Numerical analysis of the contemporary interaction between the Phoenix
Metro Area Urban Boundary Layer and the local thermo-topographical
circulation
Abstract
Anthropogenic modification of natural landscapes to urban environments
impacts land-atmosphere interactions in the boundary layer. Ample
research has demonstrated the effect of such landscape transitions on
development of the near-surface urban heat island (UHI), while
considerably less attention has been given to impacts on regional wind
flow. Here we use a set of high-resolution (1 km grid-spacing) regional
climate modeling simulations with the Weather Research and Forecasting
(WRF) model coupled to a multi-layer urban canopy scheme to investigate
the dynamical interaction between the urban boundary layer (UBL) of the
Phoenix Metro (U.S.) area and the thermal circulation of the complex
terrain it resides within. We conduct paired simulations for the
extremely hot and dry summer of 2020, using a contemporary urban
representation and a pre-settlement landscape representation to examine
the effect of the built environment on local to regional scale wind
flow. Analysis of our simulation results shows that, for a majority of
the diurnal cycle, 1) the thermo-topographical circulation dominates, 2)
the built environment obstructs wind flow in the inertial sublayer
during the nighttime, and (3) the built environment of Phoenix Metro
produces an UHI circulation of limited vertical extent that interacts
with the background flow to modulate its intensity. Such interaction is
modulated by greater daytime urban sensible heat flux and dampens the
urban roughness induced drag effect by promoting a deeper UBL through
vigorous mixing. Our results highlight the need for future research –
both observational and simulation based - into urbanizing regions where
multi-scale flows are dominant.