Comprehensive Evaluation of Projects with Respect to Sea-Level Change
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Frequently Asked Questions
Sea Level Change in this case is the change in the average water surface with respect to the local land mass. Depending on your location, the height of the local water surface is either rising or falling. This is currently being tracked by the Center for Operational Oceanographic Products and Services , a division of the National Oceanic and Atmospheric Administration.
Geologic factors can drive local sea-level change. Vertical land movement can occur due to tectonics (earthquakes, regional subsidence or uplift), compaction of sedimentary strata, crustal rebound in formerly glaciated areas, and withdrawal of subsurface fluids. Networks of long-term Continuously Operating Reference Stations (CORS) are being monitored by NOAANGS and when co-located with tide stations will begin to provide direct estimates of local vertical land uplift or subsidence.
Atmospheric factors can affect local or regional water levels. Decadal-scale phenomena include El Niño-Southern Oscillation (ENSO) in the Pacific and North Atlantic Oscillation (NAO) in the Atlantic, among others (see IPCC 2007a for a more complete discussion). Climate change may also alter the frequency and severity of tropical storms which could secondarily influence sea level. This is currently the subject of scientific research. Although the coupled effects of decadal and seasonal water level variations and episodic storm events are important to consider throughout the project life cycle, the incorporation of the influence of tropical storm on the application of sea level trends is outside the scope of this website.
There are a number of factors that contribute to long and short-term variations in sea level. Short-term variations generally occur on a daily basis and include waves, tides, or specific flood events, such as those associated with a winter snow melt, or hurricane or other coastal storm. Long-term variations in sea level occur over various time scales, from monthly to several years, and may be repeatable cycles, gradual trends, or intermittent anomalies. Seasonal weather patterns, variations in the Earth's declination, changes in coastal and ocean circulation, anthropogenic influences (such as dredging), vertical land motion, and the El Niño Southern Oscillation are just a few of the many factors influencing changes in sea level over time. When estimating sea level trends, a minimum of 30 [NB: USACE guidance requires at least 40 years] years of data are used in order to account for long-term sea level variations and reduce errors in computing sea level trends based on monthly mean sea level. Accounting for repeatable, predictable cycles, such as tidal, seasonal, and interannual variations allows computation of a more accurate long-term sea level trend. (excerpt from NOAA, http://tidesandcurrents.noaa.gov/sltrends/faq.shtml )
Sea-level change can cause a number of impacts in coastal and estuarine zones, including changes in shoreline erosion, inundation or exposure of low-lying coastal areas, changes in storm and flood damages, shifts in extent and distribution of wetlands and other coastal habitats, changes to groundwater levels, and alterations to salinity intrusion into estuaries and groundwater systems.
The rate of relative sea level rise changes with respect to location. In this case, we are talking about the change in the average water level relative to the local land mass. Because of changes in elevation of the land due primarily to subsidence or post glacial rebound, which are regional phenomena, the height of the water relative to the land is the sum of global sea level rise and the local land movement. Global sea level rise is somewhere around 1.7 millimeters per year. To estimate the sea level change in your area, go to Sea Level Change Curves.
revised 19 November 2014
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