Estimating Salinity Effects Due to Climate Change on the Georgia and South Carolina Coasts

摘要

The Fourth Assessment Report (AR4) of the United Nations’ Intergovernmental Panel onrnClimate Change (IPCC) states that, in addition to sea level rise, climate change will increase thernfrequency and intensity of extreme weather events such as droughts and offshore storms, whichrnincrease tidal range. AR4 “is the largest and most detailed summary of the climate changernsituation ever undertaken, involving thousands of authors from dozens of countries”. It alsornstates that climate change will affect the world’s health and macro-scale economies. The need tornadapt to future climatic conditions will be especially challenging in coastal regions, where searnlevel rise, droughts, and increased tides will lead to more frequent and longer duration seawaterrnintrusions into estuaries, affecting drinking water supplies.rnThis paper describes research performed partially under Water Research Foundation Project No.rn4285 into how coastal water supplies might be impacted. Two systems that supply fresh water tornseveral municipalities in South Carolina and Georgia were chosen for study - the LowerrnSavannah River in the vicinity of the City of Savannah, and the Pee Dee / Waccamaw Rivers andrnthe Atlantic Intracoastal Waterway in the vicinity of the Grand Strand / Myrtle Beach area. Thernresearch used modified versions of estuary models that had originally been developed for otherrnapplications. The “Savannah model” was developed for predicting salinity intrusion impactsrncaused by a proposed deepening of Savannah Harbor on the freshwater portion of the SavannahrnRiver. As part of the relicensing process for six hydroelectric facilities on the Pee Dee River byrnthe Federal Energy Regulatory Commission, the “Pee Dee model” was developed to determinernhow hydroelectric operations affect salinities at coastal intakes, which had experienced episodesrnof seawater inundation. Both models have unique features: 1) they were calibrated with 20 yearsrnof data that included near-historically low inflows and high sea levels caused by severe droughtsrnand hurricanes like those anticipated from climate change; 2) they were developed usingrnadvanced, multivariate, multi-spectral artificial neural network-generated empirical modelingrntechniques that make them significantly more accurate than conventional mechanistic modelsrnover the widely ranging input conditions; and 3) they are deployed as Excel? spreadsheetrnprograms so that they easily disseminated and used by all stakeholders.rnThe initial models runs were predominantly parametric, i.e., input sea levels and riverine flowsrnare ranged incrementally. AR4 predicts sea level increases of approximately ? to 2 feet,rnexcluding the melting of glacial ice in Greenland and Antarctica. This alone translates intorndoubling to quadrupling the frequency and duration of seawater intrusion events. The research also includes precipitation change scenarios predicted by a Global Circulation Model (GCM) thatrnwere “downscaled” to the study regions.