Urban Hpac and a Simple Urban Dispersion Model Compared with the Joint Urban 2003 (ju2003) Field Data

The Hazard Prediction and Assessment Capability (HPAC) dispersion model is widely used by the U.S. Department of Defense and the results of previous evaluations have been presented at Harmonization conferences. The version of its diagnostic wind model that is applied to urban areas has been significantly updated to remove biases in wind speed estimates, requiring reevaluations with urban tracer data sets such as the Joint Urban 2003 (JU2003) data base. For comparison purposes, a simple Gaussian-format urban dispersion model has been run for the same JU2003 data base. The simple urban model has previously been evaluated with the Madison Square Garden 2005 (MSG05) data. The evaluations focus on 30-minute averaged (1) arc maximum concentrations and (2) concentrations paired in space. It is shown that the revisions to the diagnostic wind model in urban HPAC have resulted in improved performance. Similar good performance is found for the simple urban dispersion model, although it has more errors for off-centerline and upwind receptors in the downtown area.