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乍得湖位于中非撒哈拉沙漠边界,是非洲重要的淡水湖,湖面大小对气候变化高度敏感。近40年,由于干旱等自然灾害和大规模灌溉等人为因素的影响,乍得湖面积急剧减少,受到广泛关注。本文利用多种光学遥感数据提取1973-2012年乍得湖面积,分析其变化趋势和驱动机制。结果表明,1973-2012年间乍得湖面积总体上在变小,1973-1975年间乍得湖面积急剧减少了约71%,1975-2012年面积在2000~5000 km2范围内波动。为验证变化趋势的可靠性,本文利用MODIS影像与同期Landsat和AVHRR影像的提取结果进行比较,来检验多源数据的可比性;通过MODIS影像监测乍得湖面积的月变化,来检验所选数据时相对乍得湖面积变化分析的可能影响。根据气象资料分析,乍得湖面积与降水量变化存在一致性,沙里盆地降水量变化是乍得湖面积变化的重要原因;其次,大量修建水库是导致面积减少的另一重要原因;最后,将乍得湖分为南北两部分的天然拦截坝通过阻碍水流增加蒸发,也加剧了乍得湖面积的减少。
Located on the border of China and Africa in the Sahara Desert, Lake Chad is an important freshwater lake in Africa. The size of the lake is highly sensitive to climate change. In the recent 40 years, due to human factors such as drought and other natural disasters and large-scale irrigation, the area of Lake Chad has dropped dramatically and attracted wide attention. In this paper, we use a variety of optical remote sensing data to extract Lake Chad from 1973 to 2012, and analyze its changing trend and driving mechanism. The results show that Lake Chad generally decreased in size from 1973 to 2012, with a drastic reduction of about 71% of Lake Chad’s area between 1973 and 1975 and an area of 2000-5000 km2 fluctuating between 1975 and 2012. In order to verify the reliability of the trend of change, this paper uses MODIS images to compare the extraction results of Landsat and AVHRR images in the same period to test the comparability of multi-source data and to test the selected data by monitoring the monthly variation of Lake Chad area by MODIS image Possible impact on changes in Lake Chad area. According to the analysis of meteorological data, there is consistency between the area of Lake Chad and the change of precipitation. The change of precipitation in the Sali Basin is an important reason for the change of area of Lake Chad. Secondly, a large amount of reservoirs is another important reason to reduce the area. Finally, The natural interceptor dams divided into two parts, north and south, exacerbate the decrease in Lake Chad by hindering the flow of water from evaporating.