A groundbreaking study led by researchers from Technical University of Munich has produced the world’s first global map showing how tidal movements from oceans travel inland through rivers, exposing millions to previously underestimated flood risks.
The research highlights that tides do not stop at coastlines. Instead, their influence moves upstream through coastal rivers, creating what scientists call a “tidal pulse.” These periodic fluctuations can significantly increase flood risks in inland regions, especially as climate change drives rising sea levels and extreme weather events.
According to the study, more than 725 million people worldwide are directly affected by these tidal influences. The findings reveal that over 175,000 kilometres of rivers across the globe are impacted by tides, making vast populations more vulnerable than previously understood.
The team analysed high-resolution satellite data from over 3,000 rivers to build the most comprehensive database of tidal river dynamics to date. One striking example comes from the Amazon River, where tidal effects can travel as far as 892 kilometres inland from the ocean. This demonstrates how far-reaching the impact of ocean tides can be, even in areas far from coastlines.
The newly developed global atlas allows scientists and policymakers to track where, how far and how strongly tides influence river systems. This is crucial for identifying flood-prone zones and planning infrastructure, disaster preparedness and water resource management more effectively.
The study also underscores the growing risks linked to climate change. As sea levels continue to rise, the reach and intensity of tidal pulses are expected to increase, shifting flood risk zones further inland. This could affect freshwater availability, agriculture and settlements located along these rivers.
Researchers say the map fills a major gap in global data and offers a powerful tool for governments and planners. By understanding how tides interact with rivers, authorities can design better flood protection systems and adapt to changing environmental conditions.
Ultimately, the findings reveal a hidden dimension of flood risk that has long gone unnoticed. As climate pressures intensify, recognising and preparing for tidal influences in rivers may become essential for protecting vulnerable communities worldwide.