Rooftop mitigation strategies (RMSs) can alleviate extreme heat in highly urbanized cities under global warming. In this study, gridded urban canopy parameters for Tokyo, a coastal metropolis, were integrated into the Weather Research and Forecasting model, coupled with a multilayer urban canopy model. The effects of rooftop photovoltaic (PV) panels, sedum green roofs (GRs), and grass GRs on the urban thermal environment during high-temperature days were then analyzed. PV panels, sedum GR, and grass GR with 50 % coverage achieved the most significant reductions in regional average pedestrian-level air temperatures at 2 PM, 10 AM, and 12 PM, respectively, with reductions of 0.10 °C, 0.11 °C, and 0.13 °C. The daily peak of regional maximum cooling effects for all RMSs were observed around 2 PM, reaching 0.25 °C, 0.25 °C, and 0.30 °C, respectively. Despite the daytime cooling effect, both GRs increased heat stress, which was particularly noticeable in grass GRs due to their stronger evaporative capacity, resulting in an increase in WBGT of up to 0.15 °C in approximately 75 % of the study areas. Additionally, the impacts of RMSs in coastal areas extended to the northwestern hinterland, indicating a non-local pattern influenced by sea-breeze advection. Furthermore, under high-temperature conditions, the cooling effect of GRs at midday increased linearly with background temperature.

中文翻译：

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高温天气下城市规模屋顶减灾策略降温效应的时空分布——以沿海大都市东京为例


在全球变暖的情况下，屋顶缓解策略 （RMS） 可以缓解高度城市化城市的极端高温。在本研究中，沿海大都市东京的网格化城市冠层参数被整合到天气研究和预报模型中，并耦合了多层城市冠层模型。然后分析了屋顶光伏 （PV） 板、景天绿屋顶 （GRs） 和草 GRs 在高温日对城市热环境的影响。覆盖率为 50% 的光伏板、景天属植物 GR 和草坪 GR 分别在下午 2 点、上午 10 点和中午 12 点实现了区域平均行人水平气温的最显着降低，降低了 0.10 °C、0.11 °C 和 0.13 °C。 所有 RMS 的区域最大冷却效应日峰值出现在下午 2 点左右，分别达到 0.25 °C、0.25 °C 和 0.30 °C。尽管具有白天降温效果，但两种 GR 都增加了热应激，由于它们的蒸发能力更强，这在草 GR 中尤为明显，导致大约 75% 的研究区域的 WBGT 增加高达 0.15 °C。此外，RMS 对沿海地区的影响延伸到西北腹地，表明受海风平流影响的非局域模式。此外，在高温条件下，GRs 在正午的冷却效果随背景温度线性增加。