METHODOLOGY FOR MAPPING SEA-LEVEL RISE VULNERABILITY on DIGITAL ELEVATION MODELS USING LOCAL TIDE RECORD; MAUI, HAWAII

Thermal expansion and meltwater add to the volume of the sea such that the present rate of sea-level rise (SLR) is now twice as fast as the average of the 20^th century. It has been pointed out that observed SLR has exceeded the worst case projections thus far; hence, it is appropriate to plan for SLR impacts on a scenario-basis (i.e., best and worst cases). Projections of future SLR (0.75 to 1.9 m ca. 2100; Vermeer and Rahmstorf 2009) provide a basis for defining scenarios. We use high resolution digital elevation models of coastal topography (topo and bathy, RMSEz = 0.21 m) to model SLR impacts in the form of passive flooding. To determine the temporal schedule of flooding we remove the trend and tidal component of historical water level variability from a local tide gauge (Kahului, Maui). The residual represents historical local sea level variability. We use this as the basis for predicting future sea level variability on a smoothly accelerating trend to 2100 based on best and worst case scenarios. The future tidal component is predicted and added to the model. Using this model of SLR and local variability, we predict exceedence (hr/yr) for 25 cm contour intervals on the Maui coast starting at present MHHW. Our results indicate that 25 cm above present MHHW will experience inundation on the following worst case schedule: 1 week per year by 2020-2030; 6 weeks per year by 2040-2050, and 10 months per year by 2060-2070. The best case scenario schedule is: 1 week per year by 2030-2040, 3 weeks per year by 2050-2060, and 3 months per year by 2070-2080. As recommended by the NOAA and USGS “Community framework for responding to SLR and inundation”, these results provide the geographic scope and temporal scales of concern for formulating SLR adaptation plans.