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

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.

An Innovative Scheme to Confront the Trade‐Off Between Water Conservation and Heat Alleviation With Environmental Justice for Urban Sustainability: The Case of Phoenix, Arizona

“…The desert‐adapted trees require minimum irrigation under most circumstances. In contrast, other non‐native tree species (e.g., deciduous trees, orchards) that grow widely in local neighborhoods rely on extensive irrigation to stay alive in a desert region (C. Wang et al., 2021; Zhu et al., 2022). Even so, overall, trees present higher water use efficiency than grass.…”

“…Hence, the GWR model is integrated into the spatial optimization models to predict LST and OWU changes with LULC changes when optimizing the configuration of new green space. We hypothesized that the spatial variation in LST and OWU is due to landscape heterogeneity (Zhu et al., 2022). Thus, GWR model can be built to predict LST and OWU (Gober et al., 2012; C. Wang et al., 2021; Zhang et al., 2022).…”

“…In general, a more significant cooling effect can be produced by adding new green spaces. However, in practice, they are restricted by limited land resources, budgets, and water resources (Gober et al, 2009(Gober et al, , 2012Zhang et al, 2017;Zhu et al, 2022). For instance, Gober et al (2012) explored the trade-off between water conservation and temperature reduction in Phoenix, Arizona, and Portland, Oregon by building simple regression relationships, which showed that increasing green infrastructure could lower urban temperatures but increase outdoor water use (OWU) by ∼20%.…”

“…It is reported that Phoenix had over three times more heat-related emergency 911 dispatches than Chicago during the four years from 2003 through 2006 (Hartz et al, 2013). Urban surface temperatures in Phoenix have demonstrated that the lower-income neighborhoods often face more significant risks of heat-related mortality and morbidity than those living in wealthier neighborhoods, which rise the social inequality issue (Jenerette et al, 2011;Sheehan et al, 2022;Zhu et al, 2022). Significantly, in the context of urban climate change, trends in environmental changes (e.g., LST and OWU change trends) are outstanding variables for identifying the opportunity areas representing favorable areas where OWU can be lowered for future water conservation (Gober et al, 2009(Gober et al, , 2012.…”

Spatio-temporal analysis of urban heat island (UHI) and its effect on urban ecology: The case of Mekelle city, Northern Ethiopia

“…UTFVI has an advantage over other indicators because it exclusively uses thermal satellite data, which enables it to provide a large-scale urban proxy value for SUHI impacts at the pixel resolution level as well as a categorical ecological rating scale for rapid assessments of the quality of the global urban thermal environment with extended, demonstrated reliability across various climatic regions and urbanization [ 31 ]. The energy balance impacts produced by the various land classes and their geographical distribution in the urban area have an impact on how strongly SUHI consequences are perceived [ 32 ].…”