基于多源遥感数据的非洲乍得湖水面变化监测

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。

Remote sensing analysis on lake area variation of Lake Chad

Lake Chad, on the border of the Sahara desert in central Africa, is well known for its high sensitivity to hydroclimatic events. Over the last 40 years, Lake Chad, once the sixth largest lake in the world, has shrunk by more than 90% in area. In this paper, variations of the open water areas, extracted from multi-source remote sensing data during 1973-2012, are analyzed. The results showed that in general Lake Chad was getting smaller and smaller during 1973-2012. Between 1973 and 1975 its area sharply reduced by about 71%. From then on its area ranges from 2000 km² to 5000 km². In order to validate the reliability of the trends, this paper first compares it with Birkett's results to analyze area accuracy, and next compares the results of MODIS with Landsat and AVHRR to validate the comparability of multi-source data, and last monitors monthly variation of Lake Chad area to validate the feasibility of multi-temporal data. Meteorological data analysis showed that the area of Lake Chad and the fluctuation of annual precipitation were in good correlation. Secondly, a large number of reservoirs built are another important cause of area reduction. Lastly, the Great Barrier that divided the lake into two smaller lakes has made it more vulnerable to water loss.