Planning the urban forest: Adding microclimate simulation to the planner’s toolkit

Abstract

While cities across the United States are developing urban forest plans to capitalize on a myriad of ecosystem services provided by trees, the tools that are used to support this planning do not necessarily meet the needs and achieve the desired results of these municipal initiatives. This paper highlights the disconnect between how planners and academics are approaching the task of planning and managing the urban forest for climate change adaptation. Although planners tend to focus on maximizing canopy coverage, academics utilize microclimate simulation to evaluate the impact of different interventions on heat island mitigation. We argue that while the i-Tree suite is the most commonly used tool and is immensely helpful for urban forest planners, cities and communities concerned with heat island mitigation should also leverage microclimate simulation tools to better understand the likely impacts of a plan. This study provides a general critique of the i-Tree tool for planning and illustrates how, when used with a microclimate simulation tool, the siting of street trees can have a greater impact on heat island mitigation. The focus here is on the community-scale impact of trees and a microclimate simulation model of a neighborhood in Chicago, Illinois where tree canopy coverage is less than 10% and consistently declining is presented. We find that when microclimate is considered during the tree siting process, trees have a greater impact on surface and air temperatures during the summer. Reduced ground surface temperatures of around 3 ℃ to 7.5 ℃ were achieved around 13:00 (1:00 pm), whereas the impact of trees from shading had the greatest impact (0.75 ℃ to 7.75 ℃) on nearby buildings in the mid-afternoon (15:00 to 17:00 h).