建设固若金汤的大都市

    去年十月,飓风“桑迪”猛烈袭击纽约市时，城市规划者知道，他们不仅仅在目睹一个极端的自然现象，而且也在注视着未来。由于桑迪来袭时不幸正赶上接近最高潮位的潮汐，飓风上岸时，海平面略高于平均水平，这种情况不仅加剧了洪水泛滥及灾害损失的程度，而且也让我们初步认识到，如果全球气候变化可以预见的两个影响——恶劣天气发生频率的增加以及海平面的持续上升——协同作用的话，情况会如何。答案是，结果不妙。

    土木工程与建造公司Skansa USA Civil Inc.总裁理查德•卡瓦拉罗说：“对我来说，恢复力（resiliency）最多是几天的功夫。”他引用的“恢复力”是工程师常用的一个术语，通常用来描述一座城市从一场灾难中恢复过来的能力。“基础供应中断七八天——居民没有电、没有汽油——城市完全不能没有这些东西，我会说我们城市的恢复力并不好。”

    本月早些时候，纽约市市长迈克尔•布隆伯格大步走上布鲁克林海军造船厂（Brooklyn Navy Yard）的讲台，宣布了一项旨在加强纽约市沿海防灾能力、耗资总额达200亿美元的宏伟计划。它不仅是为了防御像桑迪那样的强烈风暴，而且是为了对抗气候变化本身——主要是海平面上升问题。他执掌的纽约市政府认为，到本世纪20年代，纽约市周围的海平面会上升四到八英寸，致使数十万居民所处的区域遭遇“百年一遇的洪水”。通过一系列工程解决方案——沿一线海滩加强沙丘体系，恢复天然湿地以保留水资源，一系列挡浪堤和挡潮堤、防洪堤，防水壁以及防洪墙，甚至类似于曼哈顿下东区（Lower East Side）炮台公园城（Battery Park City）的一个抬升地平面的新建街区，纽约市政府认为，它可以通过加强工程建设来绕开气候变化问题，阻挡渐渐侵入的大西洋。他们准备对上述构想投资数十亿美元。

    从全球范围来讲，有这种想法的人并不是只有布隆伯格一个。世界各国及各大城市都在迅速认识到如下事实：不管对关气候变化的来源看法如何，相关数据表明海平面正在以越来越快的速度上升。与此同时，全球保险业组织——日内瓦协会（ the Geneva Association）本周警告说，海洋变暖正在使得包括英国和美国的部分沿海地区在内的一些沿海地区变成按照行业标准衡量的“不可保”地区，而且随着海平面上升以及海洋持续变暖，符合这个“不可保”标准的城市数量很可能会继续增加。对于21世纪的城市而言，“恢复力”正迅速成为一项要求，但全球许多主要枢纽城市由于到处都是20世纪、19世纪甚至18世纪建设的正在日趋老化的基础设施，极其缺乏恢复力。

    所有这一切都使得布隆伯格的计划显得相当大胆，而与此同时，什么都不做的代价也可能会轻松超过他估计这项计划需要耗费的200亿美元（有些人估计说，“桑迪”过后的停电期间，纽约市每天在经济活动方面的损失就高达10多亿美元）。卡瓦拉罗说，世界各地有几个城市正在采取明智的应对措施，这些城市考虑到了恢复力问题，但没有一个城市拥有能够控制海平面上升、极端天气以及洪水等诸多风险的综合体系。现在，任期即将结束的布隆伯格市政府似乎急于为纽约市打造这样一个体系，而桑迪已经让这个问题得到了足够的重视（而且得到了足够的联邦基金），从而使之成为一个政治现实。

    When Hurricane Sandy slammed into New York City last October, city planners knew they weren't just looking at a freak natural occurrence -- they were looking at the future. Thanks to an unfortunate coincidence of very high tides that were nearly peaking when Sandy struck, sea levels were slightly higher than average when the storm came ashore, a circumstance that not only exacerbated flooding and damage but also provided a glimpse of what it looks like when two of the predicted effects of global climate change -- increased incidence of severe weather and rising sea levels -- work in tandem. The result was not pretty.

    "To me resiliency is a couple of days, tops," says Richard Cavallaro, president of civil engineering and construction outfit Skansa USA Civil Inc., invoking the term engineers commonly use to describe a city's ability to bounce back from a disaster. "Being down seven or eight days -- people didn't have power, no gasoline -- these are things that just can't be. I would say our resiliency was not good."

    Earlier this month, New York City Mayor Michael Bloomberg strode to the podium at the Brooklyn Navy Yard and announced an ambitious $20 billion plan to shore up NYC's coastal defenses, not only against severe storms like Sandy but against climate change itself -- chiefly from rising sea levels, which his office believes could rise four to eight inches by the 2020s, putting hundreds of thousands more residents in the 100-year flood plain. Through a series of engineering solutions -- enhanced dune systems along front-line beaches, restoration of natural wetlands for water retention, a series of surge and tidal barriers, levees, bulkheads, and floodwalls, and even a new, built-from-scratch elevated neighborhood similar to Battery Park City in the Lower East Side -- the administration is ready to wager billions on the idea that it can engineer its way around climate change and keep the encroaching Atlantic at bay.

    Globally speaking, Bloomberg is not alone. Cities and nations around the world are rapidly coming to grips with the fact that regardless of how one feels about the source of climate change, data show that sea levels are on the rise at an accelerating rate. Meanwhile, global insurance industry group the Geneva Association warned this week that warming oceans are making some coastal regions -- including parts of the U.K. and the U.S. -- "uninsurable" by industry standards, and that the number of cities meeting that criteria will likely grow as sea levels rise and oceans continue to warm. Resiliency is quickly becoming a requirement for 21st centuries cities, and one that many major global hubs -- packed with aging infrastructure laid down in the 20th, 19th, and even 18th centuries -- sorely lack.

    All of this makes Bloomberg's plan quite audacious even as the cost of doing nothing could easily eclipse his $20 billion price tag (some estimates say NYC lost more than $1 billion per day in economic activity during the post-Sandy blackouts). There are several cities around the world doing many smart things where resiliency is concerned, Cavallaro says, but there's no single city that has an ideal, integrated system for managing the risks of sea level rise, extreme weather, and flooding. Now on the downslope of its tenure, the Bloomberg administration appears eager to create such a system for New York, and Sandy has brought enough attention (and federal funds) to the problem to make it a political reality.