ارزیابی رفتار هیدرولوژیکی سناریوهای پیشرفته در سقف بالادست بالقوه در پکن

Although the study of hydrological performance of green roofs is of great significance to urban water security and sustainable development, large-scale roofs greening within a city range has not received sufficient attention. In this study, a typical urban area of 675 km2 within the fifth ring road of Beijing was chosen as a case study. The potential green roofs were defined before being identified from high resolution images. Under three retrofitting scenarios (100%, 50% and 20%) of extensive green roofs, the hydrological behaviour of potential green roofs was investigated at catchment units by employing the Soil Conservation Service Curve Number model. The behaviour was evaluated finally through two aspects of the runoff reduction effect and the flooding mitigation effect. According to this study, a 19.6% of the potential green roofs within the study area indicates a strong potential for the future greening. In the city scale, the average runoff reduction rates decrease from 9.38% to 6.13% with the increasing return period of rainfall events. Catchments in the core of northern city play key roles in reducing runoff, by more than 10% with the 100% implementation scenario. This study also showed that flooding in 13 of the 20 underpasses would have been avoided in the 7.21 Rainstorm if only 20% of the potential green roofs had been implemented. This study demonstrated a potentially positive hydrological behaviour contributed by roof greening in the future Beijing at a city scale, and effective runoff reduction can be achieved if only with a 50% greening of the potential green roofs. However, urban planners should take notice of the predicament that the deposit of high potential green roofs do not match spatially well to the severe flooding sites.