Future average water levels – Based on data from IPCC AR6 WG 1 (2021)

Future mean water levels in RH 2000 and the approximate future location of the shoreline along Sweden’s coastline are calculated for several different scenarios and for each decade from 2030 to 2150. The data are based on regional projections from the IPCC compilation “AR6 Interim Report 1 – The Science Foundation” published in August 2021. The calculations are adjusted for the local land uplift. The calculations are based on projections, which the IPCC considers likely, for five different emission scenarios: SSP1-1.9, SSP1-2,6, SSP2-4,5, SSP3-7.0 and SSP5-8.5. In addition to these, there are two calculations based on projections that the IPCC deems less likely, as they include processes associated with deep uncertainty related to inland ice instability: SSP1-2.6 less likely and SSP5-8.5 less likely. Three different levels are given for each scenario and decade. The three levels are the median and the 17th and 83 rd percentiles. The extremes are not shown, i.e. neither the highest possible level nor the lowest possible. Data on future mean water levels in cm in RH 2000 are available for download in CSV format for each coastal municipality in Sweden (87). The levels can also be seen in an interactive table at https://www.smhi.se/klimat/stigande-havsnivaer/framtida-medelvattenstand-1.165493 . Data on the future location of the shoreline are available for download in SHAPE format for each year and likely, or less likely scenario. These can also be consumed through a WMS service. The average water level in cm in RH 2000 is available for download in TIFF format for each year and likely, or less likely scenario. RESTRICTIONS The geographical distribution of the map layers is limited to the area between about 10 km off the shoreline and 1-1.5 km within the shoreline. Larger rivers and lakes located within this area can have a sharp limit in the map layers. Islands less than 1 000 km² are filtered out and are not included in the map layers. Comment on data in CSV format The future mean water level for each SSP scenario and year may vary between grid squares within a coastal municipality. This is mainly due to variations in the pace of land elevation, especially in municipalities that are spreading north-south direction. Gotland has the greatest difference in long-term land elevation within its coastal area, where it differs just under 1.8 mm/year between different areas. This makes a difference of 9 centimeters in 50 years. The average water level during the reference period (1995-2014) may also vary within a municipality’s coastal area, but these are minor variations of up to about 4 centimeters. The future mean water level is therefore provided as an average for each coastal municipality. Comments on: 1. Average water levels are combined with topographic information from Lantmäteriet. Areas with an altitude level lower than the calculated mean water level are classified as permanently flooded. Any variation in the accuracy of the topographic information may affect the outcome of the map layers. There may also be newer or more detailed topographic information than the one used when the map layers were created. 2. In the topographic map data used in the calculations, there may be a lack of detailed information on where natural or constructed obstacles or passages between land and sea exist or are missing. This means that land areas that are lower than the future sea level can be shown as flooded even though in reality there may be obstacles for the sea to reach it. 3. It occurs that the land rise in parts of Sweden is larger than the sea level rise. This means that in the near future sea level will be lower than it is today. In these places, where land rises faster than the sea rises, the future sea level is shown as if it were unchanged, i.e. at the same level as today. 4. Any effects on the coastline of a change in mean water level (e.g. erosion) cannot be inferred from the map layers. USE The average water level determines where the sea surface and the shoreline are normally located. The data can be used to study possible future mean water levels based on different emission scenarios and years. The data provides a comprehensive basis for information on future sea levels. The aim is not to provide a full basis for decision-making, but to provide an indication of the areas in which a more detailed basis should be produced. When there is a lot of wind, the sea can rise sharply above the average water level for a short period of time. This is called a high-water event. In the planning context, there may be a need to take into account high-water events, wave effects and the like. High-water events and wave effects are not included in the data on future mean water levels. Read more about this on the following website: https://www.smhi.se/klimat/stigande-havsnivaer/hogvattenhandelser-och-extremnivaer-1.165445.