Floods: Holding back the tide
Floods: Holding back the tide
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DOI：
10.1038/508164a
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发表时间：
2014-04
期刊：
影响因子：
64.8
通讯作者：
Q. Schiermeier
中科院分区：
文献类型：
--
作者：
Q. Schiermeier
164|性质|VOL 508| 2014年4月10日© 2014麦克米伦出版有限公司。世纪的第一个十年里，世界上85%的最大三角洲都遭受了严重的洪水。根据目前预测的沉积物下沉和海平面上升速度，预计到2100年，全球三角洲面临危险的陆地面积将至少增加一半。孟加拉国以前的防洪努力并没有解决这些问题。1990年，第一个防洪行动计划要求在主要河流沿着修建堤坝：在不到10年的时间里，大约3 500公里的堤坝拔地而起。2000年，孟加拉国的重点转向建造更多的风暴避难所和改善预警系统--但即便如此，孟加拉国仍有约四分之三的人口面临严重的洪涝灾害。问题的很大一部分是缺乏对三角洲各地行为差异的了解。堤坝可能在一定程度上起到保护首都达卡的作用;但正如32号圩田所表明的那样，它们在其他地方并不总是起作用。科罗拉多博尔德大学的地质学家詹姆斯·西维茨基说：“每个说大三角洲简单的人都没有去过三角洲。”对于孟加拉国的沉降率，他说，“取决于你测量的方式和地点，你可能会得到15个不同的值”。例如，三角洲东西两侧的情况就截然不同。在过去的几个世纪里，地质力量和侵蚀已经将恒河的下游稳步向东移动，使三角洲的西部地区特别缺乏沉积物。这使得西南部地区特别容易受到这两方面的影响
164| NATURE| VOL 508| 10 APRIL 2014© 2014 Macmillan Publishers Limited. All rights reserved85% of the world’s largest deltas suffered severe flooding in the first decade of the twenty-first century. Under current projected rates of sediment sinking and sealevel rise, the area of land at risk on deltas globally is expected to increase by at least half by 2100. Previous efforts at flood defence in Bangladesh have not solved the problems. In 1990, the first flood action plan called for barriers to be built along main rivers: in less than 10 years, some 3,500 kilometres of embankments sprang up. In 2000, the country’s focus shifted towards constructing more storm shelters and improving warning systems—but even so, about three-quarters of Bangladesh’s population remains exposed to severe flooding.A big part of the problem is a lack of understanding of how the delta’s behaviour differs from one place to another. Embankments might work to some extent to protect the capital, Dhaka; but as Polder 32 demonstrates, they do not always do their job elsewhere.“Everyone who says something simple about a big delta has never been to one,” says James Syvitski, a geologist at the University of Colorado Boulder. For subsidence rates in Bangladesh, he says,“depending on how and where you measure, you might get 15 different values”. Things are dramatically different between the west and east sides of the delta, for example. Over the past several centuries, geological forces and erosion have shifted the lower stretch of the Ganges steadily to the east, leaving the western parts of the delta especially starved of sediment. That makes the southwest particularly vulnerable to both