亚热带季风区城市典型绿化屋顶的径流削减效应

屋顶绿化能够削减暴雨径流,降低城市内涝发生频率,促进可持续雨洪管理。针对亚热带季风气候区典型绿化屋顶的全年径流削减效应,以南京为研究区,以简易型、花园型两类绿化屋顶为研究对象,基于1年现场观测数据及水量平衡方程,分析屋顶雨水的滞蓄、蒸发与径流量随季节变化规律及其关键影响因子,采用SCS-CN模型计算绿化屋面的径流曲线数(CN),并估算城市尺度大面积屋顶绿化的暴雨径流削减效果。结果显示,简易型、花园型绿化屋顶全年径流削减率分别为42%和60.7%;径流削减效应的四季排序为春季冬季秋季夏季,平均径流削减率依次为78.6%、47.5%、33.2%、32.9%(简易型)及98%、84.3%、49.5%、48.1%(花园型);土壤基质层对雨水截留起主导作用,分别占径流削减总量的52%和62%;雨量和雨强是影响径流削减效应的关键因子,与径流削减率均呈显著负相关关系(P0.01),初始土壤湿度与简易型绿化屋顶的径流削减率呈显著负相关(0.01P0.05),但与花园型的径流削减率无显著相关性;基于全年77次降雨事件的降雨量-径流量数据测算得到简易型和花园型绿化屋顶的CN值分别为92和88;若南京主城区所有建筑屋顶面积的60%实施两类绿化,则其全年径流量可分别削减2.8×10~7 m~3和4.2×10~7 m~3。以上研究结果可为城市雨洪管理和海绵城市建设提供科学依据。

Assessing the rainwater runoff reduction effects of typical green roofs in a humid subtropical city

Roof greening provides a promising solution to urban flooding because of the commonly assumed effect on rainwater runoff reduction; however, few studies have investigated this effect in humid subtropical areas using long-term monitoring data. In this study, we evaluated two typical types of green roofs, extensive and intensive, in Nanjing City for their capacity to reduce runoff based on empirical hydrological equations calibrated with field measurement data collected over a whole year circle. We analyzed the variations in rainwater retention, evaporation, and runoff with respect to season and rainfall types. Based on paired rainfall-runoff data of 77 events over the year, the curve numbers (CN) of the two green roofs were calculated, and the annual runoff reduction of the city-scale roof greening was assessed. The results showed that annual runoff reduction rates of the extensive and intensive green roofs were 42% and 60.7%, respectively. The runoff reduction magnitude was highest in spring, followed by winter, autumn, and summer, with respective average reduction rates of 78.6%, 47.5%, 33.2%, and 32.9% for the extensive green roof and 98%, 84.3%, 49.5%, and 48.1% for the intensive roof. Soil played a dominant role in rainwater retention, accounting for 52% and 62% of the total runoff reduction for the extensive and intensive green roofs, respectively. Precipitation and rainfall intensity were key factors affecting runoff effects, both being negatively correlated with the runoff reduction rate (P < 0.01). Antecedent soil moisture was negatively correlated with the runoff reduction rate for the extensive green roof (0.01 < P < 0.05) but showed no significant correlation for the intensive green roof. The CNs of the extensive and intensive green roofs were assessed to be 92 and 88, respectively, compared with the value of 98 for conventional impervious roofs. A hypothetical 60% coverage of extensive and intensive greening on all building roofs in the main city of Nanjing might lead to an annual runoff reduction of 2.8×10⁷ m³ and 4.2×10⁷ m³, respectively. These results can provide a scientific basis for urban stormwater management and sponge city construction.