Spotlight article “Flood hazards in urban environment”

Georisk launched the “Spotlight” series in 2013. The purpose of this series is to invite distinguished scholars and practitioners to review an important topic, to highlight research gaps and to suggest fruitful research directions. Volume 17, Issue 2 (2023) of Georisk is pleased to present a Spotlight Article on “Flood hazards in urban environment” by five prominent researchers in the field, Liang Gao, Limin Zhang, Yang Hong, Hongxin Chen and Shijin Feng. Prof. Gao is an assistant professor at the State Key Laboratory of Internet of Things for Smart City and Faculty of Science and Technology, University of Macau, Macao, China. Her research focuses on developing numerical methods for simulating water-related hazards and integrating remote sensing techniques with numerical models. Her research has been supported by several funding agencies. She also serves on the Editorial Board of Georisk. Prof. Zhang is Head and Chair Professor in the Department of Civil and Environmental Engineering of the Hong Kong University of Science and Technology. He is also Director of Geotechnical Centrifuge Facility and Associate Director of GREAT Smart Cities Institute. Prof. Zhang is Editor-in-Chief of Georisk. He received the 2023 Ralph B. Peck Award from the American Society of Civil Engineers (ASCE). Prof. Hong is Chair Professor with NOAA/National Weather Centre and the University of Oklahoma. His research interests include hydrological modelling, water resources management, radar and satellite remote sensing retrieval/validation/application, and data assimilation systems for improved hazard prediction under a changing climate. Dr Hong has published more than 350 refereed articles, books and book chapters, which have been cited for more than 23,000 times. Prof. Chen is an associate professor in the Department of Geotechnical Engineering of Tongji University. His research interests include geoenvironmental engineering and numerical modelling of natural hazards. He is Associate Editor of Natural Hazards Review-ASCE and Journal of Intelligent Construction. Prof. Feng is Chair Professor of the Department of Geotechnical Engineering of Tongji University. His research interests include geoenvironmental engineering and soil dynamics. He was Young Chief Scientist of the “973 Program” and the recipient of the National Science Fund for Distinguished Young Scholars and first-class prize of Shanghai Science and Technology Progress Award. Effective urban flood risk management requires accurate estimation of flood inundation extent and fast information exchange. The urban environment is featured by anthropogenic changes, impervious land cover, artificial surface and underground drainage systems, and densely populated building clusters. Urban flood hazard analysis is therefore more challenging. This Spotlight Article presents a critical review of the basic theory, major urban environment factors, modelling approaches and uncertainties related to the evaluation of flood hazards in urban environment. It starts by reviewing the state of the knowledge of urban floods from a multi-disciplinary viewpoint, followed by presenting physics-based modelling approaches and urban environmental factors. Numerical modelling of storm water flows in the urban settings has become a standard practice. Modelling capabilities that incorporate surface runoff and conduit flows are essential in predicting urban flood hazards and presenting spatiotemporal analysis results. Urban environmental factors such as building distribution, impervious surface representation, and integration of overland flow, and drainage network flow must be properly represented in hazard assessment. Uncertainties in hydraulic modelling processes originate mainly from input data, model parameters, model structures and validation processes. When a hydraulic model is calibrated and applied for prediction, uncertainties also arise from the variability of the calibrated parameters, validation algorisms, assumptions and limitations of the analysis models. Promising progress in understanding the processdependent indicators relies on the development of both improved measurement techniques and physical models. A data-rich environment encourages the development of new models and new insights. The authors opined that evaluating storm-induced flood hazards in an urban environment is a multi-