Urban green space cooling effect in cities

Critical review on the cooling effect of urban blue-green space: A threshold-size perspective

The absence of vegetation in urban areas contributes to the establishment of the urban heat island, markedly increasing thermal stress for residents, driving morbidity and mortality. Mitigation strategies are, therefore, needed to reduce urban heat, particularly against a background of urbanization, anthropogenic warming and increasing frequency and intensity of heatwaves. In this Review, we evaluate the potential of green infrastructure as a mitigation strategy, focusing on greenery on the ground (parks) and greenery on buildings (green roofs and green walls). Green infrastructure acts to cool the urban environment through shade provision and evapotranspiration. Typically, greenery on the ground reduces peak surface temperature by 2–9 °C, while green roofs and green walls reduce surface temperature by ~17 °C, also providing added thermal insulation for the building envelope. However, the cooling potential varies markedly, depending on the scale of interest (city or building level), greenery extent (park shape and size), plant selection and plant placement. Urban planners must, therefore, optimize design to maximize mitigation benefits, for example, by interspersing parks throughout a city, allocating more trees than lawn space and using multiple strategies in areas where most cooling is required. To do so, improved translation of scientific understanding to practical design guidelines is needed. The urban heat island effect poses increasing morbidity and mortality challenges in a warming world. This Review discusses how urban vegetation — specifically, green parks, green roofs and green walls — can be used as a strategy to mitigate heat.

Greenery as a mitigation and adaptation strategy to urban heat

Importance Recent studies indicate that living near more green space may support mental and general health and may also prevent depression. However, most studies are cross-sectional, and few have considered whether some types of green space matter more for mental health. Objective To assess whether total green space or specific types of green space are associated with better mental health. Design, Setting, and Participants This cohort study included a residentially stable, city-dwelling sample of 46 786 participants from Sydney, Wollongong, and Newcastle, Australia, in the baseline of the Sax Institute’s 45 and Up Study (data collected from January 1, 2006, to December 31, 2009). Follow-up was conducted from January 1, 2012, to December 31, 2015. Analyses were conducted in January 2019. Exposures Percentage of total green space, tree canopy, grass, and other low-lying vegetation measured within 1.6-km (1-mile) road network distance buffers around residential addresses at baseline. Main Outcomes and Measures Three outcome variables were examined at baseline (prevalence) and follow-up (incidence without baseline affirmatives): (1) risk of psychological distress (10-item Kessler Psychological Distress Scale), (2) self-reported physician-diagnosed depression or anxiety, and (3) fair to poor self-rated general health. Results This study included 46 786 participants (mean [SD] age, 61.0 [10.2] years; 25 171 [53.8%] female). At baseline, 5.1% of 37 775 reported a high risk of psychological distress, 16.0% of 46 786 reported depression or anxiety, and 9.0% of 45 577 reported fair to poor self-rated health. An additional 3.3% of 32 991 experienced psychological distress incidence, 7.5% of 39 277 experienced depression or anxiety incidence, and 7.3% of 40 741 experienced fair to poor self-rated health incidence by follow-up (mean [SD] of 6.2 [1.62] years later). Odds ratios (ORs) adjusted for age, sex, income, economic status, couple status, and educational level indicated that exposures of 30% or more total green space (OR, 0.46; 95% CI, 0.29-0.69) and tree canopy specifically (OR, 0.69; 95% CI, 0.54-0.88) were associated with lower incidence of psychological distress. Exposure to tree canopy of 30% or more, compared with 0% to 9%, was also associated with lower incidence of fair to poor general health (OR, 0.67; 95% CI, 0.57-0.80). Exposure to grass of 30% or more, compared with 0% to 4%, was associated with higher odds of incident fair to poor general health (OR, 1.47; 95% CI, 1.12-1.91) and prevalent psychological distress (OR, 1.71; 95% CI, 1.25-2.28). Exposure to low-lying vegetation was not consistently associated with any outcome. No green space indicator was associated with prevalent or incident depression or anxiety. Conclusions and Relevance Protection and restoration of urban tree canopy specifically, rather than any urban greening, may be a good option for promotion of community mental health.

/pdf/association-of-urban-green-space-with-mental-health-and-16x31rpdqk.pdf

Association of Urban Green Space With Mental Health and General Health Among Adults in Australia.

Evaluation of green infrastructure effects on tropical Sri Lankan urban context as an urban heat island adaptation strategy

The influence of small green space type and structure at the street level on urban heat island mitigation

Extreme heat exposure has severe negative impacts on humans, and the issue is exacerbated by climate change. Estimating spatial heat stress such as mean radiant temperature (MRT) is currently difficult to apply at city scale. This study constructed a method for estimating the MRT of street canyons using Google Street View (GSV) images and investigated its large-scale spatial patterns at street level. We used image segmentation using deep learning to calculate the view factor (VF) and project panorama into fisheye images. We calculated sun paths to estimate MRT using panorama images from Google Street View. This paper shows that regression analysis can be used to validate between estimated short-wave, long-wave radiation and the measurement data at seven field measurements in the clear-sky (0.97 and 0.77, respectively). Additionally, we compared the calculated MRT and land surface temperature (LST) from Landsat 8 on a city scale. As a result of investigating spatial patterns of MRT in Seoul, South Korea, we found that a high MRT of street canyons (>59.4 °C) is mainly distributed in open space areas and compact low-rise density buildings where the sky view factor is 0.6–1.0 and the building view factor (BVF) is 0.35–0.5, or west-east oriented street canyons with an SVF of 0.3–0.55. However, high-density buildings (BVF: 0.4–0.6) or high-density tree areas (Tree View Factor, TVF: 0.6–0.99) showed low MRT (<47.6). The mapped MRT results had a similar spatial distribution to the LST; however, the MRT was lower than the LST in low tree density or low-rise high-density building areas. The method proposed in this study is suitable for a complex urban environment consisting of buildings, trees, and streets. This will help decision makers understand spatial patterns of heat stress at the street level.

/pdf/estimation-of-mean-radiant-temperature-in-urban-canyons-17r8leym.pdf

Estimation of Mean Radiant Temperature in Urban Canyons Using Google Street View: A Case Study on Seoul

Impact of climate and socioeconomic changes on fire carbon emissions in the future: Sustainable economic development might decrease future emissions

Landscape Design for Improved Thermal Environment: An Optimized Tree Arrangement Design for Climate-Responsive Outdoor Spaces in Residential Buildings Complexes

Developing a Three-Dimensional Urban Surface Model for Spatiotemporal Analysis of Thermal Comfort with Respect to Street Direction

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