Collaborative Research: Geoengineering of Urban Green Infrastructure to Improve Outdoor Livability

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Urban population in the United States is confronted with degraded air quality and elevated thermal stress, especially under heat waves. These two environmental stressors impact human health impose new challenges to urban livability. Urban green infrastructure (UGI), as an integral part of the built environment, has been considered as one of the effective mitigation strategies for potentially improving air quality and reducing thermal stress. Past research extensively evaluated the impact of UGI on either heat or air pollution separately but a few recent studies account for the non-trivial interactions between heat and air pollution. Such interactions raise the question of whether heat and air pollution mitigation is always achievable when implementing UGIs. This project therefore aims to elucidate how UGIs impact the interactions between urban thermal environment and air pollution across multiple spatial scales. Additionally, this project will develop a new method for evaluating the design strategies of UGI by considering the human health implications of heat stress and air pollution combined. The project will address two scientific questions: 1) How does the occurrence of extreme heat events affect the joint impacts of heat and air quality? 2) What mitigation outcomes are expected given different design strategies of UGI under normal and extreme heat conditions? To answer these questions, the research team will apply the Weather Research and Forecast model (WRF) coupled with chemistry (Chem) and urban canopy model (UCM) with improved representation of UGI. The coupled model will be evaluated with observational data under normal summer and high temperature conditions. The effects of the present UGI in both NYC and Phoenix in mitigating heat stress and air pollution will be quantified by considering a combined statistic that measures the joint health impacts. Different UGI implementations (spatially undifferentiated vs. targeted) at both the neighborhood and city scales will be evaluated. The study will include: (i) integrated representation of urban vegetation at the neighborhood scale in the urban canopy model; (ii) a process-based method based on a combined statistic to evaluate the health impacts of heat stress and air pollution at the neighborhood and city scales; (iii) fusing livability assessment, urban climates, and urban planning on multiple spatial scales through synergistic activities with landscape architects and stakeholders. Advanced numerical atmospheric physics and chemistry modeling, in conjunction with a new approach for analysis and quantification of UGI design scenarios is targeted to shed new light on engineering solutions and environmental sustainability. The main research outcomes anticipated are: (1) a process-based approach to systematically examine the influence of vegetation for both local climate zones and city level; (2) a portfolio of urban landscape planning strategies at the neighborhood scale, that is scalable to the city level; (3) a novel objective indicator of outdoor livability informed by new science based on heat- pollution coupling. Close interaction with landscape architects and stakeholders will facilitate public awareness of the importance of urban green infrastructure, particularly for environmental stressors that have important consequences of sustainable and healthy outdoor livability. An initiative for establishing a shared database for the urban livability indicators with different UGI scenarios will be established at the end of the project, accessible to other academic researchers, citizens, and stakeholders.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.