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Global Change Seminar Recap: Current State of Sea Level Rise in North Carolina

This post was written by Chandramauli Awasthi, 2018-2019 Global Change Fellow. It summarizes the first of the Global Change Seminar series on sea level rise organized by the Global Change Fellows on February 7, 2019, Current State of Sea Level Rise in North Carolina, view the full series here.
Sea Level Rise seminar title screen, panel, audience
The one-hour seminar was divided into two halves. In the first 30 minutes, each of the three speakers were given ten minutes to present their work on the above related area while in the remaining 30 minutes panelists addressed questions from the audience.

Bio of speakers:

  1. Dr. Alejandra C. Ortiz is an assistant professor in the Department of Civil, Construction, and Environmental Engineering at NC State University. She is a coastal geo-morphologist and coast line engineer, interested in studying coastal evolution during rising sea levels using numerical modeling, remote sensing, lab-based physical modeling, and fieldwork.
  2. Dr. Devon Eulie is an assistant professor in the Department of Environmental Sciences at the University of North Carolina Wilmington. She has worked on shoreline erosion and currently is working with numerical models to look into the impact of sea level rise and how coastal habitat is going to respond to that.
  3. Mariko Polk is a PhD student in Marine Biology Program at UNC Wilmington with a focus on coastal ecology and management decisions.



Presenter Mariko PolkAlejandra Ortiz: Dr. Ortiz talked about the science behind sea level rise and how coastlines are impacted because of sea level rise. Thermal expansion of water is one of the reasons for sea level rise because as the sea temperature rises, volume of water increases proportionally. At geologic time scale, the last glacial maximum, which is the last largest extent of land ice, occurred about 20-22 thousands years ago, and since then sea level has risen but at different rates. Present sea level stabilized about 6-8 thousand years ago and after that the global change in sea level rise is relatively very low. Most of the coast lines developed in those 6000 years when we had low rate of sea level rise.  If global mean sea level rise is looked into at historic scale using satellite data, it has risen with an average rate of about 1.4 mm/year (1900-1930) to 2.6 mm/year (1930-1992), while current rate is 3.3 mm/year. Global and local rates of sea level rise differ from each other based on the location. So there are locations where a drop in sea level is witnessed too. Global mean sea level rise is predicted to be between 0.2-1 meters over the next 100 years based on the different projection scenarios as per IPCC 2013 report. Local sea level rise predictions for New York City, Miami, Galveston and San Francisco are found to be between 0.4-1.2 meters over this same period for different GHG emission scenarios. We have had large variation in global mean sea level over the history of the planet, but recent projection rates are much higher than what we have witnessed over last 6000 years. Few local locations could witness even much higher rates of sea level rise. IPCC reports are very helpful for looking at sea level rise scenarios at a global scale while reports from agencies like NOAA and USGS are very helpful for seeing local effects.
Devon Eulie: Impact of sea level rise is going to be very different depending upon the location even at local scale. Dr. Eulie worked on a project with North Carolina Coastal Federation to look into the issues pertaining to fishery and sea level rise in the lower Cape Fear River. She worked on the Sea Level Affecting Marshes Model (SLAMM), which is a mathematical model that simulates the dominant processes in wetland conversion caused by sea level rise. It takes Digital Elevation Model (DEM), National Wetland Inventory, National Land Cover Dataset, tidal data, sea level rise data, and Accretion data as input. It considers three sea level rise scenarios, based on tide gauge projections assuming sea level rise at historical rates, RCP 2.6, and RCP 8.5, giving a sea level rise of 6.1 cm, 14.7 cm and 17.3 cm, respectively by 2045 against the baseline year 2010. Under above three sea level rise scenarios, total habitat change is estimated to be about 3700 m2, 18000 m2 and 77000 m2. Next step of her research is to extend the above study of application of SLAMM to entire Lower Cape Fear River Estuary, to bridge the gap between sea level rise impact and infrastructure design planning in coastal areas, including bringing the human dimension side into it, and to couple SLAMM-NNBF resilience model.
Mariko Polk: Mariko talked about the condition of sea level rise at North Carolina (NC) and its implication along the coast. Ice melt, thermal expansion of water, slowing of the Gulf Stream, and subsidence are major causes of sea level rise in NC. Since 1950, NC has experienced up to 12 inches of sea level rise. The current rate of rise is 0.5 inch per year, and sea level is set to rise by an average of 6 inches by 2045. There is a substantial rise in the northern portion of the state compared to southern portion, with the reason being underlying geology of the coast. The amount of affected land is estimated to be 820, 1700, and 3300 square miles for a sea level rise of 1, 3, and 10 feet, respectively. Similarly, the number of affected people are estimated to be between 13,000 and 238,726 with an estimated loss in property value to be $1.8-$25.6 billion under a sea level rise scenario of 1-10 feet. Because of the rise in sea level, NC is expected to experience nuisance and storm flooding, large storm surge, and saltwater intrusion, which will in turn result in economic losses, displacement of communities, and loss of habitat. Construction along coast line function as impediments to the natural barrier island affecting marshes. Marshes play an important role in blue carbon production and function as nursery habitat. Rise in sea level and its temperature changes the sand temperature which will subsequently affect the sex ratio of sea turtle. Salt water intrusion is another concern because of rising sea level affecting freshwater stored as groundwater. One of the solutions to reduce the effects of sea level rise is living shoreline structures, which preserves entire habitats and gives it the ability to retain sediment and nutrients.