Assessing the role of urbanization on flashiness: case study analyses for Atlanta, Georgia

Using a WRF-based numerical modeling framework, case study analyses were conducted to assess the role of urban land cover on two high-impact flooding events across the metropolitan area of Atlanta, Georgia. An overarching goal of this study is to advance the concept of the urban rainfall effect (URE) from theoretical paradigms to applied hydrometeorological prediction. The URBAN simulated runs generally captured the magnitude and spatial coverage of extreme rainfall over and downwind of Atlanta, as compared to the observations. NO URBAN runs consistently underestimated extreme rainfall in both cases. Our results support previous studies that the urban environment can serve as an amplification mechanism when an environment is primed for convective processes. A key finding is that extreme rainfall – urbanization – flash flooding connections are partially explained by a “prime and pump” mechanism. Urban destabilization primes the environment with enhanced convective available potential energy (CAPE), while surface-based convergence spatially focuses the extreme rainfall. To further quantify how the URE translates to a flood hazard, we introduced a new model-based metric to represent hydrological “flashiness,” known as the Flash Flood Potential Index (FFPI). This may be one of the first attempts to quantify flashiness within a hydrometeorological modeling framework.