Fluvial sediment supply to a mega-delta reduced by shifting tropical-cyclone activity
Fluvial sediment supply to a mega-delta reduced by shifting tropical-cyclone activity
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DOI：
10.1038/nature19809
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发表时间：
2016-11-10
期刊：
影响因子：
64.8
通讯作者：
Aalto, Rolf
中科院分区：
文献类型：
--
作者：
Darby, Stephen E.;Hackney, Christopher R.;Aalto, Rolf
世界上的河流每年向沿海地区输送190亿吨沉积物，其中相当一部分沉积在大型三角洲，居住着5亿多人。大多数（70%以上）大型三角洲受到海平面上升、地面沉降和人为沉积物截留的威胁（2、3），因此，可持续的河流沉积物供应对于防止三角洲被相对海平面上升“淹没”至关重要（2-4）。在这里，我们结合联合收割机从湄公河的悬浮泥沙负荷数据与水文模型模拟隔离的作用，热带气旋在传输悬浮泥沙到世界上最大的三角洲之一。我们表明，湄公河的悬浮泥沙负荷的空间变化相关（r = 0.765，P < 0.1）与所观察到的热带气旋气候变化，并达到三角洲的悬浮泥沙负荷的相当一部分（32%）是由与热带气旋相关的降雨产生的径流。此外，我们估计，近几年（1981-2005年）三角洲的悬浮负荷下降了52.6 +/- 10.2兆吨，其中33.0 +/- 7.1兆吨是由于热带气旋气候学的转变。因此，热带气旋在控制悬浮沉积物向海岸输送的规模和变化方面发挥着关键作用。上游水库中的人为沉积物截留很可能是解释过去（5-7）和预测未来（8、9）到达世界主要三角洲的悬浮沉积物负荷下降的主要因素。然而，我们的研究表明，热带气旋气候学的变化会影响河流悬浮泥沙负荷的趋势，因此也是充分评估脆弱沿海系统所面临风险的关键。
The world's rivers deliver 19 billion tonnes of sediment to the coastal zone annually(1), with a considerable fraction being sequestered in large deltas, home to over 500 million people. Most (more than 70 per cent) large deltas are under threat from a combination of rising sea levels, ground surface subsidence and anthropogenic sediment trapping(2,3), and a sustainable supply of fluvial sediment is therefore critical to prevent deltas being ` drowned' by rising relative sea levels(2-4). Here we combine suspended sediment load data from the Mekong River with hydrological model simulations to isolate the role of tropical cyclones in transmitting suspended sediment to one of the world's great deltas. We demonstrate that spatial variations in the Mekong's suspended sediment load are correlated (r = 0.765, P < 0.1) with observed variations in tropical-cyclone climatology, and that a substantial portion (32 per cent) of the suspended sediment load reaching the delta is delivered by runoff generated by rainfall associated with tropical cyclones. Furthermore, we estimate that the suspended load to the delta has declined by 52.6 +/- 10.2 megatonnes over recent years (1981-2005), of which 33.0 +/- 7.1 megatonnes is due to a shift in tropical-cyclone climatology. Consequently, tropical cyclones have a key role in controlling the magnitude of, and variability in, transmission of suspended sediment to the coast. It is likely that anthropogenic sediment trapping in upstream reservoirs is a dominant factor in explaining past(5-7), and anticipating future(8,9), declines in suspended sediment loads reaching the world's major deltas. However, our study shows that changes in tropical-cyclone climatology affect trends in fluvial suspended sediment loads and thus are also key to fully assessing the risk posed to vulnerable coastal systems.