Impacts of future climate change on urban flood risks: benefits of climate mitigation and adaptations

Abstract

Abstract. As China is urbanized, flooding has become a regular feature in major cities. Assessing potential urban flood risks under climate change has become crucial for better managing such risks given the severity of the devastating disasters (e.g., the current 2016 flooding across China). Although the impacts of future climate change on urban flood risks have been investigated in many existing studies, the effects of both climate mitigation and adaptations have rarely been accounted for in a consistent framework. In this study, we assess the benefits of (1) avoided greenhouse gas (GHG) emissions and (2) adapting drainage systems on urban flood risks within the context of global warming through a case study in the Northern China. The urban drainage model, Storm Water Management Model (SWMM), was employed to simulate urban floods under current conditions and two feasible adaptation scenarios (i.e., pipe enlargement and low impact development), driven by bias-corrected meteorological forcing from five general circulation models (GCMs) in the Coupled Model Intercomparison Project Phase 5 (CMIP5) archive Based on the results, the volume of urban floods is projected to increase by 52 % in the period of 2020–2040 when compared to that in 1971–2000 under the business-as-usual scenario (i.e., Representative Concentration Pathways (RCP) 8.5). The magnitudes of urban floods are found to increase nonlinearly with changes in precipitation intensity, and highest risks associated with floods with smaller return periods below 10 years are identified. Despite the high level of uncertainty, it is obvious that avoided greenhouse emissions will be beneficial in terms of reducing risks associated with urban floods. On average, the magnitude of projected urban floods under RCP 2.6 is 13 % less than that under RCP8.5, demonstrating the importance of global-scale efforts on GHG emission reduction in regulating local to regional hydrometeorological responses. Moreover, the two feasible adaptation scenarios are shown to be able to further reduce risk associated with floods effectively. This study highlights the importance of accounting for local climate adaptation efforts in assessing urban flood risks under a changing climate.