60 Largest Cities

• An analysis of the 60 largest U.S. cities found an average of 8 more days above 90 degrees than surrounding rural areas. Hot and Getting Hotter: Heat Islands Cooking U.S. Cities. Climate Central. Mar. 30, 2017.
• 57 cities had measurable heat island effects over the past 10 years with an average of 2.4 degrees F warmer, with Las Vegas averaging 7.3 degrees, Washington, DC 4.7 degrees, and Kansas City 4.6 degrees. Hot and Getting Hotter: Heat Islands Cooking U.S. Cities. Climate Central. Mar. 30, 2017.

Evapotranspiration

• Evapotranspiration, the return of water vapor from trees and other vegetation to the atmosphere, alone or in combination with shading of buildings can help reduce peak
  summer temperatures by 2–9°F. Using Trees and Vegetation to Reduce Heat Island. US Environmental Protection Agency. Apr. 12, 2017.
• Larger patches of forest have a greater impact on temperature than isolated trees. https://www.fs.fed.us/research/docs/webinars/urban-forests/microclimate-heat-islands/slides-troy.pdf