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Climate Change Assessment for Water Resources Region 03 South Atlantic -Gulf least a few days later for the current period (2001 — 20 10) compared to an earlier baseline reference decade (1951 — 1960) (Figure 2.2). This is particularly evident for the north and west portions of the area. In other words, an apparent small shift in seasons has been identified for most of the South Atlantic -Gulf Region, with spring warming occurring later than in the past. �* If 'r * * * 0 ",l 4 Figure 2.2. Change in spring onset (first leaf date), in days for 2001 — 2010 compared to 1951 — 1960. The South Atlantic -Gulf Region is within the red oval (Schwartz et al., 2013). A 2011 study by Obeysekera et al. focused on identifying climate (temperature and precipitation) trends for South Florida using historical data. This study examined a number of climate metrics with data extending back to the 1890s. For all of the metrics, including average and maximum daily temperatures, number of hot days, and extreme temperature events, no discernible trends were found for their study region. While some climate stations showed an increasing trend, just as many displayed a decreasing trend, and even more showed no trend at all. Two years later, many of these same authors conducted a similar study of climate stations distributed across the entire state of Florida (Irizarry -Ortiz et al., 2013). They found similar results, although focused on slightly different metrics. Based on the same historical observation period as the 2011 study, no consistent, discernible trend in daily average temperature was found. However, the authors present evidence of increasing trends in the number of extreme heat days and in daily minimum temperature, with many stations exhibiting statistically significant increasing trends in one or both of these metrics. A 2012 study by Patterson et al. focused exclusively on historical climate and streamflow trends in the South Atlantic region. Monthly and annual trends were analyzed for a number of stations distributed throughout the South Atlantic -Gulf Region for the period 1934 — 2005. Results (Figure 2.3) identified a largely cooling trend for the first half of the historical period and the period as a whole. However, the second half of the study period (1970 — 2005) exhibits a clear warming trend with nearly half of the stations showing statistically significant warming over the period (average increase of 0.7 °C). The circa 1970 "transition" point for climate and streamflow in the U.S. has been noted elsewhere, including Carter et al. (2014). Trends in overnight minimum temperatures (Turin) and daily maximum (TmaX) temperatures for the southeast U.S. were the subject of a study by Misra et al. (2012). Their study region encompasses nearly the full extent of the South Atlantic -Gulf Region and used data from 1948 to 2010. Results of this study show increasing trends in both Tmin and TmaX throughout most of the study region. The authors attribute at least a portion of these changes to the impacts of urbanization and irrigation. USACE Institute for Water Resources 9 January 9, 2015