Hydroclimatology of flash flooding in Atlanta

The objective of this study is to characterize the climatology of extreme rainfall and flash flooding in Atlanta, Georgia using high-resolution land surface, rainfall, and discharge datasets. We examine nine urban watersheds in the Atlanta area that range in size from 3.7 to 225 km ² and exhibit a range of urban development and land-use characteristics. We develop a high-resolution 15 min, 1 km ² radar rainfall data set for the 2002-2010 period using the Hydro-NEXRAD system with volume scan reflectivity observations from the Atlanta WSR-88D radar and rainfall observations from a dense network of 72 U.S. Geological Survey rain gauges. Bias-corrected radar rainfall fields accurately capture the spatial and temporal structure of heavy rainfall. There is enhancement of heavy rainfall within and east of the urban core, and a rainfall minimum north and northwest of the city. There has been an increase in variability of annual flood peaks in Atlanta since the 1960s associated with urban impacts on runoff production. Flood response is dependent on a combination of basin size, drainage network structure, spatial distribution of land use, and basin storage in urban soils and storm water detention ponds. Future studies of urban rainfall modification in Atlanta and elsewhere should consider the influence of regional topography and other geographic features on the storm environment.