Flash Flood Risk Assessment in the Context of Economic Change Scenarios

Abstract

Abstract Flash flood disasters pose a constant threat to socioeconomic factors in southeastern China. This study analyzes the risk change of flash floods in the Yantanxi River basin, southeastern China, under five economic scenarios [shared socioeconomic pathways (SSPs); SSP1, SSP2, SSP3, SSP4, and SSP5]. We built a regional flash flood hazard assessment model by combining hydrological and hydrodynamic models with fieldwork. Asset value was used to represent regional exposure, which was spatialized using data from industrial structure and land use. Flash flood risk assessment influenced by economic change was developed using different industry responses to flash floods. The results clarify how economic factors drive flash flood risk changes. The return period of the 2019 flash flood in the Yantanxi River basin is 150 years. In 2019, flash floods affected 5.04% of the river basin; the inundation depth was concentrated at under 2.00 m, resulting in CNY 0.55 billion in economic damage. With economic change, the flash flood risk increases by 91.34% (SSP2—current economic development level) and 94.39% (SSP5—extreme economic development level). This study emphasizes the balance between economic development and disaster management at the river basin scale; in addition, our method provides a reference for risk assessment in flash-flood-prone areas lacking statistical information. Significance Statement The mountainous and hilly areas of southeastern China are vulnerable to flash floods, and the region faces a constant threat from flash flood disasters. The analysis of historical flash flood disaster events is a critical step in understanding the current rank of the disaster risk and its changes over time. The Supertyphoon Lekima–extreme precipitation–flash flood chain effects resulted in severe economic damage and casualties within the Yantanxi River basin, Zhejiang Province, in August 2019, thus raising concerns about the characteristics of flash floods within the region. The study results highlight the importance of flood risk management in regional adaptation strategies and provide new information for regional planning and the construction of flood control facilities.