To help New York City plan for its future in a climate-smart way, the scientists working on the report used NOAA tide data as a way to understand both historical sea level rise in the region and historical flood risk, something Horton said "serves as a foundation for projections of future sea level rise and future coastal storm risk." Data from NOAA's National Climatic Data Center and the United States Historical Climatology Network acted as baselines to determine future predicted increases in air temperature, precipitation and sea level rise, as well as to predict quantitative changes in extreme events such as heat waves and cold weather events, intense precipitation and coastal floods at the Battery in southern Manhattan.
The scientists also partnered with NOAA, FEMA and the U.S. Army Corps of Engineers to create the Sea Level Rise Tool for Sandy Recovery. This tool was designed to help communities, residents, and other stakeholders consider risks from future sea level rise in planning for reconstruction following Sandy. It allows state and local officials, community planners, and infrastructure managers the opportunity to understand possible future flood risks from sea level rise under extreme conditions such as those during Sandy and use that information in planning decisions. The New York City Panel on Climate Change provided regional sea level rise scenarios for the five boroughs in New York City out to 2050. These scenarios include sea level rise from both ocean warming and ice sheet melt, and factor in local conditions such as vertical land movement and regional climate variations.
The report states that if these extreme scenarios prove true, there could be four times more people living in the 100-year floodplain in New York City than what was previously estimated based on old maps, which don't consider sea level rise. "You've gone up from about 200,000 people in the New York City flood zone to about 800,000 when you update the flood maps and consider the 90th percentile sea level rise scenario," said Horton.
The report also focused on the potential costs of storms like Sandy in the future given projected sea level rise. "While Sandy caused about $19 billion in losses for our city, rising sea levels and ocean temperatures mean that by the 2050s, a storm like Sandy could cause an estimated $90 billion in losses (in current dollars)—almost five times as much," said Mayor Bloomberg in the report's introduction. After outlining the potential losses, Bloomberg put forth a plan including coastal protection measures and major power and building protections that, he said, could reduce expected losses by up to 25 percent.
"By moving forward with the latest science, New York City has the information they need to help support decisions about where to spend money on elevating and protecting, about difficult societal decisions, about who should spend what, and when the spending should be done to help reduce risk," said Horton. For its part, the city put forth a set of initiatives in PlaNYC, including the launch of a coastal protection study, the launch of an interactive Web platform for communicating flood-related risk information, and amendments to construction codes for new and existing health care facilities within the city, along with many other potential milestones.
"By combining officials from NOAA, from New York City, and members of the scientific community, a product was developed that bridges the local up to the national scale," said Horton. "It's an example of partnering between the federal and local scale that perhaps can serve as a template for other regions."