Xiaoguang Ouyang, Rod Connolly, Shing Yip Lee

Tidal marshes are not only lost to human disturbance but also face the threat of sea level rise (SLR). However, current earth system models used to estimate future changes in wetland extent omit wetland’s real responses to SLR without field observations. We synthesised global data on sediment accretion rate (SAR) and surface elevation change (SEC) for tidal marshes and developed a mathematical model to assess their resilience to future SLR. Sediment loadings and precipitation largely explain the variance of marsh SAR and SEC. Human disturbance resulted in less sediment accretion and existing conservation activities were inefficient in promoting sediment accretion. Under the representative concentration pathways and nature-based human adaptation scenarios, tidal marshes will gain up to 63% of the current area by 2100 if sufficient sediment loadings and accommodation space allow landward migration. If current accommodation space maintains, net areal losses of > 30% are possible and hotspots of future marsh loss are largely in North America, Australia and China. Projections for most SLR scenarios see marsh area peaking in the mid rather than late 21st century. This implicates that tidal marshes may contribute to achieve a climate neutral world by 2050. We highlight the importance of nature- based adaptation in enhancing the resilience of tidal marshes to future SLR.