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Climate Change Assessment for Water Resources Region 03 South Atlantic -Gulf <br />w,r T ,: <br />) <br />(All 26 <br />366 5 <br />C): <br />GMT .;..2..5 <br />C;;`02 560 <br />BNORC l.alUC <br />wa'wr N kekJ 4 Vault s 4VVIIM <br />I'll M1 <br />Figure 3.14. Projected change in water yield (from historical baseline), under various climate <br />change scenarios based on 2 GCM projections. The South Atlantic -Gulf Region is within the <br />red oval (Thomson et al., 2005). <br />The results presented by Thomson et al. (2005), described above, highlight the significant <br />uncertainties associated with global climate modeling, particularly with respect to hydrologic <br />parameters. Additional uncertainty is generated when these climate models are combined with <br />hydrologic models that carry their own uncertainty. This comparison and quantification of <br />uncertainty is the subject of a 2013 study by Hagemann et al. In this study, the authors apply <br />three GCMs, across two emission scenarios to seed eight different hydrologic models for <br />projecting precipitation, ET, and runoff on a global scale. Their findings, in agreement with <br />CDM Smith (2012), indicate that the uncertainty associated with macro -scale hydrologic <br />modeling is as great, or greater, than that associated with the selection of climate models. Study <br />projections from Hagemann et al. (2013) for the general South Atlantic -Gulf Region show an <br />overall decrease in runoff by approximately 200 mm per year for their future planning horizon <br />(2071 — 2100) compared to the recent historical baseline (1971 — 2000) (Figure 3.15), assuming <br />an A2 emissions scenario. <br />USACE Institute for Water Resources 31 January 9, 2015 <br />