National Aeronautics and Space Administration

Research Results

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

Title | Introduction | Methods | Results | Discussion

Results

Results of Historical Storm Analysis

Figure 12 shows that the number of storms capable of producing severe damage in New York City (defined as storms which produce flood heights equal to or above three standard deviations from the mean) shows no significant trend over the period 1958-2002. The slightly upward linear trend is statistically insignificant, and is mainly due to the local sea level rise and sharp increase in storm events during the 1990s. This graph demonstrates the inherent interannual variability in storm events. Overall, the majority of the top nine storms (based on tide heights) occurred during the 1990s, with 50% of these extreme storm events occurring during that decade. The 1990s are followed by the 1960s, which contains 30% of those storm events.

In Figure 13, it can be seen that on a decadal basis, the 1960's, 1970's and 1980's had more or less the same amount of storm events per decade, on average 25 events. In 1990, however, the number of storm events increases significantly from that amount, up to a high of 42. This could be indicative of a trend towards more frequent storm events. As far as the intensity of these events, no conclusion can be drawn at this time.

Table 1: Top Ten Storms 1958-2002

Storm Date	Storm Name	Lowest Central Pressure (mb)	Flood Heights (m)	Wind Speed (mph)	Track Description
September 12, 1960	Hurricane Donna	932	2.55	115	No data available
April 13, 1961	Nor'easter 1961	979.17	2.03	50 to 75	Started in western US over Nevada, traveled east and passed over NY from the southwest; ending on 17th over the Atlantic, east of Canada.
March 7, 1962	Ash Wednesday Storm	980.87	2.21	76 (84mph gust)	Started in the 6th north of NY over the Atlantic by Charlotte, North Carolina. It traveled southeast direction and made a counterclockwise semicircle to the east of Newfound Land.
February 7, 1978	Great Blizzard '78	980.11	2.10	86 (111 mph gust)	Commenced on the 6th by NC and traveled northward by NY, changed course to the east and semicircle back to Quebec.
March 29, 1984	Nor'easter 1984	N.A.	2.10	80	Started over Nevada on 27th, traveled southeast, changed course traveling northeast. Passed NY on the 29th ending 31st over the sea, south east of Nova Scotia.
October 31, 1991	Perfect Storm	972	2.14	49 knots (65 knot gusts)	Started over the Atlantic on 29th east of NY, traveling southwest and ended on the 31st, east of Virginia.
December 11, 1992	Nor'easter 1992	991.57	2.45	49 knots (65 knot gusts)	Started over Nevada on 27th, traveled southeast, changed course traveling northeast. Passed NY on the 29th ending 31st over the sea, south east of Nova Scotia.
December 11, 1992	Nor'easter 1992	991.57	2.45	40 to 60	Started west of Lake Erie in Michigan on the 10th, traveling northeast and then southeast, ending over the ocean on the 15th.
March 14, 1993	Nor'easter 1993	963.90	2.04	40 to 60 (gusts >100)	Started on the 12th in Mexico, traveling Southeast, changing course on the 12th. Traveled from the northeast over NY and ended on the 17th north east of Iceland.
March 20 1996	Nor'easter 1996	987.10	2.03	35	Started on the 18th in Mexico, traveling north east, passing NY on the 21st, changing course over Montreal traveling northward.

Descriptions of Top Seven Storms

Hurricane Donna on September 12 of 1960 began as a category 4 hurricane off the coast of Florida. It was a unique storm in that it invaded the entire East Coast. It originated near the Floridian coast. It had wind gusts of up to175mph. When it reached the northeast coast, it had weakened to a category 2 hurricane. Although 50 people were reported dead, about 50 million people were impacted due to the damages of the storm. Its minimum central pressure was 932mb.

The Nor'easter of 1961, which occurred on April 13, battered the New York metropolitan area. Three boys were killed in a boat. Large coastal flooding was associated with this storm that invade New England. Tides ran three to five feet above normal. Sleet and snow invaded the northeast coast. Transportation was crippled temporarily due to flooding. This included major highways, bridges, ferries, and streets. Throughout the city, power lines and trees trampled. Wind speeds ranged from 50 to 75mph. It lowest central pressure reached 979mb.

The Ash Wednesday Storm, which occurred March 6-8 of 1962, was one of the most devastating storms of the century. Thirty deaths were reported, along with about 1252 injuries. The storm caused about 200 million dollars in damage. Wave heights reached 40 feet by the shore of NYC. Flood heights reached 0.76 meters. This Nor'easter had a storm surge of 0.503m. Winds reached speeds of 76mph and gusts reached 84mph. It was one of the most destructive storms of the century, due in part to the high tides occurring at the time of a new moon and the spring equinox.? This is sometime called the five-tide storm.

The Nor'easter of 1978 struck the Metropolitan area in February of that year. Wind speeds reached 86mph with gusts of 111mph. The lowest central pressure was 980mb. This blizzard left thousands of people stranded, in vehicles and their homes. Transportation, including interstate highways, was crippled. The storm produced heavy coastal flooding along the New England coast. Beachfront homes were washed away due to strong winds and coastal flooding. It was one of the worst in the century.

Nor'easter of 1984 was the biggest storm of this year. The storm caused tremendous flooding along the eastern US coast. Winds reached speeds of 80mph and waves that reached twenty feet. Beaches and shorelines, including beach houses and other properties in this area were flooded. These damages caused extensive beach erosion. Emergencies were declared in the New York metropolitan area. Thousands of homes were left without power. This caused the closure of schools and businesses. Transportation was thrown into disarray highways, roads, and subways were flooded. Thousands of residents along the shores of Brooklyn were evacuated.

The Perfect Storm of 1991, also known as the Halloween Storm, was a clash of the Canadian cold front and Hurricane Grace. The storm caused severe beach erosion along the east coast and brought to the east coast one of the worst coastal floods since the Ash Wednesday Storm of 1962.

The Nor'easter of 1992 hit the New York metropolitan area on December 11-12. Its lowest central pressure was 991.57mb. Three people were reported dead. It almost reached hurricane strength, with pre-winter storm reached wind speeds of up to 90mph, although for the most part it maintained winds of about 75mph. This storm disrupted the lives of millions of people. Due to flooding, transportation and commerce remained at a standstill. The storm stretched from upstate New York to North Carolina. High tides caused heavy flooding, and forced the evacuation of thousands of people from coastal communities.

Projections of Future Sea Level Rise

Sea level in this region can be expected to rise at a minimum of the current rate of sea level change, which is 0.276 cm/year. At current rates of sea level rise, in 2050 we can expect a 22 cm change in sea level by the 2050s, and a 35 cm change by 2100, with respect to the base period. Figure 14 shows where the current trend and Gary Russell's version of the GISS General Climate Model (GCM) falls relative to the IPCC models. The IPCC upper estimate proposes that sea level will increase by about 40 cm (400 mm) in 2050, and 90 cm (900 mm) by 2100, above the 1961-1990 base period. In comparison, the GISS model gives a 25 cm increase in sea level by 2050, and a projected change of approximately 58 cm by 2100. This comparison of models shows that Gary Russell's version of the GISS model is fairly conservative, and falls within the upper and lower bounds prescribed by IPCC. Thus, the GISS model will be used in the regional sea level rise projections to follow.

Since the climate models provide the expected change in sea level, flood heights can be directly calculated from these. In order for these flood heights to be useful, however, they must be based on a set standard. The standard will be the current 100-year flood, which is a storm that has a chance of occurrence of only 1/100 in any given year. Figure 15 shows the flood heights for New York City based on the GISS GCM. Overall, the flood heights will increase, resulting from the higher sea level. This means that weaker storms will be able to produce the equivalent of the "100-year storm" of today. In addition, there will be an increase in the number of "100-year storms" relative to the year 2000. In order to determine the return period for these types of storms as a result of sea level change, a recurrence curve was created from the historical storm data.

The recurrence plot shows the relationship between flood height and the probability of occurrence of a storm with that flood height. For example, a storm with a recurrence period of 10 years has a 1 in 10, or 10% chance of occurring in a given year. On the whole, this graph shows that we can expect severe episodes of coastal flooding to occur more frequently in coastal regions as a direct result of sea level rise.

Case Study Site Results

The Rockaways, Queens

The storm recurrence plot, figure 16, shows the relationship between flood heights and the probability of a storm that flood height occurring. For example, if a storm had a recurrence period of 10 years, it has a 1 in 10, or 10% chance of occurring in a given year. Altogether, this graph displays what can be expected if severe episodes of coastal flooding are to occur in coastal regions as a direct result of sea level rise.

Figure 17 shows the projected sea levels and projected flood heights at Rockaway Beach for the 2050s and in the 2100s, based on extrapolation of the current trend and on the GISS model. The green area shows the expected sea level rise in 2050 (resulting in about a meter of lost beach, excluding beach erosion) and in 2100 (about 2.5 m of lost beach based on the current trend, and 3.5 m of lost beach based on the GISS model, excluding beach erosion).

In figure 17, the green indicates the amount of inundated beach by 2050 due to sea level rise alone (both GISS GCM and current trends). The red indicates the expected amount of inundated beach as projected by the GISS GCM, while the purple is the expected amount of inundated beach based on the current trend in 2100.

Downtown Manhattan

Figure 18 shows the projected sea levels in relation to the projected flood heights in downtown Manhattan, from the Battery to the Federal Building. The year 2000 is the zero point. The 2050s projection is the lower red line and in the 2100s, based on both the current trend and on the GISS model. They demonstrate the 100-year flood heights for a storm occurring in both 2050 and 2100. The flood heights in 2050 are predicted to be 2.58m (8.59ft), flooding Battery Park City and South Street Seaport. In 2100, increased flooding will reach 2.84m (9.46ft).

Jamaica Bay, Queens

Figure 19 shows the projected sea level as well as projected flood heights for the 2050s and in the 2100s in the Jamaica Bay Wildlife Refuge, based on both the current trend and the GISS model. The year 2000 is used as the zero point. The projected flood height Figure 19 represents a storm occurring in both 2050s and 2100s. The green area is the projected sea level rise expected to occur by the 2050s. The result is approximately one meter of inundated salt marsh. In 2100, 2.5 m of salt marsh are projected to flood based on the current trend, and 3.5 m of salt marsh are projected to flood based on the GISS model.

---

Figure 20 is a USGS topographic map with areas of the potential 100-year flood events shaded in blue. The projections are for the 2050s and 2100s. The inner red circle shows the 2050 100-Year Flood Storm and the outer yellow circle is the current 100-Year Flood Storm.

Title | Introduction | Methods | Results | Discussion