MITIGATING THE URBAN HEAT ISLAND EFFECT:Thermal Performance of Shade-Tree Planting in Downtown Los Angeles

With the continuous development of cities, the scale of cities continues to expand, and the rapid increase of urban populations are followed by many urban environmental problems, such as urban heat island effects, urban air pollution, urban light pollution, and so on. Especially the urban heat island effect, increasing extreme heat in urban areas will create longer periods of unhealthy and dangerous conditions for humans and other species. Focusing on studying the thermal environment problems related to the urban heat island effect and the use of trees to mitigate the problem. Using ENVI-met to simulate different factors that can affect the cooling ability of trees which include the different time of the year, the building shade, transpiration, the location of the trees, and the spacing of trees are the main variables studied. Based on tree-planting strategies that can improve the cooling ability of trees obtained from the above tests, a new tree-planting scheme is designed, and the thermal comfort condition inside the new scheme can also be analyzed. Finally, the influence of the new planting scheme on the thermal environment in the sidewalk area of the study area compared with the existing tree planting scheme in different months of the year is compared, so as to evaluate whether the new tree planting scheme can alleviate the heat island effect in the study area. This study found that, for the area under consideration in Los Angeles, the new tree planting scheme can decrease the UTCI temperature by 2.2 degrees Celsius on the sidewalks on the hottest day of the year, 0.97 degrees Celsius on the coldest day of the year, and 1.52 degrees Celsius for the entire year comparing with the existing tree planting scheme.