Determination of Future Sea-Level Rise Planning Scenarios for Delaware

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Sea-Level Rise (SLR) is one of the most significant consequences of climate change. Delaware is especially vulnerable to the effects of SLR due to its flat topography, low mean elevation, and significant community development and infrastructure investments along the coast.  Rates of relative SLR measured at tide gauges in and around Delaware are approximately twice the rate of global mean SLR.  The State of Delaware has had future SLR scenarios (projecting SLR out to year 2100) in place since 2009 to use in long-term planning activities.  Those scenarios were integrated into many town and county plans and formed the basis of the Delaware Sea-Level Rise Vulnerability Assessment and Adaptation reports, the Delaware Climate Impact Assessment, and Executive Order 41: Preparing Delaware for Emerging Climate Impacts and Seizing Economic Opportunities from Reducing Emissions, which specifically mentions the periodic update of the SLR planning scenarios.

All state agencies shall consider and incorporate the sea level rise scenarios set forth by the DNREC Sea Level Rise Technical Committee into appropriate long-range plans for infrastructure, facilities, land management, land-use, and capital spending. DNREC shall periodically update the scenarios with the best scientific data available and distribute new guidance to state agencies.

 

The Delaware Geological Survey worked closely with DNREC Delaware Coastal Programs to lead the formation and discussions of the Delaware SLR Technical Committee, composed of regional scientific and local planning experts, with the primary goal to determine if the existing SLR planning scenarios require modification, and if so, what those modifications would be.  Much research has been conducted since 2009 regarding both historical reconstructions and modeling of the various factors that affect SLR, resulting in several key reports, such as the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report in 2013 and the third U.S. National Climate Assessment in 2014.  A technical report was developed from these efforts summarizing the impacts of SLR in Delaware, recent research on historic SLR reconstructions, data from tide gauges located within the Delaware region, several recent international and national assessments on projecting future SLR conditions, and recommendations of new SLR scenarios to use in Delaware long-range planning activities.

The new SLR planning scenarios recommended in the report correspond to increases of mean sea level in Delaware by the year 2100 of 1.53 m / 5.02 ft (High scenarios), 0.99 m / 3.25 ft (Intermediate scenario), and 0.52 m / 1.71 ft (Low scenario.)  These scenarios were based on a scientific methodology that combines the latest physical climate model results from the IPCC, locally observed tide gauge data, and expert elicitation into a probabilistic approach, described in Probabilistic 21st and 22nd century sea-level projections at a global network of tide-gauge sites, published in the journal Earth's Future by Robert Kopp et al. (2014).   The methodology also provides a physical basis of the time evolution of SLR, enabling estimates of SLR amounts at times before year 2100.  The new SLR curves are referenced to year 2000 mean sea level.

 

 

 

SLR Planning Scenario

SLR by 2100

Low Scenario (5%)

0.52 m

1.71 ft

Intermediate Scenario (50%)

0.99 m

3.25 ft

High Scenario (95%)

1.53 m

5.02 ft

 

Additionally, the report provides guidance on how best the state and local communities could use the new scenarios, including reasons why for some cases, planning for SLR amounts greater than the High planning scenario might be appropriate. This work will help planners, developers, coastal managers, and state regulatory agencies in Delaware make more informed decisions based on the level of risk projects are willing to assume regarding the effects of sea-level rise.

Coastal Inundation Mapping

Concurrently to the work of the SLR Technical Committee and development of the SLR technical report containing the new planning scenarios, DGS worked with DNREC Delaware Coastal Programs to produce a series of coastal inundation maps.  These maps are based on the high-resolution, digital elevation model derived from the recently acquired 2014 lidar collection. The bathtub-model based maps depict the potential extent of inundation from current average high tide (MHHW level) to 7 feet above in 1-ft increments. They can be used as a planning tool for potential future effects of sea-level rise or from surge due to coastal storms. More information on the development methodology of the maps and to access the ArcGIS map services or to download the data can be found at http://www.dgs.udel.edu/projects/coastal-inundation-maps-delaware