While the methodology and data sources of Thieler and Hammar-Klose (2000b) (fig. 10) were used to generate an initial CVI for the Northern Gulf of Mexico in this report, recent studies have also been utilized to update variables within the CVI framework without significantly altering the methodology. Updates to the original CVI datasets include: a change from NOS water-level records to a subsidence and sediment load model (Ivins and others, 2007) for sea-level rise rate, and updates to the shoreline change database to include land-loss data (Barras and others, 2008) for Louisiana and shoreline change along sandy shores (Miller and others, 2004) and the Louisiana Gulf Coast (Martinez and others, 2006). Updated variables for shoreline change and land-loss do not have the same coverage extent as the original CVI; thus a CVI for the entire study area based solely on updates of shoreline change or land-loss rates cannot be produced. However, an updated CVI that accounts for 91 percent of the shoreline in the original variable CVI is calculated with higher resolution data sources. These higher resolution datasets capture local to regional changes in vertical movement, slope, and shoreline and land-area change and improve the resolution and applicability of the CVI assessment. CVI assessments are still limited by the omission of coastal storm information, and the episodic and nonlinear nature of storms makes them difficult to incorporate into the CVI framework. The CVI results presented in this report are an indication of vulnerability based on coastal processes and geologic qualities that are ever-present and predictable and should be used in conjunction with storm vulnerability studies within the region (for example, Stockdon and others, 2007; Fearnley and others, 2009; Doran and others, 2009) in order to obtain the most comprehensive vulnerability assessment.

The update in figure 11 has the same vulnerability ranges as the original data source CVI in figure 10, and there are some similarities and differences between the original and updated source CVIs that are important to point out. The update CVI (fig. 11) ranks the majority of the Mississippi Delta as very high vulnerability, a similar result to the original CVI where the Mississippi Delta is ranked as high to very high vulnerability. While it is not surprising that the Mississippi Delta region is high to very high vulnerability in both determinations, the updated CVI ranks most of the Florida panhandle as low vulnerability. However, in the original source CVI, the Florida panhandle is mostly moderate vulnerability. Furthermore, the updated CVI shows that the Chenier Plain and Texas coast, with low vertical movement rates and low shoreline change rates, may be more vulnerable to sea-level rise than the Florida panhandle coast. This difference is likely due in part to slightly larger wave heights off the coast of Texas.

Although the overall differences between the original and the updated CVI for the Northern Gulf of Mexico may be slight, the vulnerability pattern in the updated data source CVI seems to be more consistent with regional geology than was the original CVI. This is especially apparent in the first principal component of the updated CVI, where the direct relationship between sea-level rise and shoreline change or land loss is responsible for nearly half of the CVI variance. In the original CVI, wave height alone is the primary variable in the first principal component, because the lower resolution SLR and shoreline change data do not capture many of the local to regional variations in sea-level and shoreline change.