Historical shoreline changes in Rincón provide a basis for a general interpretation of this small but complicated coastal system. Past changes alone are an insufficient source of information to guide future planning; therefore, further studies of regional geology and sediment transport are needed to provide information on the major processes that govern shoreline change. Ideally, management decisions about Rincón’s coast will be based on long-term and multidisciplinary considerations such as principal uses of the shoreline and the potential effects of various structures (for example, continued construction of seawalls will over time eliminate the fronting beaches), as well as the potential effects of future sea-level rise and climate change.

Model simulations reported by the Intergovernmental Panel on Climate Change (IPCC) indicated that sea level may rise by as much as 0.6 m over the remainder of this century (Bindoff and others, 2007). Some scientists have argued that this estimate is conservative and have suggested that a rise of 1 to 2 m by 2100 may be more realistic, given the exclusion of contributions of ice-melt from land-based ice from the IPCC projections (Overpeck and others, 2006; Hansen and others, 2007; Rahmstorf, 2007; Rahmstorf and others, 2007). A sea-level rise of 0.6 m by 2100 would represent more than a threefold increase in the rate of relative sea-level rise over that observed in San Juan from 1962 to 1999 (National Oceanographic and Atmospheric Administration, 2006). The historical trend of erosion along much of the Rincón coast indicates that future sea-level rise will likely result in a continuation of, or perhaps increase in, the rate of coastal erosion.

The coastal sedimentary system in Rincón contains a substantial carbonate component, presumably derived from the adjacent coral reefs. Future climate change that results in damage to the reefs (for example, Winter and others, 1998; Waddell, 2005), such that reef-sediment production is decreased, could cause a regional decrease in sediment supply and, in turn, increase coastal erosion.