22
Michal Belda
Department of Meteorology and Environment Protection,
Faculty of Mathematics and Physics, Charles University, Prague (CUNI),
Prague, Czech Republic
1.3.4.1 Introduction
Big cities or urban aglomerations can significantly impact both climate and environment. The emissions of large amount of gaseous species and aerosols, which affect
the composition and chemistry of the atmosphere (Timothy et al. 2009), can have
adverse effect on the environment in the cities and their vicinity. Moreover, this can
negatively impact the population (Gurjar et al. 2010). In addition, this pathway can
result in indirect impact on the meteorology and climate as well, due to radiation
impact of the atmospheric composition on the thermal balance and thus affect the
temperature as well. Especially within the canopy layer in the cities, the changes
can be quite significant.
However, the primary reason for temperature increase within the cities or urban
aglomerations with respect to the rural vicinity, is the effect of so called urban heat
island (UHI, Oke 1973), which is mainly due to construction elements within the
urban environment. This is extensively covered by artificial objects, buildings, using
by large stone, bricks or concrete, and by quite large spaces often paved. This kind
of surface clearly differs from natural surfaces (e. g. grassland, forest) by mechanical, radiative, thermal, and hydraulic properties, therefore, these surfaces represent
additional sinks and sources of momentum and heat, affecting the mechanical, thermodynamical, and hydrological properties of the atmosphere (Lee et al. 2010).
Neverthelles, the changes of meteorological conditions within the urban areas due
to UHI can further affect the air-quality. This has been studied recently by e.g. Ryu
et al. (2013), they found significant impact on the ozone day and night-time levels
especially due to circulation pattern changes for the Seoul metropolitan area.
For WP3 we have focused on the aspects of climate conditions changes in urban
environment, yet especially on those with strong potential to impact the air-quality,
based on the experiment setup described below. For the region of Central Europe,
we investigate the impact of the urban environment by means of its introducing into
the regional climate model. As the spatial scale of the meteorological influence due
to the cities is much smaller than the scale resolved by the mesoscale model, inclusion of urban land-surface requires additional parameterizations. The most common
parameterizations considering the urban effects are the slab models (bulk parameterization), where the urban surface constants (e.g., surface albedo, roughness
length, and moisture availability) can vary to better describe those of the urban
surfaces. This treatment however ignores the three-dimensional character of the
urban meteorological phenomena, moreover, in feasible resolutions the urban environment cannot be well resolved. Therefore, a more accurate approach is provided
using urban canopy models (single layered – SLUCM, or multi-layered MLUCM)
coupled to the driving mesoscale model (Chen et al. 2011). Our study describes in
J. Fallmann et al.
Michal Belda
Department of Meteorology and Environment Protection,
Faculty of Mathematics and Physics, Charles University, Prague (CUNI),
Prague, Czech Republic
1.3.4.1 Introduction
Big cities or urban aglomerations can significantly impact both climate and environment. The emissions of large amount of gaseous species and aerosols, which affect
the composition and chemistry of the atmosphere (Timothy et al. 2009), can have
adverse effect on the environment in the cities and their vicinity. Moreover, this can
negatively impact the population (Gurjar et al. 2010). In addition, this pathway can
result in indirect impact on the meteorology and climate as well, due to radiation
impact of the atmospheric composition on the thermal balance and thus affect the
temperature as well. Especially within the canopy layer in the cities, the changes
can be quite significant.
However, the primary reason for temperature increase within the cities or urban
aglomerations with respect to the rural vicinity, is the effect of so called urban heat
island (UHI, Oke 1973), which is mainly due to construction elements within the
urban environment. This is extensively covered by artificial objects, buildings, using
by large stone, bricks or concrete, and by quite large spaces often paved. This kind
of surface clearly differs from natural surfaces (e. g. grassland, forest) by mechanical, radiative, thermal, and hydraulic properties, therefore, these surfaces represent
additional sinks and sources of momentum and heat, affecting the mechanical, thermodynamical, and hydrological properties of the atmosphere (Lee et al. 2010).
Neverthelles, the changes of meteorological conditions within the urban areas due
to UHI can further affect the air-quality. This has been studied recently by e.g. Ryu
et al. (2013), they found significant impact on the ozone day and night-time levels
especially due to circulation pattern changes for the Seoul metropolitan area.
For WP3 we have focused on the aspects of climate conditions changes in urban
environment, yet especially on those with strong potential to impact the air-quality,
based on the experiment setup described below. For the region of Central Europe,
we investigate the impact of the urban environment by means of its introducing into
the regional climate model. As the spatial scale of the meteorological influence due
to the cities is much smaller than the scale resolved by the mesoscale model, inclusion of urban land-surface requires additional parameterizations. The most common
parameterizations considering the urban effects are the slab models (bulk parameterization), where the urban surface constants (e.g., surface albedo, roughness
length, and moisture availability) can vary to better describe those of the urban
surfaces. This treatment however ignores the three-dimensional character of the
urban meteorological phenomena, moreover, in feasible resolutions the urban environment cannot be well resolved. Therefore, a more accurate approach is provided
using urban canopy models (single layered – SLUCM, or multi-layered MLUCM)
coupled to the driving mesoscale model (Chen et al. 2011). Our study describes in
J. Fallmann et al.