Tidal flats are shrinking in extent globally. The dynamics of the response of estuarine tidal flats to global environmental changes remain unclear. Tidal-flat morphology is shaped by the interplay among wave and tidal forces, river discharge and sediment supply, and preservation of tidal flats requires a balance between erosional and depositional processes be maintained. Here we assess tidal-flat morphodynamic changes of 40 globally distributed estuaries with contrasting tidal amplitudes between 1986 and 2011 from analyses of 4,939 satellite images. We consider both vegetated and unvegetated intertidal areas. From comparisons with remote-sensing-derived turbidity estimates, we identify a critical turbidity threshold indicative of a minimum sediment supply along with the hydrodynamic forces, which is necessary to maintain tidal flats. Tidal flats in intertidal areas in estuaries with low turbidity face retreat, with the critical turbidity threshold increasing with increasing tidal amplitudes. By contrast, estuaries with high turbidity tend to exhibit laterally or vertically expanding tidal flats. However, despite estuaries with limited tidal ranges having relatively low turbidity thresholds, environmental or anthropogenic alterations can still adversely affect the morphology of tidal flats. Our findings demonstrate the need to consider sediment supply in integrated estuarine management strategies to maintain the ecological integrity and flood defence function of tidal flats.

全球潮滩面积正在缩小。河口滩涂对全球环境变化的响应动态仍不清楚。潮滩形态是由波浪和潮汐力、河流流量和沉积物供应之间的相互作用形成的，而潮滩的保护需要保持侵蚀和沉积过程之间的平衡。在这里，我们通过对 4,939 个卫星图像的分析，评估了 40 个全球分布的河口的潮滩形态动力学变化，并对比了 1986 年至 2011 年的潮汐幅度。我们考虑了有植被和无植被的潮间带地区。通过与遥感浊度估计值的比较，我们确定了一个临界浊度阈值，该阈值指示了最小沉积物供应以及水动力，这是维持滩涂所必需的。低浊度河口潮间带滩涂面临后退，临界浊度阈值随着潮汐幅度的增大而增大。相比之下，高浊度的河口往往会出现横向或纵向扩展的潮滩。然而，尽管潮差有限的河口具有相对较低的浊度阈值，但环境或人为变化仍然会对滩涂的形态产生不利影响。我们的研究结果表明，需要在河口综合管理策略中考虑沉积物供应，以维持滩涂的生态完整性和防洪功能。