Global Climate Change and Urban Development as Drivers of Urban Heat: Relative Magnitude, Interactions, and Mitigation

Surface climates are projected to warm due to global climate change over the course of the 21^st century. Moreover, demographic projections suggest urban areas in the United States will continue to expand and develop, with attendant local climate outcomes. Interactions between these two drivers of urban heat have not been robustly quantified to date. Here, simulations with the Weather Research and Forecasting model (coupled to a Single-Layer Urban Canopy Model) are performed at 20 km resolution over the continental U.S. for two 10-year periods: contemporary (2000-2009) and end-of-century (2090-2099). Present and end of century urban land use are derived from the Environmental Protection Agency’s Integrated Climate and Land-Use Scenarios. Modelled effects on near-surface temperature, precipitation, and synoptic-scale persistence of features associated with extreme events are evaluated. Sensitivity to climate projection (NCAR Community Climate System Model 4.0; RCP 4.5 vs. RCP 8.5) and associated urban development scenarios are assessed. Results suggest climate change effects on near-surface urban air temperature are greater than those attributable to urban development in many regions. Interaction effects vary by region, and while of lesser magnitude, are not negligible. Interaction effects on temperature result from the different meteorological effects of urban areas under current and future climate. Additionally, the potential for design implementations such as green roofs and high albedo roofs to offset the projected warming is considered. Effects of these implementations on precipitation are also assessed.