Health implications of urban tree canopy policy scenarios in Denver and Phoenix: A quantitative health impact assessment

Abstract

Background: Urban tree canopy (UTC) goals are a popular policy to increase urban vegetation, support climate strategies, and encourage a healthy environment. Health studies related to UTC are needed across cities to support evidence-based decision-making.Methods: We used a quantitative Health Impact Assessment (HIA) to model the annual number of premature deaths prevented, and the number of stroke and dementia cases, under UTC goals in Denver, Colorado, and Phoenix, Arizona, USA, using standing policy goals (20% and 25% UTC, respectively) and 50% (“half-way”) attainment scenarios from current levels (16.5% and 13% UTC, respectively), using publicly accessible national datasets, and a proportional representation of UTC change to standardize across methodologies. We estimated UTC health impacts by relating UTC with scenario-based changes in the Normalized Difference Vegetation Index (NDVI) and considered health equity in UTC distributions and benefits.Results: We projected that at 2020 populations, uniform 20% UTC attainment across Denver block groups would avert 200 (95% uncertainty interval: (UI) 100, 306) annual premature deaths among adults 18 and older, along with 4.1 (95% UI: 2.2, 6.7) annual cases of stroke (adults ≥35), and 2.6 (95% UI: 1.5, 4.1) cases of dementia (adults ≥65), with “halfway” attainment from current levels (16.5% UTC) capturing ∼64% of these benefits. In Phoenix, uniform 25% UTC would annually prevent 368 (95% UI: 181, 558) premature deaths, 8.7 (95% UI: 4.7, 13.9) cases of stroke, and 5,1 (95% UI: 2.9, 8.0) of dementia, with the “halfway” scenario (17% UTC) achieving ∼44% of these results. Both cities saw significantly different greenspace exposures and health outcomes by socioeconomic vulnerability. Denver had more spatially and socioeconomically heterogeneous projected health benefits than Phoenix.Conclusions: Implementing UTC goals can prevent excess mortality and chronic diseases among urban residents. UTC goals can be used as a health promotion and prevention tool.