古老的树揭示了婆罗门mega-dam的风险

[新德里]科学家在一项新研究中警告说，勃拉马普特拉（Brahmaputra）发生灾难性洪水的潜力 - 中国和印度计划在该河流中建造巨型 - 达姆斯（Mega-Dams），可能已经被低估了。

Published 26 November in自然通讯， 这studyinvolved examination of the rings of ancient trees in and around the river’s watershed, covering Bangladesh, Bhutan, India, Myanmar, Nepal and Tibet autonomous region, which showed that the post-1950s period has been one of the driest over the last 700 years.

“The tree rings suggest that the long-term baseline conditions are much wetter than we thought,” says Mukund Palat Rao, lead author of the study and a recent PhD graduate ofColumbia University’sLamont-Doherty Earth Observatory。“我们应该为比目前预测的要高的洪水频率做好准备。”

“树环表明长期基线条件比我们想象的要湿得多。”

Mukund Palat Rao

The study comes as China announced plans to go ahead with the construction of a mega-dam across Yarlung Zangbo, the upper stream of the Brahmaputra flowing through Tibet, dismissing protests by India that the project could disrupt downstream flows into Arunachal Pradesh and Assam states and also Bangladesh.

On 30 November,全球的Times，中国国营日报报道说，该大坝将由PowerChina下的成都工程公司设计，并将具有三倍的生成能力的三倍hydroelectricproject — the world’s largest at 22,500-megawatts.

印度在12月1日宣布，不要淘汰，计划在Siang上建立自己的10,000兆瓦水力发电项目，因为Brahmaputra在阿鲁纳恰尔邦州被称为。印度新闻社的新闻信托基金会引用了Jal Shakti（Hydropower）部的高级官员T. S. Mehra，他说该项目将“抵消中国的水力发电项目的影响”。

Rao tellsscidev.netthat the dam in Tibet would not have a large impact on monsoon season flows because most precipitation originates south of the Himalayas. “However, any diversion of flow would negatively impact dry season flow which is derived from snow and glacial melt from the Tibetan plateau.”

Rao说，一个主要问题是沉积物的损失。“这条河是世界上最高的沉积物负荷之一。这些沉积物对于维持洪泛区的生育和维持大河岛至关重要。大坝不可避免地会捕获沉积物，从长远来看，这可能威胁到居住的河群岛的完整性。”

其他大riskRao说，该地区大坝建设的因素包括“该地区在构造身上是活跃的，而Brahmaputra是一条高度编织的河流，经常迁移其路线”。

在7月至9月的季风季节，布拉马普特拉（Brahmaputra）通常会淹没周围的区域，当时富含水分的风从印度洋扫入，并沿着河的长度带来了雨水，这是喜马拉雅脑海中的增强。

For the study, core samples were taken from ancient trees at 28 sites within the Brahmaputra watershed and analysed at the Lamont-Doherty Tree Ring Lab. Since tree rings grow wider in years when soil moisture is high, reflecting rainfall and river runoff, the scientists could assemble a 696-year chronology up to 2004. By comparing the rings with modern instrumental records as well as historical records, they could establish that the widest rings matched known flood years.

According to the authors, higher temperatures drive up more evaporation from the oceans resulting in more precipitation with the monsoon rains and increased flooding south of the Himalayas.

作者指出，近年来，勃拉马普特拉的洪水不仅增加了季风降雨，而且由于周围的人口和基础设施的增长迅速。作者在研究中写道：“将来的洪水危害可能性增加将继续与增加的可能性有关。”

C.P. Rajendran, top paleoseismologist and adjunct professor at the National Institute of Advanced Studies, Bangalore, says: “Proxy data obtained using tree rings between 1309 and 2004 reveal the long-term hydroclimate variability in the Brahmaputra river system and demonstrate that the early period when instruments were used (1956—1986) ranks amongst the driest of the past seven centuries.

“The model simulations suggest amplified precipitation over the Brahmaputra river basin, leading to increased discharge towards the end of the 21st century,” Rajendran tellsscidev.net。

The Brahmaputra combines with the Ganges river to create the world’s third largest ocean outflow, behind the Amazon and the Congo in discharge. At points, the river is 20 kilometres wide and with 130 million Bangladeshis living on its delta and several millions more upstream.

婆罗门河河流域。图片来源：Renzut（CC由3.0）。

Rao说，在涉及大坝建设的地方需要更好地共享孟加拉国，中国和印度的数据。他补充说：“尤其是由于上游国家，中国和印度对水资源有更多控制权。”

Flooding hits low-lying Bangladesh hardest, the study points out. Two-thirds of the country went underwater in 1998, destroying crops, roads and infrastructure. Floods in September affected a third of Bangladesh and left three million people homeless.

But reduced river water flows in deltaic Bangladesh could also be problematic.

“A reduction in dry season flow by a dam would raise concerns about saltwater intrusion in the low-lying Sundarbans delta [which straddles India and Bangladesh]. Since the delta is so low- lying, the main factor holding back the saline waters from the ocean is the high rate of river discharge,” says Rao.

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