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

Cities in warmer climate zones have experienced extreme heat and unbearable drought conditions due to climate change. Developing a practical and integrated framework to tackle the trade-off between land surface temperature (LST) reduction and water conservation is essential for heat mitigation and resilience planning. We developed a multi-objective framework of spatial optimization for priority areas that considers environmental justice. We identified the priority areas (i.e., residential districts, socio-economically disadvantaged neighborhoods, hotspot regions, and opportunity areas) using ECOSTRESS-based LST, actual evapotranspiration (ETa, as a proxy to outdoor water use [OWU]), Landsat-based LST and ETa changes (2000–2020), and the evaporative stress index. The configuration of vegetation was spatially optimized to achieve the highest co-benefits by equally balancing both objectives. We found that LST decreased and OWU increased as the vegetation percentage rose from 25% to 45%. The trade-off between heat reduction and water conservation indicates that LST is not significantly reduced, as OWU reaches above the mid-level if we focus mainly on LST reduction. The associated green space configurations suggest that grass coverage gradually increases as tree coverage decreases slightly in unmanaged soil. Overall, hotspot regions have a higher potential to lower LST by consuming less water than other areas with the same percentage of new vegetation. Based on this perspective, we suggest that urban planners and city managers prioritize hotspot regions by considering environmental justice and co-benefits to ensure highly efficient LST amelioration and OWU conservation.