Quantifying Flood Regulation Dynamics: A Systematic Approach

Floodplain urbanization shapes exposure to floods, and necessitates the deployment of structural water infrastructure (e.g., dams) to mitigate the exposure. While the flood regulation capacity of a basin is traditionally assessed by the total capacity of its infrastructures, the changing hydro-climatic factors and increasing floodplain urbanization creates continuously evolving demands on the system. These changes highlight flood regulation as a complex and multivariate challenge, yet a systematic framework to capture these dynamic interactions remains underdeveloped. This study introduces a novel quantification framework that models the key elements and the dynamics of flood regulation. Specifically, we quantify the floodplain urbanization pattern by the cumulative distribution function of Height Above Nearest Drainage (HAND), and estimate the pressure it poses on the infrastructures under different flood magnitudes (e.g., 100-year and 500-year floods) under different flood exposure levels. To test the proposed approach, we apply it to the Ganjiang River Basin in China, focusing on the interactions between Ji’An city and the upstream Wan’An Dam. We find that during a 100-year flood with urban expansion up to 2015, the Wan’An Dam must operate at 42.5% capacity to limit flood exposure in Ji’An to below 5%. The effectiveness of our framework is supported by validating results against historical flood data from the Ganjiang River Basin. Moreover, our analysis reveals a monotonic increase in flood regulation pressure as both urban exposure levels and flood magnitude rise. We further define a characteristic curve that synthesizes the interactions among all components of the system, which offers a systematic illustration of the dynamics at play. Our proposed framework represents the first standardized quantitative approach for assessing multivariate flood regulation dynamics, offering a valuable tool for probing into the complex interplay of flood regulation under changing climate and urbanization conditions at large scales.