基于Google Earth Engine平台的官厅水库流域开水体动态研究

利用二阶段城市水体指数（two steps urban water index）结合地形坡度掩膜方法，基于Google Earth Engine (GEE)平台调用了5 196幅Landsat影像，提取并分析了官厅水库流域1987—2018年长时间序列的开放水体动态．水体提取总体精度达到93.5%，Kappa系数达到0.871，提取的开放水体可用于动态分析．在此基础上，基于分段线性回归，将1987—2018年官厅水库流域开放水体面积划分为缓慢上升、快速下降和迅速回升3阶段的变化．相应地，1987—1996、1997—2010和2011—2018年水体面积年均变化量分别为5.50、?7.45和15.19 km2．年均降水量的变化是官厅水库流域开放水体面积变化的重要影响因素，一元线性回归决定系数为0.29（P<0.01）．1997年后，流域水体面积变化受人类用水增加及土地利用变化的影响增强．研究结果可为城市化背景下区域水资源保护，促进区域可持续发展提供借鉴． 

Dynamics of open-surface water in Guanting Reservoir basin:a Google Earth Engine platform study

Open-surface water plays an important role in social-ecological system．Dynamics of open-surface water has significant effect on variations in water resource supply and ecological integrity．Timely long-term monitoring of open-surface water would provide guidance for protection and sustainable utilization of water resources．The Google Earth Engine platform was used to extract 5196 Landsat TM, ETM+ and OLI images from 1987 to 2018, which were then processed and composed to medians per year．The two-step urban water index and slope-mask method were then used to obtain long-term dynamics of open-surface water in Guanting Reservoir basin．Validation revealed an overall accuracy of up to 93.5% with a Kappa coefficient of 0.87．Piecewise linear regression was applied to analyze the dynamics of open-surface water．The open-surface water from 1987 to 2018 experienced a slow increase, followed by a rapid decrease, and a sharp increase．The average annual changes in open-surface water area were found to be 5.50 km2 during the slow increase period from 1987 to 1996, ?7.45 km2 during the rapid decrease period from 1997 to 2010, and 15.19 km2 during the sharp increase period from 2011 to 2018．Variations in annual precipitation had major influence on the area of open-surface water, with a regression determination coefficient of 0.29 (P < 0.01)．Anthropogenic impacts, i.e., increased water consumption from both open-surface water and groundwater, and land use change associated with open-surface water, became more notable after 1997．This study provides helpful tips for water resource protection and regional sustainable development in the context of rapid urbanization．