cover products MOD10A2. MODIS snow products with the advantage of high spatial resolution and high temporal resolution， have become an important data source for the study of spatial-temporal variation of snow cover. The 129 meteorological stations’data are derived from National Climate Center （NCC） of China and local meteorological bureaus， including daily air temperature， precipitation， wind speed， relative humidity and sunshine duration. By using M-K test， correlation analysis and random forest regression model， combined with the meteorological data of 129 meteorological stations in the Hengduan Mountains from 2001 to 2019， the spatial and temporal distribution characteristics and influencing factors of snow cover is analyzed. Random forest model extracts and generates a subset of training samples from the original training sample set by bootstrap resampling technology， and then generates multiple decision trees according to the training sample set. Taking SCD as the explanatory variable and influencing factor as the dependent variable， the random forest regression model was constructed， and the train set and test set were divided according to the ratio of 2∶8. The result would provide an effective reference for climate warming research， ecological protection， and social and economic development in the Hengduan Mountains. The results show as follows： The interannual variation of the annual mean SCF showed an insignificant downward trend； The change within a year is a “single peak” curve， SCF in March was the highest， 55.04%； The SCF over 3 000 m a.s.l. is relatively stable， and SCF between 1 000~3 000 m a.s.l. fluctuates greatly； Affected by monsoon， the SCF of north slope is higher than that of south slope. The distribution of snow cover days in the Hengduan Mountains has latitude zonality， and snow cover is widely distributed in the northern mountainous area and the SCD is high while the SCD in the southern Yunnan-Guizhou Plateau is low. The average SCD in the Hengduan Mountains ranged between 55.16 and 79.47 days， about 28.46% area （2.65% with a significant decline） of the Hengduan Mountains showed a declining trend in SCD， while 21.66% area （0.68% with a significant increase） showed a increasing trend in SCD. Kangding City， Jiulong County and its surrounding areas in the central part of the Hengduan Mountains showed a significant decreasing trend， while the high-altitude mountains along the Zadoi County to Zoige County in the north showed an obvious increasing trend. As a whole， the SCD is positively correlated with precipitation and relative humidity， and negatively correlated with wind speed， air temperature and sunshine duration. The areas with significant positive correlation with precipitation are mainly distributed in Zadoi County and Chindu County in the northwest， the areas with significant negative correlation with wind speed are mainly distributed in Chindu County in the northwest and Kangding City in the middle， the areas with significant negative correlation with temperature are mainly distributed in Jiulong County in the middle and Chindu County in the northwest， the areas with significant positive correlation with relative humidity are mainly distributed in Zadoi County to Serxu County in the north， the areas with significant negative correlation with sunshine duration are mainly distributed in Maqu County in the northeast and Chindu County in the northwest. SCD is most affected by air temperature and elevation， and sunshine duration and wind speed are the secondary factors.