Determining the Pace and Magnitude of Lake Level Changes in Southern Ethiopia Over the Last 20,000 Years Using Lake Balance Modeling and SEBAL
Determining the Pace and Magnitude of Lake Level Changes in Southern Ethiopia Over the Last 20,000 Years Using Lake Balance Modeling and SEBAL
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DOI：
10.3389/feart.2020.00197
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发表时间：
2020-06-30
影响因子：
2.9
通讯作者：
Junginger, Annett
中科院分区：
文献类型：
--
作者：
Fischer, Markus L.;Markowska, Monika;Junginger, Annett
埃塞俄比亚裂谷以其多样的地形而闻名，从干旱和半干旱的大草原到高湿的山区。湖泊沉积物和古海岸线表明，从深水淡水湖到浅层高碱性湖泊，再到完全干涸的湖泊，可用水的波动很大。为了研究湖泊作为人类随时可用的水源所起的作用，加强对这些变化的速度、特征和规模的了解是至关重要的。水平衡模型被用来计算古降水速率和潜在的湖平面变化速度。然而，以前的模型没有考虑到裂谷系统潮湿时期水文连通性的变化，这可能导致对古降雨率的高估。在这里，我们提出了一个综合的水平衡模拟方法，它同时模拟了埃塞俄比亚南部裂谷地区的多个裂谷湖泊(阿巴亚湖、查莫湖和古丘巴赫湖)，考虑了它们在非洲湿润时期(AHP，类似于15-5ka)高水位期间的时间水文连通性。在此基础上，利用地表能量平衡算法(SEBAL)计算了古湖丘巴尔流域的蒸发量。我们还考虑了在AHP期间增加一个雨季的可能性，这是先前许多研究所建议的。结果表明，整个埃塞俄比亚南部裂谷的降雨量增加20%-30%，才能将古湖Chew Burir填满到溢流水平。此外，研究还表明，如果切断水文联系，降雨量减少到今天的情况，古湖Chew Burir高度依赖上游湖Abaya和Chamo的供水，并在大约40年内干涸。在AHP终止期间，从淡水到咸水湖，可能发生了几次如此快速的湖泊水位波动，当时潮湿的条件不太稳定。淡水可获得性的快速变化要求生活在该地区的人类具有高度的适应性，并可能在次代时间尺度上对人类施加严重的环境压力。
The Ethiopian rift is known for its diverse landscape, ranging from arid and semi-arid savannahs to high and humid mountainous regions. Lacustrine sediments and paleo-shorelines indicate water availability fluctuated dramatically from deep fresh water lakes, to shallow highly alkaline lakes, to completely desiccated lakes. To investigate the role lakes have played through time as readily available water sources to humans, an enhanced knowledge of the pace, character and magnitude of these changes is essential. Hydro-balance models are used to calculate paleo-precipitation rates and the potential pace of lake level changes. However, previous models did not consider changes in hydrological connectivity during humid periods in the rift system, which may have led to an overestimation of paleo-precipitation rates. Here we present a comprehensive hydro-balance modeling approach that simulates multiple rift lakes from the southern Ethiopian Rift (lakes Abaya, Chamo, and paleo-lake Chew Bahir) simultaneously, considering their temporal hydrological connectivity during high stands of the African Humid Period (AHP, similar to 15-5 ka). We further used the Surface Energy Balance Algorithm for Land (SEBAL) to calculate the evaporation of paleo-lake Chew Bahir's catchment. We also considered the possibility of an additional rainy season during the AHP as previously suggested by numerous studies. The results suggest that an increase in precipitation of 20-30% throughout the southern Ethiopian Rift is necessary to fill paleo-lake Chew Bahir to its overflow level. Furthermore, it was demonstrated that paleo-lake Chew Bahir was highly dependent on the water supply from the upper lakes Abaya and Chamo and dries out within similar to 40 years if the hydrological connection is cut off and the precipitation amount decreases to present day conditions. Several of such rapid lake level fluctuations, from a freshwater to a saline lake, might have occurred during the termination of the AHP, when humid conditions were less stable. Fast changes in fresh water availability requires high adaptability for humans living in the area and might have exerted severe environmental stress on humans in a sub-generational timescale.