Storm Surge: Hurricane Sandy
By Adam Sobel
30 October, 2014
Realclimate.org
On the second anniversary of Superstorm Sandy making landfall, we are running an extract from a new book by Adam Sobel “Storm Surge: Hurricane Sandy, Our Changing Climate, and Extreme Weather of the Past and Future”. It’s a great read covering the meteorology of the event, the preparation, the response and the implications for the future.
Excerpts
On October 28, 2012, a giant, misshapen hurricane made a left turn from its previous northward trajectory over the Atlantic Ocean and headed for the New Jersey coast. On the evening of October 29, following a track never before seen in one hundred sixty years of Atlantic hurricane observations, the center of the storm made landfall near Atlantic City.
The size of the storm, like the track, was unprecedented in scientific memory. Sandy was the largest hurricane ever observed in the several decades since good measurements of hurricane size have existed in the Atlantic. At its landfall, gale-force winds covered a large fraction of the Eastern Seaboard and an enormous patch of oceanic real estate as well. To the north of the center, Sandy’s easterlies traversed a thousand-mile-plus fetch before coming onshore, driving a massive storm surge: a giant, slow wave that dragged the ocean inland, on top of the high tide, and onto some of the most heavily populated, economically active, and valuable land on earth.
The scale of the disaster was historic. In New York City, the water had not come this high since at least 1821, if then. For people in the hardest-hit areas, it was a life-crushing event—in some cases, literally. While the death toll was low compared to Hurricane Katrina’s, and extremely low compared to those of the worst tropical cyclone disasters in recent history worldwide, it was high enough to be grievously shocking here in New York City, where losing one’s life to a hurricane is thought of as something that happens only in faraway places. Many, many people saw their homes destroyed, and in some cases entire neighborhoods. The storm crippled the infrastructure of one of the world’s most vibrant economic and cultural centers for a period of weeks. The economic damage has been counted at fifty billion dollars at least, and perhaps as high as sixty-five billion.
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The most fundamental lessons we can draw from Sandy revolve around predictions: how we make predictions of the atmosphere’s behavior, and how we respond to them once they are made. Weather prediction is a unique enterprise. People make predictions of many kinds: about the outcomes of elections or baseball games, or the fluctuations of the stock market or of the broader economy. Some of those forecasts are based on mathematical models. Most of those mathematical models are statistical, meaning they use empirical rules based on what has happened in the past. The models used for weather prediction (and its close relative, climate prediction), in contrast, are dynamical. They use the laws of physics to predict how the weather will change from one moment to the next. The underlying laws governing elections or the stock market—the rules of mass human behavior that determine the outcomes—are not known well, if they exist at all. The models need to be built on assumptions that past experience will be a guide to future performance. If weather prediction were still done in this way, it would have been simply impossible to predict, days ahead of time, that Hurricane Sandy would turn left and strike the coast while moving westward. No forecaster had ever seen something like that occur, because no storm had ever done it. For the same reason, no statistical model trained on past behavior would have produced it as a likely outcome.
In Sandy’s case, forecasters not only could see this outcome as a possibility over a week ahead of time, but they were quite confident of it by four or five days before the storm hit. Forecasts such as the ones we had as Sandy formed and moved up the coast don’t come from the heavens. They’re the result of a century of remarkable scientific achievement, beginning in Norway in the early 1900s. The intellectual foundation of the whole enterprise of weather prediction was the idea that the laws of physics could be used to understand the weather, a radical idea in the early twentieth century. Carrying this out required multiple conceptual advances, over decades, and improvements in technology (especially digital computers).
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[T]he most serious problems highlighted by Sandy were not in the preparations right before the disaster or in the response right after. They were in the construction of our coastlines over the span of many decades. Over that long term, too, there had been good forecasts of what could happen to our built environment along the water in the New York City area. These were not forecasts of a specific storm at a specific date and time, but rather scientific assessments of the risk of a storm as bad as Sandy, or worse. It had been known for decades at least that New York City was vulnerable to flooding by a hurricane-induced storm surge. The consequences that would follow were also clear, in broad outline. The flooding of the subways, for example, had been envisioned since the 1990s. …
Sandy didn’t need climate change in order to happen, and the story of the disaster doesn’t need climate change to make it important. The main subject of this book is Sandy, and you can read large fractions of the book without seeing climate change mentioned at all. But climate change looms large when we try to think about what Sandy means for the future.
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Sandy was not just an extreme fluke, something that we can assume won’t happen for another few hundred years. But neither is it “the new normal”—something that is sure to happen again soon, and often from now on.
Almost certainly it’s somewhere in between. We’re very unlikely to see another Sandy this year, or next, or even in the next decade or two. We’re not that much more vulnerable today than we were a few decades ago. But at the time of Sandy, we were always more vulnerable than we realized. And the pace of change is quickening.
Because of sea level rise, most of all, our risk of more Sandy-type disasters is increasing. The science of hurricanes and climate change is still young, and some of the features that made Sandy’s surge so big (its enormous size, its hybrid character, the left turn and westward-tracking landfall) are among those whose connections to climate are least well understood. But because of sea level rise, we know that big coastal flooding events will become more frequent, almost regardless of what those connections are.
As far as the potential for flooding is concerned, every foot of sea level rise is equivalent to a substantial increase in storm intensity. Under the old Saffir-Simpson Hurricane Intensity Scale, when it still accounted for storm surge (before it was simplified to measure only the maximum wind speed), the step from category one to two, or the step from two to three, carried a three-foot increase in surge. By 2100 however, we are likely to see a permanent three-foot increase in sea level, and even six feet is not at all out of the question. That’s roughly equivalent to an increase of either one or two categories in hurricane intensity.
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On the other hand, sea level rises slowly. We have time to prepare. If we adapt to it as it happens, then one foot of sea level rise in the future will not be equivalent to one foot of storm surge now, because we’ll be better protected. We could put other defenses in place that would have the same effect as if we had raised our cities and towns along with the sea. Then, a four-foot surge in the future, like a four-foot surge today, will not be a disaster. That would be climate adaptation. In the language of climate policy, that word refers to any action taken to reduce the harm from warming.
Even better, we could simultaneously do climate mitigation… If we were to reduce it enough, we could significantly slow the rate of global warming, and the rate of sea level rise. Some warming and some sea level rise are already locked in, because of the carbon we have already put into the atmosphere. But if we were to reach a serious international agreement to transform our energy systems to be more efficient, and more reliant on renewables such as solar and wind energy—or even nuclear, though that brings another set of risks—we could make a significant dent in the problem. Will we do any of that, though?
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