Dongting Lake plays an important role in water regulation and biodiversity protection, but it is vulnerable to climate change and human activities. To quantify surface water changes and factors driving them, long-term surface water variation in Dongting Lake was investigated using the multiple spectral indices method based on a decision tree classification for full time-series Landsat and MODIS datasets. Factors influencing surface water changes were explored by combining the annual maximum surface water and annual permanent occurrent water with meteorological and hydrological data. The results showed that both annual maximum surface water and annual permanent water decreased from 1975 to 2019 and the trends of rainfall and runoff at three outlets also changed. The annual maximum surface water surface of Dongting Lake increased during the 1990s due to high rainfall but decreased again after 2000. A significant change in both the hydrological stage and surface water sequence from 1986 to 2019 occurred in 2003, which coincided with the beginning of work to construct the Three Gorges Dam (TGD). The surface water decreased by about 360 km² and runoff at the three outlets decreased by about 150 ×10⁸ m³ after the impoundment of the TGD, which was likely the main cause of surface water changes after 2003. The area of surface water that changed from permanent water in the pre-TGD period into seasonally occurring water in the post-TGD periods is 209 km², while the area of surface water that changed from seasonally occurring water in the pre-TGD period into permanent occurrent water in the post-TGD period is 31 km². Meteorological elements and human activities have had a comprehensive impact on surface water changes in Dongting Lake. Rainfall and temperature account for about one-third of the influence on long-term changes of surface water, and rainfall is the main meteorological driving factor of surface water in the wet season, while temperature is the main factor in the dry season. Runoff at three outlets, four rivers and the Chenglingji explain about half of the change in surface water; the three outlets runoff is mainly affected by human activities and is the main hydrological driving factor of surface water. The monthly maximum surface water fluctuates regularly and Dongting Lake has a strong seasonal characteristic. Indeed, the seasonal changes are significantly altered when drought or flooding occurs, the causes of which are diverse and complex.

中文翻译：

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基于多源遥感的1975-2019年洞庭湖地表水变化

洞庭湖在水的调节和生物多样性的保护中发挥着重要作用，但它易受气候变化和人类活动的影响。为了量化地表水变化及其驱动因素，基于全时间序列Landsat和MODIS数据集的决策树分类，使用多光谱指数方法研究了洞庭湖的长期地表水变化。通过结合年度最大地表水和年度永久性地表水与气象和水文数据，探索影响地表水变化的因素。结果表明，从1975年到2019年，年度最大地表水和年度永久性水量均下降，三个出口处的降雨和径流趋势也发生了变化。洞庭湖的年最大地表水面在1990年代由于高降雨而增加，但在2000年后又下降。2003年至1986年至2019年，水文阶段和地表水序列发生了重大变化，这与工作开始相吻合。建造三峡大坝（TGD）。地表水减少了约360 km²和径流在三个出口减少了约150×10 ⁸米³的TGD蓄水，这是可能的表面水的变化的主要原因2003表面的水的区域之后，从永久水在预改变之后TGD时期后的TGD转变为季节性水的面积为209 km ²，而从TGD时期前的季节性变化为TTG后时期的永久性地表水的地表水面积为31 km ^2。。气象要素和人类活动对洞庭湖地表水变化产生了全面影响。降雨和温度约占地表水长期变化影响的三分之一，降雨是湿季地表水的主要气象驱动因素，而温度是旱季的主要因素。3个出口，4条河流和城陵矶的径流解释了大约一半的地表水变化。这三个出口径流主要受人类活动影响，是地表水的主要水文驱动因素。每月最大地表水有规律地波动，洞庭湖具有很强的季节性特征。的确，当发生干旱或洪水时，季节变化会显着改变，其原因是多样且复杂的。