The contribution of diminishing river sand loads to beach erosion worldwide

Abstract 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.