@article{22517,
  abstract     = {The capacity of vegetation to mitigate excessive urban heat has been well documented. However, the cooling potential provided by urban vegetation during heatwaves is less known even though heatwaves have been projected to be more severe with climate change. Across 24 global metropolises, we combine 30 m resolution satellite observations with a theoretical leaf energy balance model to quantify the change of the leaf-to-air temperature difference and stomatal conductance during heatwaves from 2000 to 2020. We found the responses of urban vegetation to heatwaves differ significantly across cities and they are mediated by climate forcing and human management. During heatwaves, vegetation in Mediterranean and midlatitude-humid cities shows a significant decrease in cooling potential in most cases due to large stomatal closures, while vegetation in arid cities shows a cooling enhancement with an unmodified stomatal opening likely in response to intense irrigation. In comparison, the cooling potential of vegetation in high-latitude humid cities does not show significant changes. These responses have implications for future urban vegetation management strategies and urban planning.},
  author       = {Zhao, Jiacheng and Meili, Naika and Zhao, Xiang and Fatichi, Simone},
  issn         = {1748-9326},
  journal      = {Environmental Research Letters},
  keywords     = {Urban vegetation, Heatwave, Cooling potential, Stomatal behavior},
  number       = {1},
  publisher    = {IOP Publishing},
  title        = {{Urban vegetation cooling potential during heatwaves depends on background climate}},
  doi          = {10.1088/1748-9326/acaf0f},
  volume       = {18},
  year         = {2023},
}

@article{22561,
  abstract     = {Urban tree planting is an effective strategy to reduce temperature locally and eventually mitigate Urban Heat
Island. Although its cooling effects have been widely reported, understanding of coupling effects of street
morphologies and tree characteristics on thermal environment is insufficient, especially in high-density cities. A
parametric study is conducted to investigate effects of leaf area index (LAI = 1.0,2.0,3.0,4.0,5.0,6.0) and tree
crown radius (rtree = 2.0,3.4,4.4,5.0 m) on thermal environment inside streets with various aspect ratios (street
height/width, H/W = 1.0–5.0). A mechanistic urban canopy model Urban Tethys-Chloris (UT&C) is selected and
integrated with a new semi-empirical wind parameterization based on drag coefficients and frontal area densities
of buildings and trees. Modified UT&C is validated by a unique and controllable scaled outdoor experiment. The
research outputs can be summarized as follows: (1) Calculated air temperature (Ta), wind speed (V), and thermal
comfort indices (Mean Radiant Temperature (Tmrt) and Universal Thermal Climate Index (UTCI)) are in good
agreement with results from scaled outdoor experiments, while slight overestimation of relative humidity (RH)
occurs in tree cases; (2) Increasing LAI and rtree both bring stronger cooling effects by up to 20.2 ◦C (Tmrt) and
4.0 ◦C (UTCI); (3) Narrower streets weaken trees’ cooling effects and increasing LAI and rtree could be less
efficient for higher H/W than lower H/W; (4) LAI = 4.0 and rtree = 5.0 m are optimal for wide streets (H/W =
1.0–3.0) to provide maximum UTCI cooling (about 4.0 ◦C), while LAI = 4.0 and rtree = 3.4 m are suggested for
narrow streets (H/W = 3.0–5.0). Our study provides useful information on evidence-based urban tree selection
strategies for urban planning and design. },
  author       = {Chen, Taihan and Meili, Naika and Fatichi, Simone and Hang, Jian and Tan, Puay Yok and Yuan, Chao},
  issn         = {1873-684X},
  journal      = {Building and Environment},
  keywords     = {Urban canopy model, Scaled outdoor experiment, Street aspect ratio, Urban vegetation, Pedestrian thermal comfort},
  publisher    = {Elsevier},
  title        = {{Effects of tree plantings with varying street aspect ratios on the thermal environment using a mechanistic urban canopy model}},
  doi          = {10.1016/j.buildenv.2023.111006},
  volume       = {246},
  year         = {2023},
}