Model Urbanization Strategy: Summaries, Recommendations and Requirements - Meteorological and Air Quality Models for Urban Areas - page 137

to achieve a balance between the level of detail and precision desired to describe the
urban boundary layer with the computational costs and availability of commensu-
rate descriptive data to run such models. This leads to a practical guideline that the
choice of level of descriptive complexity of these UCPs be based both on “fitness-
for-purpose” and the appropriate grid resolution of the requisite application. Here
we list and highlight the requirements of five common applications.
(1) Air quality exposure studies to assess the impact of atmospheric pollutants on
human health. Model concentration outputs are needed that accurately char-
acterize pollution “hot spots” or gradients at a sufficiently fine grid resolution
commensurate to the extent in which significant exposure impacts occur.
(2) Urban climatology studies and development of strategies for mitigating the
intensity of heat islands. Information is needed to estimate human comfort and
stress based on air temperature, relative humidity, and solar radiation. Model
parameterization schemes need information about physical attributes of the
underlying surface (buildings and vegetation), such as albedo, soil moisture,
building material's thermal conductivity, and capacity as well as anthropogenic
sources of heating.
(3) Emergency response and predicting for site locations where toxic gases have
been released . Needs improved methods and modeling of urban-scale trans-
port and building and street canyon resolved dispersion and inverse modeling
approaches for determining release location.
(4) Advanced air quality and weather forecasting to improve on the predicted
future state of the atmosphere (clouds, rain, air, temperature, winds, etc.) and to
inform and provide guidance to the public on adverse air quality conditions.
(5) Urban planning to evaluate local climate and air quality impacts caused
by urban developments and three-dimensional (3D) urban morphological
structures.
Air quality exposure, urban climatology, emergency response, and urban
planning models need detailed resolution of UC features, whereas weather and air
quality forecasts are more focused on estimating the gross vertical exchange of heat,
momentum, and pollution between the top of the canopy and the atmosphere. Case
studies supporting air quality assessments, urban climatology, and urban planning
studies are not relatively constrained by large computer demands to achieve their tar-
get accuracy and precision estimates; whereas weather forecasting and emergency
response model applications must, for practical reasons, scale down the details of
their UC descriptions to achieve the required rapid output response times.
At some point, it will be necessary to perform evaluation of models based on
their fitness for purpose. Depending on the type of application, the ranking of atmo-
spheric variables by their roles or importance may be useful for operational model
evaluation purposes (see Table 15.1). This exercise is somewhat subjective as the
atmospheric variables are interconnected in some way. For example, wind speed and
direction is considered more important for air quality and dispersion applications
than for urban climatology studies as those variables control pollutant transport.
However, the role of wind is of indirect importance because it affects the magnitude