FUMAPEX Experience of Model Urbanisation - Meteorological and Air Quality Models for Urban Areas - page 60

resolution or finer, enabling the provision of high quality urban meteorological
data. Thus, NWP models are now approaching the necessary horizontal and vertical
resolution to provide weather forecasts for the urban scale (e.g. Baklanov et al.,
2002, 2008).
Many urban features can influence the atmospheric flow, its turbulence regime,
the microclimate, and, accordingly modify the transport, dispersion, and deposition
of atmospheric pollutants within urban areas, namely:

•

Local-scale non-homogeneities, such as sharp changes of roughness and heat
fluxes;

• Sheltering effects of buildings on wind;

• Redistribution of eddies, from large to small, due to buildings;

• Trapping of radiation in street canyons;

• Effects on urban soil structure;

• Differing diffusivities of heat and water vapour in the canopy layer;

• Anthropogenic heat fluxes;

• The so-called urban heat island;

• Urban internal boundary layers and the urban mixing height;

• Effects of pollutants (including aerosols) on urban meteorology and climate;

• Urban effects on clouds and precipitation.

Despite the increased resolution and various improvements, current operational
NWP models still have several shortcomings with respect to urban areas including:

• Urban areas are mostly described by the same sub-surface, surface, and boundary

layer formulations as rural areas.

• These formulations do not account for specific urban dynamics and energetics

or for their impacts on the simulation of the atmospheric urban boundary layer
(UBL) and its intrinsic characteristics (e.g. internal boundary layers, urban heat
islands, precipitation patterns).

•

NWP models have not been primarily developed for air pollution and emergency
modelling and as such, their outputs need to be designed as suitable input for
such urban-scale models.

Apart from Urban Air Quality Information and Forecasting Systems (UAQIFS)
per se , improved urban meteorological forecasts will also provide information to
city managers regarding additional hazardous urban climate features (e.g. urban
runoff and flooding, ice and snow accumulation, high urban winds or gusts, heat or
cold stress in growing cities and/or a warming climate). Moreover, the availability of
reliable urban scale weather forecasts might be relevant in assisting the emergency
management of fires, accidental toxic emissions, potential terrorist actions, etc.