Department of Botany and Plant Sciences, University of California, Riverside, California, USA.
Department of Botany and Plant Sciences, University of California, Riverside, California, USA; School of Science, University of Waikato, Hamilton, New Zealand.
Sci Total Environ. 2017 Feb 1;579:495-505. doi: 10.1016/j.scitotenv.2016.11.069. Epub 2016 Nov 25.
Our study examines the urban vegetation - air temperature (T) - land surface temperature (LST) nexus at micro- and regional-scales to better understand urban climate dynamics and the uncertainty in using satellite-based LST for characterizing T. While vegetated cooling has been repeatedly linked to reductions in urban LST, the effects of vegetation on T, the quantity often used to characterize urban heat islands and global warming, and on the interactions between LST and T are less well characterized. To address this need we quantified summer temporal and spatial variation in T through a network of 300 air temperature sensors in three sub-regions of greater Los Angeles, CA, which spans a coastal to desert climate gradient. Additional sensors were placed within the inland sub-region at two heights (0.1m and 2m) within three groundcover types: bare soil, irrigated grass, and underneath citrus canopy. For the entire study region, we acquired new imagery data, which allowed calculation of the normalized difference vegetation index (NDVI) and LST. At the microscale, daytime T measured along a vertical gradient, ranged from 6 to 3°C cooler at 0.1 and 2m, underneath tall canopy compared to bare ground respectively. At the regional scale NDVI and LST were negatively correlated (p<0.001). Relationships between diel variation in T and daytime LST at the regional scale were progressively weaker moving away from the coast and were generally limited to evening and nighttime hours. Relationships between NDVI and T were stronger during nighttime hours, yet effectiveness of mid-day vegetated cooling increased substantially at the most arid region. The effectiveness of vegetated T cooling increased during heat waves throughout the region. Our findings suggest an important but complex role of vegetation on LST and T and that vegetation may provide a negative feedback to urban climate warming.
我们的研究考察了微观和区域尺度上的城市植被-空气温度（T）-地表温度（LST）关系，以更好地了解城市气候动态以及使用卫星 LST 来描述 T 所带来的不确定性。虽然植被降温已被反复证明与城市 LST 的降低有关，但植被对 T 的影响，即通常用于描述城市热岛和全球变暖的数量，以及 LST 和 T 之间的相互作用，其特征描述还不够完善。为了解决这一需求，我们通过在加利福尼亚州洛杉矶大都市区的三个子区域内设置了 300 个空气温度传感器网络，量化了夏季 T 的时空变化，该网络跨越了从沿海到沙漠的气候梯度。在内部子区域内，还在三种地面覆盖类型（裸土、灌溉草地和柑橘树冠下）的两个高度（0.1m 和 2m）处放置了额外的传感器。对于整个研究区域，我们获取了新的图像数据，这使得可以计算归一化差异植被指数（NDVI）和 LST。在微观尺度上，沿着垂直梯度测量的白天 T 值，在高大树冠下比在裸土下分别低 6 到 3°C。在区域尺度上，NDVI 和 LST 呈负相关（p<0.001）。随着远离海岸，T 的昼夜变化与日间 LST 之间的关系逐渐减弱，通常仅限于傍晚和夜间时段。在夜间，NDVI 和 T 之间的关系更强，但在最干旱的地区，中午植被冷却的效果大大增强。整个地区热浪期间，植被对 T 的冷却效果增强。我们的研究结果表明，植被对 LST 和 T 具有重要但复杂的作用，并且植被可能对城市气候变暖提供负反馈。
