Optimizing the spatial arrangement of trees in residential neighborhoods for better cooling effects: Integrating modeling with in-situ measurements

Abstract

A B S T R A C TTrees have long been recognized as effective for mitigating urban heat islands by reducing air temperature through evapotranspiration and intercepting shortwave radiation that heat up land surfaces. Many studies have shown that both the composition and configuration of vegetation can contribute to heat reduction at the city scale. Fewer studies, however, have focused on cooling mechanisms at the neighborhood scale. Here, we integrate modeling with in situ measurements to investigate how different spatial arrangements of trees in residential neighborhoods affect their cooling effects. We conducted the research in a residential neighborhood with high-rise apartment buildings in Beijing. We tested four scenarios with different spatial arrangements of trees, and quantified their effects on cooling. We used the high spatial and temporal resolution microclimate model ENVI-met and validated the model with in situ measurements. We found: (1) Different spatial arrangements had differentiated effects on intercepting shortwave radiation, which led to variations in air temperature. For example, new trees that were completely exposed to solar radiation had stronger cooling effects (air temperature was 0.22°C lower) than new trees that were located in the shadow of surrounding buildings. (2) Different spatial arrangements led to obviously different effects of sensible heat reduction, with a maximum difference of 14.84 × 10 8 J/ha. Our results underscore the importance of the spatial arrangement of trees on cooling in residential neighborhoods. These results have important implications in urban planning and design at the neighborhood scale.

Seasonal Variation in Air Temperature and Relative Humidity on Building Areas and in Green Spaces in Beijing, China

“…Tan et al (2015) noted that shade was the main factor providing the cooling effect of trees (Tan et al, 2015). Wu and Chen (2017) certified that trees had effects on the interception of shortwave radiation and reasonable heat abatement (Wu and Chen, 2017). Furthermore, the cooling effect of the park might be due to evapotranspiration and the higher albedo of green vegetation, which retains less solar heat and lower ambient temperatures than do impervious surfaces (Shahmohamadi et al, 2011).…”

Urban Warming and Cities’ Microclimates: Investigation Methods and Mitigation Strategies—A Review

“…The acquired results revealed a maximum summer T air reduction, ranging between 2.1 • C and 5.0 • C, depending on the examined vegetation scenario, while a significant decrease of T mrt , even up to 35.0 • C, has been also achieved, due to the radiation control by the trees' foliage. In the same context, Wu and Chen [112] have investigated the effect of increasing the GCR by 10% in areas having different surface densities in Beijing, China on the local microclimatic conditions. A reduction on the peak T air between 0.20 • C and 0.50 • C was found, under summer conditions, while the average diurnal T air decrease did not exceed 0.10 • C in all cases.…”

Green Infrastructure as an Urban Heat Island Mitigation Strategy - A Review

“…The research also found that trees were planted in high density areas are more effective in improving thermal comfort condition than those were planted in open spaces. Some studies regarding urban trees suggested that arrangement of trees led to sensible heat reduction and temperature variation [19,48]. Although trees bring positive impact to the environment, especially on the microclimate and thermal comfort, trees can also act as barriers and decrease wind speed, which ultimately will increase heat stress at a pedestrian level [37,46].…”

“…University campuses were frequently used as field measurement areas [18,84,89,90]. Some of the studies were performed in residential areas [19,45,61], heritage sites/old city [81,91], urban parks [20] and coastal area [66].…”

“…Considering potential harmful impacts of UHI to human lives, mitigation approaches are currently a major priority for researchers. Several studies have proposed, developed and implemented mitigation strategies such as: (1) modification of building and surface material [13,14], (2) alteration of urban morphology [15,16], (3) installation of irrigation systems [17] and (5) inclusion of Green Infrastructure (GI) in the planning of cities [18][19][20]. In a broad term, GI is defined as "interconnected network of green spaces that conserve natural systems and provides assorted benefits to human population" [21].…”