| The consequences of a flood are amplified when it occurs in urban environments by virtue of the large concentration of people and wealth affected. This dissertation is devoted to advancing the understanding of the ways that warm season thunderstorm systems interact with the urban environment to produce flooding. The area of study is the northeastern United States with particular focus over the urban environments of Baltimore, Washington, DC, and New York City. The complex topography of the northeastern United States, with the Appalachian Mountains to the west, and the land-ocean boundary to the east of the heavily urbanized northeastern corridor, presents the analyses with great challenges. At the same time, it increases their relevance since most of the world's urban cores are built close to complex terrain. Warm season thunderstorm systems that produce short-duration, high-intensity rain-fall events are shown to be the major flash flooding agents over the urban corridor of the northeastern US. Established theories of inadvertent weather modification by urban environments are put to the test with the use of advanced models and multiple observational techniques. The results reveal unexplored links of inadvertent weather modification arising from synergies between the urban canopy layer and the land-ocean boundary. Aerosols are also shown to play an important role in rain-fall enhancement, under certain environmental conditions that are examined through combined observational analyses and numerical model experiments. The last part of this dissertation is devoted to synthesizing the links between flooding and the urban environment to perform a critical review of the US flood policy framework. Projections of end-of-the 21st Century annual flood costs are made, and recommendations are provided for a modernization of the policy framework to more efficiently mitigate the effects of floods in the future. |
