Web Tool for Mapping Storm Surge and Sea-Level Rise

The Norwegian Mapping Authority is responsible for the national sea-level observing system in Norway.

The tool Se havnivå i kart has applications for preparedness and prevention in risk management and adaption to climate change. You can get statistics on buildings, area and roads affected by coastal flooding in your community, and download inundation layers for custom GIS applications.

The data shown in this web tool do not include the effect of waves, possible future changes to the tidal regime or characteristics of storm surges that may occur with climate change and sea level rise, or erosional processes or other future changes to the shoreline. River and estuary flooding due to extreme precipitation events is not accounted for in the visualizations shown here and is the responsibility of the Norwegian Water Resources and Energy Directorate (NVE).

The purpose of this tool is to assist coastal planners and help communicate the risks associated with storm surge and sea-level rise. For coastal planning, this web tool can help identify areas at risk of inundation, it may not be appropriate for site-specific decision making. In some cases, an onsite visit to verify information in the field is advisable.

While every effort has gone into ensuring the accuracy and correctness of these data and maps, appropriate use and conclusions drawn from the information presented here are the responsibility of the user. Users should note that the information shown can contain errors, and that there are uncertainties related to the data used and methods applied. The Norwegian Mapping Authority reserves the right to make changes, corrections or improvements to this web tool and the information presented within.

Tool guidelines for Se havnivå i kart

Begin by searching for a location or zooming in on the map. Blue areas show the parts of Norway where you can visualize storm surge levels and future sea level change. These areas correspond to where there are existing data with adequate accuracy for inundation mapping.

Options on the "sea level" and "storm surge height" tab correspond to current guidelines on how to account for future sea-level changes and use storm-surge return heights in planning. The guidelines are available from the Norwegian Directorate for Civil Protection (DSB) (only Norwegian text available): "Havnivåstigning og stormflo - samfunnssikkerhet i kommunal planlegging" (pdf). The numbers and projections are based on those given in the report "Sea Level Change for Norway- Past and Present Observations and Projections to 2100" and take into account vertical land motion.

Alternatively, you can use the manual slider embedded in the map to visualize different scenarios of future sea level rise. This slider can be used to help communicate how uncertainty associated with future sea level rise can be understood in terms of risk or vulnerability. Global sea level is rising and we expect that trend to continue. There are, however, large uncertainties related to the rate of future sea level rise that depend on our future greenhouse gas emissions pathway (i.e. decisions on climate mitigation) and how the climate system will respond to future emissions. The slider can also be used to help understand and visualize the implications of long-term (post 2100) sea level changes. For the time beyond 2100, it is virtually certain that global sea level rise will continue due to the long response times of the oceans and ice sheets.

Sea level

On the "sea level" tab choose "Now" for applications related to present-day climate adaption. Alternatively choose "2090" for adaption measures related to future climate change. For this option, the inundation maps shown include a rise in sea level based on the projected top of the likely range (95 %) for the emissions scenario RCP8.5 and for the period 2081-2100 relative to 1986-2005. This is the number recommended for use in planning and in the guidelines from the Directorate for Civil Protection.

As sea level change varies along the Norwegian coast, these numbers are different from municipality to municipality.

Storm surge height

The "storm surge height" tab allows you to choose between "areas permanently inundated" and areas inundated for different storm surge return heights.

The option "Mean High Water" corresponds to the height of the tidal datum Mean High Water (MHW). Mean High Water is calculated as the average of all the high water heights observed over a 19-year period. [MS1] The present Mean High Water height is calculated for the period 1996 to 2014. Mean High Water is the coastline boundary in the web tool and on both land maps and nautical charts. You can use the options on the "sea level" tab or on the manual slider to visualize areas permanently inundated with future sea level rise (i.e. future height of Mean High Water).

Alternatively choose one of the storm surge return heights available. They are the 20-, 200- and 1000-year return heights which correspond to the safety classes 1, 2 and 3 given in national building regulations (TEK17) § 7-2.

Slider

Use the vertical slider embedded in the map to set sea level to 1 to 5 meters above present MHW. The slider can be used to visualize sea levels beyond the levels recommended for coastal planning, e.g., long-term estimates of sea-level (after 2100).

Mapping methods

Elevation data are provided in the form of Digital Terrain Models (DTMs). The DTMs used for inundation mapping in this web tool are based on airborne LiDAR data and can be downloaded via hoydedata.no.

The DTMs applied here have a horizontal resolution of 1 x 1 m (DTM1). The vertical accuracy (systematic error) of these DTMs generally has a root mean square error (RMSE) of better than 0,1 m. However, accuracies will vary depending on the terrain and when the data was collected.

Users should note that the visualizations shown here are limited to areas of the coast where we have existing data with adequate accuracy for inundation mapping. These areas correspond to areas adjacent to the coast, where elevation data with adequate accuracy is available, and where data on storm surge levels and tidal datums are available.

Kartverket has plans to survey more coastal areas of Norway with airborne LiDAR in the coming years. Thus, the coverage of the inundation maps in this web tool will improve and be updated as new elevation data becomes available.

Elevation data are converted from ellipsoidal heights to heights in the national height system using the Norwegian height reference surface HREF. Elevation data are thus given in the national height system NN2000.

Inundation mapping requires knowledge of different vertical datums. For example, to visualize the height of Mean High Water in the national height system NN2000 requires knowledge of these two vertical datums and also the relationship between them. MHW and the height difference between Mean High Water and NN2000 is well known close to the permanent tide gauges. However, tidal datums and storm surge levels and their heights with respect to NN2000 are less well defined along other parts of the coast. Uncertainties associated with tidal datums and storm surge levels may well exceed errors on the elevation data in some areas.

Cartographic data (area type, roads, and buildings) used in the analysis are from the Norwegian Mapping Authority's N50 map dataset. The data have a positional accuracy of 2 to 50 meters dependent on object type and the method used to determine position. Note that the N50 map data have been cartographically edited in accordance with presentation rules for the Norge 1:50 000 map series. This may cause the cartographic data and maps used here to deviate from reality.

Users should keep in mind the above information when interpreting the data and maps presented in this web tool.

Any questions should be addressed to the customer center of Kartverket at kundesenter@kartverket.no.

Publications

For further details, the storm surge levels and sea level projections shown in this web tool are described in the following reports and peer reviewed publications:

• Sea Level Change for Norway - Past and Present Observations and Projections to 2100
• Breili, K.; Simpson, M.J.R.; Nilsen, J.E.Ø. Observed Sea-Level Changes along the Norwegian Coast. J. Mar. Sci. Eng. 2017, 5, 29.
• Simpson, M.J.R.; Ravndal, O.R.; Sande, H.; Nilsen, J.E.Ø.; Kierulf, H.P.; Vestøl, O.; Steffen, H. Projected 21st Century Sea-Level Changes, Observed Sea Level Extremes, and Sea Level Allowances for Norway. J. Mar. Sci. Eng. 2017, 5, 36.