Recent advances in modeling 21st-century sea level rise (SLR) and its associated societal outcomes have demonstrated that the spatial pattern of SLR combined with highly variable population density along global coastlines exert a strong control on its impacts. Here, we extend this research by examining differential costs arising from two sources of SLR that exhibit distinct spatial ”fingerprints” - mass flux from the Antarctic (AIS) and Greenland (GrIS) Ice Sheets. To do this, we employ the DSCIM-Coastal data and modeling platform to quantify flood extents and population exposure to inundation from sea level changes associated with an ensemble of Ice Sheet Model Intercomparison Product projections between 2015 and 2100 CE. We also introduce the Social Cost of Ice Sheet Melt (SC-ISM) metric and calculate this for both AIS and GrIS melt scenarios. Due to the distinct sea level fingerprints of the two ice sheets, we find that mass flux from the AIS floods a larger area and would inundate a greater (present-day) population than an equivalent mass flux from the GrIS and yields a substantially higher SC-ISM. Across a suite of future climate scenarios, the SC-ISM associated with AIS melt is ~30% higher than that of GrIS, driven largely by differential SLR rates along the North Atlantic coastline. However, for either source, SC-ISM normalized by local GDP shows strongly disproportionate impacts, with low-income regions experiencing a significantly greater economic burden than high-income regions.

This paper reports a new and significantly enhanced analysis of US flood hazard at 30m spatial resolution. Specific improvements include updated hydrography data, new methods to determine channel depth, more rigorous flood frequency analysis, output downscaling to property tract level and inclusion of the impact of local interventions in the flooding system. For the first time we consider pluvial, fluvial and coastal flood hazards within the same framework and provide projections for both current (rather than historic average) conditions and for future time periods centred on 2035 and 2050 under the RCP4.5 emissions pathway. Validation against high quality local models and the entire catalogue of FEMA 1% annual probability flood maps yielded Critical Success Index values in the range 0.69-0.82. Significant improvements over a previous pluvial/fluvial model version are shown for high frequency events and coastal zones, along with minor improvements in areas where model performance was already good. The result is the first comprehensive and consistent national scale analysis of flood hazard for the conterminous US for both current and future conditions. Even though we consider a stabilization emissions scenario and a near future time horizon we project clear patterns of changing flood hazard (-3.8 to +16% changes in 100yr inundated area at 1° scale), that are significant when considered as a proportion of the land area where human use is possible or in terms of the currently protected land area where the standard of flood defence protection may become compromised by this time.