@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},
}

@article{22457,
  abstract     = {An increase in urban vegetation is an often proposed mitigation strategy to reduce urban heat and improve outdoor thermal comfort (OTC). Vegetation can alter urban microclimate through changes in air temperature, mean radiant temperature, humidity, and wind speed. In this study, we model how street tree and ground vegetation cover and their structural, optical, interception, and physiological traits control the diurnal cycle of OTC in different urban densities in a tropical city (Singapore). For this purpose, we perform a variance based sensitivity analysis of the urban ecohydrological model UT&C. Model performance is evaluated through a comparison with local microclimate measurements and OTC is assessed with the Universal Thermal Climate Index (UTCI).
We find a pronounced daily cycle of vegetation effects on UTCI. Tree cover fraction is more efficient in decreasing UTCI during daytime, while a higher vegetated ground fraction provides more cooling during night. Generally, increasing vegetation cover fractions do not deter OTC, except in certain urban densities during some periods of the day. An increase in tree and ground vegetation fractions provides a higher average UTCI reduction compared to a change in vegetation traits (0.9 – 2.9  °C vs. 0.7 – 1.1  °C during midday, 10 month average). The increase in humidity related to plant transpiration prevents further reduction of UTCI. However, the choice of vegetation traits enhancing tree transpiration can decrease UTCI during hot periods. These results can inform urban planners on the selection of vegetation amount and traits to achieve feasible OTC improvements in tropical cities.},
  author       = {Meili, Naika and Acero, Juan Angel and Peleg, Nadav and Manoli, Gabriele and Burlando, Paolo and Fatichi, Simone},
  issn         = {0360-1323},
  journal      = {Building and Environment},
  publisher    = {Elsevier},
  title        = {{Vegetation cover and plant-trait effects on outdoor thermal comfort in a tropical city}},
  doi          = {10.1016/j.buildenv.2021.107733},
  volume       = {195},
  year         = {2021},
}