Practice of coupling and interconnecting "Three Lines of Defense" for rainfall and flood monitoring and forecasting in Lushui River Basin

Under the background of global warming, the increasing frequency of extreme rainstorm-induced floods poses severe challenges to traditional rainfall and water regime monitoring and forecasting systems. Focusing on the Lushui River Basin, a key flood control area in the middle reaches of the Changjiang River, this study established an integrated "sky-space-earth-water-project" monitoring and perception system in the basin, coupling hydrometeorological radar retrieval, rainfall fusion forecasting, rainwater retention capacity assessment, distributed hydrological modeling, hydrodynamic coupling computation, and "forward-reverse-forward" optimization. The resulting "Three Lines of Defense" framework spans "cloud precipitation-ground rainfall-riverine floods", which realizes full-chain accurate flood forecasting and proactive control. Application of this approach to the 2025 extreme rainfall event showed that it successfully limited the forecast error for the Lushui Reservoir′s inflow flood peak to within 3%, achieved a deterministic coefficient of 0.94 for the flood process forecast, and accurately predicted the end time of the heavy precipitation event three hours in advance. By comparing and recommending optimized reservoir operation schemes, it ensured the safe operation of the Lushui Reservoir. This achievement marks a shift in operational decision-making from passive response to active judgment, providing robust support for scientific and early decision-making in basin flood control operations.