The development of the tidal basins in the Dutch Wadden Sea until 2100: the impact of accelerated sea-level rise and subsidence on their sediment budget – a synthesis

Abstract

Climate change is very likely to cause a global acceleration in sea-level rise (SLR). The projected acceleration of SLR will also affect the Wadden Sea.In addition to an accelerated SLR, gas and salt extraction will cause subsidence that adds to an increase in water depth in the tidal basins. This will have consequences for the sediment budget of the Wadden Sea and especially for the intertidal flats that have a high ecological value. This synthesis presents projections of the future state of the Dutch Wadden Sea for the years 2030, 2050 and 2100.The projected changes in mean sea level by 2100 for Den Helder and Delfzijl are above the global mean projections, mainly due to the above-average ocean dynamics and glacio-isostatic adjustment contributions in the regional projections. The projected rise in mean sea level for 2100 with relation to 2018 in these locations is 0.41 m, 0.52 m and 0.76 m for, respectively, the RCP2.6, RCP 4.5 and RCP8.5 climate scenarios.When we combine the presented SLR scenarios with the subsidence estimates and compare these rates to the critical rates for 'drowning' of intertidal flats that were calculated for the individual tidal basins, we can determine the moment that the maximum imported sediment volume can no longer compensate the increase in accommodation space in a basin and the intertidal flats will start to diminish in surface area and/or height. In the RCP2.6 scenario, the projected rates of relative SLR will be below the critical rate for drowning of the inlet systems in the Dutch Wadden Sea. For the RCP4.5 scenario, the critical SLR rate will be exceeded for Vlie Inlet in 2030, and for the RCP8.5 scenario the critical SLR rate will be exceeded for Vlie Inlet in 2030, Texel Inlet in 2050 and Ameland Inlet in 2100. For the other basins the critical rate will not be exceeded until 2100 or later.The way the intertidal flats in a basin will react to 'drowning' is not clear beforehand. It is highly possible that erosion of flats in one place will produce the sediment to maintain flats in other places. Tidal flats close to the sediment-delivering tidal inlet are not likely to disappear, because there the balance between supply and erosion is not likely to change.

Understanding of Contemporary Regional Sea‐Level Change and the Implications for the Future

“…Repeated satellite and airborne laser and radar altimetry provide detailed surface height change observations over ice sheets, but conversion from surface height to mass loss requires knowledge of spatial and temporal variability in firn density, a parameter that is poorly constrained due to sparse observations within the ice sheet interior (Pritchard et al, 2009). The input-output method (Gardner et al, 2018;Rignot et al, 2011Rignot et al, , 2019Shirzaei & Bürgmann, 2012, 2018)-the only method that gives a longer time series of ice sheet mass balance (Kjeldsen et al, 2015;Rignot et al, 2019;Mouginot et al, 2019)-combines observations of ice flux across the grounding line from satellite remote sensing with modeled SMB estimates. In general, most observational time series are less than 20 years old, making the detection of mass loss acceleration in the presence of large natural variability challenging, especially in ice sheet SMB (Wouters et al, 2013).…”

“…Sediment transport results in significant mass redistribution in many deltaic and estuarine regions, which in turn result in GRD-induced SLCs. Several recent studies have discussed sediment transport in detail for the Dutch Wadden Sea (e.g., Bing Wang et al, 2018;Fokker et al, 2018;Van der Spek, 2018;Vermeersen et al, 2018), although the direct link between transport and the resulting GRD response has not yet been quantified for this region. Since the last glacial maximum, river routing and sediment yields vary in both space and time.…”

Adaptation to uncertain sea-level rise; how uncertainty in Antarctic mass-loss impacts the coastal adaptation strategy of the Netherlands

“…Hence, high rates of SLR will eventually lead to drowning of the system by a reduction in flat surface area and/or height [69]. For the Dutch Wadden Sea, the critical rate at which the intertidal flats will start to 'drown' is between 6 and 10 mm yr −1 [88]. These rates would be exceeded by 2030 and 2045 under the RCP8.5 A scenario, and by 2050 and 2065 under RCP4.5 A (median values).…”

Evolution Modeling and Protection Scheme for Tidal Flats Under Natural Change and Human Pressure, Central Jiangsu Coast

“…Another challenge in forecasting future trends is the validation of prediction models. Many predictive works have not been tested based on past coastal processes (Schuerch et al., 2018; van der Spek, 2018), resulting in uncertain adaptability of models in future, more uncertain coastal environments. To date, especially in the context of further reduced predictability of coastal evolution caused by natural environmental changes and human activities, we still lack a comprehensive and accurate understanding of tidal flat processes.…”