Location matters: planting urban trees in the right places improves cooling

Abstract

Available space and other resources associated with urban greening initiatives are limited, yet demand for urban cooling to mitigate high urban temperatures is growing. Consequently, identifying the best locations for urban greening to maximize the cooling effects of the urban tree canopy (UTC) is taking on new urgency. We present a cross‐city comparison and show how cooling efficiency (CE) varies spatially within a city. CE tends to be higher in locations with less UTC due in part to evapotranspiration from non‐uniformly distributed trees, but results from a subtropical city included within our comparison underscore the strong effect of a city’s background climate on CE. Mapping the spatial variation of CE can guide tree planting to enhance the cooling effects of UTC, expand the role trees play in urban adaptation to local warming, and help achieve urban sustainability.

Vehicle pollution is associated with elevated insect damage to street trees

“…Regardless, our study highlights the importance of planting decisions along major roadways. The concept of “right tree, right place” has long stated that tree selection should be aimed at maximizing the performance in urban areas (Minckler, 1941; Morakinyo et al, 2020; Wang et al, 2022). Quercus lobata and other species that are highly susceptible to herbivores may provide ecosystem services sub‐optimally along highways, and may have shorter lifespans due to chronic damage promoted by on‐road pollution (Pearse et al, 2015).…”

Satellite‐based evidence highlights a considerable increase of urban tree cooling benefits from 2000 to 2015

“…The use of an invariant TCE (Estoque et al, 2017;Wang et al, 2019Wang et al, , 2020Zhou et al, 2017), usually expressed as the slope of a linear relationship between land surface temperature (LST) and tree cover, has recently been challenged. Compared with treeless urban areas, previous studies indicate those with high tree cover could locally have lower T a but higher humidity due to substantial canopy transpiration, which results in a decreased local VPD L that suppresses TCE (Wang et al, 2022;Yu et al, 2018). Hence, it is preferable to derive TCE for different tree cover levels and TCEs across cities are only comparable at similar tree cover levels (see Data S1 for a more detailed discussion).…”

Evaluating the Cooling Performance of Green Roofs Under Extreme Heat Conditions

“…Studies have shown that the higher urban temperature has adverse impacts, such as the alteration in species composition and distribution (Niemela, 1999;White et al, 2002), the increase in energy consumption (Castleton et al, 2010;Susca, 2019), and the increased mortality and heat-stress illness (Sailor and Fan, 2002;Knowlton et al, 2004). Thus, effective urban heat mitigation and adaptation strategies are highly desirable for a more comfortable urban thermal environment (Zhou et al, 2021;Wang et al, 2022).…”

“…Urban greening has been recognized as an effective means to alleviate extreme urban temperature (Zhou et al, 2011;Kong et al, 2014). However, although many cities have ambitious intentions to increase their urban vegetation, there are limited space and resources for urban planting, especially in cities with high density (Wang et al, 2022). Roofs, commonly accounting for approximately 20-25% of the total urban areas (Izquierdo et al, 2008;Besir and Cuce, 2018), can provide extra and optional surfaces and space for urban greening (Berardi, 2016).…”

“…Against global warming and rapid urbanization, extreme heat conditions, such as heatwaves, have become more frequent (IPCC, 2014;Cao et al, 2021). Urban greening can reduce urban temperature, but its cooling effect has been affected by weather conditions, such as air temperature (Wang et al, 2022). For example, the extremely high air temperature may lead to a decrease in the cooling effect of urban vegetation (Wang C. et al, 2019;Wang et al, 2020).…”