Simulation of Changes in Tropical Coastal Wetlands Distribution in the Context of Sea Level Rise and Coastal Development

Coastal wetlands are vulnerable to human coastal activities and accelerated sea level rise brought out by climate warming, yet great uncertainties exist for the in situ survival and the landward migration potential of coastal wetland. The vulnerability is particularly prominent for small mountainous islands with limited coastal flat plains but intense coastal development and tourism, such as the tropical island of Puerto Rico in the Caribbean. In this study, we simulated the potential changes in the distribution of coastal wetlands in Puerto Rico by 2100 in the context of rising sea level and urbanized coastal plain. We used the NWI data for the initial wetland distribution and the Lidar data from NOAA to derive the topography. We adopted the Sea Level Affecting Marshes Model to simulate coastal wetlands distribution by 2100 under the scenarios of 1 m and 2 m rise in sea level. Our results indicated that under rising sea level mangroves and estuarine water would move landward and distribute to the areas currently occupied by saline marsh and non-saline marsh / swamp. Saline marsh would encounter the most relative loss in the vegetated wetlands. Coastal vegetated wetlands would reduce their total distributions under both sea level rise scenarios. The reduction is nonlinear in response to rising sea level: the loss under the 2-m scenario is three times more than that under 1-m scenario. A moderate rise of 1 m in sea level by 2100 would lead to expansion of mangroves but decrease the distribution of saline marsh and non-saline marsh / swamp. A 2-m rise would reduce the distributions of all vegetated wetland types, mostly replaced by estuarine water. Coastal hilly topography constrains the potential migration of wetlands towards inland. The mangroves distributed in the north and northeast of the island have greater potentials to move inland than those in the south and southwest due to the larger flat coastal plains in the former. In addition to the challenges of accelerated rising sea level and coastal tourism, strong tropical cyclones would bring devastating damages to coastal woody wetlands and induce significant coastal erosion. Further studies to incorporate both press and pulse drivers to coastal wetland ecosystems will help understand the mechanisms and therefore bring knowledges for wetland restoration and management.