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Research Results

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

Title | Introduction | Methods | Results | Discussion



The data for this report were taken from several sources. The Center for Operational Oceanographic Products and Services (CO-OPS), National Ocean Service (NOS), National Oceanographic and Atmospheric Administration (NOAA) provided hourly tidal heights and graphs of predicted/observed tidal heights. The original data were in mean lower low water (MLLW) and the time period studied was from May 1958-April 2002.

Once these data were graphed, researchers then used information from the National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) Storm Tracks Images. These images show global storm tracks for a particular month and year. Data are available from 1961-2002 in monthly images. The NCEP Storm Track Data is used in conjunction with the storm track images, and it provided daily storm data: dates of the storm, pressure readings in millibars recorded every 12 hours, and the longitude and latitude of the storms' progression. Weekly weather maps from the Department of Commerce, NOAA, National Weather Service (NWS) were also used to help verify storms and determine storm type.

Once the most severe eight storms of the study period were determined, newspaper accounts were used to assess damages and flood levels.


The Goddard Institute for Space Studies (GISS) Model:
The GISS combined ocean-atmosphere model includes certain assumptions about the growth of greenhouse gases, population, energy, policy, productivity, and other socioeconomic factors. The model uses a resolution of four degrees latitude by five degrees of longitude, with 13 vertical layers. This version of the model is based on the B2 scenario used by the Intergovernmental Panel on Climate Change (IPCC). This scenario "describes a world in which the emphasis is on local solutions to economic, social, and environmental sustainability"7. In addition, it also assumes a continuously increasing global population, intermediate levels of economic development, and a focus on geographically regional levels 8.

Time series plot of sea level rise as predicted by 6 IPCC models. See text for details.

Figure 11: Models used in IPCC assessment of sea level rise. Source: IPCC, 2001

The IPCC Models
In their projecting future sea level change, the different IPCC models assume similar trends of population and socioeconomic growth rates. IPCC does not put out one definitive model of global sea level change; rather it uses a range of models, such as the Hadley Center's model, the Geophysical Fluid Dynamics Laboratory (GFDL) Model, and a model from NCAR9. The IPCC upper bound interval and the lower-bound interval were used to represent a range of possible outcomes, to illustrate the uncertainty that is always inherent in using climate models for an analysis of future conditions.

Current Trends
Since the Industrial Revolution, the increase in carbon dioxide levels has raised the earth's temperature. This rise in temperature has in turn led to an increase in sea level due to thermal expansion and melting mountain glaciers. In extrapolating the current trend of sea level rise, we assume no additional climate change. This scenario represents the very minimum level of sea level rise.


Tide-height data from 1958-2002 were collected from tide-gauge readings for the Battery, New York City, from the CO-OPS website. The 43-year mean, anomalies and standard deviation were calculated.

A graph for the entire 43-year period was created showing anomalies at one, two and three standard deviations above the mean. Anomalies greater than or equal to two standard deviations were selected above the National Geodetic Vertical Datum (NGVD). (See Figure 10). Suspected storm surges were validated by checking data from the same data from at least one other tide-gauge station (Sandy Hook, NJ or Atlantic City, NJ). The Storm Tracks program using NCEP/NCAR data was then used to relate tide-height anomaly (potential storm surge) to actual storm events. For the top nine storm height anomalies, weekly weather maps and newspaper accounts were examined to characterize storms in terms of central pressure, wind strength and local flooding.

As a basis of future projections, three major past storms were chosen -- March 6, 1962 (Hurricane Donna); March 29, 1984 (Nor'easter) and October 31, 1991 (The Perfect Storm). The predicted tide heights from the NOAA data were subtracted from the actual recorded tide heights to estimate the surge levels. Then the sea level projections (including local subsidence rates) from the GISS coupled ocean-atmosphere model for greenhouse gases and sulfates for the 2050s and the 2100s were added onto these surge levels. This total flood height was then transposed onto United States Geological Survey Maps (USGS) (7.5' intervals) to make flood projections for both 2050 and 2100.

The maps with the transposed potential flood heights plus the GISS sea level rise projections showed what areas would flood in the event of a storm similar to ones New York has experienced in the past. From here flood extents can be determined.


7. Manning, M. and Nobre, C., eds., "IPCC Technical Summary: Climate Change 2001: Impacts, Adaptation and Vulnerability." 2002.
8. Manning, M. and Nobre, C., eds., "IPCC Technical Summary: Climate Change 2001: Impacts, Adaptation and Vulnerability." 2002.
9. Manning, M. and Nobre, C., eds., "IPCC Technical Summary: Climate Change 2001: Impacts, Adaptation and Vulnerability." 2002.

Title | Introduction | Methods | Results | Discussion