北京北护城河河岸带的温湿度调节效应

以北京北护城河为例,探讨具有不同结构的河岸带对温湿度的调节效应.于2011年5-10月,根据河岸带在宽度、坡度、植物种类、植被覆盖度、距路距离和距路高度等结构指标上的差异,沿南北两岸各选取4类河岸带,并在与河岸带垂直的道路两侧分别设置相应的紧邻不同城市土地利用类型的对照区.在每月下旬的晴天或多云天,从8:00到18:00,对南北8类河岸带及其对照区的气温和相对湿度进行连续10 h的观测.t检验分析表明,与对照区相比,河岸带具有明显的温湿度调节效应,能有效地改善人体的舒适度.各类河岸带的气温极显著低于对照区,而相对湿度极显著高于对照区；河岸带的日气温和日相对湿度变化较对照区和缓,且存在季节差异,河岸带在春秋季表现出更明显的温湿度日极值调节效应.各类河岸带与其对照区在温湿指数上也存在显著差异:对照区在夏季均会使人体感到很不适,而河岸带南岸在6月和8月可有效地提高人体的舒适度,北岸在8月也可改善舒适度.同时,不同类型河岸带的温湿度调节效应也存在差异:南岸对温湿度的调节效应强于北岸,北岸气温显著高于南岸,而相对湿度显著低于南岸.差异显著性的多重比较表明,南北不同类型河岸带之间在温湿度上的差异随季节而异:5月和10月的差异较显著,但6-9月的差异不显著,这些与植被覆盖度、乔木密度、冠层结构、河岸带宽度、距路距离,以及周边土地利用方式有关.研究的结果可作为城市河岸带生态服务功能评价的一部分,并可为城市河岸带的建设、修复和管理提供依据.

Effects of riparian buffers of North Mort of Beijing on air temperature and relative humidity

The study explored the effects of urban riparian buffers (RBs) with different structures on air temperature (T) and relative humidity (RH) in the North Mort of Beijing. From May to October in 2011, four RB types were selected on both the north and south RBs based on structural differences (such as width, slope, plant species, vegetation coverage, and distance and height to road). By both sides of the roads vertical to these RBs, the corresponding control areas (CAs) were set, adjacent to surrounding different urban land cover types. From 8:00 to 18:00, 10-hour measurements for T and RH were taken in different RB types and their CAs on sunny or cloudy days of late each month. Statistical analysis was used to test significance of differences in T, RH, and Thermohygrometric Index (THI) between RBs and CAs, between north and south RB types, and among different RB types and cross sectional zones. The results demonstrated that RBs had significant adjusting effects on T and RH compared with CAs, and could effectively improve human comfort. Firstly, from May to September, T and RH for RBs were extremely significantly lower and higher than those for CAs, respectively. Secondly, most daily variations in T for CAs showed a bimodal trend, but they had a single peak for RBs; the highest T for RBs occurred between 14:00 and 15:00, which was one hour later than that for CAs; RBs could significantly reduce the highest daily T, although it changed the lowest daily T little; meanwhile it could also effectively decrease high-temperature days. Thirdly, daily variations in T and RH for RBs were less than those for CAs. These differences depended on season, that is, the adjusting effects of RBs on microclimate range were especially strong in spring and autumn, but not in summer. Finally, THI for different RB types were significantly different from those for their CAs: all the CAs made human feel uncomfortable in the summer; the south RB types could effectively enhance human comfort level in June and August, and the north RB types could also do that in August. The results also showed that differences in adjusting effects on T and RH also existed in different RB types. Firstly, south RBs had stronger adjusting effects than north RBs, that is, T and RH for the north RB types were significantly higher and lower than those for the south RB types, respectively. It was mainly due to tree density, canopy structure, and riparian width. The wider south RB with higher tree density and denser upper canopy could partly block direct solar radiation. Secondly, the differences in T and RH among different RB types changed with seasons: there were significant differences in May and October, but not from June to September, related to vegetation coverage, riparian width, distance to the road, and surrounding land cover types. When vegetation coverage was higher than a certain threshold, its increase would not obviously influence T and RH for RB. Wider RB with open surroundings and larger distance to road would lead to stronger effects on microclimate. Finally, the differences in THI among different RB types were almost the same as those in T. In addition, there were no significant differences among different cross sectional zones within each RB type because of the limited RB width. The study may play an essential role on ecosystem service assessment of urban riparian buffer, and further provide theoretical basis for the planning, restoration and management of urban riparian buffers.