Andrew J. Miller

Extreme hydrometeorological events and the urban environment: Dissecting the 7 July 2004 thunderstorm over the Baltimore MD Metropolitan Region

[1]xa0Observational analyses and mesoscale modeling studies, using the Weather Research and Forecasting (WRF) model, are used to dissect the mechanisms associated with record lightning, rainfall, and flooding over the Baltimore metropolitan region on 7 July 2004. Storm evolution on 7 July 2004 exhibited characteristic features of warm season thunderstorms producing flash flooding over the Baltimore–Washington DC metropolitan region. The storm system was initiated along the Blue Ridge mountains, with model simulations suggesting that convergence-induced spin-up of a meso-low was responsible for initial thunderstorm development. Observations and model analyses show that thermal effects associated with Chesapeake Bay had a pronounced impact on storm evolution and rainfall distribution. Analyses of radar reflectivity and lightning observations suggest that the urban environment played a significant role in storm evolution and heavy rainfall distribution. Model analyses show that urban canopy effects from both the Baltimore and Washington DC urban regions play an important role in determining the storm environment associated with heavy rainfall. Urban Heat Island effects did not play a significant role in the storm evolution. Observations of aerosols and drop-size distributions from a vertically pointing LIDAR and a disdrometer and model analyses suggest that the aerosols may have played an important role in stimulating efficient precipitation mechanisms and extreme rainfall rates for the 7 July 2004 storm.

Coupling of the Water Cycle with Patterns of Urban Growth in the Baltimore Metropolitan Region, United States†

Regional municipal water plans typically do not recognize complex coupling patterns or that increased withdrawals in one location can result in changes in water availability in others. We investigated the interaction between urban growth and water availability in the Baltimore metropolitan region where urban growth has occurred beyond the reaches of municipal water systems into areas that rely on wells in low-productivity Piedmont aquifers. We used the urban growth model SLEUTH and the hydrologic model ParFlow.CLM to evaluate this interaction with urban growth scenarios in 2007 and 2030. We found decreasing groundwater availability outside of the municipal water service area. Within the municipal service area we found zones of increasing storage resulting from increased urban growth, where reduced vegetation cover dominated the effect of urbanization on the hydrologic cycle. We also found areas of decreasing storage, where expanding impervious surfaces played a larger role. Although the magnitude of urban growth and change in water availability for the simulation period were generally small, there was considerable spatial heterogeneity of changes in subsurface storage. This suggests that there are locally concentrated areas of groundwater sensitivity to urban growth where water shortages could occur or where drying up of headwater streams would be more likely. The simulation approach presented here could be used to identify early warning indicators of future risk.