Comparison of the Impacts of Topography and Urbanization on an Extreme Rainfall Event in the Hangzhou Bay Region

Abstract

AbstractThe impacts of topography and urbanization on an extreme rainfall (ER) event in the Hangzhou Bay (HZB) region were investigated using the Weather Research and Forecasting model with one control simulation and three artificial scenarios of no‐HZB, no‐mountains on the south bank of HZB, and no‐urban. Thirty members with different combinations of physical parameterizations were considered for each scenario. The control test results were evaluated and they showed that the model well reproduced the ER that occurred in the HZB region, and the ensemble results were valuable and credible. The existence of HZB, mountains, and urbanization would increase the ensemble mean of accumulated precipitation by 52.07%, 37.11%, and 9.35%, and the probability of heavy rainfall by about 25%, 20%, and 15% in the main rain belt region, respectively. In addition, these factors also introduced more uncertainties in the same physical scheme combination. The impacts of these factors on the distribution, intensity, and mechanism were different. The comparison results showed that the existence of HZB played the most important role in this ER event by the remarkable influence of low‐level wind field and horizontal convergence, followed by the existence of mountains, which mainly affected the distribution of rainfall caused by the airflow climbing up the hill before the mountain. Although urbanization exerted positive effects on this ER event, the impact was relatively small and locally near the urban regions compared with the other two factors.