The Impacts of Urban Green Infrastructure on Water and Energy Resources: Lessons from and the Need for Integrated Studies

Green infrastructure (GI) can bring both water and energy benefits to urban environments. Yet, installation and maintenance may incur additional water and energy demand. This chapter synthesizes to what extent and how existing empirical and modeling studies generally quantify GI impacts on urban water and energy resources and which impacts and performance affecting factors are applied in green roof studies. We conclude that relatively few studies quantify impacts on both water and energy resources. Studies tend to focus on positive impacts, such as heat abatement, energy savings, and runoff reduction, with little attention for negative impacts, such as energy demands or emissions. From a water and energy perspective, green roofs are the most promising urban GI. They are easy to install and maintain in dense urban areas, reduce energy demand, and require little water. Yet, impacts of green roofs highly depend on local climate and design, especially structural and storage parameters, vegetation, and soil depth. Moreover, their performance depends on vegetation, soil moisture, substrate characteristics and depth; and different combinations of these factors lead to important tradeoffs for water and energy. The results call for extending and improving life cycle assessments, by quantifying negative impacts such as the energy costs of irrigation, and optimizing the identified tradeoffs.