Adaptation to sea level rise: Learning from present examples of land subsidence

Current climate change discourses have expressed fear that many coastal communities would be forced to relocate in the face of rising water levels. However, despite the frequency and intensity with which such messages are being broadcasted throughout the world's media, there is little actual evidence of any relocation actually taking place, even though there are a number of past examples of relative sea level rise due to earthquake induced subsidence or groundwater extraction. Thus, in order to better understand the consequences of future sea level rise the authors analysed four instances of land subsidence that have taken place in the 20th and early 21st centuries (namely, adaptation strategies around Tokyo and Jakarta, and the experience of islands on the Danajon bank in the Philippines, and Kepulauan Seribu close to Jakarta). In all cases the inhabitants of densely populated coastal areas remain in place, despite the challenge of living with higher water levels. Adaptation was done through a five-phase process, starting with the construction of rather weak seawalls, which is then followed by the placement of pumps to drain water. Eventually, as the economic and technical capacities of coastal settlements improved, better seawalls were built, which then led to the reclamation of new areas, the elevation of entire districts or the construction of super levees. Thus, while it is clear that sea level rise will pose an additional financial strain on urbanised coastal areas, the authors found no evidence that any major coastal settlements will surrender a significant portion of its land area to the sea, given the range of adaptation options available. Rather, the opposite is true, and evidence indicates that new lines of defence will be built further into the water, effectively meaning that humans will encroach on the sea.