Adaptation to Sea Level Rise in Cities: Lessons from Present Examples of Land Subsidence

As a result of sea level rise a number of authors have stated that many coastal communities would be forced to relocate unless expensive adaptation countermeasures are employed. However, most of the forecasted problems and their knock-on consequences on coastal communities remain hypothetical, despite a number of past examples of relative sea level rise due to earthquake induced subsidence or groundwater extraction. In order to better understand the consequences of future sea level rise the authors have analysed the effects of three instances land subsidence that have taken place in the 20^th and early 21^st century, in which densely populated coastal areas still inhabited despite the challenge of living with higher water levels (namely, adaptation strategies around Tokyo and Jakarta, and the experience of islands on the Danajon bank in the Philippines). Through this analysis the authors highlight how there appears to be a five phase adaptation process, which starts with the construction of rather weak seawalls, followed by the placement of pumps to drain water, the improvement of the seawalls, the reclamation of new land areas, and finally the elevation of entire districts or the construction of super levees. While it is clear that sea level rise will pose an additional financial strain on urbanised coastal areas (with this additional cost likely to increase if mitigation strategies are not implemented at the global level), it would appear extremely doubtful that any major coastal cities will surrender any areas to the sea, given the range of adaptation options available.