🌊 Rising waters or sinking shores?

When we talk about rising waters, we often imagine oceans gaining ground. Yet a new study reveals that ground subsidence is just as much to blame for flooding in many coastal cities.

To accurately measure this phenomenon, researchers from the German Geodetic Research Institute at the Technical University of Munich and Tulane University quantified its extent. In their paper in Nature Communications, they show that densely populated coastal areas are experiencing a relative sea level rise of about 0.24 inches (6 mm) per year. This figure is nearly double the rise due to climate change alone and three times the global average weighted by coastline length.


Land subsidence has several main causes. Excessive groundwater extraction, oil and gas production, and the compaction of young sediments in deltas are major factors. The weight of buildings and infrastructure in rapidly growing cities also contributes. Long-term geological processes, such as tectonic movements and post-glacial adjustment, also play a role.

The most affected areas include Jakarta (0.54 in/yr, or 13.7 mm/yr), Tianjin (0.53 in/yr, or 13.5 mm/yr), Bangkok (0.33 in/yr, or 8.5 mm/yr), Lagos (0.26 in/yr, or 6.7 mm/yr), and Alexandria (0.16 in/yr, or 4 mm/yr). Within the same city, rates can vary widely: in Jakarta, some areas are sinking while others are rising. Conversely, regions like Sweden and Finland are experiencing geological uplift that lowers the relative sea level.

The good news is that subsidence can be slowed. Dr. Julius Oelsmann, lead author, explains that groundwater management is an effective local measure. Tokyo, for instance, saw its relative sinking drop from more than 3.9 inches (10 cm) per year to a much lower level thanks to pumping restrictions and alternative water sources.