By Alexis Sloan Nussbaum, Director of Research and Operations, Climate Institute
With our attention focused on Hurricane Katrina’s devastating blow to New Orleans and its surrounding areas, Hurricane Rita’s wreckage along the Texas and Louisiana coastlines, as well as Hurricane Wilma's destruction in Florida, it’s easy to forget that numerous American cities are at risk for severe damage from extreme weather events, including hurricanes and northeasters. One such metropolis is the United States’ most populous region, the New York metropolitan area, comprised of over 22 million people and encompassing 13,000 square miles (about 34,000 square kilometers).
According to the catastrophe-modeling and weather-risk management firm AIR Worldwide Corporation, New York City is the American city at second highest risk for potential total economic loss from nearly worst-case hurricane scenarios, preceded only by the Miami/Fort Lauderdale area of Florida. In the wake of the damaging storms along the Gulf Coast, it’s important to consider whether proper measures are being taken to see that the tragedy unfolding in and around the Big Easy does not also occur in other metropolitan areas, whether or not climate change is driving the increase in the ferocity of hurricanes and other devastating weather events.
Hurricanes Katrina, Rita, and Wilma in 2005 and the four costly hurricanes that battered Florida and Alabama in 2004 would suggest that the Southeast is the region of the United States that is most susceptible to damage from major storms. However, such an assumption overlooks the enormous threat that such storms pose for the East Coast and, in particular, for New York City, which is considered to be quite vulnerable to the types of impacts that can be inflicted by hurricanes (tropical cyclones), northeasters (extratropical cyclones), and coastal flooding events. Contributing to this vulnerability are the area’s nearly 1500 miles (about 2400 kilometers) of coastline and that four out of five boroughs are islands, supported by a regional transportation infrastructure that includes approximately 2,200 bridges and tunnels. In addition, massive development and high population density make evacuation difficult and therefore put coastal residents at high risk of storm damage and loss of life.
New York City has a long history of turbulent weather and consequent damage from major tropical storms and hurricanes during the summer and early fall. A few of the most damaging storms include:
Devastating northeasters can also cause significant damage to New York City; in addition, overall damage can be even more widespread than for hurricanes, sometimes extending along the entire East Coast. Northeasters are cyclonic storms that begin as low-pressure systems off the mid-Atlantic coast and ravage the Northeast as they move up the coast during the fall, winter, and early spring. Despite their winds being weaker than those of hurricanes, they inflict heavy damages because they often maintain their strength over several tidal cycles at a particular location. Among the most damaging northeasters have been:
Despite a history of tumultuous weather, climate scientists warn that New York City’s earlier weather patterns and current climate may pale in comparison to the possible onslaught of weather-related changes being brought about by global warming, including increased temperatures and higher precipitation levels. According to the regional climate change assessment for the Metro East Coast (“The Potential Impacts of Global Warming on the Metropolitan East Coast,” findings included in the U.S. Global Change Research Program’s National Assessment of the Potential Consequences of Climate Variability and Change), the minimum and maximum temperatures in New York City have shown a long-term warming trend during the past century, each rising by approximately 4°F (about 2.2°C) since 1880. Global climate models project that the region’s temperatures could increase by about 1°-4°F (about 0.6°-2.2°C) by 2030 and by about 5°-10°F (about 2.8°-5.6°C) by 2100. Furthermore, projections summarized by the Intergovernmental Panel on Climate Change estimate a 10%-20% increase in precipitation by 2100 (with a range of 0%-40%), with less change in the spring and more in the winter.
It is generally understood that it is not scientifically possible to positively connect any particular weather event to global warming. However, most scientists now concur that a warmeratmosphere amplifies the potential for destructive weather. Climate change is likely to produce more numerous heat waves and droughts, less frequent cold spells, and more severe downpours and storms. Although it is not yet known whether climate change will affect the frequency of cyclones, most scientists agree that global warming is likely to lead to more intense northeasters and stronger hurricanes that generate greater amounts of rainfall. This phenomenon will occur because warmer ocean waters and higher atmospheric water vapor concentrations will provide a more abundant source of energy for cyclone development. Therefore, even if it is determined that global warming does not increase the number of hurricanes, it may lead to more of the extremely destructive Category 4 and 5 storms on the Saffir/Simpson Hurricane Scale. Recent analyses indicate that the number of these powerful hurricanes has nearly doubled in the last 35 years.
Scientists have identified a broad range of possible storm-related impacts on the New York metropolitan area that could result from global warming, including sea level rise, increased storm surge, coastal and inland flooding, coastal erosion, and the loss of wetlands. More intense hurricanes and northeasters are also expected to have devastating effects on the region’s infrastructure, including its transportation systems.
One impact of climate change that has the potential to have profound effects on the New York metropolitan area is sea level rise. Sea level rise is not a new phenomenon, as global sea levels have been rising since the 19th century, although at a relatively small rate compared to projections of future rates of rise. By raising the temperature of the oceans, thus increasing their volume since water expands when it’s heated, and melting land-based glaciers and sections of ice sheets in West Antarctica, East Antarctica, and Greenland, global warming will cause the rate of sea level rise to increase significantly. Observations summarized by the Intergovernmental Panel on Climate Change indicate that global sea level increased 6-8 inches (15-20 centimeters) during the 20th century; this rate was roughly ten times greater than the average rate of rise over the preceding 2000 years. The relative rate of sea level rise in the region is currently about 9-15 inches (23-38 centimeters) per century, because geologic subsidence in the region causes the New York metropolitan area’s sea level to rise more quickly than the increase measured in most other areas of the United States and the world. It is estimated that the region’s ocean levels may rise roughly another 4-12 inches (10-30 centimeters) over the next 15 years, 7-24 inches (18-61 centimeters) by the 2050s, and 9-43 inches (23-109 centimeters) by the 2080s.
The numerous consequences of sea level rise, including higher storm surge, more frequent flooding, increased beach erosion, and ultimately the loss of low-lying areas and coastal wetlands, could result in very serious economic and environmental impacts for the New York metropolitan area.
Another threat to New York City’s citizens and property during an extreme weather event is storm surge, which is the cause of approximately 90% of all deaths and injuries associated with hurricanes in the United States. Storm surge is produced when a huge dome of water is pushed towards the shore by a hurricane’s surface winds and low barometric pressure. Since its height is augmented by a rise in sea level, rising seas due to global warming can trigger significantly greater damage (especially because the maximum height of storm waves increases by 50% more than the amount of sea level rise). New York City’s geographic location also amplifies the effects of this phenomenon. The New York Bight, the sharp bend in the Atlantic coastline where New York and New Jersey converge, intensifies the storm surge associated with even a moderate hurricane, resulting in a larger area of destruction and flooding.
Much of the New York metropolitan region is potentially susceptible to storm surge damage. The low elevations of Long Island’s southern shore leave it particularly vulnerable to such damage. Other areas at risk from the devastating consequences of storm surge include but are not limited to: much of southern Brooklyn and Queens; Manhattan’s Lower East and West Sides; and Staten Island’s perimeter.
Coastal and inland flooding is another potentially serious consequence that will be amplified by sea level rise and higher storm surges. As the ocean’s level rises, the flooding generated by extreme weather events is likely to damage larger areas. The New York metropolitan area’s coastline is highly developed, placing a rapidly growing population and a tremendous amount of private property and public infrastructure at enormous risk of flooding. Much of the region’s population is concentrated near the shore, with coastal populations in New York, New Jersey, and Connecticut expanding by approximately 17% between 1960 and 1995. Population growth in seven coastal counties in the region has exceeded 100% during the last few decades, as cited in the Climate Change Information Resources for the New York Metropolitan Region, a by-product of the Metropolitan East Coast Assessment.
Based on past experience, flooding of the same magnitude as the northeaster in December 1992 is expected to occur every 8 to 18 years by the 2050s, and every 1 to 13 years by 2100. If these scenarios prove accurate, much of lower Manhattan, including Battery Park City, would be at risk from frequent flooding by the end of this century, even if hurricanes and northeasters did not become more intense or frequent. Both Coney Island and Staten Island would also flood almost annually, submerging them or creating temporary islands.
Other serious consequences of sea level rise include coastal erosion and the potential loss of wetlands. The shore’s gentle slope along the Atlantic seaboard exacerbates erosion because even a small rise in sea level results in a substantial inland shift of the coast. When seawalls, dikes, jetties, roads, or buildings prevent this natural coastal movement, further shoreline erosion occurs, particularly during extreme weather events. This erosion endangers freshwater aquifers, fisheries, transportation infrastructure, and tourism. It is projected that the erosion rates of some of the area’s beaches could increase 3 to 6 times by the 2050s and 4 to 10 times by the 2080s. Coastal wetlands, the marshes and mangroves that serve as the habitat of birds, fish, and other wildlife, are already disappearing at a significant rate. For example, approximately 12% of the total area of salt-marsh islands in the Jamaica Bay wetland was lost between 1959 and 1998. Because wetlands serve as a barrier against coastal flooding, their loss to rising seas could increase the impact of climate change on the region’s coast, including the potential loss of public transportation routes at the water’s edge. Furthermore, human development along the coastline reduces the adaptability of coastal and marine systems, leaving them less capable of adjusting to the variability brought about by climate change.
Another important likely impact of sea level rise is the potential for flooding and inundation of coastal and low-lying transportation facilities, threatening all aspects of the region’s transit system. The New York metropolitan area has the most extensive public transportation system in the United States, with the Metropolitan Transportation Authority’s subways, buses, and railroads transporting 2.4 billion riders annually, and its tunnels and bridges servicing nearly 300 million vehicles each year. As four of the five boroughs are situated on islands, the tunnels and
bridges that connect them with the region’s suburbs and outer counties are critical to transit in the area. After the December 1992 northeaster, which disrupted commuter transit between New York City and New Jersey for ten days, floodgates were installed at the top of stairways leading down to subway stations and a decision was made that the building of any new entrances must allow for current flood levels.
However, this plan does not take into account the projected rise in sea level and flood elevations. Much of the area’s transportation system is situated only 2-6 feet (about 0.6-2 meters) above current sea level, even though storms often generate over 6 feet (about 2 meters) of floodwater and it is estimated that future floods may submerge some facilities in up to 16 feet (about 5 meters) of water. In addition, subways and other connecting tunnels serve as channels for floodwater, potentially allowing for such great destruction underground that the support structures for buildings above could collapse. Projections of the flood level resulting from a Category 2 hurricane demonstrate that such an event would put all three of the major airports in the region (La Guardia, JFK, and Newark-Liberty), the Holland and Lincoln Tunnels, entrances to road and rail tunnels, bridge access roads, and many of the cities’ major thoroughfares at risk. One potential means of averting significant flooding during major storms would involve the erection of moveable storm surge barriers at several locations off of New York City's coast. These giant sea walls would remain open during tranquil weather, but could be closed during hurricanes or northeasters to hold back rising waters.
Concern about considerable loss of life arises because there are likely to be significant problems associated with evacuating New York City in the lead-up to extreme storms. Evacuation of the high-density regions near the flood-prone coastline would be extremely difficult because many evacuation routes, including both roads and public transportation, extend through areas that may be inundated with water. In addition, because many of the bridges connecting Manhattan to the mainland are elevated, they would respond to the wind effects of an approaching storm well before such winds would be felt at ground level. As a result, their use as evacuation routes would have to be restricted well before roads at ground level, further complicating an evacuation. The problem of unusable evacuation routes is compounded by the fact that, as of 2001, only 50% of households in New York City and 20% of households in Manhattan had access to their own vehicles, which would mean that a large percentage of the city’s population would need to be evacuated using potentially compromised public transportation systems.
After the difficult evacuations prompted by Hurricanes Katrina and Rita, authorities in the New York metropolitan region are reviewing and revising their own evacuation plans for extreme weather events. Officials stress that it is crucial that New York City residents prepare for such events before they occur by determining if their houses, offices, and schools fall within the boundaries of the City’s evacuation zones and learning how to protect themselves if they must shelter in place. Since New York City has not yet developed a response culture, a significant amount of additional regional planning will be necessary to ensure that residents are protected from the effects of hurricanes and northeasters.
As evidence of the link between climate change and the intensification of hurricanes and northeasters continues to mount, it is important to identify those areas at greatest risk for consequential damage to the environment, and loss of life and property. Substantial data suggest that, should an extreme storm strike, especially during times of high tide, the New York metropolitan area is likely to suffer significant damage and loss of life. Although global warming’s effect on storm severity is not yet perfectly understood, the risk to New York City is already significant, and global warming will only make the situation worse. Recognizing this, greater consideration needs to be given to reducing both the near-term and increasing long-term risks.
* Special thanks to NASA GISS; Hunter College, CUNY; and CIESIN for use of their pictures.
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