Our cities are staying hotter longer and are not cooling off as much during nighttime hours, increasing land surface temperatures. Ground temperatures are intensifying, straining HVAC and causing heat-stress.
Indoor thermal comfort and energy bills are strained in many locations, and without careful design associated energy costs will swell beyond manageable levels.

Learning from best-practices and proven mitigation strategies will help with broad implementation, these resources are identified as good starting places to understand what UHI reduction advocates are doing:
How many trees does it take to cool a city?
https://www.caryinstitute.org/news-insights/press-release/how-many-trees-does-it-take-cool-city
A scaling law for predicting urban trees canopy cooling efficiency
https://www.pnas.org/doi/full/10.1073/pnas.2401210121#sec-3
The impact of vegetative and solid roadway barriers on particulate matter concentration in urban settings
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0296885
Health impact of urban green spaces: a systematic review of heat-related morbidity and mortality
https://bmjopen.bmj.com/content/14/9/e081632
Georgia State University Study
Trees, Bushes Near Highways Can Significantly Reduce Air Pollution
A Review of the Formation and Mitigation Strategies from 50 Years of Global UHI
Studies
Causes, Modeling and Mitigation of Urban Heat Island: A Review
https://www.sciencepublishinggroup.com/article/10.11648/j.earth.20211006.11
Study of the Urban Heat Island Using Remote Sensing Data