Effects of Land Use Changes Across Different Urbanization Periods on Summer Rainfall in the Pearl River Delta Core Area

The Pearl River Delta(PRD)is one of the three urban agglomerations in China that have experienced rapid development.For this study,a core area of the PRD was identified,comprising the highly urbanized areas of Guangzhou,Foshan,Zhongshan,Zhuhai,Shenzhen,and Dongguan Cities.The expansion of these urban areas was tracked across three time periods—the year population urbanization rate exceeded 70%(2000),18 years before(1982),and 18 years after(2018).This study used the Weather Research and Forecasting(WRF)model to explore summer rainfall changes across different urbanization periods in the PRD core area.The results show that urban land expansion mainly occurred in the post urbanization period.Rainfall changes acros s different urbanization periods were roughly consistent with previously observed spatial and temporal changes accompanying urban expansion in the PRD core area.Extreme rainfall mainly increased in the post urbanization period,shifting rainstorm center towards the PRD core area.Further causal analysis revealed that land use changes affected rainfall by altering thermodynamics and water vapor transfer.The urban expansion changed the surface energy balance,resulting in increased surface heating and heat island effects.The heat island effects thickened the planetary boundary layer and increased vertical wind speeds,which initiated dry island effects,thereby causing more water vapor transportation to the atmosphere.Consequently,rainstorms and extreme rainfall events have become concentrated in urban areas.

Urban Stormwater Modeling with Local Inertial Approximation Form of Shallow Water Equations: A Comparative Study

This study focused on the performance and limitations of the local inertial approximation form model(LIM)of the shallow water equations(SWEs)when applied in urban flood modeling.A numerical scheme of the LIM equations was created using finite volume method with a first-order spatiotemporal Roe Riemann solver.A simplified urban stormwater model(SUSM)considering surface and underground dual drainage system was constructed based on LIM and the US Environmental Protection Agency Storm Water Management Model.Moreover,a complete urban stormwater model(USM)based on the SWEs with the same solution algorithm was used as the evaluation benchmark.Numerical results of the SUSM and USM in a highly urbanized area under four rainfall return periods were analyzed and compared.The results reveal that the performance of the SUSM is highly consistent with that of the USM but with an improvement in computational efficiency of approximately 140%.In terms of the accuracy of the model,the SUSM slightly underestimates the water depth and velocity and is less accurate when dealing with supercritical flow in urban stormwater flood modeling.Overall,the SUSM can produce comparable results to USM with higher computational efficiency,which provides a simplified and alternative method for urban flood modeling.

Simulation Performance Evaluation and Uncertainty Analysis on a Coupled Inundation Model Combining SWMM and WCA2D

Urban floods are becoming increasingly more frequent,which has led to tremendous economic losses.The application of inundation modeling to predict and simulate urban flooding is an effective approach for disaster prevention and risk reduction,while also addressing the uncertainty problem in the model is always a challenging task.In this study,a cellular automaton(CA)-based model combining a storm water management model(SWMM)and a weighted cellular automata 2D inundation model was applied and a physical-based model(LISFLOOD-FP)was also coupled with SWMM for comparison.The simulation performance and the uncertainty factors of the coupled model were systematically discussed.The results show that the CA-based model can achieve sufficient accuracy and higher computational efficiency than can a physical-based model.The resolution of terrain and rainstorm data had a strong influence on the performance of the CA-based model,and the simulations would be less creditable when using the input data with a terrain resolution lower than 15 m and a recorded interval of rainfall greater than 30 min.The roughness value and model type showed limited impacts on the change of inundation depth and occurrence of the peak inundation area.Generally,the CA-based coupled model demonstrated laudable applicability and can be recommended for fast simulation of urban flood episodes.This study also can provide references and implications for reducing uncertainty when constructing a CA-based coupled model.