Evaluation of Green Infrastructure Co-benefits Across Various Regions in the United States

The utilization of Green Infrastructure (GI) technologies in stormwater management plans has increased in municipalities due to their capacity to reduce flooding and water pollution. These GI technologies are often vegetation covered infrastructure with storage capacity. In addition to the direct benefits of water storage and water quality improvement, GI can provide social and ecological 'co-benefits,' externalities that are provided by the vegetation used in GI. This study aims to compare the co-benefits under different GI design types and project scales among several cities and provide recommendations for selecting GI designs that maximize co-benefits. It builds off previous research of quantifying co-benefits of commonly used trees in GI systems across five United States cities (Baltimore, Denver, New York City, Philadelphia, Portland). The current study uses the i-Tree Eco urban forestry model to predict various co-benefits for trees. A 'composite' tree was used in this study to represent the average individual tree's co-benefits based on the frequency of tree species planting. Municipal scale co-benefits were estimated by the number of trees used by GI design types and GI systems employed in each city through inspection of GI manuals. The co-benefits of carbon storage and sequestration, air pollution removal, UV reduction, and the cooling effects of the trees used in GI were quantified and compared among the study cities. The results of this study present valuable insights into the co-benefit evaluation among different GI in each of the cities. Regional environmental factors, differences in municipal design, and implementation scales, were evaluated to find what influences the assessment of GI co-benefits. The project scale of certain designs in each city heavily influenced the number of trees in GI systems (Figures 1-2). Large scale GI, such as tree-lined extended detention basins, employ more trees per unit than small scale GI systems like rain gardens. Furthermore, there were more co-benefits provided in cities with large-scale GI (Figure 3). Regional differences were evident among the cities as environmental factors influenced the value of co-benefits across different climates. Small scale GI performed better in humid cities in the east and Portland than an arid city like Denver (Figure 4). This research expands on current literature in developing GI programs that provide the highest quantity of co-benefits for specific climates and cities.