Coastal zones are fragile and complex dynamical systems that are increasingly under threat from the combined effects of anthropogenic pressure and climate change. Using global satellite derived shoreline positions from 1993 to 2019 and a variety of reanalysis products, here we show that shorelines are under the influence of three main drivers: sea-level, ocean waves and river discharge. While sea level directly affects coastal mobility, waves affect both erosion/accretion and total water levels, and rivers affect coastal sediment budgets and salinity-induced water levels. By deriving a conceptual global model that accounts for the influence of dominant modes of climate variability on these drivers, we show that interannual shoreline changes are largely driven by different ENSO regimes and their complex inter-basin teleconnections. Our results provide a new framework for understanding and predicting climate-induced coastal hazards.

<p><span>A major challenge facing climate change and sea level rise is to predict coastal evolution and in particular coastal erosion, which seems likely to increase in the next century. Coastal erosion affects many regions of the world, often highly populated. In addition to natural processes, coastal erosion is closely interrelated with anthropic activities such as sea defence building or the modification of river sediment supply (e.g. river dam sediment trapping and land use changes). Several studies have already focused on predicting coastal change using more or less complex models on local scales. However, the majority of these models don't take into account one of the main components: the input of sediment from rivers. There are also difficulties in adequately representing the shoreline evolution by a partial understanding of processes and the difficulty of obtaining detailed and long-term data. We present simplified dynamic model on a global scale fed with new satellite observations of coastal ocean hydrology and morphology. The main objective of this study is to explore, thanks to this new model, future scenarios of shoreline change with the identification of potentially vulnerable hotspots. It will help in improving sustainable coastal management strategies. </span></p>

The erosion of sandy beaches can have a profound impact on human activities and ecosystems, especially on developed coasts. The scientific community has, to date, primarily focused on the potential impact of sea-level rise on sandy beaches. While being abundantly recognized at local to regional scales in numerous studies over the last two decades, the contribution of diminishing fluvial sediment supply to sandy beach erosion at the global scale is still to be investigated. Here, we present the first global sand pathway model from land to sea. We show that recent sandy beach evolution trends worldwide are strongly controlled by fluvial sand input to the ocean, and that there is a global convergence of sand at the Equator due to wave-induced longshore transport. The reduction of sand supplies to beaches caused by river-basin changes such as dam constriction has a profound effect on beach stability. Our analysis demonstrates the massive impact of the thousands of river dams on beach erosion worldwide.