Vex 4 Level 4
Elvina Cannizzaro
There is not 100% confidence in the elevation data and/or mapping process. It is important not to focus on the exact extent of inundation, but rather to examine the level of confidence that the extent of inundation is accurate (see mapping confidence tab).
The four relative sea level rise (RSL) scenarios shown in this tab are derived from the 2022 Sea Level Rise Technical Report using the same methods as the U.S. Army Corps of Engineers Sea Level Change Curve Calculator. These new scenarios were developed by the U.S. Sea Level Rise and Coastal Flood Hazard Scenarios and Tools Interagency Task Force as input into the U.S. Global Change Research Program Sustained Assessment process and, Fifth National Climate Assessment. These RSL scenarios provide an update to the NOAA 2017 scenarios, which were developed as input to the Fourth National Climate Assessment.
Note: We do not show the low scenario, as it is a continuation of the current global trend since the early 1990s and has been determined to have a low probability of occurring by 2100. Furthermore, this scenario would be associated with low levels of risk even if it did occur.
Another important change from the 2017 scenarios is the exclusion of the extreme (2.5 meter) scenario. Based on the most recent scientific understanding, and as discussed in the IPCC AR6, the uncertain physical processes that could lead to much higher increases in sea level are now viewed as less plausible in the coming decades before potentially becoming a factor toward the end of the 21st century. A GMSL increase of 2.5 meters is thus viewed as less plausible and the associated scenario has been removed.
For almost all the scenarios, RSL rise is likely to be greater than the global average in the U.S. Northeast and the western Gulf of Mexico. In intermediate and low scenarios, RSL rise is likely to be less than the global average in much of the Pacific Northwest and Alaska. For high scenarios, RSL rise is likely to be higher than the global average along all U.S. coastlines outside Alaska.
A RSL-change adjustment to the current National Tidal Datum Epoch (1983-2001) will cause a minimal offset that may be needed for some applications. The USACE Sea Level Change Curve Calculator can correct for this offset.
The inundation areas depicted in the Sea Level Rise tab are not as precise as they may appear. There are many unknowns when mapping future conditions, including natural evolution of the coastal landforms (e.g., barrier island overwash and migration), as well as the data used to predict the changes. The presentation of confidence in these maps only represents the known error in the elevation data and tidal corrections.
Blue areas denote a high confidence of inundation, orange areas denote a high degree of uncertainty, and unshaded areas denote a high confidence that these areas will be dry given the chosen water level.
In this application 80% is considered a high degree of confidence such that, for example, the blue areas denote locations that may be correctly mapped as 'inundated' more than 8 out of 10 times. Areas with a high degree of uncertainty represent locations that may be mapped correctly (either as inundated or dry) less than 8 out of 10 times. For a detailed description of the confidence levels and their computation, see the methods document.
Predictions represent the potential distribution of each wetland type (see legend) based on their elevation and how frequently they may be inundated under each scenario. As sea levels increase, some marshes may migrate into neighboring low-lying areas, while other sections of marsh will change type or be lost to open water.
Note: We do not show the low scenario as it is a continuation of the current global trend since the early 1990s and has been determined to have a low probability of occurring by 2100. Furthermore, this scenario would be associated with low levels of risk even if it did occur.
The Social Vulnerability Index, which shows areas of high human vulnerability to hazards, is based on population attributes from Census 2010 (e.g., age and poverty) and the built environment. By looking at the intersection of potential sea level rise and vulnerable Census tracts, one can get an idea of how vulnerable populations might be affected by sea level rise. Dark red indicates tracts having a high vulnerability, and the lighter reds indicate decreasing vulnerability.
Click on a NOAA tide station icon in the map to see historical inundation events in flood days per year. The flood thresholds used in these plots are derived national flood thresholds from NOAA Technical Report NOS CO-OPS 086: Patterns and Projections of High Tide Flooding Along the U.S. Coastline Using a Common Impact Threshold. The derived thresholds used here provide a national definition of coastal flooding and impacts for quantifying and communicating risk. These thresholds may deviate from NWS impact thresholds which take into account local flood risk and are used to issue NWS coastal flood watches, warnings, and advisories.
The purpose of this map viewer is to provide federal, state, and local coastal resource managers and planners with a preliminary look at sea level rise and coastal flooding impacts. The viewer is a screening-level tool that uses best-available, nationally consistent data sets and analyses. Data and maps provided can be used at several scales to help estimate impacts and prioritize actions for different scenarios.
Long-term sea level rise will affect the extent, frequency, and duration of coastal flooding events. High-tide flooding events that occur only a few times a year now may occur once a month, or once a week in the coming decades. These same water level changes may also increase coastal erosion and groundwater levels. Elevated groundwater levels can lead to increased rainfall runoff and compromised underground infrastructure, such as public utilities, septic systems, and structural foundations. Higher water levels also mean deadly and destructive storm surges, wave impacts, and rainwater are unable to drain away from homes and businesses.
Another reason for differences in regional sea level is vertical land motion. Across the U.S., land is sinking or rising at different rates and times, and this affects how high sea level rises in a region. Vertical land motion can be a result of geologic processes (e.g. the movement of tectonic plates); human activity, such as removing groundwater or fossil fuels from underground, which can cause the land to sink; or naturally-occurring sediment compaction and settling over time (e.g., subsidence in the Mississippi River delta).
Global mean sea level, or the average height of the ocean surface, has risen 6 - 8 inches (15 - 20 centimeters) since 1920. In the continental U.S., relative sea level has risen about 10 - 12 inches (25 - 30 centimeters) over the same period. Observational data from tide gauges and satellites also show that sea level rise, both globally and along the continental U.S., is accelerating, with more than a third of that rise having occurred in the past two and a half decades (see NOAA and NASA portals for altimeter-based global rates and NOAA for local tide gauge rates).
In the 2017 sea level rise technical report, scenarios were related to representative concentration pathways. The 2022 report and data employ the underlying methods and output from the Sixth Assessment Report and their dependency on shared socioeconomic pathways, but focus more on how these scenarios relate directly to different amounts of end-of-century surface warming associated with the pathways (see Question 3).
There are two types of uncertainty that are important to consider when thinking about future sea level changes: 1) uncertainty in representing or modeling the physical processes that cause sea level change known as process uncertainty, and 2) uncertainty in how human behavior will drive future emissions and ensuing warming known as emissions uncertainty. The suite of projections in this report captures both process uncertainty and emissions uncertainty.
Process uncertainty is associated with how well we currently understand why sea level has changed in the past and how it will change in the future at specific times and locations. To capture process uncertainty in sea level rise projections, there is a range of uncertainty around each individual scenario (i.e., the low/17th%, median/50% and high/83rd% values for each particular scenario). The farther forward in time we move, the greater the uncertainty around each projection.
In addition to process and emissions uncertainty, there is still scientific discussion and investigation underway on the potential for rapid ice sheet melt and collapse, sometimes referred to as low confidence processes. Currently there is no scientific consensus on whether rapid melt will occur and, if it does, what that process will look like. Given that it is possible, those processes are included in international and federal assessments. The possibility of rapid ice sheet melt is a significant driver in reaching the highest scenarios in the 2022 technical report.
The 2100 projections for each global scenario stayed the same, since science suggests this range of futures remains possible. However, the timing for different rates of rise for the different scenarios was updated based on new modeling and more realistic assumptions of Greenland and Antarctic ice sheet behavior based upon the Intergovernmental Panel on Climate Change Sixth Climate Assessment. A result is that there is less acceleration in the higher scenarios until about 2050 and greater acceleration toward the end of this century. This has two primary implications. First, despite maintaining the same target values and having the same range between scenarios in 2100, the range covered by the scenarios is smaller in the near term than in the 2017 report. Second, the likely (17th-83rd percentile) ranges of projections for each scenario before and after the 2100 time point used to define the scenarios are wider than in the 2017 report.
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