Green Roof Mitigation Potential for a Proxy Future Climate Scenario in Chicago, Illinois

Abstract

The Advanced Research version of the Weather Research and Forecasting Model (ARW) coupled with an urban canopy model is used to investigate the potential of vegetative (green) roof technology to mitigate against ongoing climate warming and continued urban sprawl for a day representing average summer conditions in late-twenty-first-century Chicago, Illinois. Effects related particularly to human health hazards resulting from excessive heat and high pollution concentrations are emphasized. Continued expansion of the urban environment over the next century is shown to lead to an expansion of the warming signal across the metropolitan region. Widespread adoption of vegetative rooftops, through increased albedo and evapotranspiration, reduces temperatures in the urban environment by as much as 3°C, an effect similar to the simpler but less appealing alternative of employing painted or other reflective rooftop structures (e.g., white roofs). A significant limitation to the green roof approach for the case studied is that the increase in moisture resulting from transpiration leads to only marginal cooling when apparent temperatures are considered. An additional complication arises in that the reduced temperatures alter the lake-breeze circulation, potentially reducing circulation of pollutants into the city core, but also reducing natural cooling in the most urbanized areas during the climatologically warmest hours. Future work that evaluates these impacts over a broader range of synoptic settings, documents changes in the planetary boundary layer structure and attendant pollution, and considers the multiple-day dependence of these effects is needed.