Past, present, and future nuisance flooding on the Charleston peninsula

Abstract

A forecast of nuisance flooding of Charleston peninsula is presented, based on an analysis of tide records from Charleston Harbor, SC. The forecast was based on past trends in local sea level and tidal harmonics, including the 18.6-yr lunar nodal and annual cycles. The data document an exponential rise in mean sea level. Extrapolating to year 2060 shows that the sea-level trend already is equivalent to the RCP4.5 scenario and on track to exceed NOAA’s intermediate low sea-level rise scenario of 0.5 m this century. If the trend continues, MSL will have risen by 0.22 m in 50 yr at an annual rate of 0.5 cm/yr in 2069. Simulations to 2064–2068, based on an empirical relationship between the annual number of flood events, defined as a water level exceeding 1.17 m NAVD (North American Vertical Datum of 1988), and the annual sum of monthly mean high water (r2 = 0.84), predict annual flood events will rise to the 60 to 75 range. Application of the hourly tidal harmonics to the long-term sea-level trend provided estimates of total land area flooded and duration of flooding. Flood duration is expected to rise to 6.5% by 2046–2050 and 8.2% of time by 2064–2068. The area exposed to flooding will be 4.23 km2 in 2046–2050 and 4.46 km2 in 2064–2068, corresponding to about 20–21% of peninsular area on what was formerly marshland and creeks, filled in earlier centuries. Finally, the estimated cost of defending the city and a proposal for a climate tax are discussed.