In many coastal and delta cities land subsidence exceeds absolute sea level rise up to a factor of ten. Without action, parts of Jakarta, Ho Chi Minh City, Bangkok and numerous other coastal cities will sink below sea level. Increased flood risk and other widespread impacts of land subsidence result in damage totalling billions of dollars per year. A major cause of severe land subsidence is excessive groundwater extraction due to rapid urbanization and population growth. A major rethink is needed to deal with the often ‘hidden’ but urgent threat of subsidence, as well as more guidance to support decision making.

The policy brief, entitled: 'Subsidence in urbanizing deltas and coastal zones' describes briefly the challenges and the actionable approaches to counteract subsidence. Recommendations are made on policy and governance, technology, capacity building and financing aspects. This reflects the vision of the Delta Alliance community. 

Subsidence for several coastal cities compared to absolute sea level rise in the same time period

 
The policy brief has its rationale and recommendations from an updated version of the ‘Sinking Cities’ brochure, which provides a more in-depth step-wise guidance in addressing high rates of subsidence, illustrated by a number of case studies and actionable practices. The lessons learned from these experiences provide valuable information and inspiration for decision makers and experts to address subsidence in urbanising deltas. It is expected that this guidance will further raise awareness and contribute to lowering the threshold to act while acknowledging the progress made over the last years.