Chao Mei

Urban Storm Flooding Management in Beijing

Beijing is located in the piedmont plain of Taihang Mountains. It suffers from the floods formed in the Taihang Mountains as well as the local waterlogging. The precipitation in flood season (June to September) accounts for more than 80% of the annual precipitation, and it is often concentrated in late July to early August, which sometimes leads to serious urban flood disasters. For instance, in 1939 the precipitation in July and August was up to 1137 mm (recorded in Changping rain gauge); in August of 1963 the precipitation from 4th to 9th is more than 350 mm. Under the rapid urbanization in Beijing, the urban flood is becoming more serious, such as the pluvial disasters on 21st July of 2012. This chapter analysed the characteristics, evolution processes and main influencing factors of urban flood in Beijing based on the historical records. The four main measures of flood management in Beijing are summarized, which are: (1) upgrading and reconstruction of rainwater pumping stations; (2) improvement projects of small and medium rivers; (3) Sponge City construction; and (4) the West Suburb Storm-water Regulation Project. These measures have been put into use, and have played significant benefits on pluvial disaster mitigation in Beijing. On 20th July of 2016, the precipitation in urban area is 274 mm, which is more than that on 21st July of 2012, but there were no serious waterlogging events in urban area. In addition to early prevention measures, the flood warning and emergency management system has been established in Beijing. Beijing has also planned two deep tunnels to deliver overflowed rain water, which would greatly improve the defence standards of urban waterlogging in Beijing in the future. With the improvement of management and engineering measures, Beijing will be more resilient and safer under the heavy rains. The experiences of Beijing can also provide references for flood control in other cities.

Integrated assessments of green infrastructure for flood mitigation to support robust decision-making for sponge city construction in an urbanized watershed

Green Infrastructure (GI) has become increasingly important in urban stormwater management because of the effects of climate change and urbanization. To mitigate severe urban water-related problems, China is implementing GI at the national scale under its Sponge City Program (SCP). The SCP is currently in a pilot period, however, little attention has been paid to the cost-effectiveness of GI implementation in China. In this study, an evaluation framework based on the Storm Water Management Model (SWMM) and life cycle cost analysis (LCCA) was applied to undertake integrated assessments of the development of GI for flood mitigation, to support robust decision making regarding sponge city construction in urbanized watersheds. A baseline scenario and 15 GI scenarios under six design rainfall events with recurrence intervals ranging from 2-100 years were simulated and assessed. Model simulation results confirmed the effectiveness of GI for flood mitigation. Nevertheless, even under the most beneficial scenario, the results showed the hydrological performance of GI was incapable of eliminating flooding. Analysis indicated the bioretention cell (BC) plus vegetated swale (VS) scenario was the most cost-effective GI option for unit investment under all rainfall events. However, regarding the maximum potential of the implementation areas of all GI scenarios, the porous pavement plus BC + VS strategy was considered most reasonable for the study area. Although the optimal combinations are influenced by uncertainties in both the model and the GI parameters, the main trends and key insights derived remain unaffected; therefore, the conclusions are relevant regarding sponge city construction within the study area.

Effect of climate change on water resources in the Yuanshui River Basin: a SWAT model assessment

The Yuanshui River Basin is one of the most important river basins ensuring food production and livelihoods in the Hunan and Guizhou Provinces of China. Based on digital elevation model, land use, soil, and meteorological data, the soil and water assessment tool was used to analyze the response of water resources in the basin to climate change. Specifically, the monthly runoff from the Yuanshui River Basin was simulated. Runoff measurements from the 1961–1990 series were used to calibrate model parameters, and measurements from the 1991–2010 series were used for model validation. The Nash–Sutcliffe efficiency coefficient, correlation coefficient, and water balance error were used to evaluate the simulation results; the values obtained for these parameters were 0.925, 0.929, and 2.0%, respectively, indicating that the established model can be applied successfully to runoff simulations. To evaluate the effects of climate change and human activities on runoff, 24 different climate scenarios were modeled. By comparing the model simulation results with the baseline scenario, the effects of climate change were analyzed by year, during the dry season, and during extremely dry conditions. The results showed that runoff decreased with increasing air temperature and decreasing precipitation, and that the effects of rainfall on runoff were greater than those of air temperature. Under the same baseline conditions, the effects of climate change on runoff were most pronounced during extremely dry months.