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RESEARCH RESULTS

Climate Impacts in New York City: Sea Level Rise and Coastal Floods

NOAA representation of a storm surge.
Figure 1: Storm surge and damage on coastlines. (NOAA)
Time series plot of Average Temperature and Sea Level Height for New York City. See text for discussion.
Figure 2: Sea level rise and temperature 1869-1999. (D. Alade 2002)

Introduction

In the United States, approximately 53% of the population lives near the coast1. Thermal expansion of the oceans and mountain glacier melting are the greatest contributors to present sea level rise2. Continued global climate change could increase the intensity and frequency of storms along the East Coast, causing serious flooding. Damages to coastlines and infrastructure found there, in addition to fatalities, could increase.

New York City has over 600 miles of coastline3. Its infrastructure is closely connected to the coastal areas -- highways, subways, tunnels, sewage, sanitation facilities, power plants and factories are all located adjacent to waterways. Severe flooding with increased frequency could flood the FDR Drive, the West Side Highway, West Street, Battery Park, sections of East Harlem, Coney Island and entire neighborhoods in Staten Island. Almost the entire subway system in NYC is underground and is potentially vulnerable to flooding as well.

Hundreds of millions of dollars in damage to public works and private property in NYC have been caused by storms and storm surges. In addition, already-fragile ecosystems have been stressed drastically by these storms. Nor'easters do the most damage to the metropolitan area -- striking on average 1 - 2 times per year, with severe storms causing major flooding every 40-50 year4. Hurricanes strike less frequently, but often leave greater damage in their wake. Responses funded at the public level have included beach re-nourishment, rebuilding coastal infrastructure (boardwalks, parks, docks, residential and commercial buildings, and groins off local beaches) and repairing or replacing public works (highways, tunnels, sanitation systems, and public transit).

Map of New York City. with red boxes indicating study sites.
Figure 3: Map of New York City. Red boxes indicate study sites.
Satellite photograph of New York City with red boxes indicating study site.
Figure 4: Satellite photograph of New York City. Red boxes indicate study site. (Digital Globe 2002)
Photograph of Beach 101 Street, Rockaway, Queens.
Figure 5: Beach 101 Street, Rockaway, Queens. (D. Asafu-Adjei 2002)
Map of the Rockaways, Queens, NY.
Figure 6: The Rockaways, Queens, NY. (USGS 2000)
Photograph of Battery Park City, NY.
Figure 7: Battery Park City, NY. (M. Gonzales 2002)
Map of downtown Manhattan.
Figure 8: Downtown Manhattan. (USGS 2000)
Photograph of West Pond, Jamaica Bay.
Figure 9: West Pond, Jamaica Bay. (D. Alade, 2002)
Map of Jamaica Bay.
Figure 10: Jamaica Bay. (USGS, 2000)

Case Study Sites

Using tide gauge data from the Battery, New York and Sandy Hook, New Jersey stations, historical record and projections from global climate models, storms and storm surges were examined. Three areas in New York City were chosen for more detailed study: The Rockaways, Downtown Manhattan and Jamaica Bay. Each represents the diversity of New York City's environments. The Rockaways, Queens is important because it is both a residential beach community and popular recreation area situated on a vulnerable barrier island. Should this island become inundated due to sea level rise, adjacent areas of Brooklyn and Queens would be exposed to greater flooding and erosion.

The Rockaways contain a much public infrastructure (e.g., sewage system, subways, public beaches) on its low elevation (less than 10 feet).

The Downtown Manhattan was selected because it represents a major global commercial and financial center. Ten trillion dollars were traded on the New York Stock Exchange in 1999. The last study site is Jamaica Bay, a fragile wetlands area, home to much wildlife and an important storm-buffer zone for the John F. Kennedy Airport and surrounding Queens neighborhoods.

One of the main objectives of this study is to analyze past storms that have produced significant coastal damage in New York City. In order to determine their common characteristics and to assess the future damage potential of comparable storms with increased sea level. This study also examines potential flooding and inundation resulting from extreme coastal events superimposed on sea level rise. Lastly, this study aims to assess some of the potential social and economic impacts of these potential floods.

Science Background

In order to fully understand the potential future impacts of flooding in New York City, we must explain the nature of mid-latitude cyclones and tropical cyclones. Two types of storms that reach the New York area most often develop over the Gulf of Mexico or occasionally over the Pacific Ocean. The formation of mid-latitude cyclones, or low-pressure systems, occurs when two different air masses (along the Polar front) of different densities rotate around a center of low pressure. Hurricanes, on the other hand, form between the latitudes of 5 degrees and 20 degrees and are characterized by a steep pressure gradient that generates rapid inwardly-spiraling winds. A hurricane is typified by central pressure reaching 980 millibars, wind speeds of at least 119 km/hr and storm surges of a minimum 1.6 meters.

Storm surges resulting from either a mid-latitude cyclone or hurricane do the most devastating damage. A storm surge is a mass of water that develops under a low-pressure system, allowing the water to expand and move landward, flooding the coastline. In addition, waves on top of the storm surge cause additional erosion5.

What are contributing factors to local sea level rise? The major factors in NYC include thermal expansion due to ocean warming, melting of mountain glaciers and subsidence (sinking of the East Coast due to isostatic adjustments of the crust from the last Ice Age). Sea level in New York City has risen on average 0.27 cm/year or 0.2286 - 0.381 cm/year over the last hundred years. Looking ahead, it is expected that sea levels in the area will rise on average 0.3885 cm/year or anywhere from 0.175 - 0.602 cm/year by the 2050s6. When extrapolating for the 2100s from these data, sea level can be expected to rise on average 0.635 cm/yr or in the range of 0.37 - 0.90 cm/year. Thermal expansion of the oceans has been and will continue to be the greatest contributor to sea level rise. A simple increase in temperature will directly relate to an increase in sea-level rise.

References

1. Gornitz, 2000
2. IPCC2001
3. Bloomfield, J., Smith, M. & Thompson, N. (1999). "Hot Nights in the City." Washington, D.C: Environmental Fund.
4. McCabe, Gregory, Clark, Martyn P. and Serreze, Mark C. "Trends in Northern Hemisphere Surface Cyclone Frequency and Intensity". Journal of Climate, June 15, 2001 pps. 2763 2768.
5. Lutgens, Frederick K. & Tarbuck, Edward J. (2001). The Atmosphere. Upper Saddle River: Prentice Hall.
6. Rosenzweig, Cynthia & Solecki, William D., ed. (2001). Climate Change and a Global City. New York: Columbia Earth Institute.