The Use of Climate Information in Vulnerability Assessments
Details of Pilot Sea-Level Rise Estimation Approaches
Each of the FHWA pilot studies accounted for sea-level rise vulnerability differently. The following sections attempt to outline some of the key aspects of their respective technical choices regarding data sets and methods, as well as the goals and partnerships involved in their assessments.
Specifically, we've tried to capture the following decisions made by the pilots:
- How will sea-level rise vulnerability information be used (e.g. for public education, internal communication, community planning, project level planning)?
The intended purpose of the map should shape the inundation mapping approach. For example, a map intended to inform community or project planning purposes will likely require elevation data at a higher resolution than a map intended to educate the public or communicate overall sea-level rise risk to the region.
- What estimates of sea-level rise are used? Why or how were these chosen?
Many of the studies relied on estimates adopted by state or regional planning organizations, or those appearing in published literature.
- What was the source of the elevation data?
The source of the data is typically related to both the purpose of the project and the availability of data sets for a particular region or locality.
- To what extent should other factors, such as land subsidence or shore protection, be taken into consideration?
Similar to the elevation data, these considerations are often tied to the purpose of the project and the availability of appropriate data sets.
Since sea-level rise is a very important impact to the New Jersey coastal study area, the pilot conducted its own inundation mapping.
- Elevation data: The pilot was able to obtain very high resolution LiDAR data that had not yet been publically released by USGS. They then processed these LiDAR points into digital elevation models.
- Sea-level rise scenarios: One of the partners in the New Jersey pilot was the Department of Environmental Protection (DEP). The pilot worked closely with the DEP to ensure that all sea-level rise scenarios and projects matched the assumptions of the DEP. Since the DEP had already decided to use 0.5m, 1.0m, and 1.5m 2100 projections for global sea-level rise, the New Jersey pilot began with these estimates.
- Adjustment to local sea-level rise: The pilot calibrated these global sea-level rise projections to the study area by adjusting based on local subsidence data. To localize the data further, New Jersey also took salinity, temperature, and other factors into consideration.
- Storm surge modeling: The New Jersey pilot chose to use the SLOSH (Sea, Lake, and Overland Surges from Hurricanes; http://slosh.nws.noaa.gov/sloshPub/) model in order to consider the impacts of storm surge. The pilot felt it would be advantageous to examine a range of potential storm paths, which SLOSH does well.
The Oahu MPO pilot worked closely with Dr. Chip Fletcher and his lab at the University of Hawaii to develop high resolution inundation maps of the study area.
- Elevation data: Dr. Fletcher and his team compared two LiDAR datasets, one from the U.S. Army Corps of Engineers and the other from NOAA. These data were calibrated against the Kahului tide station.
- Sea-level rise scenarios: Dr. Fletcher considered two sea-level rise scenarios, 0.75m and 1.9m. These scenarios are for global sea-level rise and are based on Vermeer and Rahmstorf (2009).
- Mapping inundation: The pilot used a 'bathtub' approach to identify areas of land which are lower in elevation than each of the sea-level rise scenarios based on the LiDAR digital elevation data.
- Challenges with the vertical datum: During the course of this study, Dr. Fletcher and his lab found that there is no established vertical datum for Hawaii. This data gap affects the accuracy of the digital elevation models.
- Overlays with asset data: Once he had established the inundation area, Dr. Fletcher analyzed the total land area, length of roads, land and building value, number of Census 2010 blocks, and number of land parcels vulnerable to each sea-level rise scenario.
There are several additional pieces of information that the Oahu MPO would like to explore, including:
- Response of the water table to sea-level rise,
- Improving the understanding of current impacts associated with flooding, wave overwash, erosion, and coastal rock fall, and
- Commuter volumes in vulnerable areas.
Oahu MPO has engaged regional transportation planners and other stakeholders regarding sea-level rise. During the MPO's workshop with stakeholders, the Oahu MPO pilot used "what if" scenarios to help participants think through consequences of climate change, including scenarios of sea-level rise.
The purpose of the San Francisco pilot sea-level rise mapping was to inform community and project level planning. Therefore, the pilot's inundation maps are based on very high resolution elevation data and account for local factors such as shoreline protection, inundation depth and extent, wind and wave effects, and hydrologic continuity. The pilot worked closely with Noah Knowles and updated the methodology in Knowles (2009) with new LiDAR data.
- Elevation data: The pilot combined five different sources of high resolution elevation data in order to create a digital elevation model (see Knowles 2009 for additional information on data sources).
- Sea-level rise scenarios: The pilot assumed 16 inches of global sea-level rise in mid-century and 55 inches at the end of the century. These scenarios are based on the amount of global sea-level rise projected based on CCSM3 global climate model temperature outputs under an A2 greenhouse gas emissions scenario. For each time period, the pilot analyzed both the still water and the 100 year return high tide level with wind and wave effects.
- Inundation modeling: In order to quantify the high water levels in the Bay accurately, the pilot used a hydrodynamic model of the San Francisco Bay estuary, based on the methodology described in Knowles (2009).
- Weak link analysis: The pilot conducted a weak link analysis to assess inundation depth in order to determine the thresholds at which different share protection barriers would fail.
Virginia DOT/Hampton Roads
The goal of the Virginia DOT/Hampton Roads inundation and storm surge work was to generate realistic scenarios that could be used as inputs into the pilot's multi-criteria decision analysis framework. The Hampton Roads region is highly vulnerable to sea-level rise partially because the area is already subsiding due to geological processes and groundwater withdrawals (HRPDC 2011). One of the main goals of the Virginia pilot was to construct and assess the influence of climate-change scenarios (primarily sea-level rise and storm surge) to the strategic priorities of long-range transportation plans. The pilot relied on sea-level rise and storm surge data from an ongoing Hampton Roads Planning District Commission study.
To get a sense of sea-level rise exposure, HRPDC analyzed historical sea-level rise trends, including subsidence of the land surface, and found that the regional average is 1-2 feet of sea-level rise over the past 100 years. The project assumed that the historical rate of sea-level rise will continue in the future, while recognizing the importance of monitoring trends and adjusting for any acceleration in sea-level rise.
The Hampton Roads Planning District Commission (HRPDC) is currently in its second year of a climate change adaptation project that focuses on sea-level rise and storm surge.
- Elevation data: The project used elevation data of varying resolution. While several localities had already developed their own detailed elevation data, the remainder used the USGS topographic data from the National Elevation Dataset (NED).
- Storm surge modeling: In order to identify specific areas and assets of Hampton Roads that are at risk from sea-level rise, the project relied on the Virginia Hurricane Evacuation Study, a cooperative effort involving the U.S. Army Corps of Engineers, the Federal Emergency Management Agency, and other state and local agencies. This analysis used the SLOSH model to determine the maximum tide elevations from a set of storms of differing magnitude. Using GIS, the Virginia Hurricane Evacuation Study applied these tide elevations to local elevation data in order to create flood hazard areas.
- Sea-level rise: Since not all of the areas had high resolution elevation data, HRPDC is assuming that the storm surge zones are also the areas exposed to sea-level rise (HRPDC 2011). The project is planning future analyses which will further distinguish sea-level rise impacts from storm surge impacts (HRPDC 2011).
Washington State DOT
The Washington State DOT worked closely with the Climate Impacts Group at the University of Washington to develop LiDAR-based inundation maps of the study area. During the pilot's workshops to identify vulnerable assets, workshop participants "ground-truthed" the maps by pointing out missing assets, areas already being impacted, or other factors that should be considered in the vulnerability assessment. The pilot anticipates that these maps will also serve as communication tools to educate influential decisionmakers in Washington State.
- Elevation data: The Washington DOT pilot used LiDAR data for the Puget Sound from different sources along with tide gauge data going back at least 70 years.
- Sea-level rise scenarios: The pilot adopted the sea-level rise estimates that are used by the Puget Sound Regional Council (2 feet and 4 feet).
- Much of the analysis from the Washington State Climate Assessment (http://cses.washington.edu/cig/res/ia/waccia.shtml) was also incorporated in the sea-level rise considerations.
CCSP (2009). Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [James G. Titus (Coordinating Lead Author), K. Eric Anderson, Donald R. Cahoon, Dean B. Gesch, Stephen K. Gill, Benjamin T. Gutierrez, E. Robert Thieler, and S. Jeffress Williams (Lead Authors)]. U.S. Environmental Protection Agency, Washington D.C., USA, 320 pp.
Hampton Roads Planning District Commission (HRPDC) (2011). Climate Change in Hampton Roads Phase 2: Storm Surge Vulnerability and Public Outreach. May 2011. http://www.hrpdc.org/MTGS_%20AGDS/JEC/2011/June/Attachment_8A_Draft%202010%20Climate%20Change%20Report.pdf
Knowles, Noah. 2009. Potential Inundation Due to Rising Sea Levels in the San Francisco Bay Region. A Paper From: California Climate Change Center (CEC-500-2009-023-F), March 2009. http://www.energy.ca.gov/2009publications/CEC-500-2009-023/CEC-500-2009-023-D.PDF
NOAA (2011). Tidal Datums. Tides and Currents Website. http://tidesandcurrents.noaa.gov/datum_options.html
NOAA, Coastal Services Center (2010). Mapping Inundation Uncertainty. Charleston, South Carolina. http://www.csc.noaa.gov/digitalcoast/_/pdf/ElevationMappingConfidence.pdf
NOAA, Coastal Services Center (2009). Coastal Inundation Mapping Guidebook. Charleston, South Carolina. www.csc.noaa.gov/digitalcoast/inundation/_pdf/guidebook.pdf