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Climate Change Assessment for Water Resources Region 03 South Atlantic -Gulf Figure 2.6. Linear trends in annual precipitation, 1895 — 2009, percent change per century. The South Atlantic -Gulf Region is within the red oval (McRoberts and Nielsen- Gammon, 2011). Changes in extreme precipitation events observed in recent historical data have been the focus of a number of studies. Studies of extreme events have focused on intensity, frequency, and /or duration of such events. Wang and Zhang (2008) used recent historical data and downscaled Global Climate Models (GCMs) to investigate changes in extreme precipitation across North America. They focused specifically on the changes in the frequency of the 20 -year maximum daily precipitation event. The authors looked at both historical trends in observed data and trends in future projections. Statistically significant increases in the frequency of the 20 -year storm event were quantified across the southern and central U.S., in both the recent historical data and the long -term future projections (described below). For the South Atlantic -Gulf Region, significant changes in the recurrence of this storm were identified for the period 1977 — 1999 compared to the period 1949 — 1976. An increase in frequency of approximately 25 to 50% was quantified. Pryor et al. (2009) performed statistical analyses on 201' century rainfall data to investigate for trends across a range of precipitation metrics. They used data from 643 stations scattered across the continental U.S. For the South Atlantic -Gulf Region, the analysis showed generally increasing, and statistically significant, trends in the number of precipitation days per year (Figure 2.7 d). However, no clear trends for the region were evident for total annual precipitation, extreme high precipitation events (901' percentile daily), or precipitation intensity (Figure 2.7 a — c). The authors note that the trends identified are not necessarily linear, with an apparent increase in the rate of change in the latter part of the century for most of the trends. USACE Institute for Water Resources 13 January 9, 2015