Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong.
Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong.
Sci Total Environ. 2021 Apr 15;765:142718. doi: 10.1016/j.scitotenv.2020.142718. Epub 2020 Oct 6.
Measuring energy fluxes in a dense and high-rise urban area is extremely challenging, thus our knowledge in such area remains limited. This study assessed the surface energy fluxes and investigated the energy balance closure (EBC) over such complex urban surface in Hong Kong. Net radiation (Q), sensible (Q) and latent (Q) heat fluxes were measured using an eddy covariance system from September 2018 to August 2019. Anthropogenic heat flux (Q) was simulated by a large-scale urban energy model (i.e., LUCY) and validated by an anthropogenic heat database (i.e., AHE_KL). Storage heat flux (Q) was estimated by an objective hysteresis model (OHM). Among five energy terms, Q showed the largest values of around 750 Wm especially in the afternoon. Whereas, Q varying within 150 Wm showed the smallest values. The variation range of net radiation, sensible heat flux and storage heat was respectively from -50 to 600, 0 to 450 and -30 to 300 W m. EBC generally showed a negative relationship with surface heterogeneity. Best EBC was observed in the direction with a relatively constant and large aspect ratio, and with the most occurrence of unstable stratifications. The uncertainties of Q and Q fluxes were respectively estimated to be approximately 8% and 7%. The result of LUCY was consistent with that of AHE_KL. EBC was not sensitive to different coefficients estimating Q. This study helped to fill a gap in our understanding of surface energy and turbulent fluxes in compact cities with high-rise buildings and shed insights into the future installation of eddy covariance tower in similar areas. The required height of the eddy covariance tower in such urban sites might not be as restrictive as that in other urban areas with low-rise buildings or with low building density, thus making it more feasible to set up such observation towers.
在密集且高楼林立的城市地区测量能量通量极具挑战性，因此我们对该地区的了解仍然有限。本研究评估了此类复杂城市表面的地表能量通量并研究了能量平衡闭合（EBC）。从 2018 年 9 月到 2019 年 8 月，使用涡度相关系统测量了净辐射（Q）、感热（Q）和潜热（Q）通量。人为热通量（Q）通过一个大规模城市能量模型（即 LUCY）进行模拟，并通过人为热数据库（即 AHE_KL）进行验证。存储热通量（Q）通过目标滞后模型（OHM）进行估算。在五个能量项中，Q 表现出最大的值，约为 750 Wm，特别是在下午。而 Q 变化范围在 150 Wm 以内，值最小。净辐射、感热通量和存储热通量的变化范围分别为-50 至 600、0 至 450 和-30 至 300 W m。EBC 通常与地表非均质性呈负相关。在具有相对恒定且较大纵横比且不稳定分层最常发生的方向上观察到最佳 EBC。Q 和 Q 通量的不确定性分别估计约为 8%和 7%。LUCY 的结果与 AHE_KL 的结果一致。EBC 对不同的 Q 估算系数不敏感。本研究有助于填补我们对具有高层建筑的紧凑型城市的地表能量和湍流通量的理解空白，并为未来在类似地区安装涡度相关塔提供了深入了解。在这种城市地区，涡度相关塔所需的高度可能不像低层建筑或低层密度的其他城市地区那样具有限制，因此更可行建立这样的观测塔。
