Human Footprint on Tides in Estuaries

Tides exert strong control over flooding and ecological processes in estuaries, yet their dynamics are often altered by human activities such as dredging and land reclamation. Using archival and modern records from 25 estuaries worldwide, we assess human-driven changes in tidal dynamics over timescales of decades to centuries, from the coast to the landward estuarine boundaries. Over the past two centuries, local interventions have typically amplified tidal ranges (mean maximum increase of 110%), accelerated tidal propagation (mean increase of 42%), and shifted tidal asymmetry. The most pronounced changes occur far inland, often more than 100 km from the coast. Land reclamation and channel deepening are the most widespread and impactful interventions, affecting nearly all systems studied. The magnitude and location of maximum change point to local human activities as the dominant drivers, exceeding the influence of long-term processes such as sea-level rise and subsidence. These findings demonstrate that, historically, anthropogenic modifications have had a far greater impact on estuarine water levels than global sea-level rise in human-influenced estuaries. Recognizing this human footprint opens opportunities for targeted local management strategies to reverse past changes, reduce flood risk, and build resilience to climate change.