When you see completely mangled English in a paper that has supposedly passed peer review, you have to wonder about the quality of the peer review. Nonetheless, I was interested in the results of this study that looked at trees, shrubs, and lawn to see which had the most effect on urban heat.
For air temperature at 1.5 m and thermal comfort and safety (PET and WBGT), the sequence is trees> lawn> shrubs, but for surface temperature, the sequence is lawn> shrubs> trees
I’m always interested in the idea of designing urban areas to maximize hydrologic function, ecological function, and human comfort simultaneously. There is so much that could be done, and so much closed-mindedness and poor communication among the various professions and disciplines that could be doing it.
I’ve always assumed trees are the gold standard, because you get both the evapotranspiration function and the shading function, whereas with lawn and shrubs you only get the former. Also, you only need a small area of soil to plant the tree (although often more than we allow in urban areas), and then its leaves can cover a large area of concrete or asphalt, which would otherwise be generating a lot of heat and polluted runoff. Also, grass provides very little ecological function (unless you let it grow taller and/or take a lenient approach to what some of your neighbors choose to define as “weeds”, which can be socially unacceptable), where trees and bushes provide ecological function. Bushes take up a lot of space, either in a sidewalk context or a small urban yard – paradoxically, once trees mature a little bit they take up less space because there is space under them. On the other hand, I’ve argued with purists that if people really want lawn in urban areas, it is a lot better than concrete in terms of hydrology, heat, and aesthetics. Although if you’re in a water-stressed area, that adds another factor to the hydrology equation that those of us in wetter areas have the luxury of not worrying about too much.