Regulatory requirements and voluntary interventions create contrasting distributions of green stormwater infrastructure in Baltimore, Maryland

Abstract

Green stormwater infrastructure (GSI) has been increasingly promoted as a strategy to augment gray infrastructure because it can reduce flooding, improve water quality, and provide additional social and ecological benefits. Government regulations in many places now require or encourage the use of GSI to mitigate impacts of development, while numerous funding opportunities incentivize installation of additional GSI features to enhance community and environmental benefits. The equity of GSI benefits may be affected by these different underlying motivations for GSI installation—mandatory compliance with regulations vs voluntary community improvement—which could create distinct patterns of GSI across the landscape. We examined this hypothesis in Baltimore, Maryland, USA, by comparing the city’s database of GSI facilities that meet regulatory requirements (“regulatory GSI”) to a dataset we compiled of GSI installed voluntarily by nonprofit organizations and community groups (“voluntary GSI”). We found that regulatory GSI included more facility types than voluntary GSI, which was dominated by microscale practices like rain gardens. The presence of regulatory GSI was negatively related to greater Black populations, while voluntary GSI was more likely to be found both in low-income areas with predominantly Black populations and in high-income areas with predominantly white populations. Voluntary GSI was much more commonly located on public land, and GSI on public land tended to be in more disadvantaged areas. These patterns of GSI distribution, which reflect different motivations and constraints in a fragmented implementation process, provide an opportunity for improving equitable access to GSI benefits through more systematic planning and management efforts.