极端降雨条件下绿色屋顶径流调控效益研究

Stormwater retention performance of green roofs under extreme rainfall conditions

气候变化导致极端降雨频发,绿色屋顶作为海绵城市建设的重要措施之一,可有效调控雨水径流,但目前缺少极端降雨条件下绿色屋顶径流调控效益的实测研究.本研究于北京市搭建了3种基质类型(改良土、田园土和轻质生长基(轻质基))的绿色屋顶,每种基质绿色屋顶分别设置2种植被类型(大花马齿苋(Portulaca grandiflora)和佛甲草(Sedum lineare))以及无植被覆盖的裸露基质(对照组).基于2017—2019年实测降雨特征,采用百分位阈值法筛选极端降雨,定量分析极端降雨条件下不同配置绿色屋顶的径流调控效益.结果表明,采用百分位阈值法第90百分位值确定的2017—2019年研究区极端降雨的阈值为30.1 mm;极端降雨条件下绿色屋顶的平均径流削减率和洪峰削减率(44.5%和48.6%)均极显著低于非极端降雨(94.6%和94.3%,p<0.01),但平均产流延迟时间和峰现延迟时间与非极端降雨条件均无显著差异(p>0.05);极端降雨条件下不同植被类型与基质类型绿色屋顶的平均径流削减率、洪峰削减率、产流延迟时间和峰现延迟时间均无显著差异(p>0.05),表明调整植被或基质类型对提升绿色屋顶在极端降雨条件下的径流调控效益作用有限.研究结果可望为气候变化背景下绿色屋顶设计和径流调控效益评估提供科学参考.

The frequency of extreme rainfall events is increasing under the background of climate change.As a crucial measure of sponge city construction,green roofs are widely adopted for urban stormwater management.However,there is a lack of experimental studies on the stormwater retention performance of green roofs under extreme rainfall conditions.In this study,various green roofs were set up in Beijing,featuring three substrate types(i.e.,engineered soil,local planting soil,and light growing medium),and two vegetation types(i.e.,Portulaca grandiflora and Sedum lineare)and a non-vegetated substrate(control).The study analyzed rainfall characteristics from 2017 to 2019 and employed the percentile threshold method to identify extreme rainfall events.Besides,the stormwater retention performance of green roofs with different configurations were quantitatively analyzed under extreme rainfall conditions.The results show that the extreme rainfall threshold,identified by using the 90%percentile threshold method,is 30.1 mm.Under extreme rainfall conditions,the average runoff reduction rate and peak flow reduction rate of green roofs(44.5%and 48.6%,respectively)are significantly lower than those under non-extreme rainfall conditions(94.6%and 94.3%,respectively,p<0.01).However,there is no significant difference in the average runoff generation delay time and peak delay time of green roofs between extreme and non-extreme rainfall conditions(p>0.05).Under extreme rainfall conditions,there is no significant difference in stormwater retention performance of green roofs with different vegetation or substrate types(p>0.05).It indicates that optimizing vegetation or substrate types has a limited influence on enhancing stormwater retention performance of green roofs under extreme rainfall conditions.The results provide scientific references for the design and stormwater retention performance evaluation of green roofs under the background of climate change.