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The impact of green space on heat and airpollution in urban communities:A meta-narrative systematic reviewMARCH 2015

THE IMPACT OF GREEN SPACE ON HEAT AND AIR POLLUTION INURBAN COMMUNITIES: A META-NARRATIVE SYSTEMATIC REVIEWMarch 2015By Tara Zupancic, MPH, Director, Habitus ResearchClaire Westmacott, Research CoordinatorMike Bulthuis, Senior Research AssociateCover photos: centre by Jonathan (Flickr user IceNineJon) courtesy Flickr/Creative Commons, background by Jeffery Young.This report was made possible with the support ofthe Friends of the Greenbelt Foundation.Download this free literature review at davidsuzuki.org2211 West 4th Avenue, Suite 219Vancouver, BC V6K 4S2T: 604-732-4228E: [email protected]

Photo: Yけんたま/KENTAMA,courtesy Flickr/CCCONTENTSExecutive summary .4Introduction . 5Review purpose . 6Background: heat, air quality, green space and health . 7Method . 11Findings . 14Summary of findings . 41Recommendations .43Areas for future research .45Review limitations . 46Acknowledgements . 46Appendix A: Works cited .47Appendix B: Studies reviewed . 54Appendix C: Data extraction form .61Appendix D: Climate classifications . 64Appendix E: Key terms and definitions .65

EXECUTIVE SUMMARYIt is widely understood that urban green spaces have a natural ability to filter pollution from the air andreduce local air and ground temperature. This report analyzed 102 peer-reviewed studies publishedover the past five years that explored the role of urban green space in providing cooling effects andreducing air pollution.Not surprisingly, the report found that urban green spaces — from trees and parkettes to greenroofs and large natural spaces — generally provide significant health benefits for residents and thecommunity. It also found that these ecological benefits are directly related to the size, quality anddensity of the green space.Why is it important to reduce urban heat effects and air pollution? It is estimated that tens ofthousands of Canadians die prematurely each year due to acute air pollution and that high summertemperatures lead to increased illnesses, hospitalizations and deaths, especially among older adults.As the Canadian population ages and extreme heat waves become more common across the country,urban green spaces can provide essential, natural protection.This report examined various types and scales of green space, and generally found that urban greenspace can provide cooler, cleaner air at the site, neighbourhood and city level. Emerging evidence alsosuggests that closely spaced and connected smaller green spaces can provide greater cooling effectsto adjacent urban areas than large individual parks with open grass areas.It found that the density and spatial configuration of an urban forest — the sum of all urban trees,shrubs, lawns and pervious soils located in an urban setting — clearly affect land surface temperaturesin the city and that these elements are critical for improving urban air quality. In general, the researchsuggests that balancing urban forest density, particularly in areas with low green space density, wouldgreatly improve both local and city-wide urban air quality.Various plant species provide heat and pollution-mitigating capacities, and compact multi-layeringof diverse plant species can help improve overall resiliency to drought, heat and pollution. Amongplant types, trees have an exceptional ability to capture and filter multiple air pollutants, includingground-level ozone, sulphur dioxide, nitrogen oxides and particulate matter. Trees are also significantlyassociated with improved thermal comfort and relief from heat stress at the street level andneighbourhood scale, particularly during hot seasons and times of day.The report also highlighted growing evidence of disproportionate heat- and air-pollution-relatedhealth burdens associated with unequal distribution of green space in urban neighbourhoods. Furtherinvestigation is needed regarding the prevalence of green space-related health inequalities, consideringevidence in Canada that dense, low-income inner-city neighbourhoods are generally more vulnerable.The report concludes with recommendations that include improving the quantity, quality andconnectivity of green spaces; prioritizing green strategies for vulnerable urban areas; and integratinggreening policies with broader health and land-use planning policies.PAGE 4THE IMPACT OF GREEN SPACE ON HEAT AND AIR POLLUTION IN URBAN COMMUNITIES

INTRODUCTIONCities are amazing places. More than half the world’s people live, work, rest and play in urbancommunities, and it is estimated that by the year 2030, three out of five people will call a city home(Fuller & Gaston, 2009; Smith & Guarnizo, 2009). In Canada, we are ahead of the curve. More than81 per cent of us (over 27 million) live in urban areas. Between 2001 and 2006 the populations ofCanada’s six largest cities grew by almost eight per cent (Statistics Canada, 2011).While cities bring us together, their rapid and unprecedented growth has also brought seriouschallenges, including environmental degradation, loss of natural habitat and species diversity, andincreased human health risks associated with heat, noise, pollution and crowding. That means mostchildren are growing up in environments with increasing pollution, intense heat and less access todiverse green spaces (Alberti & Marzluff, 2004; Cohen, Potcher & Matzarakis, 2012; Girardet, 1996;Gregg, Jones & Dawson, 2003; Grimm et al., 2008; Hough, 2004; Moore, Gould & Keary, 2003;Newman & Jennings, 2008). Given these challenges, there is a critical need to find ways to reducehealth risks and maximize opportunities for well-being in all urban communities.In response to this need, the David Suzuki Foundation has undertaken a systematic review of theevidence to understand how green spaces can help to reduce heat, improve air quality and supporthealthy livable urban communities. This report was commissioned by the David Suzuki Foundation incollaboration with the EcoHealth Ontario Research Working Group.Photo: Young SokYun, courtesyFlickr/CCTHE DAVID SUZUKI FOUNDATIONPAGE 5

REVIEW PURPOSEWe know urban green spaces such as parks and urban forests can help reduce heat and improve airquality. Recent systematic reviews have assessed a range of evidence to understand the benefits andvalue of urban trees, urban parks and the overall effectiveness of green space to reduce heat, ozoneand ultraviolet (UV) radiation in urban areas (see Roy, Byrne & Pickering, 2012; Konijnendijk et al, 2013and Bowler, Buyung-Ali, Knight & Pullin, 2010). Trees and plants have a varying capacity to captureand/or filter air pollution, improve air circulation and decrease ambient temperatures. Despite this, thevast array of study topics, methods, green space types and examined plant species make it difficult todetermine the application of the evidence base in decision-making about community green space andhealth.A synthesis of the evidence to better understand how different, types, scales and characteristics ofurban greening can influnce heat and air polltuion, at both local and city-wide scales, is needed. Thismeta-narrative systemic review has been designed to respond to this need. The aim is to systematicallyidentify and synthesize evidence on the specific green space settings and conditions that influence heatand air quality to answer the question:What is the evidence that green space can support health in urban communities by reducing heat and airpollution?To answer this question, several question sets were developed to explore specific green space settingsand conditions that influence heat and air quality (see Table 1). This approach will help to clarify andaddress gaps identified in previous systematic reviews including the optimal amount, distribution andtypes of vegetation; differential impacts of green space scales; and, direct health impacts associatedwith reductions in heat and air pollution from greening (Bowler et al., 2010; Roy et al., 2012). The goalis to examine the state of the evidence, identify research gaps and make recommendations in supportof healthy communities.Table 1. Question sets to explore urban green space characteristics associated with heat and air pollution1.Green space type and scale: What types of green space are associated with heat and air pollutionmitigation (e.g., small green roof, large park, urban forest)? What studies, if any, compare different greenspace scales? What scales of impact have been documented (e.g., effect within green space area, effecton adjacent non-green areas, effect on entire city or region)?2. Vegetation type: What specific types of vegetation are associated with heat and air pollution mitigation(e.g., plant types)? What studies, if any, compare the effect of different vegetation types?3. Vegetation characteristics: What specific vegetation characteristics have been associated with heatand air pollution mitigation (e.g., vegetation density)? Do any studies compare the effect of differentvegetation characteristics?4. Modifying factors: What factors can modify the relationship between green space and heat or air quality(e.g., wind, season, time of day, surrounding infrastructure)?5. Negative impacts: What, if any, negative impacts or trade-offs associated with green space are identifiedin the evidence base (e.g., BVOC exposure, reduced visibility near roadways)?6. Health relevance: What health benefits have been directly associated with observed mitigation of heat orair pollution from green space?PAGE 6THE IMPACT OF GREEN SPACE ON HEAT AND AIR POLLUTION IN URBAN COMMUNITIES

BACKGROUND: HEAT, AIR QUALITY, GREEN SPACE AND HEALTHHEAT AND HEALTHHeat can be a killer. Data from around the world consistently show an association between increaseddaily temperatures and increased counts of deaths, illnesses and hospitalizations (Vutcovici, Goldberg& Valois, 2013). Older adults are particularly vulnerable. Heat-related health impacts (HRI) range frommild symptoms of fatigue and heatstroke to the worsening of preexisting illnesses, hypotension anddeath (Bernardo, Crane & Veenema, 2006; Bouchama & Knochel, 2002; Semenza, 1999; Simon, 1993).A systematic review showed that increases in heat-related morbidity is positively associated with agrowing aging population (Hajat & Kosatky, 2010). During the 2003 European heat wave, the majorityof the estimated 40,000 extra deaths from extreme heat were among older adults (García-Herreraet al., 2010). The results from a review of 15 European cities showed that even though Mediterraneanand North-Continental countries use different empiric thresholds to define a heat wave, they observedsimilar results for the 65- to 74-year-old populations across countries and strong and consistenttemperature-mortality associations for those above the age of 75 (Oudin Åström, Bertil & Joacim2011). Older adults are also more vulnerable due to social isolation (Hajat & Kosatky, 2010).Living in an urban centre increases vulnerability to heat exposure. A review on heat-mortalityrelationships in cities found that in almost half of the locations studied, the risk of mortality increasedbetween one percent and three per cent for every 1 C change in high temperature (Hajat & Kosatky,2010). Urban settings experience higher temperatures than rural areas due a lack of vegetation,properties of urban materials that have a greater thermal storage capacity, geometry of urban areas,release of waste heat (e.g., from vehicles and buildings) and a city’s size (Hajat & Kosatky, 2010).This is known as the urban heat island (UHI) effect. UHIs raise nighttime temperatures, leading togreater heat stress and limited relief from high temperatures (Kunkel et al., 1996; Harlan et al., 2006).As urban populations grow, the impact of the UHI effect becomes more dangerous. Globally, higherpopulation densities were found to correlate with higher temperatures and greater thermal discomfort,particularly in low-income settings where there is the least economic capacity to adapt in the face ofincreasing extreme heat events (Hajat & Kosatky, 2010; Harlan, Brazel & Prashad, 2006).In Canada, the number of seniors is expected to double by 2033 from about five million to 10 million(medium-growth scenario) with at least 75 per cent burdened by a chronic health condition (Sheets& Gallagher, 2013). A Toronto-based study found that, on average, for every one-degree C increase inmaximum temperature, there was a 29 per cent increase in ambulance response calls for HRI (Bassilet al., 2010). For every one-degree increase in mean temperature, there was a 32 per cent increase inambulance response calls for HRI (Bassil et al., 2010).With a rapidly aging population and most Canadians living in cities, strategies to provide relief fromheat and heat stress are important.THE DAVID SUZUKI FOUNDATIONPAGE 7

AIR QUALITY AND HEALTHAir pollution is a complex soup of chemicals and molecules that most of us breathe daily. By volume,infants and children breathe far more air than adults. For example, a resting infant breathes in twice asmuch air as an adult. This means they are more exposed to local air pollutants during a period whentheir lungs are going through vulnerable stages of development (Landrigan et al., 1998). Excess airpollution can lead to airway inflammation and reduced lung function and can worsen health problemssuch as asthma, chronic obstructive pulmonary disease and cardiovascular disease (Shah & Balkhair,2011).Common air pollutants include particulate matter (PM), sulphur dioxide (SO2), ground-level ozone(O3), nitrogen dioxide (NO2) and carbon monoxide (CO). In 2005, 89 per cent of the world’spopulation lived in areas where the World Health Organization Air Quality Guideline was exceeded(Brauer et al., 2012). Different air pollutants have different adverse health effects.Coarse particulate matter (PM10) is emitted from residential heating sources and power plants,whereas fine PM2.5 comes from cars, utilities and wood burning (Shah & Balkhair, 2011). The WorldHealth Organization estimates that PM contributes to approximately 800,000 premature deathseach year and 6.4 million lost years of healthy life in cities (Brauer, et al., 2012). The European Study ofCohorts for Air Pollution Effects (ESCAPE) review is the first multicentre study on the effects of longterm exposure to air pollution and mortality, and covers a study population of over 300,000 peoplein nine European countries. Most, but not all, studies showed statistically significant associationsbetween PM2.5 and PM10 and all-cause or natural-cause mortality. PM2.5 was the pollutant mostconsistently associated with natural-cause mortality in the study (Beelen et al., 2014). Analysis alsofound that for every increase of five micrograms per cubic metre of PM2.5 pollution, the risk of lungcancer rose by 18 per cent, and for every increase of 10 micrograms per cubic metre in PM10 pollution,the risk increased by 22 per cent. The analysis did not find a threshold below which there was no risk(Raaschou-Nielsen et al., 2013)A systematic review found exposure to sulphur dioxide (S02) was associated with pre-term births,while exposure to PM2.5 is associated with low birth weights, pre-term births and small for gestationalage births. Ozone exposure may also have negative effects on birth weight and neurodevelopment, butits direct effect on pregnancy outcomes is unclear (Shah & Balkhair, 2011).Canadian studies have reported significant associations between chronic exposure to traffic-related airpollution (specifically NO2) and an increased risk of ischemic heart disease (IHD) (Beckerman et al.,2012). Associations between ambient air pollution (nitrogen dioxide, sulphur dioxide, carbon monoxideand particulate matter with a diameter of 10 micrometres or less) and respiratory hospitalization,particularly for females up to age 14, have also been reported in Canada, as well as significantassociations between exposures to elevated levels of air pollutants and increased resting bloodpressure and lower ventilatory function (Luginaah et al., 2005; Cakmak et al., 2011).In Canada, about 10 million people (32 per cent of the population) live in areas where they are exposedto traffic-related air pollution (Brauer, Reynolds & Hystad, 2013). Approximately 54 per cent of theCanadian population lives within 500 metres of a major road or highway, leading to a high prevalencePAGE 8THE IMPACT OF GREEN SPACE ON HEAT AND AIR POLLUTION IN URBAN COMMUNITIES

of exposure (Brauer et al., 2013). Estimates suggest approximately 21,000 premature deaths arerelated to air pollution in Canada each year (Brauer et al., 2013).According to a 2008 report by Canadian Medical Association, the number of premature deathsassociated with chronic exposure to air pollution is expected to rise 83 per cent between 2008 and2031 (an estimated 90,000 deaths from the acute effects of air pollution and an estimated 710,000deaths due to long-term exposure to air pollution), with Quebec and Ontario bearing the largestproportion of acute premature deaths (Canadian Medical Association, 2008).Strategies to reduce local air pollution and improve air quality are important to the health of urbancommunities.UNDERSTANDING THE ROLE OF GREEN SPACE IN PROTECTING HEALTHY COMMUNTIESAs summarized, strong evidence documents the harmful health effects of extreme heat and airpollution. A large and growing evidence base also shows how green space can help to reduce heat andcombat air pollution in urban settings. A comprehensive systematic review by Bowler et al. in 2010assessed the effectiveness of greening strategies to reduce exposure to urban heat islands, groundlevel ozone, volatile organic compounds (VOCs) and nitrogen oxides (NOx). They assessed 212 studi

1. Green space type and scale: What types of green space are associated with heat and air pollution mitigation (e.g., small green roof, large park, urban forest)? What studies, if any, compare different green space scales? What scales of impact have been documented (e.g., effect within green space area, effect