Development and challenges of urban hydrology in a changing environment：Ⅱ：Urban stormwater modeling and management

Cities are suffering from extremely heavy rain and urban waterlogging disaster in recent years, due to the change in the natural hydrologic processes impacted by global climate change and rapid urbanization. The development and application of precipitation observation and forecasting, calculation methods for runoff generation and flow concentration, and urban stormwater simulation techniques are reviewed in the context of hydrological processing and modeling. The features, applicability and limitations of these techniques are discussed. The shortcomings and gaps of approaches on urban stormwater modeling, such as the lack of knowledge and the data to understand the response mechanism of the rainfall-runoff processes in the urban areas, are pointed out. The conceptual framework and flowchart for urban stormwater modeling is presented. Viewing from the prospective of rainwater utilization, essential principles and strategies on the urban stormwater management are presented, and the techniques and measures are also discussed. Then, the main future development direction and challenges in urban stormwater modeling and management are highlighted. Further research into the high spatio-temporal resolution observation and forecasting of urban rainfall are required to improve storm-term rainfall prediction. The performance of urban stormwater modeling technologies remain poorly quantified, which need a multisource information-fusion-based approach to the efficient estimation of urban runoff. The mechanism also remains poorly understood, which need much more research to understand the rainfall-runoff response relationship in the urban areas. In addition, urban stormwater is now increasingly regarded as a resource. The methods of harvesting, utilization and management of urban stormwater also need to pay more attention to, which imposes a requirement to ensure that stormwater management systems are adaptable and resilient to changes.