Doctor of Philosophy (PhD)


Geography and Anthropology

Document Type



Extreme daily temperatures are meteorological events that can have significant impacts on human and natural systems. As natural and anthropogenic climate changes occur, the frequency of extreme events is likely to change. Because extremes do not change linearly with mean temperatures, it is important to directly examine the record of extremes. This dissertation analyzes the temporal pattern of daily extremes over 1948-2001 in the south-central United States, and identifies significant changes in frequency and persistence, as well as relationships between extreme events and atmospheric circulation.

A global warming of approximately 0.6 Centigrade has occurred over the past century, and further warming is projected for the next century. Global warming has occurred more strongly in minimum temperatures than in maximums. Trends have varied spatially, however, and the southeastern U.S. has experienced a general cooling in maximum temperatures in recent decades. This dissertation confirms that temperature trends in the south-central U.S. have differed from the global mean, and describes the corresponding changes in extreme daily event frequencies.

Multivariate cluster analysis is used to identify seven distinct sub-regions in the study area. These sub-regions appear to be related to macro-scale climate-controlling factors, such as elevation and continentality. This regionalization provides spatial foci for this research, as well as useful regions for future projects relating circulation or GCM output to surface conditions.

For the past half-century, significant trends in monthly-mean temperatures and intra-monthly temperature variability have been identified in the study area. These trends vary spatially and temporally in direction and strength, but the dominant pattern is decreasing mean maximum temperature through the region. This overall cooling differs from the observed global warming over this period.

Generally negative trends in the frequencies of both extreme high maximum temperatures and extreme low minimum temperatures have been found in the region. Also, the frequency of consecutive extreme high-temperature days is decreasing.

Temperature means, variabilities, and extreme events have been found to be significantly related to hemispheric-scale circulation. These relationships are strongest during the cold season, when mid-tropospheric circulation is strongest. These relationships should prove valuable in assessing the regional implications of projected circulation patterns.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Robert V. Rohli