Interactions between background climate, urban morphology, and rain garden cooling potential

While green stormwater infrastructure (GSI) is a promising tactic for combating the effects of urbanization and climate change, its effect on the local climate is still not fully understood. Temperature reduction is commonly cited as a co-benefit due to evapotranspirative cooling from vegetated GSI, particularly by planners and policymakers who are more focused on heat stress adaptation. However, while evapotranspiration does provide cooling, it also increases the atmospheric moisture, potentially altering the local surface hydroclimate. Additionally, cooling performance is not fully understood across background climates and urban form. In this work, we use an Earth system model to examine the relationship between widespread implementation of rain gardens, our representative vegetated GSI technique, and resulting impacts to the urban hydroclimate across cities in the contiguous United States. Our results illustrate that while rain garden implementation does decrease the summer air temperature across most locations, there is typically a corresponding increase in humidity, ultimately leaving the human perception of temperature unchanged in many locations. These results are encouraging from a stormwater management perspective, but may not be an ideal outcome if GSI has been adopted in part for its heat stress adaptation capabilities. We find strong evidence that background climate influences the strength of rain garden impacts on the urban thermal environment, in addition to urban morphology. Suburban areas are more likely to benefit from implementation than their urban core counterparts.