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Climate Change Assessment for Water Resources Region 03 South Atlantic -Gulf words, the projections forecast small increases in the occurrence and intensity of storm events by the end of the 21" century for the general study region. In addition to the historical data trend analyses by Wang and Zhang (2008) described above, these authors also used downscaled GCMs to look at potential future changes in precipitation events across North America. They used an ensemble of GCMs and a single high emissions scenario (A2) to quantify a significant increase (c. 30 to 50 %) in the recurrence of the current 20 -year 24 -hour storm event for their future planning horizon (2075) and the general South Atlantic -Gulf Region (Figure 3.11). The projected increases in storm frequency presented by Wang and Zhang appear to be more significant than those projected by Tebaldi et al. (2006), but there is agreement on the general trend. Figure 3.11. Projected risk of current 20 -year 24 -hour precipitation event occurring in 2070 compared to historical (1974). A value of 2 indicates this storm will be twice as likely in the future compared to the past. Black dots show the locations of stations. The South Atlantic - Gulf Region is within the red oval (Wang and Zhang, 2008). The GCM applied in the Gao et al. (2012) study for the eastern U.S. generally projects increases in the magnitude of annual total (up to 200 mm yr 1) and daily (up to 20 mm day-') extreme (951' percentile) storm events and in the frequency of storm events (up to 5 days yr 1), for their 2058 planning horizon compared to current conditions (2001 — 2004) (Figure 3.12). The authors use a downscaled GCM to reproduce extreme weather events including hurricanes. Changes in the frequency and intensity of storm events were also the focus of a study by Wang et al. (2013a). These authors applied two GCMs to project future (2046 — 2069) design storm characteristics for the Florida panhandle. Results, in agreement with Gao et al. (2012), show a general shift upward of intensity- duration - frequency (IDF) curves, compared to historical baseline, for their three study sites (Figure 3.13). In other words, storm events are projected to be more intense and more frequent in the future compared to the past in northern Florida. USACE Institute for Water Resources 28 January 9, 2015