Against the backdrop of climate change, the importance of Drought–Flood Abrupt Alternation (DFAA) events has become increasingly evident; however, their dynamic mechanisms within lake hydrodynamic systems remain insufficiently understood. This study reveals the spatiotemporal distribution characteristics of DFAA events in the Poyang Lake basin through hydrological analysis and the use of the Finite-Volume Coastal Ocean Model (FVCOM) for hydrodynamic simulations. Results indicate that mild events dominate, yet the occurrence of moderate and severe events has significantly increased over recent decades, particularly in the eastern part of the basin. Additionally, this paper pioneers the use of a numerical model to simulate hydrodynamic changes in lakes under extreme drought-to-flood (DTF) and flood-to-drought (FTD) scenarios, quantifying the spatial distribution and dynamic changes in flow velocity and bottom shear stress through model simulations. Findings show that, under extreme DFAA conditions, rapid drainage during FTD phases leads to flow velocity increases of up to 170% in narrow, deep channels, while bottom shear stress rises to 2.5–3 N/m², potentially enhancing sediment resuspension and intensifying the lake's hydrodynamic processes. This study provides crucial quantitative insights into lake hydrodynamic responses to extreme climate events, offering significant reference value for lake management.

With the increasing frequency of extreme rainfall events, enhancing urban drainage systems’ regulation capacity is crucial for mitigating urban flooding. Existing studies primarily analyze infrastructure impacts on peak flow delay but often lack a systematic exploration of time-lag mechanisms. This study introduces the time-lag parameter, using the hysteresis curve of the water level–flow rate relationship to quantify drainage system dynamics. An SWMM-based drainage model was developed for the Rongdong area of Xiong’an New District to evaluate the independent roles of green, gray, and blue infrastructures in peak flow reduction and time-lag modulation. The results indicate that green infrastructure extends the horizontal width and reduces the vertical height of the hysteresis curve, prolonging time lag and making it effective for small-to-medium rainfall. Gray infrastructure enhances drainage efficiency by compressing the hysteresis curve horizontally and increasing its vertical height, facilitating rapid drainage but offering limited peak reduction. Blue infrastructure, by lowering outlet water levels, improves drainage capacity and reduces time lag, demonstrating adaptability across various rainfall scenarios. This study systematically quantifies the role of each infrastructure type in time-lag regulation and proposes a collaborative optimization strategy for urban drainage system design.