Characteristics of urban lightning hazards for Atlanta, Georgia

Weather-related hazards are the result of interactions between the physical environment and the demographics of the community that experience them. Numerous studies have documented urban heat island (UHI) modification of cloud-to-ground lightning flash densities, but none have linked flashes to the underlying demographics. In this study, I compared flash and housing densities for 25 counties encompassing Atlanta, Georgia, using ordination and cartographic visualization. Over the interval 1992-2000, two densely populated suburban counties downwind from Atlanta (Gwinnett and Dekalb) exhibited the highest cloud-to-ground flash densities. By contrast, high population density counties located upwind (Cobb) and encircling the central city (Fulton) had relatively lower flash densities. Based on the interactions among demographics, flash density, and geographic position for a subset of counties, I outline four types of urban lightning hazards: emergent, UHI-augmented, UHI-suppressed, and non-interactive. For urban lightning hazards, the often invoked idea of 'more people equals more hazards' is to an extent simplistic. Urban areas have a large range of lightning hazards as heating nodes emerge, intensify, and shift in response to historically contingent patterns of growth.