Analysis of Characteristics of Heavy Rain and Flood in Rongjiang County, Guizhou Province in June 2025

Under the intensifying impacts of global climate change amplifying the frequency and intensity of extreme precipitation, Rongjiang County in Guizhou Province experienced an unprecedented catastrophic flood event in June 2025, surpassing the 50-year recurrence standard. This study aims to unravel the spatiotemporal dynamic formation mechanisms and disaster chain amplification effects of such floods, providing theoretical and practical paradigms for flood prevention in analogous river basins. Methodologically, the study integrated multi-source datasets, including hourly high-resolution precipitation from CMA-CLDAS v2.0, flow records from the Shihuichang Hydrological Station, 30 m digital elevation model (DEM) data, and Landsat 8 imagery. Rainfall migration was spatially tracked, and ArcGIS-based spatial analysis delineated three sub-basins (Duliujiang River Mainstream, Pingyong River, and Zhaihao River) to quantify the shifting trajectory of precipitation cores. DEM data were employed to reconstruct inundation processes and analyze flood extents. Land use change analysis further quantified the expansion of impervious surfaces and their detrimental impact on reduced infiltration capacity. The results uncovered a distinctive bimodal rainfall structure, featuring two intensive phases of June 21-25 and June 27-29. The first phase delivered a peak hourly intensity of 40 mm, while cumulative rainfall at Pingyang Station reached 434 mm, equivalent to 50% of the region's annual average. Critical to disaster formation was the eastward migration of precipitation cores: initial heavy rainfall over the Duliujiang River Mainstream (June 21-23) was followed by sustained precipitation over the Pingyong and Zhaihao basins (June 24-29), creating synchronized flood peaks that converged at Rongjiang's urban confluence zone. This hydrological convergence, amplified by steep canyon topography accelerating runoff concentration and downstream cascade sluice gates impeding discharge, generated unprecedented flood metrics. The Shihuichang Hydrological Station recorded a historic peak discharge of 11 400 m³/s (63.6% higher than the previous record in 2016) and a water level of 256.71 m, inundating 80% of the county seat with maximum depths exceeding 2 m. The catastrophe caused direct economic losses surpassing 1 billion yuan (USD 140 million), including critical infrastructure damage. This disaster epitomized the compound effects of three interlocking mechanisms: climate-driven persistent extreme rainfall, topographical constraints of a three-river confluence basin, and anthropogenic landscape modifications reducing hydrological resilience. To address these multifaceted challenges, this study proposed an integrated four-pillar mitigation framework: First, enhancing precipitation monitoring capabilities through the deployment of dense rain gauge networks synergistically coupled with real-time hydrodynamic forecasting models, enabling early flood warnings. Second, implementing strategic hydraulic engineering solutions, including the construction of the Zhongcheng Reservoir and prioritized river channel widening along critical reaches from Toutang Village to Shihuichang. Third, advancing eco-hydrological restoration through the establishment of riparian buffer zones and systematic optimization of watershed vegetation structures to amplify rainwater interception and soil infiltration capacities. Fourth, institutionalizing adaptive governance mechanisms through risk-informed urban spatial planning and market-based flood insurance schemes to systematically reduce socioeconomic vulnerabilities. This integrated approach provides a transferable blueprint for flood resilience in mountainous river basins confronting climate change uncertainties.