Evaluating Impacts of a Cool Block Intervention: A Community Engaged Study

Background. As temperatures across the globe get hotter and stay hotter for longer periods of time, cities and towns continue to look for ways to cool down neighborhoods for their residents. One approach that decision makers in cities are taking is implementing multiple cooling interventions in hot neighborhoods, for example increasing recreational park space, planting trees and increasing surface reflectivity through white roofs and pavement changes. However, there is a challenge in measuring the resulting benefits. This is particularly relevant in urban environmental justice neighborhoods, which are typically local heat islands due to a history of disinvestment and racist practices that has resulted in limited greenspace and extensive impervious surface areas.

Each summer, the City of Chelsea, an environmental justice community in Massachusetts, faces extreme heat that grows worse with climate change. A collaboration between community residents, youth, academic researchers, and city staff identified “hot pockets” in the city, collected temperature data, and are working to make the city cooler. With private and public funding, the Chelsea & East Boston Heat Study (C-HEAT), a partnership of researchers at Boston University School of Public Health and GreenRoots, Inc, a local grassroots environmental justice organization, engaged with the City of Chelsea to identify a specific neighborhood block within Chelsea as being one of the hottest, most vulnerable and highly impacted areas of the city. Together we call it the “Cool Block”, and interventions implemented in the last three years included planting dozens of new trees along two sides the block, replacing the pavement of a corner into a lighter color and pervious pavers. Additionally, in collaboration with a local landscape firm, an unused lot at the end of the block was transformed into temporary greenspace and a playground, based on design charettes created with the Cool Block neighboring residents. The work presented here includes evaluation results of the Cool Block interventions.

Methods. The impact of the Cool Block on multiple temperature metrics was evaluated through longitudinal ambient temperature monitoring collected during the summer between 2021 and 2023. Temperature and relative humidity were monitored with HOBO sensors which recorded measurements every 10 minutes. Sensors were installed at ~3-meter height in city trees located in public rights of way. Based on satellite-based land surface temperature maps, sensors were placed in three hotter and cooler neighborhoods around the city, and at the Cool Block four sensors were located to capture hyperlocal temperature variability. Temperature summary statistics, hot days and heat waves were calculated at each sensor location and compared spatially and temporally. Non-temperature community benefits were captured through communications with community partners and community engaged activities such as community meetings, a survey administered through a neighborhood door knocking campaign, and meetings with tree keeper neighbors living near the Cool Block.

Results. We found that the different temperature indicators at the Cool Block changed over the first several years. When comparing the observed ambient temperatures around the Cool Block and three reference sites within the City of Chelsea, we found that the temperatures around the Cool Block were comparable to other hot neighborhoods within the city before the interventions took place and become cooler after the interventions had been implemented. Notably, during a 10-day hot period in 2020, before the interventions were implemented, the Cool Block was hotter than a reference site located in a comparably dense, core urban area 78% of the 10-day hourly period. By 2023, the first full year after the interventions had been implemented, the Cool Block was hotter than the reference site only 3% of the 10-day hot period for that year. Non-temperature benefits from the Cool Block collaboration included the fact that a vacant lot was deeded to the city for the purpose of transforming it into a park, with leadership from GreenRoots. Additionally, community engagement around the Cool Block increased awareness of extreme heat and opportunities for solutions, community empowerment to drive change, and increase in national attention and funding for community-led climate initiatives.

Conclusion. In addition to the interdisciplinary collaboration of this research, effective community engagement is underscored as a key aspect to this project. This work demonstrates that cooling even small urban areas provides both temperature and community resilience benefits, particularly in environmental justice neighborhoods. Additionally, we show the critical value of cross-sector stakeholder collaborations (i.e. community organization-city-researcher-business) to advance the mission of cooling vulnerable neighborhoods in cities.