FACING HIGHER SEA LEVELS AND INCREASED COASTAL FLOODING IN NEW YORK CITY
The average 20th century New York City metropolitan area sea level rise of 3.0 cm per decade exceeds the global average rise of 1.7 cm per decade, underscoring a potentially enhanced regional risk to coastal hazards. The NPCC (2015) projects future sea level change at the Battery (lower Manhattan) based on CMIP5 model output, expert judgment, and literature surveys. Mid-range (25th -75th percentile) sea level climbs 28-53 cm by the 2050s and 46-99 cm by the 2080s, relative to 2000-2004. High-end SLR estimates (90th percentile) reach 76 cm by the 2050s, up to 1.9 m by 2100. Given these projections, updated Federal Emergency Management Agency (FEMA, 2013) flood return curves, and assuming unchanged storm behavior, flood heights for the 100-year storm (excluding waves) would rise from 3.4 m in the 2000s to 3.9-4.5 m by the 2080s (mid-range), to a high end of 4.9 m. The annual likelihood of such a flood would increase from 1 percent to 2.0-5.4 percent by the 2080s, with an upper bound of 12.7 percent. The flood zone would expand significantly.
The NPCC will continue to collaborate with New York City to strengthen the City’s resiliency to coastal hazards. The NPCC plans to update down-scaled local climate projections, improve coastal flood mapping on the neighborhood level, and work closely with stakeholders and community groups. New work will study combined impacts of coastal storm and sea level rise, develop a monitoring and indicator framework for coastal hazards, focusing on critical infrastructure, such as energy and transportation. Results will be presented using advanced mapping techniques.