Sea-Level Rise (SLR) is one of the most significant impacts of climate change. Since approximately the middle of the 19th century, relatively high rates of SLR (as compared to the previous several thousand years) have been observed at most locations throughout the globe (Church and White, 2011; Zervas, 2013; Kopp et al., 2016), mostly due to ocean thermal expansion and transfer of mass to the sea from warming land-based glaciers. Delaware and the Coastal Plain of the mid-Atlantic region is of particular concern due to its high concentration of population and development, critical natural ecosystems and public infrastructure coincident with regional processes that add positively to the rise in global mean sea-level (GMSL), such as from 1) geologic land subsidence due to the glacial isostatic adjustment from the Laurentide ice sheet, and 2) increases in sea surface heights due to the changing nearby ocean circulation patterns, making this region a "hotspot" of potential damage and vulnerability to sea-level rise (Sallenger, 2012; Boon, 2012; Kopp, 2013; Ezer and Corlett, 2012; Kopp et al, 2015).
Primary effects of SLR to Delaware include beach erosion; loss of low-lying agricultural fields, forested wetlands and coastal communities; significant losses to tidal wetlands and wildlife habitats; damage to public infrastructure (e.g., roads, septic tanks, water supply lines) and private property along the Delaware Bay and Atlantic Ocean coast; saltwater intrusion into ground and surface waters; increased extent of coastal flooding from storm surge events and advancement of waves further inland (DNREC, 2012; DNREC, 2011). In addition to the physical effects of sea-level rise on Delaware’s natural and man-made environments, there is potential for significant social and economic impacts to Delaware.
The Delaware Geological Survey is working with DNREC Delaware Coastal Programs to update previous sea-level rise planning scenarios from 2009. At that time, the High, Intermediate, and Low SLR planning scenarios equated to 0.5, 1.0, and 1.5 meters, respectively, of increased base sea level by the year 2100 (relative to the year 1992), as shown in Figure 1. The three planning scenarios identified in 2009 were used as the basis for the Delaware Sea-Level Rise Vulnerability Assessment and Mapping Appendices as well as the Recommendations for Adapting to Sea-Level Rise in Delaware (DNREC 2012, 2013) reports, Delaware Emergency Management Agency (DEMA) State Multi-Hazard Mitigation Plan, and the Delaware Climate Impact Assessment, among others. More immediately, the scenarios are specifically referenced in Executive Order 41: Preparing Delaware for Emerging Climate Impacts and Seizing Economic Opportunities from Reducing Emissions by Governor Jack Markell in September 2013, Section 4c:
However, since 2009, the International Panel on Climate Change (IPCC) released their Fifth Assessment Report (AR5) in 2013 (Church et al., 2013) and US Global Change Research Program (USGCRP) released their National Climate Assessment for the United States 2014 (Melillo et al., 2014). Future SLR planning scenarios recommended in NCA 2014 alongside past SLR observations from tide gage records and proxy reconstructions are displayed in Figure 2. These and other technical reports, as well as much peer-reviewed science-based literature, conclude that the rate of SLR has increased over recent years and will very likely continue to do so in the future.
Specifically for Delaware, the NOAA tide gages at Reedy Point and Lewes Breakwater Harbor have been monitoring water levels for many years. Mean sea levels have been calculated for each year of data throughout the period of record for each station. In recent years, mean sea-level trends at these two gages have been continuing to increase. These observations represent local (or relative) sea level rise, including both global sea level changes and sinking of the land surface, which is significant in Delaware mostly due to glacial isostatic adjustment. Figure to the right shows the linear trend values from the beginning of the period of record to the specified year on the graph for the Lewes Breakwater gage. The top and bottom values represent the 95% confidence interval.
The DGS is coordinating the activities of the 2016 SLR Technical Committee, comprised of scientists representing both academia and state government, in Delaware and regionally, with knowledge and experience in coastal issues relating to sea-level rise. Primary goals of this project are two-fold: 1) to summarize the recent scientific peer-reviewed literature, technical reports, and international/national assessments regarding past/observed and future/projected sea-level change, globally and regionally, and 2) to recommend scenarios of future sea-level rise based on sound scientific methodologies that state, county, and local agencies in Delaware can use for incorporating SLR into their planning activities. The Technical Committee has worked together since November 2015 to review historical reconstructions and current tide gage observations of past and recent sea-level rise, and to identify the primary causes and their relative influences on relative SLR in the Delaware region. As a result of this work, the Technical Committee is developing a technical document that will summarize the relevant scientific literature and provide the basis for new SLR planning scenarios for Delaware. This document ultimately will be made publicly available through DNREC and DGS.
In addition, the DGS is working with DNREC to develop a series of SLR coastal inundation maps corresponding to water surfaces from the mean higher-high water (MHHW) level to 7 feet above MHHW, in 1-foot increments. Development of the bathtub-model inundation maps was based on a high-quality, 1-meter Digital Elevation Model (DEM) derived from the 2014 state-wide LiDAR acquisition funded jointly by DGS, DNREC, DelDOT and the USGS through Hurricane Sandy Supplemental Relief Funds. The final product of these analyses is a geodatabase containing eight layers (MHHW to MHHW + 7 ft) representing the bare-earth SLR inundation maps and eight layers showing the same regions although accounting for elevated roadways and bridges. Documentation describing the mapping methodology is attached below.
These maps and the updated SLR planning scenarios will help advise long-range planning of infrastructure, facilities, land management, land use, and capital spending.
This project is supported using Federal funds under award NA13NOS4190093 from the Delaware Department of Natural Resources and Environmental Control (DNREC), Delaware Coastal Programs and the Office for Coastal Management (OCM), National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce. The statements findings, conclusions and recommendations are those of the author(s) and do not necessarily reflect the views of the OCM, NOAA or the U.S. Department of Commerce.
- Boon, John, 2012. Evidence of Sea Level Acceleration at U.S. and Canadian Tide Stations, Atlantic Coast, North America. Journal of Coastal Research. 28(6):1437 – 1445.
- Church, J.A. and White, N. J., 2011. Sea level rise from the late 19th to the early 21st century. Surveys in Geophysics, 32(4):585–602.
- Church, J.A., P.U. Clark, A. Cazenave, J.M. Gregory, S. Jevrejeva, A. Levermann, M.A. Merrifield, G.A. Milne, R.S. Nerem, P.D. Nunn, A.J. Payne, W.T. Pfeffer, D. Stammer and A.S. Unnikrishnan, 2013. Sea Level Change. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
- DNREC, 2014. Delaware Climate Change Impact Assessment. Technical Report, Prepared by the DNREC Division of Energy and Climate. 215 pp.
- DNREC, 2013. Preparing for Tomorrow’s High Tide: Recommendations for Adapting to Sea-Level Rise in Delaware. Technical Report, Prepared for the Delaware Sea Level Rise Advisory Committee by the Delaware Department of Environmental Control. 210 pp.
- DNREC, 2012. Preparing for Tomorrow’s High Tide: Sea-Level Rise Vulnerability Assessment for the State of Delaware. Technical Report, Prepared for the Delaware Sea Level Rise Advisory Committee by the Delaware Department of Environmental Control. 210 pp.
- DNREC, 2009. Recommended Sea-level Rise Scenarios for Delaware. Technical Report, Prepared by the DNREC SLR Technical Workgroup. 13 pp.
- Ezer, T., and W. B. Corlett, 2012. Is sea level rise accelerating in the Chesapeake Bay? A demonstration of a novel new approach for analyzing sea level data, Geophysical Research Letters, 39:L19605, doi:10.1029/2012GL053435.
- Kopp, R. E., 2013. Does the mid-Atlantic United States sea level acceleration hot spot reflect ocean dynamic variability?, Geophysical Research Letters, 40:3981–3985, doi:10.1002/grl.50781
- Kopp, Robert E., Carling Hay, Christopher M. Little, and Jerry X. Mitrovica, 2015. Geographic Variability of Sea-Level Change. Current Climate Change Reports, 1:192-204. DOI 10.1007/s40641-015-0015-5
- Kopp, Robert E., and others, 2016. Temperature-driven global sea-level variability in the Common Era, PNAS, Vol 11(13):E1434–E1441, doi: 10.1073/pnas.1517056113.
- Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds. (2014) Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, 841 pp.
- Parris, A., P. Bromirski, V. Burkett, D. Cayan, M. Culver, J. Hall, R. Horton, K. Knuuti, R. Moss, J. Obeysekera, A. Sallenger, and J. Weiss. (2012) Global Sea Level Rise Scenarios for the US National Climate Assessment. NOAA Tech Memo OAR CPO-1. 37 pp.
- Sallenger, A. H., K. S. Doran, and P. A. Howd, 2012. Hotspot of accelerated sea-level rise on the Atlantic coast of North America, Nature Climate Change, 2:884–888, doi:10.1038/nclimate1597.
- Zervas, Chris, 2013. Extreme Water Levels of the United States 1893-2010. NOAA Technical Report NOS CO-OPS 067. 212 pp.