C O P I N G W I T H T H E R I S I N G W A T E R S 243

fers. Th is results in street and basement fl ooding after heavy rains. In Rotter-

dam, excess rainwater can be temporarily stored beneath municipal parking

or in water plazas that also serve as parks or playgrounds when dry. Planting

“green roofs” also helps curb excess runoff .

New York City

As they go about their daily tasks, most New Yorkers remain oblivious to the

city’s status as an island and a major seaport. Th e city boasts nearly 600 miles

(970 kilometers) of shoreline, and four of its fi ve boroughs are islands. How-

ever, the city’s waterfront is undergoing a major transformation. Shipping,

except for cruise ships, has largely moved to nearby Staten Island and Bay-

onne, New Jersey. Pedestrian walkways and bicycle paths now replace rotting

piers and abandoned warehouses and factories. New high-rise apartment

complexes sprout like mushrooms.

New York City recognizes the issues of global warming and sea level

rise in its waterfront redevelopment plans. Th e city currently is among the

10 port cities most vulnerable to coastal fl ooding, in terms of population and

assets. By the 2070s, New York City will still remain among the top 10 port

cities at risk, based on assets. Winter cyclones and hurricanes have fl ooded

parts of the city in the past, most recently during the “nor’easter” of Decem-

ber 1992, discussed above.

Th e mayor’s Offi ce of Long-Term Planning and Sustainability manages

city-owned infrastructure. Mayor Michael Bloomberg recently commis-

sioned a study by experts from the NASA Goddard Institute for Space Stud-

ies, Columbia University, other regional universities, and the private sector

to advise on climate change risks arising from changes in temperature, pre-

cipitation, and sea level change and to recommend adaptation strategies.

Table 9.1 Rotterdam and New York City Compared

City Rotterdam New York City – (rel. to ) (rel. to )

Sea Level Rise .–. m .–. m (central range) . m (max.)

“Rapid ice melt” — .–. m

-in--year fl ood height . m .–. m

Sources: Rotterdam data from Delta Commissie (); Aerts et al. (). New York City data from Horton et al. ().

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244 C O P I N G W I T H T H E R I S I N G W A T E R S

Th e New York City Panel on Climate Change (NPCC) 2010 report proj-

ects future sea level rise based on seven Global Circulation Models (GCMs)

and three greenhouse gas emissions scenarios (IPCC SRES A2, A1B, and B2).

Th ese projections, modifi ed from IPCC methodology, include global contri-

butions from thermal expansion and meltwater (glaciers, ice caps, and ice

sheets), as well as local land subsidence, mainly due to glacial isostatic ad-

justments, and local changes in water height from sea temperature, salinity,

and ocean currents. (Other factors aff ecting sea level, such as gravitational

and rotational terms, were not included.) To simulate potential dynamic ice

acceleration, an upper-limit, high-impact “Rapid Ice-Melt” scenario assumes

that glaciers and ice sheets will melt at rates comparable to those of the Last

Glacial Termination (chapter 5), when sea level climbed at an average rate

of 0.39–0.47 inches (10–12 millimeters) per year. Th is scenario assumes that

meltwater rises exponentially from the present mean ice melt rate of 1.1 cen-

timeters per decade between 2000 and 2004, going to 2100. Th is term is

added to the other three sea level terms, which remain unchanged.

Th e GCM-based projections show a sea level rise of 7–12 inches (18–

30 centimeters) by the 2050s and 12–23 inches (30–58 centimeters) by the

2080s (table 9.2). Sea level reaches ~41–55 inches (104–140 centimeters) by

the 2080s in the “Rapid Ice-Melt” scenario.

Th e frequency, intensity, and duration of coastal fl ooding will likely in-

crease along with a rising sea. Th e 100-year fl ood return curve (or “stage-

frequency relationship”) for New York City was calculated from a U.S. Army

Corps of Engineers hydrodynamic model with both surge and tidal com-

ponents. Sea level rise reduces the 100-year return period to once in 15–

35 years by the 2080s.

A higher average sea level would exacerbate street, basement, and sewer

fl ooding and disrupt transportation more frequently. It would increase rates

Table 9.2 Sea level rise projections for New York City

s s s

GCM-based scenarios – inches – inches – inches

.– centimeters – centimeters – centimeters

“Rapid ice melt” scenario – inches ~– inches ~– inches

– centimeters – centimeters – centimeters

Source: Rosenzweig and Solecki (); Horton et al. (). Numbers represent sea level rise relative to the year for the mid- percent of the model projections.

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C O P I N G W I T H T H E R I S I N G W A T E R S 245

of beach erosion, necessitating additional beach nourishment programs. Salt

water would encroach farther into freshwater sources and potentially dam-

age infrastructure.

Th e NPCC recommends that New York City begin to develop “fl exible ad-

aptation pathways” that can be adjusted periodically to the latest projections

of sea level rise. Existing risk and hazard management strategies can then be

revised as needed. Th e NPCC’s Adaptation Assessment Guidebook (AAG)

recommends that city agencies begin to prepare an inventory of infrastruc-

ture and assets at risk, link adaptation strategies to capital and rehabilitation

cycles, and periodically monitor and reassess plans in response to newer

climate information. In addition, the NPCC off ers a general process for cre-

ating a set of climate change–related design and performance standards (cli-

mate protection levels, or CPLs). Most important is to update current 1-in-

100-year fl ood zone maps (e.g., FEMA’s maps) to incorporate future sea level

rise and coastal fl ooding (table 9.2; fi g. 9.10).

Th e New York City Department of City Planning has recently unveiled

its Vision 2020: New York City Comprehensive Waterfront Plan for the re-

vitalization of the waterfront. Th e plan envisions enhanced public access

to the waterfront and utilization of the waterways, as well as new economic

development and residential construction. Th e delineation of the New York

City Coastal Zone Boundary used in waterfront revitalization should also be

updated to refl ect the latest sea level rise projections.

REACTING TO THE RISING WATERS

In Norfolk, Virginia, sea level rise is no theoretical matter—it is already oc-

curring! High spring tides regularly fl ood streets in some neighborhoods,

forcing residents to re-park their cars away from the shore and detour around

deep puddles. Norfolk, near the mouth of Chesapeake Bay, is surrounded

on three sides by water. Natural subsidence plus settling and compaction of

reclaimed marshland add to the rising water, making the relative sea level

trend of 4.44 millimeters (0.17 inches) per year one of the highest along the

East Coast. After extensive lobbying by local residents, the city decided to

raise the worst-hit street by 46 centimeters (18 inches) and to readjust storm

drain pipes to prevent street fl ooding. FEMA has also spent $144,000 to raise

six houses, stimulating objections over high costs and the futility of endless

countermeasures. Th e mayor concedes that if the sea keeps rising, the city

will eventually need to create “retreat zones,” but those most aff ected (like

their counterparts in Corton, England) strongly prefer “action at any cost.”

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246 C O P I N G W I T H T H E R I S I N G W A T E R S

Meanwhile, the city will select its fl ood-mitigation projects more carefully

and explore alternatives like infl atable dams or storm-surge fl oodgates.

In general, the response to the rising sea follows either of two divergent

pathways. Th e fi rst course entails staying put and holding the line for as long

as possible. Coastal development continues (with minor restrictions) and

the shore is defended by a mix of “hard” armoring, softer, more natural solu-

tions, or accommodation by means of innovative architecture and design.

Figure 9.10 New York City FEMA 100-year-fl ood maps with sea level rise based on NPCC sea level rise projections. (Map by K. Grady, A. Marko, L. Patrick, W. Solecki, Climate Protection Level Workbook, in Rosenzweig and Solecki, 2010, fi g. 3, p. 317.)

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