Doctor of Philosophy (PhD)
Geography and Anthropology
The continual growth of urban areas increasingly affects the environment on various spatial scales. Land cover changes, combined with decreasing vegetative cover and addition of atmospheric aerosols, potentially lead to growing urban heat islands that alter the local moisture fluxes directly or indirectly, which in turn play a role in precipitation initiation and development. Some studies suggest that a region of enhanced rainfall exists downwind of the main urban area and that frontal systems decelerate as they reach areas of high urban development. Six urban areas within the southeastern United States were examined for possible urban precipitation enhancement: Atlanta, Birmingham, Dallas/Fort Worth, Houston, Memphis, and Tulsa. Three tests were employed to detect the existence of urban-enhanced precipitation: (1) “downwind vs. upwind” test, (2) temporal analysis, and (3) the “contour” test. Houston, Memphis, and Tulsa exhibited possible urban influence, while Birmingham showed some urban influence. Dallas/Fort Worth displayed likely urban influence while Atlanta showed no urban influence. A thorough, case study-based analysis of storm bifurcation occurrence in two urban areas (Atlanta and Dallas/Fort Worth) and one control site (Columbus, MS) was also conducted using radar-derived precipitation estimates of heavy precipitation days (≥ 25 mm). Bifurcation likely occurred in Atlanta, but little evidence was seen for Dallas/Fort Worth, unless opposing factors masked the effects of bifurcation. Little evidence for bifurcation was found for Columbus. Finally, the degree of synoptic control over the heavy precipitation events and the cases of bifurcation were assessed. The first circulation-to-environment approach, the PCA scheme, showed trough-to-ridge circulation regimes and strong baroclinic zones as the dominating circulation types. The second circulation-to-environment approach, the Spatial Synoptic Classification scheme, was inconclusive as it revealed no significant link between heavy precipitation bifurcation events and synoptic pattern. Finally, composite 500 and 700 hPa geopotential heights during bifurcation days confirmed that trough-to-ridge flow patterns were most common among bifurcation days for Atlanta and Columbus. Dallas/Fort Worth exhibited a zonal flow, thereby displaying less upper-level support for surface frontal activity. These results will assist environmental planners in understanding the impact of urban areas on their surrounding regional environment.
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Trevino, Anna Marie, "Mechanisms of urban influence on precipitation in the southeastern United States: precipitation enhancement, storm bifurcation, and synoptic characteristics" (2012). LSU Doctoral Dissertations. 1893.