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Municipalities often consider heat mitigation strategies to address urban overheating, but the location of implementation rarely is co-located with the communities that are carrying the majority of the heat burden in the city. The City of Phoenix, is redeveloping a public housing community with a focus on urban cooling as a desired outcome. This research uses in situ measurements (including the mobile micro-meteorological measurement cart, MaRTy) and ENVI-met microscale modeling of the neighborhood to assess air temperature (Tair) cooling capabilities of the planned redesigns to the neighborhood. After validating the ENVI-met model of the current neighborhood with fixed and mobile measurements with an index of agreement d > 0.9 and d > 0.8, respectively, analysis of the planned urban design shows some cool spots connected to new shade and vegetated corridors with Tair cooling magnitudes as high as 3 °C. Yet, some exposed and building-adjacent areas were identified as potential hot spots in the planned neighborhood. These hotspots underscore the importance of continued collaboration among the City, researchers, and the community to address the needs of the community for the creation of healthier urban environments. 

Outdoor heat stress is a growing problem in cities during hot weather. City planners and designers require more pedestrian-centered approaches to understand sidewalk microclimates. Radiation loading, as quantified by mean radiant temperature (TMRT), is a key factor driving poor thermal comfort. Street trees provide shade and consequently reduce pedestrian TMRT. However, placement of trees to optimize the cooling they provide is not yet well understood. We apply the newly-developed TUF-Pedestrian model to quantify the impacts of sidewalk tree coverage on pedestrian TMRT during summer for a lowrise neighbourhood in a midlatitude city. TUF-Pedestrian captures the detailed spatio-temporal variation of direct shading and directional longwave radiation loading on pedestrians resulting from tree shade. We conduct 190 multi-day simulations to assess a full range of sidewalk street tree coverages for five high heat exposure locations across four street orientations. We identify street directions that exhibit the largest TMRT reductions during the hottest periods of the day as a result of tree planting. Importantly, planting a shade tree on a street where none currently exist provides approximately 1.5–2 times as much radiative cooling to pedestrians as planting the same tree on a street where most of the sidewalk already benefits from tree shade. Thus, a relatively equal distribution of trees among sun-exposed pedestrian routes and sidewalks within a block or neighbourhood avoids mutual shading and therefore optimizes outdoor radiative heat reduction per tree during warm conditions. Ultimately, street tree planting should be a place-based decision and account for additional environmental and socio-political factors. 

Abstract Cities increasingly recognize the importance of shade to reduce heat stress and adopt urban forestry plans with ambitious canopy goals. Yet, the implementation of tree and shade plans often faces maintenance, water use, and infrastructure challenges. Understanding the performance of natural and non-natural shade is critical to support active shade management in the built environment. We conducted hourly transects in Tempe, Arizona with the mobile human-biometeorological station MaRTy on hot summer days to quantify the efficacy of various shade types. We sampled sun-exposed reference locations and shade types grouped by urban form, lightweight/engineered shade, and tree species over multiple ground surfaces. We investigated shade performance during the day, at peak incoming solar, peak air temperature, and after sunset using three thermal metrics: the difference between a shaded and sun-exposed location in air temperature ( ΔT a ), surface temperature ( ΔT s ), and mean radiant temperature ( ΔT MRT ). ΔT a did not vary significantly between shade groups, but ΔT MRT spanned a 50°C range across observations. At daytime, shade from urban form most effectively reduced T s and T MRT , followed by trees and lightweight structures. Shade from urban form performed differently with changing orientation. Tree shade performance varied widely; native and palm trees were least effective, while non-native trees were most effective. All shade types exhibited heat retention (positive ΔT MRT ) after sunset. Based on the observations, we developed characteristic shade performance curves that will inform the City of Tempe’s design guidelines towards using “the right shade in the right place” and form the basis for the development of microclimate zones (MCSz).