294
10.2.2.2.5 Courtyards
The micro-climate of courtyards was studied using the micro-climatic models
RayMan and ENVI-met. The human thermal comfort conditions in two courtyards
(Schlossstrasse and Senefelderstrasse) in the Olga Hospital area were compared to
the conditions in street canyons (Breitscheidstrasse, Senefelderstrasse) and on a
green area (Elisabethenstrasse – Hasenberstraße) over 11 years. Therefore, the
micro-scale RayMan model employing fi sh-eye photos was used to describe long
term conditions. In the courtyards, the frequency of heat stress (PET > 29.1 °C) and
thermal comfort is between 45.5 % and 51.6 % from May to September. Whereas
the frequency of thermal comfort is between 3.6 % and 13.8 % higher in east-west
and NNW – SSE oriented street canyons. Additionally, PET is also higher at nighttime than during daytime due to the smaller sky view factor in courtyards. Multiple
refl ections can also increase PET in courtyards. Another factor is the low wind
speed in these sheltered locations, triggering a further increase in PET. ENVI-met
simulations for a hot summer day show that PET is up to 25 K higher over a paved
courtyard compared to a park area covered with plants and grass.
10.2.3 Macro-scale Simulations
Specifi c urban planning strategies, like green roofs or facades and highly refl ective
materials are able to reduce the UHI. Taha ( 1997 ) demonstrated that increasing the
albedo by 0.15 can reduce peak summertime temperatures for the urban area of Los
Angeles by up to 1.5 °C. During the DESIREX Campaign 2008, Salamanca et al.
( 2012 ) stated that a higher albedo leads to about 5 % reduction in energy consumption through air conditioning during summertime periods for the area of Madrid.
The regional energy saving effect of high-albedo roofs can also be found in Akbari
et al. ( 1997 ) and on a more global perspective in Akbari et al. ( 2009 ).
In the course of the project UHI – Development and application of mitigation
and adaptation strategies and measures for counteracting the global “UHI phenomenon” (3CE292P3) – CENTRAL Europe. (2011–2014), these kinds of scenarios are
conducted for the urban area of Stuttgart. Due to its geographical location in a valley, the weak mountain – valley circulation leads to increasing potential for natural
heat trapping in the urban region. Modelling work of the environmental agency of
Stuttgart shows, that the area with more than 30 days/year heat stress is anticipated
to increase from 6 % (1971–2000) up to 57 % (2071–2100). This refl ects the calculations of the Intergovernmental Panel on Climate Change (IPCC) on global climate
change.
The Karlsruhe Institute of Technology (KIT) conducts simulations using the
numerical mesoscale Weather Research and Forecasting Model WRF Skamarock
et al. ( 2005 ) on regional scale, coupled to urban parameterization schemes (Kusaka
et al. 2001 ; Martilli et al. 2002 ). The results refl ect the effects of certain urban planning strategies on near surface air temperature and on UHI intensity.
R. Rinke et al.
10.2.2.2.5 Courtyards
The micro-climate of courtyards was studied using the micro-climatic models
RayMan and ENVI-met. The human thermal comfort conditions in two courtyards
(Schlossstrasse and Senefelderstrasse) in the Olga Hospital area were compared to
the conditions in street canyons (Breitscheidstrasse, Senefelderstrasse) and on a
green area (Elisabethenstrasse – Hasenberstraße) over 11 years. Therefore, the
micro-scale RayMan model employing fi sh-eye photos was used to describe long
term conditions. In the courtyards, the frequency of heat stress (PET > 29.1 °C) and
thermal comfort is between 45.5 % and 51.6 % from May to September. Whereas
the frequency of thermal comfort is between 3.6 % and 13.8 % higher in east-west
and NNW – SSE oriented street canyons. Additionally, PET is also higher at nighttime than during daytime due to the smaller sky view factor in courtyards. Multiple
refl ections can also increase PET in courtyards. Another factor is the low wind
speed in these sheltered locations, triggering a further increase in PET. ENVI-met
simulations for a hot summer day show that PET is up to 25 K higher over a paved
courtyard compared to a park area covered with plants and grass.
10.2.3 Macro-scale Simulations
Specifi c urban planning strategies, like green roofs or facades and highly refl ective
materials are able to reduce the UHI. Taha ( 1997 ) demonstrated that increasing the
albedo by 0.15 can reduce peak summertime temperatures for the urban area of Los
Angeles by up to 1.5 °C. During the DESIREX Campaign 2008, Salamanca et al.
( 2012 ) stated that a higher albedo leads to about 5 % reduction in energy consumption through air conditioning during summertime periods for the area of Madrid.
The regional energy saving effect of high-albedo roofs can also be found in Akbari
et al. ( 1997 ) and on a more global perspective in Akbari et al. ( 2009 ).
In the course of the project UHI – Development and application of mitigation
and adaptation strategies and measures for counteracting the global “UHI phenomenon” (3CE292P3) – CENTRAL Europe. (2011–2014), these kinds of scenarios are
conducted for the urban area of Stuttgart. Due to its geographical location in a valley, the weak mountain – valley circulation leads to increasing potential for natural
heat trapping in the urban region. Modelling work of the environmental agency of
Stuttgart shows, that the area with more than 30 days/year heat stress is anticipated
to increase from 6 % (1971–2000) up to 57 % (2071–2100). This refl ects the calculations of the Intergovernmental Panel on Climate Change (IPCC) on global climate
change.
The Karlsruhe Institute of Technology (KIT) conducts simulations using the
numerical mesoscale Weather Research and Forecasting Model WRF Skamarock
et al. ( 2005 ) on regional scale, coupled to urban parameterization schemes (Kusaka
et al. 2001 ; Martilli et al. 2002 ). The results refl ect the effects of certain urban planning strategies on near surface air temperature and on UHI intensity.
R. Rinke et al.