These U.S. Cities Are Most Vulnerable to Major Coastal Flooding and Sea Level Rise

Research Report by Climate Central

In late October 2012, Hurricane Sandy took a sharp left turn into the coasts of New Jersey and New York, leading to 157 deaths, 51 square miles of flooding in New York City alone, and an estimated $50+ billion in damage (Bloomberg 2013; Kemp and Horton 2013). The name “Sandy” was retired, but risks to coastal cities for Sandy-like flooding remain. On the five-year anniversary of the storm, Climate Central has ranked the U.S. cities most vulnerable to major coastal floods using three different metrics:

1. The total population within the FEMA 100-year floodplain
2. The total population within the FEMA 100-year floodplain as augmented by sea level rise projections for the year 2050
3. The total high social vulnerability population within the same areas as group #2

Each analysis examined coastal cities with overall populations greater than 20,000. For the first one, we tabulated “at risk” population by overlaying 2010 Census block population counts against FEMA’s 100-year coastal floodplains (Crowell et al 2013) using methods adapted from Strauss et al (2012). FEMA 100-year coastal floodplains factor in storm surge, tides, and waves, and include all areas determined to have an at least one percent annual chance of flooding. Based on locations meeting these criteria and population density, New York City ranked first, with over 245,000 people at risk, followed by Miami and then Pembroke Pines, also in South Florida.

In our second analysis, we re-ranked cities based on which have the largest populations in the expanded areas that could be threatened in the year 2050 — due to sea level rise driven by climate change, plus nonclimatic factors such as local land subsidence. We determined these areas by using median local sea level rise projections for midcentury (Kopp et al 2014) under an unrestricted emissions scenario (“Representative Concentration Pathway 8.5”) to additively elevate the FEMA 100-year floodplain, and accordingly extend it as topography allows, following methods detailed in States at Risk: America’s Preparedness Report Card Technical Methodology. After this adjustment, New York City still had the greatest number of people on threatened land, followed by Hialeah, Florida and Miami. 36 cities in Florida placed in the top 50.

The top five cities with the greatest increase in population on land at risk when adding on sea level projections were New York City, with a difference exceeding 181,000, plus Hialeah, Boston, Fort Lauderdale, and The Hammocks, Florida.

The yellow, orange and red show areas at or below Sandy’s peak flood elevation at The Battery.

Finally, we also ranked coastal cities by their “high social vulnerability” population within the areas delineated by our second analysis. High social vulnerability was determined using the Social Vulnerability Index developed by the Hazards and Vulnerability Research Institute, which incorporates 29 different socioeconomic variables to evaluate the ability of communities to prepare and respond to environmental hazards such as floods. New York City, Philadelphia, Houston, Baltimore, and Miami were ranked as the top five cities with the largest high social vulnerability populations within the future FEMA 100-year floodplain — and thus face a difficult double jeopardy over time.

Sea level rise is a key indicator and consequence of climate change.

To learn more about coastal cities at risk visit Climate Central’s States at Risk and Risk Finder.

Analysis by Scott Kulp, PhD and Benjamin Strauss, PhD. Dyonishia Nieves, Shari Bell, and Dan Rizza contributed to this report

Sources:

Bloomberg, Michael. 2013. “A stronger, more resilient New York.” City of New York, PlaNYC Report.

Crowell, Mark, Jonathan Westcott, Susan Phelps, Tucker Mahoney, Kevin Coulton, and Doug Bellomo. 2013. “Estimating the United States Population at Risk from Coastal Flood-Related Hazards.” In Coastal Hazards, edited by Charles W Finkl, 245–66. Springer. doi:10.1007/978-94-007-5234-4.

Kemp, Andrew C., and Benjamin P. Horton. 2013. “Contribution of relative sea‐level rise to historical hurricane flooding in New York City.” Journal of Quaternary Science 28.6: 537-541.

Kopp, Robert E., Radley M. Horton, Christopher M. Little, Jerry X. Mitrovica, Michael Oppenheimer, D. J. Rasmussen, Benjamin H. Strauss, and Claudia Tebaldi. 2014. “Probabilistic 21st and 22nd Century Sea-Level Projections at a Global Network of Tide-Gauge Sites.” Earth’s Future 2 (8): 383–406. doi:10.1002/2014EF000239.

Strauss, Benjamin H, Remik Ziemlinski, Jeremy L Weiss, and Jonathan T Overpeck. 2012. “Tidally Adjusted Estimates of Topographic Vulnerability to Sea Level Rise and Flooding for the Contiguous United States.” Environmental Research Letters 7 (1). IOP Publishing: 014033. doi:10.1088/1748-9326/7/1/014033.

Alaska Towns At Risk from Rising Seas Sound Alarm

By Oliver Milman, The Guardian

The U.S. government’s withdrawal from dealing with, or even acknowledging, climate change may have provoked widespread opprobrium, but for Alaskan communitie…

More Hot Days Are Coming With Climate Change. Our Choices Will Decide How Many

Research Report by Climate Central

Summer still has a month to go, but extreme heat has been a major storyline through June and July. Sweltering temperatures have grounded planes, sparked wildfires and set records from coast-to-coast.

These stories are becoming annual rites of passage as the world warms. And the number of hot days is projected to increase in the coming decades.

Climate Central has developed a new web-interactive tool that brings the reality of future heat to hometowns across the U.S.  Simply enter the name of your city, town or hamlet — or any place in the Lower 48 that piques your curiosity — to see how the number of days above summer temperature thresholds will change throughout the rest of the century. The interactive also shows how reducing greenhouse gas emissions can help reduce the heat.

For example, Phoenix has averaged less than one day above 115°F a year over the past 20 years. If the rate of global greenhouse gas emissions continues on its current trajectory, Phoenix may see as many as 60 days above 115°F each year by the end of the century (and a staggering 163 days above 100°F). Moderate emissions cuts bring the number down to about 40.

Or consider Yakima, Wash. Today, Yakima sees no days above 105°F on average. But if emissions continue on their current trajectory, Yakima is projected to experience 24 days — more than three weeks — above 105°F each year, on average, by 2100.

Climate Central’s analysis includes nearly 30,000 cities and towns, from New York City to Lost Springs, Wyo. (population 4). That means you can see what climate change means for summer temperatures anywhere in the Lower 48.

More extreme heat will have serious consequences on society and the infrastructure upon which we rely. In addition to direct health impacts like heat exhaustion and heat stroke, high temperatures exacerbate other conditions like asthma and cardiovascular disease. These health impacts are particularly dangerous to the very old and very young and other vulnerable portions of the population.

Prolonged exposure to extreme heat can also affect transportation and infrastructure. Highways and railroads can buckle, and the lower air density that comes with extreme heat means aircraft must work harder to take off (as we’ve seen this summer). Air conditioning demand also increases during heat waves, stressing the electric power grid and raising cooling costs. That can increase greenhouse gas emissions from power generation, disrupting the climate further. Air conditioners also release powerful greenhouse gases known as chlorofluorocarbons, turning up the heat even more.



Future days above 95°F, 100°F, 105°F, 110°F and 115°F in these cities

About Emissions Scenarios

The scenarios are representative of different levels of greenhouse gas emissions and warming and drive the model projections of future temperatures we used in this analysis. They were adopted by the International Panel on Climate Change as part of its fifth assessment report in 2014.

“Continue without emissions cuts”: This scenario assumes that few major changes are made in the amount of greenhouse gases we release, a scenario sometimes referred to as “business as usual.” This corresponds to a future greenhouse gas scenario called RCP 8.5, which has generally followed emissions over the past 10 years. Under RCP 8.5, global temperatures are projected to increase an average of 5.9°F above the 1985-2005 baseline by 2100.

“Moderate emissions cuts”: This corresponds to RCP 4.5, a scenario where annual emissions peak in 2040 and then decrease, stabilizing at roughly half of current levels. This reduction roughly corresponds to what would be needed to achieve the goal enshrined in the 2015 Paris Agreement of limiting average global warming to 2°C (3.6°F). Specifically, temperatures under RCP4.5 are projected to top out at 4.1°F above the 1985-2005 baseline by 2100. .

“Extreme emissions cuts”: This is a dramatic level of emissions cuts, which in 2017 is probably beyond reach realistically but is still technically possible. This option corresponds to RCP 2.6. Under this scenario, annual emissions peak in 2020, decline sharply to reach zero around 2070, and then would require sustained net negative emissions after that. Negative emissions would require engineered active removal of carbon from the atmosphere at a massive scale, a process that’s likely to be extremely difficult and expensive. Such extreme cuts would provide a good chance of limiting global warming to 2°F compared to the 1985-2005 baseline, well within the bounds set by the Paris Agreement.

Methodology

Data bars represent the average number of days in a year with high temperatures above the selected temperature threshold.

Data for each year in the interactive were calculated as the mean of the preceding 20-year period.

Average maximum daily temperature (Tmax) for 2016 is gridded historical data from Daymet.

Tmax for 2050, 2075 and 2100 is the median of the temperature output from a suite of 21 global climate models from the Coupled Model Intercomparison Project phase 5. These models are bias corrected and spatiotemporally downscaled to provide daily temperature projections at 1/8-degree geographical resolution.

Additional bias correction was done using a “delta method” where we applied the temperature change between the modeled temperature for 2016 and each future period to the gridded-historical Daymet data to arrive at projected Tmax values for 2050, 2075 and 2100.

Climate Central’s James Bronzan contributed data analysis for this story.