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

Abstract

[1] Observational 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.

A relation between extreme daily precipitation and extreme short term precipitation

“…In addition, De Bilt is a non-coastal location where there is hardly or no effect of seawater temperatures on extreme precipitation therefore making it easier to link extreme precipitation to air temperature and Gwest. It is also recognized that urban areas may exacerbate formation of summer storms (Ntelekos et al 2008) due to the urban heat island and that this effect is also not reflected in the time series of De Bilt.…”

“…These scenarios are based on a large number of global and regional climate models. For urban drainage design, daily precipitation is less relevant; critical response times of storm sewerage and surface drains are in the order of minutes to hours (Smith et al 2002;Ntelekos et al 2008). Regional climate model output on peak precipitation for shorter time scales is not (yet) reliable enough to allow for a publishable estimate.…”

Urbanization, climate change and flood policy in the United States

“…This paper attempts a critical evaluation of the NFIP, as currently formulated, in the light of research results pertaining to the vulnerability of the urban environment to flooding and to our enhanced understanding of the climate system (see Changnon et al 2001;Pielke 2000;Downton and Pielke 2000;Hudgens 1999 for related studies). Conclusions are drawn from analyses of flood hazards in the Baltimore metropolitan region (Ntelekos et al 2007(Ntelekos et al , 2008Smith et al 2005aSmith et al , b, 2007Nelson et al 2006;Javier et al 2007) and in the New York City metropolitan area (Ntelekos et al 2009). The Baltimore Ecosystem Study (BES), which is an urban component of the US National Science Foundation's Long-Term Ecological Research (LTER) program, provides an exceptionally dense network of hydrologic monitoring systems for examining flood hazards.…”

“…Alterations of the land-surface environment associated with urbanization markedly increased flood magnitudes in the US during much of the 20th century for many urban watersheds (Leopold 1968). Increasing attention has also been given to the impacts of the urban environment on weather systems that produce extreme rainfall (Jin et al 2005;Ntelekos et al 2008;Shepherd 2005;Shepherd and Burian 2003;Changnon 1980).…”

Improving Heat-Related Health Outcomes in an Urban Environment with Science-Based Policy

“…However, the mid-Atlantic region of the United States has been inadequately studied within these contexts. Notable exceptions include studies of New York City's influence on precipitation systems (e.g., [20,21]) and research into the role of the Baltimore-Washington, D.C. urban area on urban heat island development and hydrometeorological responses [22].…”