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Sea-Level Rise Mapping: Insights and Best Practices
Importance of Elevation Data in Sea-Level Rise Assessments
Elevation data is crucial for assessing the impacts of sea-level rise and coastal flooding. The quality of this data significantly influences the accuracy of these assessments. Digital Elevation Models (DEMs) such as SRTM, ASTER GDEM, and ALOS World 3D are commonly used for regional, continental, or global assessments. However, these models have inherent vertical uncertainties that must be accounted for to ensure reliable results. High-resolution sources like airborne lidar provide more accurate data but are not always available globally. Current global DEMs are generally suitable for broad delineation of low elevation coastal zones but not for high-confidence mapping of fine increments of sea-level rise or short planning horizons.
Mapping Vulnerable Lands: US Atlantic and Gulf Coasts
Mapping lands vulnerable to sea-level rise involves combining elevation data with models of shoreline erosion and other coastal processes. For the US Atlantic and Gulf coasts, maps using USGS and NOAA data show that approximately 58,000 km² of land lies below the 1.5 m contour, with Louisiana, Florida, Texas, and North Carolina being the most affected states. These maps highlight the importance of elevation contours in understanding potential future shorelines, despite the inherent uncertainties in geological processes and sea-level rise rates.
Historical and Projected Sea-Level Rise
Historical data from satellite altimeters and coastal measurements indicate a global average sea-level rise of about 210 mm from 1880 to 2009, with an accelerated rate of 3.2 mm/year from 1993 to 2009. This rate is near the upper end of projections by the Intergovernmental Panel on Climate Change (IPCC). The variability in sea-level rise rates over the 20th century underscores the complexity of predicting future changes, which are influenced by factors such as volcanic activity and glacial isostatic adjustment.
Alternative Approaches to Sea-Level Rise Mapping
In Southern Miami Beach, three alternative temporal mapping approaches have been evaluated to predict sea-level rise. These include combining multiple scenarios into a single map, calculating the time horizon for inundation during high tides, and mapping the minimum average rate of sea-level rise required for inundation by 2100. These methods provide more nuanced predictions compared to traditional binary approaches and are particularly useful for urban areas.
Regional Case Studies: Italy and Portugal
In Italy, high-resolution Digital Terrain Models based on lidar data have been used to project sea-level rise scenarios for 2100. These projections indicate significant potential flooding, particularly in the subsiding North Adriatic coast and other coastal plains. The methodology developed for Italy can be applied globally to other regions facing similar risks. Similarly, in Portugal, a vulnerability assessment using a multi-attribute analysis and high-resolution maps has identified areas at risk of sea-level rise by 2050 and 2100, emphasizing the need for adaptation plans.
New Elevation Data and Global Vulnerability
Recent advancements in DEMs, such as CoastalDEM, which utilizes neural networks to reduce errors, have significantly increased estimates of global vulnerability to sea-level rise. This new model suggests that up to 630 million people could be living on land below projected annual flood levels by 2100 under high emissions scenarios, tripling previous estimates based on older models like NASA's SRTM.
Conclusion
Accurate mapping of sea-level rise impacts requires high-quality elevation data and consideration of vertical uncertainties. While global DEMs provide a broad overview, high-resolution data is essential for detailed local assessments. Regional case studies and new modeling approaches offer valuable insights for planning and adaptation strategies. As sea levels continue to rise, integrating advanced elevation models and comprehensive vulnerability assessments will be crucial for mitigating the impacts on coastal communities worldwide.
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