基于遥感的高寒灌丛分布变化及其驱动力——以峻河流域为例

The Distribution Changes of Alpine Shrub and Its Climatic Driving Forces in Junhe Sub-watershed Based on Remote Sensing

利用遥感影像和多源地理信息提取峻河流域高寒灌丛,分析近30年来区域高寒灌丛分布面积的变化,并与峻河流域年平均温度、年降水量、年蒸发量以及蒸发量和降水量的比值进行对比,探讨影响高寒灌丛面积变化的气候因子。研究结果表明:①峻河流域高寒灌丛面积在10年尺度上具有一定的波动性,1977年-1990年高寒灌丛的面积增加14.37km2,1990年-2000年高寒灌丛面积减少了12.61km2,2000年-2009年高寒灌丛面积又增加了8.53km2;②峻河流域高寒灌丛面积变化与该区域的温度和降水变化没有直接的相关关系,但与蒸发量与降水量的比值呈反相关;③峻河流域高寒灌丛面积变化与整个青海湖流域的干旱强度变化相关,干旱强度越大,高寒灌丛分布面积减小,反之,干旱强度减小,高寒灌丛面积增加。

Over the last several decades,climatic change and human activities have degraded the natural ecological condition of the Lake Qinghai basin,one of the most fragile catchments on the Tibetan Plateau. As there is no forest,the alpine shrub is an important vegetation cover in this region,and is assumed to block wind,prevent soil erosion,maintain fertility,clean air and modulate the local climate. The Junhe sub-watershed is an important area in the Lake Qinghai basin and is representative of the influence of climate change on vegetation because human activity here is trivial. Here, we map shrubs from remote sensing images （1977MSS, 1990TM, 2000ETM＋ and 2009TM） and study change in the distribution of alpine shrubs from 1977 to 2009 in the Junhe sub-watershed. We used a hierarchical classification procedure and integrated topographic data into conventional pixel-based image classification. We also compared changes in an area occupied by alpine shrub with local climate conditions,such as mean annual temperature, annual precipitation,annual evaporation and the ratio of evaporation to precipitation. We found that the area occupied by alpine shrub in the watershed has changed over a decadal time scale and increased from 1977 to 1990,decreased from 1990 to 2000,and increased from 2000 to 2009. Variation in the area occupied by alpine shrub in the Junhe sub-watershed seems indirectly related to temperature and precipitation changes,and is inversely correlated with the ratio of evaporation to precipitation. Variation in the area occupied by alpine shrub was also inversely correlated with drought intensity. Our results suggest that climate change plays an important role in alpine shrub distribution across the Junhe sub-watershed.