Because wet weather events have been increasingly overwhelming urban stormwater management systems, cities have been turning to green stormwater infrastructure (GSI) to relieve pressure on existing stormwater systems. Vegetated GSI strategies, including bioretention cells and rain gardens, provide additional, nature-based tools to slow, disperse, and/or infiltrate polluted runoff before it reaches local waterways. While the many environmental and social benefits of GSI strategies have been well-researched, life cycle assessments (LCAs) of GSI greenhouse gas emissions impacts is lacking due to inconsistencies in measurement frameworks and difficulty assessing certain carbon footprint components (e.g., emission/sequestration by vegetation). GSI strategies have been tentatively found to have lower emissions impacts than their grey counterparts, and as GSI technologies subsequently become an increasingly more integral part of urban fabrics, it is important to make an effort to choose strategies with the lowest carbon emissions impact in the interest of the future implications on the climate. Synthesizing emissions-driving actions relating to the implementation and maintenance of GSI strategies also provides valuable feedback to landscape architects and engineers as they continuously update and improve GSI designs.
Through a review of current limited literature measuring GSI LCAs and/or greenhouse gas emissions impacts of vegetated GSI strategies, we suggest a standardized set of guidelines or assumptions about what to include in LCAs of GSI greenhouse gas emissions. We also identify critical gaps in measurement of certain carbon footprint components (e.g., vegetation emissions from tree stems), and synthesize GSI design and management implications based on existing literature. With a standardized set of guidelines, groups can enact further studies, strengthen the knowledge about GSI emissions, and eventually guide policymakers in their decisions to more responsibly include GSI in their city climate action plans.