城市绿化屋顶的微气候调节与径流削减效应研究

快速城市化与气候变化双重作用下,热岛效应与城市内涝成为最为突出的城市环境问题。绿化屋顶因能有效利用闲置屋面添緑、帮助城市缓解热岛和暴雨径流而受到关注。以往研究较多探讨单种气象条件下、单个小面积实验型绿化屋面的气候水文调节功能,本研究基于夏秋两季的微气候水文观测数据,定量分析不同气象条件下5种典型绿化屋顶的降温和径流削减效应。首先选择晴朗、多云、降雨3种典型夏日天气条件,分析草坪、裸土、菜地、小面积花园、大面积花园5种类型绿化屋顶与对照光屋顶之间的温度差日变化规律,探讨绿化屋顶热效应强度及时空特征;其次,选择暴雨、大雨、中雨及小雨4次典型降雨,分析大面积草坪与花园型绿化屋顶上的降雨-滞蓄过程及径流削减率。研究结果表明:绿化屋顶降温与升温效应并存,晴朗无风天气条件下,距离屋面10 cm和150 cm两个高度上,绿化屋顶最高可降低气温5.3℃和2.5℃,多云及降雨天气条件下降温强度下降,升温时段延长;白天草坪与裸土上的大气温度高于对照光屋顶,其它绿化屋顶的温度低于对照屋顶;夜间5个绿化屋顶的大气温度均低于对照屋顶,且降温效应按照大面积花园、草坪、小面积花园、裸土、菜地的顺序递减。绿化屋顶径流削减效益与绿化类型及降雨强度密切相关,花园型绿化对一次典型暴雨、大雨、中雨、小雨的径流削减率分别为50.8%、78%、100%、100%,简易型绿化的4次径流削减率分别为24.3%,58.6%,98.2%和100%。研究结果可为同气候区其他城市绿化屋顶环境设计及管理提供一定参考价值。

GREEN-ROOF EFFECTS ON URBAN MICROCLIMATE AND STORMWATER RUNOFF

The rapid urbanization and global climate change have brought many urban environmental problems,in which the urban heat island effects and urban flooding are two serious ones.Green roof provides a potential solution for these issues by vegetating the current barren roof surfaces,and has particular significances for cities with extreme shortage of green spaces.Many previous studies analyzed the microclimatic and hydrological impacts of a single-type and small-size experimental green roof under one particular weather condition.This study aims to evaluate and compare the effectiveness of five typical types of green roofs,with different scales,plant species and soil depths over different weather conditions.The five experimental green roofs,namely grass,bare soil,vegetable land,small-size and large-size sky gardens,were installed on five office buildings in an industrial park of Nanjing city.Firstly,the daily dynamics of air temperature (10 cm and 150 cm above the roof surface) differences between the green roofs and the control roof were studied.Secondly,two of the five roofs,representing the extensive and intensive roof greening respectively,were selected for stormwater runoff analysis under four rainfall conditions.The results indicate that on a typical sunny summer day,green roofs can reduce the air temperature up to 5.3℃ and 2.5℃ at 10 cm and 150 cm heights above the roof surface,respectively.On cloudy and rainy days,some green roofs can even elevate the air temperature.The large-size sky garden has the greatest air temperature reduction ability,and other four types of roofs cooling abilities can be ordered as:grass ＞ smallsize sky garden ＞ bare soil ＞ vegetable land.The stormwater runoff control abilities of the roofs are most related to plant and soil configuration and rainfall types.The sky garden can reduce runoff by 50.8％,78％,100％ and 100％ of the extremely heavy,heavy,middle and light rainfall events,respectively.The equivalent values for the extensive green roof were 24.3％,58.6％,98.2％ and100％,respectively.These findings can shed light on green-roof design and management for cities in similar climate zones as Nanjing.