Increases in weather losses can, in part, be attributable to greater population densities in regions of the U.S. where severe weather is more common. At the broad scales over which these observations have been made, changes in the frequency and intensity of severe weather events are not clearly linked to human-induced climate change. At the smaller scales, however, such as urban regions where population is concentrated, human-induced modification of weather is more prominent. This investigation examines how the urban heat island augments convection among a range of cities in the southeastern U.S. The study develops a radar-based, warm-season climatology of convection for a multi-city region in the southeastern U.S., a thunderstorm-prone area that has seen substantial increases in urban population over the last two to three decades. The investigators will develop an urban/rural radar reflectivity climatology that will characterize the distribution of convection across several cities and rural control regions. By simultaneously assessing the patterns of reflectivity around six different sized cities plus two control regions under defined warm-season atmospheric environments, a comparative synthesis will be developed of where and at what intensities urban heat island-associated convection evolves over and in the periphery of cities. The investigators then will compare and contrast urban/rural radar reflectivity maximums for these locations and associate them with thunderstorm hazards. Finally, the development of a radar-based cell-tracking instrument will provide for the analysis of individual urban heat island enhanced events. This instrument will assess these events in terms of their orientation, meteorological setting, and their evolution relative to land use and elevation.
This research project will provide the first geographic synthesis of how urban heat island convection varies across cities of different sizes and topography. By stratifying convective events according to their reflectivity level, which is a surrogate of a storm's propensity for severe weather, the investigators will develop a set of observations that can inform researchers and practitioners regarding how cities enhance and lessen storm intensity, redirect their motion, and create hotspots of thunderstorm activity. A more complex view of the effects of differing land cover on convective storms is expected to emerge from this study, one in which interaction of surface properties, land-use, and urban modified weather patterns yield more geographic variability in thunderstorm intensity and associated hazards. The urban heat island enhancement is an important component in basic understanding of the role of land cover on shaping the distribution of thunderstorms and hazards. Furthermore, given predicted increases in thunderstorm frequency under a scenario of human-induced global warming, urban thunderstorms may amplify the economic relevance to weather and hazard planning policy. This research will permit researchers and practitioners to tune and deploy a methodological template for continued monitoring of thunderstorms in urban settings.
