Formulating Operational Mitigation Options and Examining Intra-Urban Social Inequality Using Evidence-Based Urban Warming Effects

Yuanhui Zhu,Yubin Li,Daoqin Tong,Danica Schaffer-Smith,Soe W Myint,Rebecca L Muenich

doi:10.3389/fenvs.2021.795474

Abstract

Human-induced climate change is bringing warmer conditions to the Southwestern United States. More extreme urban heat island (UHI) effects are not distributed equally, and often impact socioeconomically vulnerable populations the most. This study aims to quantify how land surface temperature (LST) changes with increasing green vegetation landscapes, identify disparities in urban warming exposure, and provide a method for developing evidence-based mitigation options. ECOSTRESS LST products, detailed land use and land cover (LULC) classes, and socioeconomic variables were used to facilitate the analysis. We examined the relationship between LST and the fractions of LULC and socioeconomic factors in the city of Phoenix, Arizona. A machine learning approach (Random Forest) was used to model LST changes by taking the LULC fractions (scenario-based approaches) as the explanatory variables. We found that vegetation features—trees, grass, and shrubs—were the most important factors mitigating UHI effects during the summer daytime. Trees tended to lower surface temperature more effectively, whereas we observed elevated daytime LST most often near roads. Meanwhile, higher summer daytime temperatures were observed on land with unmanaged soil compared to the built environment. We found that affluent neighborhoods experienced lower temperatures, while low-income communities experienced higher temperatures. Scenario analyses suggest that replacing 50% of unmanaged soil with trees could reduce average summer daytime temperatures by 1.97°C if the intervention was implemented across all of Phoenix and by 1.43°C if implemented within the urban core only. We suggest that native trees requiring little to no additional water other than rainfall should be considered. We quantify mitigation options for urban warming effect under vegetation management interventions, and our results provide some vital insight into existing disparities in UHI impacts. Future UHI mitigation strategies seriously need to consider low-income communities to improve environmental justice. These can be used to guide the development of sustainable and equitable policies for vegetation management to mitigate heat exposure impacts on communities.

Highlights

Urbanization, or the conversion of natural landscapes to the human-built environment, is driven by population growth and socioeconomic development (Bettencourt et al, 2007; Grimm et al, 2008; Peng et al, 2012; Seto et al, 2012)
We explored the relationship between urban land use and land cover (LULC) fractions, socioeconomic factors, and land surface temperature (LST) measured from ECOSTRESS satellite images in Phoenix
Vulnerable communities are disproportionately exposed to urban heat island (UHI), high summer daytime temperatures; disparities in exposure to UHI may cause a higher incidence of heat-related health problems in underprivileged communities

Summary

Introduction

Urbanization, or the conversion of natural landscapes to the human-built environment, is driven by population growth and socioeconomic development (Bettencourt et al, 2007; Grimm et al, 2008; Peng et al, 2012; Seto et al, 2012). The UHI is a important issue because it is leading to substantial challenges to urban ecosystem functionality (e.g., the loss of vegetation), the increase of energy and water consumption, and heightened risks of heat-related mortality and morbidity among vulnerable groups (Chen et al, 2006; Tran et al, 2006; Buyantuyev and Wu, 2010; Zhou et al, 2011; Jesdale et al, 2013; Wang et al, 2018) To counterbalance these negative impacts, formulating operational UHI mitigation options and examining intra-urban social inequality are needed. More attention should be paid to socioeconomic disparities in connection to LST

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