Compound floods from upstream river discharge, localized rainstorm and storm surge across the Pearl River Delta megacity region: Risks, Changes and Mechanisms

Coastal urban areas are highly exposed to different types of floods, including but not limited to fluvial floods due to high upstream river discharge, pluvial floods resulting from localized rainstorms and inadequate drainage, and coastal floods caused by storm surge. Multiple types of floods can occur concurrently or in close succession under certain weather conditions such as frontal systems and typhoons, causing more serious social, economic and environmental consequences to low-lying coastal cities than the impacts of individual floods. Therefore, it is important for cities to develop multi-hazard risk management adapt to joint occurrences of multiple floods, or called compound floods. In recent years, compound floods receive more and more attention, and related investigations have been conducted but mainly limited to the US, UK, and Netherlands. Studies focusing on the Pearl River Delta megacity region (PRD) located in the downstream of the Pearl River Basin (PRB, the second largest river in China in terms of annual discharge) and situated by the South China Sea are very limited. As one of the most populous and developed megalopolises in China, the PRD has been frequently under the threats of high upstream river discharge, localized rainstorm, and severe storm surge. The rapid urbanization in recent decades, along with inadequate urban drainage capacity and more extreme climate have raised the risks of different types of floods in the PRD. Therefore, it is urgently needed to understand the risks, changes and mechanisms of compound floods in the PRD for decision makers and urban planners for adaptation to future climate change. The proposed study will develop high-quality datasets of river discharge, localized precipitation, and sea level. Joint flood risk analysis will be conducted to estimate the probabilistic behaviors of compound floods, as well as how they have changed in the past several decades over the PRD. Synoptic weather conditions during different types of compound floods will be analyzed to understand the mechanisms of these extreme events. Numerical simulations based on physically-based hydrological model and regional weather model will be carried out to evaluate how land use changes influence compound floods by altering land-atmosphere interactions and surface hydrological characteristics. The objectives of the proposed study are: (1) to evaluate risks of compound floods from high river discharge, localized rainstorm and/or storm surge across the PRD; (2) to estimate spatio-temporal changes in compound floods due to climate change and rapid urbanization across the PRD, and; (3) to unravel the mechanisms of compound floods in terms of weather conditions and land use changes. The study outcomes will provide strong scientific support for developing multi-flood management strategies and plans for the PRD and other coastal megacity regions in China.