| Summary: | Spatial and temporal trends in temperature and precipitation extremes were investigated for the Southeast United States for the period 1948 to 2012 using 27 extreme indices developed by Working Groups headed by the World Meteorological Organization. Results show region-wide warming in extreme minimum temperatures and cooling in extreme maximum temperatures. As a result, diurnal temperature ranges are decreasing for most stations. The intensity and magnitude of extreme precipitation events appear to be rising overall, though eastern sites are experiencing increasing dryness in some indices. Seasonal trends suggest that warming in minimum temperatures is most pronounced in summer and least pronounced in winter. Fall is becoming significantly wetter, while spring and summer are getting drier, on average.
Principal component analysis (PCA) was used to develop a regionalization of extremes for the Southeast. Results based on temperature extreme indices divided the Southeast into roughly equal western and eastern regions, suggesting that western and eastern stations tend to covary but in opposite directions. This likely reflects synoptic scale weather patterns that frequently affect the region throughout the year. A PCA based on precipitation extreme indices resulted in a greater number of small groups exhibiting similar modes of variability. A seasonality of extremes was further characterized for the Southeast. Extreme seasons tend to follow traditional 3-month definitions of seasons. An extended winter season may be defined as November to March, while summer occurs from June to August, peaking in July.
Based on analysis of state and local planning and policy from six case study sites across the Southeast, this research suggests that many existing efforts may contribute to climate mitigation and adaptation. Similarities appear in sector-based planning, largely in response to federal mandates, though levels of engagement differ between sites. Threats from changing temperature and precipitation extremes are addressed only to a limited extent. Leadership priorities, federal actions, wealth, population, and experience with hazards seem to influence state and local actions. Recommendations are offered to guide future climate planning and policy. Findings can benefit planners, policy analysts, decision makers, and hazards specialists engaged in climate adaptation and hazard mitigation in the Southeast and beyond.
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