Objectives. We investigated the health and safety effects of urban green stormwater infrastructure (GSI) installments. Methods. We conducted a difference-in-differences analysis of the effects of GSI installments on health (e.g., blood pressure, cholesterol and stress levels) and safety (e.g., felonies, nuisance and property crimes, narcotics crimes) outcomes from 2000 to 2012 in Philadelphia, Pennsylvania. We used mixed-effects regression models to compare differences in pre- and posttreatment measures of outcomes for treatment sites (n?=?52) and randomly chosen, matched control sites (n?=?186) within multiple geographic extents surrounding GSI sites. Results. Regression-adjusted models showed consistent and statistically significant reductions in narcotics possession (18%–27% less) within 16th-mile, quarter-mile, half-mile ( P .001), and eighth-mile ( P .01) distances from treatment sites and at the census tract level ( P .01). Narcotics manufacture and burglaries were also significantly reduced at multiple scales. Nonsignificant reductions in homicides, assaults, thefts, public drunkenness, and narcotics sales were associated with GSI installation in at least 1 geographic extent. Conclusions. Health and safety considerations should be included in future assessments of GSI programs. Subsequent studies should assess mechanisms of this association. Exposure to trees, vegetation, nature, or green space in urban areas has been connected with multiple public health benefits, including reduced mortality, 1–3 morbidity, 4 stress, and mental fatigue. 5–7 In addition, a growing body of research has investigated the relationship between urban nature and public safety, although with mixed results. Multiple studies have found that dense vegetation may promote crime by providing criminals a place to hide themselves or illegal goods. 8–10 Other studies have found that urban nature is associated with reduced crime. As a broad measure of urban nature, vegetation abundance has been linked to reductions in violent crimes, property crimes, 11 assault, robbery, and burglary. 12 Other studies have used more specific measures. For example, larger crown spreads of street trees and residential lot trees have been associated with fewer total crimes, property crimes, and vandalism. 3,13 Another study found that increased tree canopy cover was associated with reduced incidents of shooting, theft, robbery, and burglary, especially on public lands. 13 A study of the cleaning and greening of vacant lots found significant reductions in gun assaults and vandalism. 14 One challenge in interpreting these studies for management purposes is that they often use coarse measures of both nature and safety. Public safety outcomes have traditionally emphasized measures such as total crimes, violent crimes, and property crimes. Few have investigated the effects of urban nature on specific crimes or health behaviors such as drug use and possession, illegal dumping, vandalism, and public drunkenness and disorderly conduct. In addition, with few exceptions, 11,14,15 previous studies have not applied an experimental or quasiexperimental approach to test whether urban greening can improve health and safety. Little is known about the mechanism of association between urban nature and crime. The broken windows theory 16 holds that disordered and disinvested urban environments promote criminal activity. Blighted urban environments like this can erode a sense of mutual regard among residents and passers-by, signaling that no one cares and that illegal activity will be tolerated in a space. 16,17 Greened, openly visible, and ordered spaces may contribute to defensible space, indicating territory, surveillance, and care for a space, which may reduce opportunities for violence and crime. 18–20 Other mechanistic pathways that may connect urban nature and crime are social cohesion and psychosocial stress. Environmental factors, such as vacancy, physical decay, noise, pollution, and crowding, can provoke a physiological stress response that can aggravate aggression and violence. 21 Green space may help prevent and mitigate stress, anxiety, and depression. 22,23 Access to green views has been shown to reduce mental fatigue and improve coping with stressful urban environments. 5,6 Greening has also been associated with a stronger sense of safety and feeling of security. 15 Green stormwater infrastructure (GSI) is an emerging form of urban greening initiative in the United States and other countries. Approximately 700 cities across the United States have outdated combined sanitary and storm sewer systems that are subject to overflow during heavy rain events. 24 The US Environmental Protection Agency estimates that 850 billion gallons of combined sewer overflow discharge occurs each year in the United States. State and federal regulations, in addition to concerns about public health, ecosystem health, and climate change, have put cities under mandate to reduce
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