Georgescu, Matei, Mohamed Moustaoui, Alex Mahalov,
Arizona State University, and Jimy Dudhia, National Center for Atmospheric
Research
The climatic summertime
representation of the diurnal cycle of near-surface temperature is evaluated
using the Weather Research and Forecasting System [WRF]) over the rapidly
urbanizing and water-vulnerable Phoenix metropolitan area. A suite of monthly,
high-resolution simulations are conducted during a number of July months with
both a contemporary landscape and a hypothetical Pre-Settlement scenario. We
demonstrate excellent agreement between WRF and observations in the
representation of daily to monthly diurnal cycle of near-surface temperature.
The WRF-simulated characterization of the diurnal cycle, supported by previous
observational analyses, illustrates two distinct and opposing impacts on the
urbanized diurnal cycle of the metro-area: evening and nighttime warming is
partially offset by daytime cooling. The simulated nighttime Urban Heat Island
(UHI) is explained by well-known mechanisms (e.g., slow release of heat from
within the urban fabric stored during daytime). During daylight hours the
limited vegetation and dry semi-desert region surrounding urban Phoenix warms
at greater rates than the urban complex. We show that lower urban relative to
semi-desert daytime temperatures occur as a result of PhoenixÕ surrounding
environment rather than the addition of residential and agricultural irrigation
(i.e., Òoasis effectÓ).