Contents lists available at ScienceDirect Sustainable Cities and Society journal homepage: www.elsevier.com/locate/scs Paradigm shift in engineering of pluvial floods: From historical recurrence intervals to risk-based design for an uncertain future Salar Haghighatafshar a, *, Per Becker b,c , Steve Moddemeyer d , Andreas Persson e , Johanna Sörensen f , Henrik Aspegren a,g , Karin Jönsson a a Water and Environmental Engineering, Department of Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden b Division of Risk Management and Societal Safety, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden c Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa d CollinsWoerman | Seattle Architects, 710 Second Avenue, Suite 1400, Seattle, Washington 98104-1710, USA e GIS Centre/Physical Geography and Ecosystem Science, Lund University, Lund SE-221 00, Sweden f Department of Water Resources Engineering, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden g Sweden Water Research AB, Ideon Science Park, Scheelevägen 15, SE-22370, Lund, Sweden ARTICLE INFO Keywords: Pluvial floods Urban flood risk Drainage infrastructure Climate change Deterministic design Probabilistic design ABSTRACT Precipitation is intrinsically associated with high uncertainty, which is exacerbated exponentially over time—especially concerning climate change. However, the current design practice in urban drainage infra- structure remains firmly bound to deterministic assumptions regarding the design load. This approach is too simplified—focusing only on the return period of the design event—and ignores the complexity of drainage systems and the potential changes in catchment hydrology and the at-risk valuable assets within. Therefore, the current design approach is inherently an unsustainable practice that cannot deal with extreme uncertainties associated with urban drainage and flood resilience in changing climate and society. This paper examines the current deterministic design practice and encourages a collective discussion on the need for a paradigm shift in the engineering of pluvial floods toward a risk-based design. We believe that adopting a risk-based design will partially address the uncertainty and complexity of climate and urban drainage, respectively, although a method for the new practice in a risk-based design paradigm must be developed. 1. Introduction The number of floods has been increasing globally (Fig. 1), and flood is now the most frequently reported climate-related disaster (UNDRR, 2018). Floods can be induced by storm surges (coastal flood), riverine processes (fluvial flood), and heavy rainfall (pluvial flood). Pluvial flooding occurs in urban areas that are associated with hy- draulic overloading of urban drainage systems, causing unintended inundation. Although the frequency of all 3 types of flood are affected by a changing climate, this paper focuses on urban pluvial flooding as an infrastructural challenge of urban design and planning that is antici- pated to be manageable in the urban environment. This facet is espe- cially important, because the United Nations projects that approxi- mately 68 % of the world’s population will be living in urban areas by 2050 (UN, 2018). In addition, the Intergovernmental Panel on Climate Change (IPCC) projects a higher frequency of extreme rainfall events (Hoegh-Guldberg et al., 2018; IPCC, 2014). Moreover, studies show that flooding is a growing threat to human wellbeing—both individual and social wellbeing—with substantial impacts on economy and environ- ment (Gardiner, 1994; Skougaard Kaspersen, Høegh Ravn, Arnbjerg- Nielsen, Madsen, & Drews, 2017; ten Veldhuis & Schleiss, 2017; Zeng, Guan, Steenge, Xia, & Mendoza-Tinoco, 2019). These estimates as well as flood consequences on economy, society and environment—i.e., the traditional pillars of sustainability (Feleki, Vlachokostas, & Moussiopoulos, 2018; Wilkins, 2008)—underscore the need for a cri- tical examination of current infrastructure design methods and sug- gestions for potential revisions. Pluvial flooding, in which the urban drainage system is over- whelmed, has the characteristics of both design failure—as a result of https://doi.org/10.1016/j.scs.2020.102317 Received 12 December 2019; Received in revised form 23 April 2020; Accepted 4 June 2020 ⁎ Corresponding author. E-mail addresses: Salar.Haghighatafshar@chemeng.lth.se (S. Haghighatafshar), per.becker@risk.lth.se (P. Becker), smoddemeyer@collinswoerman.com (S. Moddemeyer), andreas.persson@nateko.lu.se (A. Persson), johanna.sorensen@tvrl.lth.se (J. Sörensen), henrik.aspegren@chemeng.lth.se (H. Aspegren), karin.jonsson@chemeng.lth.se (K. Jönsson). Sustainable Cities and Society 61 (2020) 102317 Available online 06 June 2020 2210-6707/ © 2020 Elsevier Ltd. All rights reserved. T