Incorporating Overland Flow into the WRF Noah-MP Land Surface Scheme and Applying to a Record Flood Simulation in the Pearl River Basin

With global warming, the intensity and frequency of floods have markedly increased, resulting in substantial losses of life and property. The Pearl River basin (PRB) in South China, with its complex topography, remains highly susceptible to flooding. To enhance the precision of flood simulation and forecast in the PRB, an overland flow scheme was first integrated into the community Noah land surface model with multiparameterization options (Noah-MP) and subsequently coupled with the Weather Research and Forecasting (WRF) Model. These models were applied to a record precipitation event occurring over the PRB in April 2024 to validate their improvements. Results reveal that the modified Noah-MP can effectively simulate hydrological processes. The cumulative surface runoff is strongly affected by topography and has a higher magnitude in low-lying areas. The accumulated water depth generally aligns with the satellite-observed inundation, and the error in soil moisture between the model and the observation is reduced. Further, the modified WRF Model has successfully reproduced the inundation area in most regions, contrasting with the original scheme's inability to simulate flooding. In addition, the improvement in hydrological processes in the modified WRF also enhances the ability to simulate precipitation through land-atmosphere interactions. A comparison with the WRF-Hydro simulations further demonstrates that our scheme achieves a certain degree of improvement in simulating inundation. This study presents a promising approach for improving flood simulations in complex topography, which is instrumental in mitigating the loss of life and property caused by flood disasters in the PRB.