Recent remote sensing analysis has revealed extensive loss of tidal flats, yet the mechanisms driving these large-scale changes remain unclear. Here we show the spatiotemporal variations of 2,538 tidal flat transects across China to elucidate how their morphological features vary with external factors, including suspended sediment concentration (SSC), tidal range, and wave height. We observe a correlation between flat width and SSC distribution, and between flat slope and tidal range. A nation-wide decline in flat width is observed together with SSC reduction between 2002 and 2016. Intriguingly, sediment-rich flats exhibit more rapid width losses if SSC reduces, but slower width gain if SSC increase compared to sediment-starved flats. These dynamics resemble stretched (sediment-rich) or compressed (sediment-starved) springs that tend to return to equilibrium, which can be explained by synthetic morphodynamic modeling. Similar patterns can be observed from Indonesia, the United States, and Australia, implying that the impact of sediment supply change is wide-spread and large-scale sediment allocation plan based on equilibrium concept can help preserving intertidal ecosystems.

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The unprecedented resolution of a new 2D modeling approach greatly improves our understanding of how mangroves reduce flood risk.@en

Due to rising sea levels and projected socio-economic change, global coastal flood risk is expected to increase in the future. To reduce this increase in risk, one option is to reduce the probability or magnitude of the hazard through the implementation of structural, Nature-based or hybrid adaptation measures. Nature-based Solutions in coastal areas have the potential to reduce impacts of climate change and can provide a more sustainable and cost-effective alternative to structural measures. In this paper, we present the first global scale assessment of the benefits of conserving foreshore vegetation as a means of adaptation to future projections of change in coastal flood risk. In doing so, we extend the current knowledge on the economic feasibility of implementing global scale Nature-based Solutions. We show that globally foreshore vegetation can contribute to a large decrease in both absolute and relative flood risk (13% of present-day and 8.5% of future conditions in 2080 of global flood risk). Although this study gives a first proxy of the flood risk reduction benefits of conserving foreshore vegetation at the global scale, it shows promising results for including Nature-based and hybrid adaptation measures in coastal adaptation schemes.

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Exposure to coastal flooding is increasing due to growing population and economic activity. These developments go hand-in-hand with a loss and deterioration of ecosystems. Ironically, these ecosystems can play a buffering role in reducing flood hazard. The ability of ecosystems to contribute to reducing coastal flooding has been emphasized in multiple studies. However, the role of ecosystems in hybrid coastal protection (i.e. a combination of ecosystems and levees) has been poorly quantified at a global scale. Here, we evaluate the use of coastal vegetation, mangroves, and marshes fronting levees to reduce global coastal protection costs, by accounting for wave-vegetation interaction.The research is carried out by combining earth observation data and hydrodynamic modelling. We show that incooperating vegetation in hybrid coastal protection results in more sustainable and financially attractive coastal protection strategies. If vegetated foreshore levee systems were established along populated coastlines susceptible to flooding, the required levee crest height could be considerably reduced. This would result in a reduction of 320 (range: 107-961) billion USD2005 Power Purchasing Parity (PPP) in investments, of which 67.5 (range: 22.5- 202) billion USD2005 PPP in urban areas for a 1 in 100-year flood protection level.@en