Research in Tel Aviv determined that the presence of trees cooled the air from between 0.5°F on a heavily trafficked street to 2°F in a small (0.37 acre) garden. The study also found that the cooling effects could be felt up to 330 feet from the site.
Shashua-Bar, L., and M. E. Hoffman. (2000). Vegetation as a climatic component in the design of an urban street: an empirical model for predicting the cooling effects of green urban areas with trees. Energy and Buildings. 31(3). 221-235.