According to a Dutch research team, evidence shows that many coastal cities around the world are now sinking at a rate up to ten times that of sea level rise. The researchers state that, without action, parts of Jakarta, Ho Chi Minh City, Bangkok and numerous other coastal cities will sink below sea level, hence becoming much more vulnerable to flooding.

In addition, differential land movement causes significant economic losses in the form of structural damage and high maintenance costs. This effects roads and transportation networks, hydraulic infrastructure – such as river embankments, sluice gates, flood barriers and pumping stations -, sewage systems, buildings and foundations. The total damage worldwide is estimated by the researchers at billions of dollars annually.

The main cause of severe land subsidence is excessive groundwater extraction after rapid urbanization and population growth is the main cause of severe land subsidence. In addition, coastal cities are often faced with larger natural subsidence, as they are built on thick layers of soft soil.

The researchers state that there is a need for an integrated approach in order to manage subsidence and to develop appropriate strategies and measures that are effective and efficient on both the short and long term. Urban groundwater management, adaptive flood risk management and related spatial planning strategies are just examples of the options available. A major rethink is needed to deal with the ‘hidden’ but urgent threat of subsidence.

A detailed abstract of the paper is available at http://media.egu.eu/media/documents/2014/11/gilles_erkens_scientific_abstract.pdf