The complexities of urban flood response
Flood frequency analyses for the Charlotte metropolitan region
Zhengzheng Zhou (Princeton University, UNEP-Tongji Institute of Environment for Sustainable Development, Tongji University)
James A. Smith (Princeton University)
Long Yang (Princeton University)
Mary Lynn Baeck (Princeton University)
Molly Chaney (Princeton University)
Marie Claire Ten Veldhuis (TU Delft - Civil Engineering & Geosciences)
Huiping Deng (UNEP-Tongji Institute of Environment for Sustainable Development, Tongji University)
Shuguang Liu (Tongji University, UNEP-Tongji Institute of Environment for Sustainable Development)
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Abstract
We examine urban flood response through data-driven analyses for a diverse sample of “small” watersheds (basin scale ranging from 7.0 to 111.1 km2) in the Charlotte Metropolitan region. These watersheds have experienced extensive urbanization and suburban development since the 1960s. The objective of this study is to develop a broad characterization of land surface and hydrometeorological controls of urban flood hydrology. Our analyses are based on peaks-over-threshold flood data developed from USGS streamflow observations and are motivated by problems of flood hazard characterization for urban regions. We examine flood-producing rainfall using high-resolution (1 km2 spatial resolution and 15 min time resolution), bias-corrected radar rainfall fields that are developed through the Hydro-NEXRAD system. The analyses focus on the 2001–2015 period. The results highlight the complexities of urban flood response. There are striking spatial heterogeneities in flood peak magnitudes, response times, and runoff ratios across the study region. These spatial heterogeneities are mainly linked to watershed scale, the distribution of impervious cover, and storm water management. Contrasting land surface properties also determine the mixture of flood-generating mechanisms for a particular watershed. Warm-season thunderstorm systems and tropical cyclones are main flood agents in Charlotte, with winter/spring storms playing a role in less-urbanized watersheds. The mixture of flood agents exerts a strong impact on the upper tail of flood frequency distributions. Antecedent watershed wetness plays a minor role in urban flood response, compared with less-urbanized watersheds. Implications for flood hazard characterization in urban watersheds and for advances in flood science are discussed.