Boundary Layer, Urban Meteorology and Land-Surface Processes

A Study of Urban Heat Island Intensity Trends in the Dallas-Fort Worth Region during Wet and Dry Summers

Jinxin Wang

School of Meteorology

15 April 2016, 2:00 PM

National Weather Center, Room 4140
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

The canopy-layer urban heat island (UHI) intensities in the Dallas Fort-Worth (DFW) region in a dry summer (July 2011) and a wet summer (July 2015) are investigated using observations from Texas Commission on Environmental Quality (TCEQ) stations. The 2011 version of the high-resolution National Land-Cover Database (NLCD2011) is applied to classify TCEQ stations by their dominant surrounding land-use category. Spatial and temporal analyses both show that the UHI characteristics during the dry summer and wet summer are quite different. Major differences can be noted in the thermal inertia of rural sites and daytime UHI. During the wet summer, thermal inertia at rural sites is larger and accordingly rural temperatures do not increase as rapidly during the day as in the dry summer. Thus, daytime rural temperatures are higher during dry summers than during wet summers. Temperatures at urban sites are much less affected by changes in precipitation and soil moisture. During the wet summer, urban daytime temperatures are slightly higher than rural temperatures, giving rise to a weak daytime urban heat island. During the dry summer, lower daytime temperatures are recorded at urban sites, leading to a daytime urban cool island. At night, an urban heat island developed during both summers, but the intensity was slightly higher during the dry than wet summer.

Numerical simulations are performed to better understand the observed trends. With updated anthropogenic heating profiles and updated land cover, a set of month-long WRF simulations, including two control simulations and two sensitivity experiments, is run to investigate the soil moisture impact on near-surface air temperature. Surface Energy Balance (SEB) analyses indicate that the energy partitioning difference between latent heat flux and sensible heat flux is the primary reason for the different urban-rural surface temperature contrast found in the two summers.

Boundary Layer, Urban Meteorology and Land-Surface Processes Seminar Series website