Influence of projected climate change, urban development and heat adaptation strategies on end of twenty-first century urban boundary layers across the Conterminous US

Abstract

The urban environment directly influences Urban Boundary Layer (UBL) dynamics. Commonly proposed heat adaptation strategies focused on reducing the impacts of global change and urban induced warming are also expected to decrease the intensity of convective mixing thereby reducing UBL depth, with important consequences for air pollutant dilution and dispersion. We use 20-km grid spacing Regional Climate Model decadal scale simulations that account for end of twenty-first century greenhouse gas emissions, urban development and intensive and uniform implementation of a suite of heat adaptation strategies, to investigate the individual and combined impacts of such drivers on UBL dynamics over the Continental US (CONUS). Results indicate that combined impacts of climate change and urban development are expected to increase summer (JJA) daytime UBL height in the eastern CONUS. Heat adaptation strategies lead to a summer daytime UBL depth reduction of several hundred meters across CONUS regions, primarily as a consequence of reduced surface sensible heat fluxes and associated turbulence. Our results confirm that heat adaptation is expected to increase the static stability of both daytime and nighttime UBLs and decrease the magnitude of vertical winds, inducing stronger subsidence. In addition, the large geographical scale of our analysis indicates that adaptation impacts are greater inland and smaller over coastal cities. In Southern California, the adaptation induced increase in latent heat can counterbalance the projected decrease in UBL depth. Future work addressing these projected UBL impacts with convection permitting, high-resolution coupled atmosphere-chemistry simulations is needed to explicitly determine potential unintended consequences for urban air quality.