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Climate Change Assessment for Water Resources Region 03 South Atlantic -Gulf unnatural (i.e., anthropogenic greenhouse gas emissions) forcings. When additional detail is needed the reader is referred to the specific references cited, including the third National Climate Assessment (NCA), which includes not only regional assessments, but also foundational resources related to climate science literacy. The climate trends presented in this section are based on peer- reviewed literature on the subject of observed climate. To the extent possible, studies specific to the South Atlantic -Gulf Region or its sub - watersheds were relied upon. A focus is placed on identified primary variables including: • mean temperature • extreme temperatures • average precipitation • extreme precipitation events • mean streamflow In addition to primary variables, peer- reviewed literature addressing climate change within the geographic region or inclusive of the Water Resources Region revealed additional, secondary, climatic variables that have been studied such as the spring index (SI), drought indices, and soil moisture. The results presented below indicate a mild upward trending in temperature and a mild downward trending in streamflow in the South Atlantic -Gulf Region, particularly since the 1970s. However, clear consensus does not exist for either. Studies on precipitation show mixed results but with more findings showing an upward, rather than downward, pattern over the past 50 to 100 years. 2.1. Temperature A number of studies focusing on observed trends in historical temperatures were reviewed for this report. These include both national scale studies inclusive of results relevant to Water Resources Region 03 and regional studies focusing more specifically and exclusively on the area. Results from both types of studies are discussed below. A 2009 study by Wang et al. examined historical climate trends across the continental United States. Gridded (0.5 degrees x 0.5 degrees) mean monthly climate data for the period 1950 — 2000 were used. The focus of this work was on the link between observed seasonality and regionality of trends and sea surface temperature variability. The authors identified positive statistically significant trends in recent observed mean air temperature for most of the U.S. (Figure 2.1). For the South Atlantic -Gulf Region, mixed results are presented. A positive, but mild, warming trend is identified for most of the area in the spring and summer. For the fall months, the southern portion of the area is shown to be warming while mild cooling is shown in the northern portion of the area. For the winter months, the divide appears to be more east -west, with warming in the east and cooling in the western portion of the area. A later study by Westby et al. (2013), using data from the period 1949 — 2011, moderately contradicted these findings, presenting a general winter cooling trend for the entire region for this time period. The third NCA report (Carter et al., 2014) presents historical annual average temperatures for the southeast region. Their southeast study region is larger than, but inclusive of the South Atlantic -Gulf USACE Institute for Water Resources 7 January 9, 2015