Two Mapping Tools from Federal Scientists Illustrate a Sobering Future
Two new online mapping tools from the National Oceanic and Atmospheric Administration (NOAA), the federal scientific agency responsible for study of oceans, major waterways, and the atmosphere, paint a sobering portrait of Lower Manhattan’s future.
The first of these, NOAA’s Sea Level Rise Viewer, visualizes the local landscape at various points in the future, using multiple scenarios as competing predictive models. By 2030, this dataset says, the level of Mean Higher High Water (MHHW)—defined as the average level of the highest tide for each day—in the rivers surrounding the southern tip of Manhattan will be between eight and nine inches higher than today. A decade later, those tides will lap at Lower Manhattan’s shores 11 to 13 inches higher than now. From that point, however, the gap between the most optimistic and pessimistic narratives diverges sharply. By 2070, the rosiest projections says MHHW will be one foot, eight inches higher than today, while the darkest predictions call for almost than double that figure, with three feet, three inches of increase. By 2100, the same brackets have spread to a range of two feet, fives inches and six feet, seven inches.
By that point, according the interactive map that accompanies these data points, so-called “nuisance flooding” (or “sunny-day flooding”)—meaning inundations not associated with any weather event more extreme than a steady breeze that happens to coincide with high tide—is likely to swamp large parts of Tribeca, the World Trade Center complex, the Greenwich South neighborhood, the Financial District, and the South Street Seaport multiple times each week.
While these projections use current data to infer likely future trends, they do not take into account flood-protection barriers currently planned but not yet built. Such measures, now planned for Battery Park City, the Battery, and the Financial District, could mitigate considerably the local impact of the rising sea levels described here.
In the meantime, a second NOAA tool, the Coastal Flood Exposure Mapper, quantifies current levels of risk for Lower Manhattan. On a scale of one to eleven (with the lower number denoting the mildest level of exposure, and the higher indicating graver risk), most of Downtown is categorized as levels six, seven, eight, and nine.