262 Abram et al: Land Cover and Summer Cooling Electricity Consumption benefits of UTC, like i-Tree (USDA; Madison, WI, USA)(Nowak 2020), have shown that trees near buildings can also reduce indoor energy use in the summertime (McPherson and Simpson 1999; Nowak 2002; Nowak et al. 2008; Nowak et al. 2017). These studies have led city managers to consider increasing UTC as one potentially valuable strategy for reducing the negative impacts of urban heating. Although the overall phenomenon of the UHI effect and its impacts are well-known and widely recog- nized (Oke 1982; Tan et al. 2010; Santamouris 2014), how exactly to mitigate increased urban heating over time, at different scales, and across a variety of cli- mates and sociocultural contexts remains a research priority and policy challenge (Myint et al. 2015; Hamstead et al. 2020). For instance, it is generally expected that increased impervious surfaces lead to increased temperatures, as these surfaces affect mois- ture availability and radiative energy transfer (Moha- jerani et al. 2017). Contrastingly, UTC has been shown to have an impact on temperature by decreasing aver- age near-surface air temperatures, which enhances radiative cooling and improves thermal comfort (Mid- del et al. 2015; Wang et al. 2018). Yet the magnitude of the negative impacts of impervious surfaces and positive impacts of vegetated landscapes varies sub- stantially across studies, leading to research on the role of climate, latitude, season, time of day, urban density, and urban form on increased urban heating in cities (Zhou et al. 2014; Wheeler et al. 2019). A liter- ature review by Wheeler et al. (2019) on mitigating urban heating in dryland cities delved into counter- intuitive results on how tree canopy can both reduce and increase air temperatures at different times of day and in different configurations. At the same time, there is ample evidence that UTC does impact outdoor tem- perature, providing an estimated $5.3 to $12.1 billion in various heat-reduction services across the entire US urban population, including the avoidance of heat-related morbidity and mortality (McDonald et al. 2020). Given the temperature reductions UTC can pro- vide outdoors, many studies have tried to quantify the indoor energy savings from UTC in summer months. Studies have found that trees planted beyond 18 m of a home do not impact energy use by creating shade (McPherson et al. 1988; McHale et al. 2007; Donovan and Butry 2009; Nelson et al. 2012) and that maxi- mum shade benefit comes from larger trees planted ©2022 International Society of Arboriculture within 5 m of a home (Gómez-Muñoz et al. 2010; Hwang et al. 2015). Additionally, it is widely docu- mented that azimuth can play a role in the impact trees have on energy use, and that trees planted on the west, east, and south sides of homes yield the most energy savings during the cooling season in the Northern Hemisphere (Simpson and McPherson 1996; McPherson and Simpson 2003; Donovan and Butry 2009; Ko and Radke 2014; Hwang et al. 2015). For example, McPherson and Simpson (2003) used a simulated model and projected that planting 50 mil- lion shade trees to the east or west side of homes would reduce cooling energy use by 1.1% over 15 years. Despite well-documented evidence that UTC has potential to provide energy savings in the summer months, the magnitude of those savings varies largely throughout the literature. In North America alone, a recent review found substantial evidence to support the energy-saving effects of trees; however, the range of reduced cooling-energy consumption varied from 2% to 90% (Ko 2018). One reason for the differences in findings could be due to the dissimilar nature of simulation and empirical methods. Simulation stud- ies inherently come with various assumptions depending on the models, inputs, and software used. While they do not necessarily reflect real-world cases, they are still common in the literature. Empirical approaches, unlike simulation studies, use data from real-world scenarios. The methodology used in empir- ical studies varies considerably, with larger energy- saving performances being found from more controlled settings, such as treatment and control (tree shade and no shade) studies (Ko 2018). Other empirical studies use real energy-consumption data, but results are heavily dependent on the resolution and quality of the data obtained (Ko 2018). Variation in results can also be attributed to differences in study locations. Many studies that have looked at the impact of UTC have taken place in warmer climates, most notably in Cal- ifornia. However, even within the same metropolitan area of Sacramento, California, the estimated annual cooling energy savings per tree has ranged between 80 kWh and 180 kWh in simulation studies (Simpson and McPherson 1996; Ko et al. 2015). In an entirely different climate, Nelson et al. (2012) concluded that trees did not significantly impact summertime energy savings in the heavily forested Raleigh, North Caro- lina. Very few studies have addressed the impact of
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