An analysis of satellite data for 14,000 cities and towns in the United States showed that areas within a 10-minute walk of a park can be up to 6° F cooler than areas further away from parks.
Trust for Public Land and MKThink. (2020). The Heat Is On: With temperatures rising and quality parks too few and far between, communities of color face a dangerous disparity. https://www.tpl.org/sites/default/files/The-Heat-is-on_A-Trust-for-Public-Land_special-report.pdf.