Characterizing the thermal effects of vegetation on urban surface temperature
Characterizing the thermal effects of vegetation on urban surface temperature
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表征植被对城市表面温度的热效应
DOI：
10.1016/j.uclim.2022.101204
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Sawaid Abbas
中科院分区：
文献类型：
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作者：
Jinxin Yang;Qian Shi;Massimo Menenti;Yanhua Xie;Zhifeng Wu;Yong Xu;Sawaid Abbas
植被对城市热缓解具有重要意义。植被降温强度受背景气候和城市设计的影响。如何评价不同气候条件下植被的降温效率仍然是一个有待探讨的问题。本文提出了一种城市植被降温效率归一化指标（NVCE），作为城市植被降温效率在不同气候和城市条件下的适用性和可比性指标。当地表仅被植被覆盖时，在局地气候尺度下，其降温效果应高于其他像元。纯植被地表与无植被地表的地表温度差（T r, b−T r, v）为相同局地气候条件下植被降温强度的范围。混合像元的辐射地表温度与混合像元内植被温度（t1, r−t1, v）之差为像元i的过量温度。（t1, r−t1, v）与（t1, b−t1, v）的比值可以表示在该局地气候条件下像元i经过植被降温作用后存在的过量温度的百分比。因此，定义NVCE为(t1, r−t1, v)/(t1, b−t1, v)。以高空间分辨率数据为基础，推导出每个30 m × 30 m网格内的T i、v和T i、r，计算NVCE，并研究了不同条件下NVCE与植被覆盖度的关系。结果表明，NVCE可以减小背景气候对植被降温效率评价的差异，使不同气候条件下的植被降温效率具有可比性。NVCE对植被覆盖度也很敏感。植被覆盖度小于0.2时，NVCE均值约为0.5，变化不明显。这意味着当植被分数小于0.2时，植被没有明显的降温效果。当植被覆盖度大于0.2时，NVCE随植被覆盖度的增加呈线性降低。当植被覆盖度大于0.9时，NVCE趋于0。这表明0.2是植被降温效应的阈值。该研究可为不同气候和几何条件下植被降温效率的评价提供依据。研究结果可为城市绿色基础设施的设计和规划提供参考，如城市降温的植被分数应大于0.2，当SVF约为0.5 ~ 0.6时，植被降温效率最高。•提出了城市植被降温效率（NVCE）的归一化指标。•NVCE对植被覆盖度也很敏感。•城市降温的植被分数应大于0.2。•植被降温效率在SVF约为0.5 ~ 0.6时达到最大。
Vegetation is important for urban heat mitigation. The cooling intensity of vegetation is affected by background climate and urban design. How to evaluate vegetation cooling efficiency under different climate conditions is still an issue open to discussion. In this study, a normalized indicator of urban vegetation cooling efficiency (NVCE) is proposed as a metric of urban vegetation cooling efficiency applicable and comparable under different climate and urban conditions. When surfaces are only covered by vegetation, the cooling effects should be highest than other pixels at the local climate scale. The difference of surface temperature between the pure vegetation surfaces and surfaces without vegetations ( T r , b − T r , v ) is the range of the vegetation cooling intensity at the same local climate conditions. Difference between radiometric surface temperature of a mixed pixel and the vegetation temperature within the mixed pixel ( T i , r − T i , v ) is excess temperature of pixel i . The ratio of ( T i , r − T i , v ) to ( T r , b − T r , v ) can indicate how much percent of existed excess temperature after vegetation cooling effects for pixel i under such local climate condition. Thus, the NVCE is defined as ( T i , r − T i , v )/( T r , b − T r , v ). Based on the high spatial resolution data, the T i , v and T i , r within each 30 m × 30 m grid are derived to calculate the NVCE and the relationships between NVCE and fractional vegetation cover were studied under different conditions. Results showed that NVCE can reduce the differences caused by background climate in the assessment of vegetation cooling efficiency, i.e. making vegetation cooling efficiency under different climate conditions comparable. The NVCE is also sensitive to the vegetation fraction. When vegetation fraction is smaller than 0.2, the mean value of NVCE is about 0.5 and no obvious change. This means that the vegetation has no obvious cooling effects when vegetation fraction is smaller than 0.2. When the vegetation fraction is higher than 0.2, NVCE decreases linearly with increasing vegetation fraction. When the vegetation fraction is higher than 0.9, NVCE tends to 0. This indicates that 0.2 for vegetation fraction is the threshold of vegetation cooling effects. This study can provide information for evaluating the vegetation cooling efficiency under different climate and geometric conditions. This study also can provide useful information for urban green infrastructure design and planning, e.g. the vegetation fraction should be higher than 0.2 for urban cooling and the vegetation cooling efficiency can reach maximum when SVF is about 0.5 to 0.6. • A normalized indicator of urban vegetation cooling efficiency (NVCE) is proposed. • The NVCE is also sensitive to the vegetation fraction. • The vegetation fraction should be higher than 0.2 for urban cooling. • The vegetation cooling efficiency can reach maximum when SVF is about 0.5 to 0.6.