Seasonal migration of flood risk: Multi-ecosystem threshold triggering and adaptive management

To gain a deeper understanding of the evolving characteristics of floods across different ecosystems and their meteorological driving conditions, in this study, a transferable, all-season, multi-ecosystem methodology for setting meteorological threshold warnings for floods of various magnitudes is established. An in-depth analysis of the differences in evolving flood characteristics and driving conditions between ecosystems that have been intensely disturbed by human activities and natural/seminatural systems is conducted. A flood management measure is proposed, which draws on the ecological resilience of forest and grassland systems. We emphasize that the philosophy of flood control should shift from hard-defence to adaptive governance. In the Yellow River Basin, the universal driving factors of floods are precipitation, humidity, and sunshine, with atmospheric pressure requiring additional consideration in water bodies and wetlands. Winter floods are most sensitive to sunshine percentage and precipitation, whereas floods in spring, summer, and autumn are primarily driven by humidity and sunshine hours. Since 1985, flood risk in the Yellow River Basin has entered a phase of persistent intensification. This intensification has accelerated across the entire basin in the 21st century and has reached 4–57 times the average rate of increase. Flood severity will continually rise throughout the basin. In this study, the peak flood months for each ecosystem are identified, with the most significant increases in flood momentum observed in January and September. The traditional summer-and-autumn flood season boundary has extended into winter and spring, indicating that flood risk in the Yellow River Basin has broken through traditional seasonal patterns and is intensifying across all seasons and multiple ecosystems. Human activities could increase flood risk. However, agricultural and settlement systems, which are entirely human-dominated, have the potential to mitigate floods in the long term through sustained management. Deserts are the most prone to triggering floods, grasslands carry the hidden danger of long-term persistent increases in flood risk, and floods in water bodies and wetlands are prone to evolving into high-intensity events. The research findings provide decision-makers with actionable pathways for flood early warning and adaptive management. • The flood risk in the Yellow River Basin has undergone seasonal shifts. • Key driving conditions for triggering floods vary by ecosystem and season. • Spatiotemporally differentiated thresholds for flood warnings are established. • Adaptive flood management strategies based on ecosystem resilience are proposed. • Human activities have increased the risk of floods.