Parameter dynamics of distributed hydrological model in simulating or forecasting flood processes of urbanizing watersheds

Abstract. In the past decades, the world has experienced rapid urbanization and observed the appearances of large amount urbanizing watersheds with enhanced flooding, which has a constant changing land use/cover(LUC) types as the most significant feature. Simulating and forecasting urbanizing watershed flood processes faces great challenges, one is how to relate model parameters with the changing LUCs to secure an accurately and reliable simulation and forecasting results. In this study, a methodology for simulating and forecasting urbanizing watershed flood processes is proposed, which employs Liuxihe model as the watershed hydrological model. This methodology sets up the Liuxihe model with latest terrain properties, then derives initial parameter look-up table based on terrain properties, and optimizes it if there is observed hydrological data. If there is LUC changes, then the parameters are updated with the changed LUCs based on the optimized parameter look-up tables. Case study in a highly urbanizing watershed in the Pearl River Delta Area in southern China has shown that this method acquires accurate and reliable flood processes simulation results. Further more, this study has proven an assumption that the hydrological model parameters are LUC stationary, i.e., with the LUC changes, the parameter look-up table will not change, parameter look-up table optimized in a specific time with current LUCs will not change even the LUCs changed. With this assumption, the parameter look-up table only needs to be optimized once. This is a science question that has not been not well answered yet by the scientific communities.