Gaining or losing ground? Tracking Asia's hunger for 'new' coastal land in the era of sea level rise.

Many coastal cities are short of land for development and, coupled with the need to mitigate the impact of extreme events against a background of ongoing sea-level rise, coastal land reclamation (CLR) has emerged as a frequently applied solution, most especially in Asia. However, the sustainability of these newly reclaimed lands under the combined onslaught of increasing population pressure, SRL, greater frequency of extreme events, and land subsidence is largely unknown. In order to assess the spatial extent and temporal trends in recent CLR projects, we mapped and tabulated the annual magnitude of change in coastal land gain from 1988 to 2018 for eight major Asian coastal cities. Across these cities, both the spatial extent and rate of CLR is remarkable; some 700 km has been reclaimed in just three decades. >35% of this new coastal land has been constructed in Shanghai alone (562 km), while Singapore and Incheon have also experienced substantial land gains. These three cities alone account for almost 10% of all the land gained globally over the last three decades. An analysis of the spatio-temporal patterns reveals that, since recently reclaimed areas are predominantly characterized by construction, including ports, airports, commercial and residential uses, economic development is the most prominent driver. Shanghai, however, represents a significant departure from this trend, whereby >50% of the new coastal land gained during the recent past has not been devoted to construction projects and is vegetated, suggesting a different policy context. Commercial or otherwise, subsidence is widely reported as a major characteristic of recently reclaimed coastal land and is a major environmental challenge. Mapping recent rates of land subsidence over these newly reclaimed lands reveal that most are subject to significant levels of deformation, in the case of the international airport at Incheon, Republic of Korea, exceeding 25 cm annually.