基于视觉指数的城市热环境效应——以徐州市为例

城市热环境与人居环境、居民健康以及城市可持续发展密切相关。本研究以绿视率(GVI)为基础,提出地上构筑物视率(CVI)和硬化地表视率(R&PVI)2种新的视觉指数,使用移动观测方法,在夏季末获取徐州市主城区、风景区、大学校园外部以及大学校园的城市热环境数据,并同步获取采样沿线的影像和坐标信息,分析以视觉指数所表示的城市构成对城市热环境的影响。结果表明: 在采样沿线上,研究区主城区平均气温(T_a,30.42 ℃)最高但相对湿度(RH,40.7%)最低,风景区的平均T_a(29.35 ℃)最低但RH(48.4%)最高;平均风冷温度(T_aW)在主城区最高(32.95 ℃),在风景区最低(31.93 ℃)。CVI由高至低依次为:主城区、大学校园、大学校园外部和风景区,GVI与CVI相反。CVI分别与T_a和T_aW呈极显著正相关,与RH呈极显著负相关;GVI分别与T_a和T_aW呈极显著负相关,与RH呈极显著正相关;R&PVI分别与T_a和T_aW呈显著和极显著正相关,与RH的相关性不显著。CVI和GVI对T_a的贡献显著,独立贡献率分别为10.4%和18.9%,联合贡献率分别为7.8%和11.3%;对RH而言,二者贡献同样显著,独立贡献率分别为37.5%和15.7%,联合贡献率分别为51.4%和30.2%;对T_aW而言,3种参数的贡献均达到显著水平,三者的独立贡献率和联合贡献率均低于对T_a的影响;3种参数对RH的影响高于对T_a和T_aW。研究结果可为优化城市热环境和缓解城市热岛效应提供思路,也对城市更新以及人居环境质量提升具有实践意义。

Urban thermal environment effects based on visual indices: A case study in Xuzhou City,China

Urban thermal environments are closely related to habitats, citizens' health, and sustainable development. Based on green view index (GVI), we proposed two new visual indices, construction view index (CVI) and imperious surface view index (R&PVI). Mobile observation was used to obtain urban thermal environment data, images and coordinates synchronously in Xuzhou City in late summer, including urban area (U), scenic area (S), exterior of university campus (E), and university campus inside (CUMT). We analyzed the impacts of the urban composition represented by the visual index on the urban thermal environment. The results showed that, along the sampling line, mean air temperature (T_a) was highest (30.42 ℃) and mean relative humidity (RH) was lowest (40.7%) in urban area, while mean T_a was lowest (29.35 ℃) and mean RH was highest (48.4%) in scenic area. The situation of mean wind-chill temperature (T_aW) was the highest (32.95 ℃) in the urban area and the lowest (31.93 ℃) in the scenic area. As for CVI, urban area, university campus inside, exterior of university campus and scenic area ranked in descending order, while GVI showed an opposite pattern. CVI was significantly positively correlated to T_a and T_aW, but negatively to RH. GVI was significantly negatively correlated to T_a and T_aW, but positively to RH. R&PVI was significantly positively correlated to T_a and T_aW, but not correlated to RH. CVI and GVI influenced T_a significantly, with the independent effects being 10.4% and 18.9%, and joint effects being 7.8% and 11.3%, respectively. As for RH, CVI and GVI contributed significantly as well, independent effects were 37.5% and 15.7%, and joint effects were 51.4% and 30.2%, respectively. As for T_aW, the three visual indices contributed significantly, but independent and joint effects were lower than those on T_a. Moreover, visual indices contributed more on RH than T_a or T_aW. The results could provide ideas for optimizing urban thermal environments and mitigating urban heat island effects, and have practical implications for urban renewal and improvement of the quality of human living environment.