KLIMES - a joint research project on human thermal comfort in cities
Helmut Mayer1, Lutz Katzschner2, Michael Bruse3
1
Meteorological Institute, Albert-Ludwigs-University of Freiburg, Germany
Department of Environmental Meteorology, University Kassel, Germany
3
Institute for Geography, Johannes-Gutenberg-University Main, Germany
2
Abstract
The general objective of the BMBF joint research project KLIMES is the development of urbanistic concepts to mitigate the impacts of extreme heat on citizens. The fundamentals are
worked out in four KLIMES subprojects. Within the scope of the subproject KLIMES ALUF-2,
experimental investigations on human thermal comfort in different urban quarters in Freiburg,
the warmest city in Germany, are conducted on typical summer days. The internationally used
physiologically equivalent temperature is used as thermo-physiologically significant assessment
index. The investigation design as well as exemplary results obtained for the selected site “Rieselfeld” are presented and discussed.
1.
Introduction
Due to their specific features, cities modify the large-scale weather conditions, that a
distinct urban climate is formed. Its most well-known phenomenon is represented by the
urban heat island (e.g. Grimmond, 2006; Oke, 2006) or urban heat archipelago, if the
intra-urban thermal conditions of interest.
Freiburg
35
heat waves 2003
30
25
Ta,1961-1990 + σ
20
Ta (°C)
Ta, 2003
15
Ta,1961-1990 - σ
10
5
0
Ta, 1961-1990
1961-1990: Ta,mean = 10.7 °C; s = 6.5 °C
2003: Ta,mean = 12.7 °C; s = 9.0 °C
-5
-10
0
30
60
90
120
150
180
DOY
210
240
270
300
330
360
Fig. 1: Daily mean values of air temperature Ta in Freiburg (SW Germany) in the 2003
and averaged over the climate standard period 1961-1990, σ: standard deviation, data source: Deutscher Wetterdienst DWD
Large-scale heat in summer is intensified within cities and, therefore, affects efficiency,
well-being and health of people within cities. The two heat waves in Central Europe in
2003, which can be seen in Fig. 1 for the city of Freiburg in south-west Germany, are
examples for extreme heat in summer. The heat waves covered almost the whole June
2003 and the first half of August 2003.
Regional climate models predict the likelihood that heat waves will be more frequent,
more intense and longer lasting in the future (e.g. Meehl and Tebaldi, 2004). Therefore,
methods of town planning, which are aimed for the optimisation of human thermal comfort within cities, become more and more important (e.g. Eliasson, 2000). They must
consider the limited area of action due to the existing urban structures in central European cities.
The joint research project KLIMES, which is introduced, meets this demand. The main
objective of this study is (i) to explain human thermal comfort in cities in general, (ii) to
describe the coordinated design of different methodological approaches applied in
KLIMES and (iii) to discuss preliminary results.
2.
Joint research project KLIMES
The joint research project “Development of strategies to mitigate enhanced heat stress in
urban quarters due to regional climate change in Central Europe”, abbreviated by
KLIMES, is carried out by four German research groups within the scope of the research initiative “klimazwei” funded by the German Federal Ministry of Education and
Research (BMBF) from 2006 to 2009. Based on an overview on the state-of-the-art in
the planning-related urban human-biometeorology and identification of deficits, working hypotheses were derived, which lead to the general aims of KLIMES: (i) update of
human-biometeorological methods available to quantify the perception of heat by citizens under current and future climate conditions, (ii) quantification of the perception of
human thermal comfort (discomfort) in different urban quarters (outdoors and indoors)
during extreme summer heat, (ii) development and verification of urbanistic strategies
based on human-biometeoro-logical results to mitigate the negative impacts of climate
trends and extreme weather on citizens in different urban quarters (optimisation of human thermal comfort under consideration of objectives of environmental protection, e.g.
abandonment of electric air conditioning), (iv) synthesis of all results in a guideline for
urban planning orientated to the challenges due to regional climate change in Central
Europe.
To achieve the aims, a coordinated design of different methods is applied in KLIMES:
(i) experimental investigations on the perception of heat by people in different urban
quarters in Freiburg (SW Germany), which is the warmest city in Germany, (ii) questionnaires about citizens' current perception of heat under consideration of their thermal
history and their use of open spaces (see also Knez and Thorsson, 2006), (iii) modelbased simulations of human thermal comfort in different urban quarters (outdoors and
indoors) under current and future thermal conditions using the stationary model ENVImet (Bruse and Fleer, 1998) and the unsteady model BOTworld (Bruse, 2007), (iv) development of human-biometeorologically based strategies for urban planning to optimise human thermal comfort outdoors and indoors against the background of predictions on heat in the future, (v) permanent dialogue with the planning practice and the
public.
3.
Experimental design of the subproject KLIMES ALUF-2
For each KLIMES site, the experimental design of the subproject KLIMES ALUF-2
consists of a stationary human-biometeoro-logical station (Fig. 2) and a mobile humanbiometeorological station.
Fig. 2: Stationary human-biometeorological station used in experimental investigations on human thermal comfort in Freiburg (SW Germany)
Table 1: Instrumentation of the stationary and mobile human-biometeorological measurement stations used in 2007 in the subproject KLIMES ALUF-2
meteorological variable
stationary
mobile
air temperature
Humicap HMP45D, Vaisala
Comp., 1.1 m a.g.l.
via psychrometer principle containing Pt 100, Friedrichs Comp., 2 m
a.g.l. (since 2008: 1.2 m a.g.l.)
vapour pressure
Humicap HMP45D, Vaisala
Comp., 1.1. m a.g.l.
via psychrometer principle, Friedrichs Comp., 2 m a.g.l. (since
2008: 1.2 m a.g.l.)
wind speed
3-D sonic anemometer 81000
VRE, Fa. Young, 1.2 m a.g.l.
hot-wire anemeometer, Dantec
Comp., 2 m a.g.l. (since 2008: 1.2
m a.g.l.)
short-wave radiation
CM3 (as part of CNR1), Kipp &
Zonen Comp., 1.1 m a.g.l.
CM21, Kipp & Zonen Comp., 1.1
m a.g.l.
long-wave radiation
CG3 (as part of CNR1), Kipp &
Zonen Comp., 1.1 m a.g.l.
CG1, Kipp & Zonen Comp., 1.1 m
a.g.l.
data recording
CR3000 datalogger + AM16/32
multiplexer, Campbell Comp.
manually
averaging period
1 min
1 min
As the mean radiant temperature Tmrt was calculated on the basis of measured short- and
long-wave radiation flux densities from the three-dimensional surroundings of a standing person according to Höppe (1992) and Thorsson et al. (2007), both types of humanbiometeorological stations include appropriate systems to measure the incoming and
outgoing radiation flux densities in vertical direction as well as the radiation flux densities from the four main horizontal directions. Technical details of the experimental
equipment are described in Table 1.
4.
Exemplary results of experimental investigations on human thermal comfort
Within the subproject KLIMES ALUF-2 experimental investigations on human thermal
comfort were conducted in the urban quarter “Rieselfeld” in Freiburg. In the following,
selected results based on human-biometeorological measurements at the stationary station and at the measurement point no. 1 (= MP1) of the mobile investigations are discussed as examples for the spatial variability of human thermal comfort within urban
street canyons. Both micro-sites were located within the same NW-SE oriented street
canyon, but on the opposite sidewalks.
The difference between the daily patterns of the mean radiant temperature Tmrt at both
micro-sites can be detected from Fig. 3. As soon as MP1 was shaded, Tmrt decreased
directly at this micro-site. When Tmrt reached its peak value (63.4 °C) at the stationary
micro-site in the afternoon, the maximum Tmrt difference (≈ 33 °C) between the sunny
stationary micro-site and the shaded micro-site MP1 was observed. As Tmrt was calculated for a standardised standing person, the absorbed short- and long-wave radiation
flux densities from the four main horizontal directions basically determined Tmrt.
Freiburg, Rieselfeld, 19-06-2007
70
60
Tmrt (°C)
50
40
30
20
stationary, NW-SE street canyon, H/W=0.49, SW exp. sidewalk, SVF=0.51
mobile, MP1, NW-SE street canyon, H/W=0.49, NE exp. sidewalk, SVF=0.47
10
8:00
10:00
12:00
14:00
16:00
18:00
20:00
22:00
0:00
CET (hrs)
Fig: 3: Mean radiant temperature Tmrt at the stationary micro-site and at MP1 of mobile investigations within the “Rieselfeld” site in Freiburg on 19 June 2007
Freiburg, Rieselfeld, 19-06-2007
50
PET (°C)
40
30
20
stationary, NW-SE street canyon, H/W=0.49, SW exp. sidewalk, SVF=0.51
mobile, MP1, NW-SE street canyon, H/W=0.49, NE exp. sidewalk, SVF=0.47
10
8:00
10:00
12:00
14:00
16:00
18:00
20:00
22:00
0:00
CET (hrs)
Fig: 4: Physiologically equivalent temperature PET at the stationary micro-site and at
MP1 of mobile investigations within the “Rieselfeld” site in Freiburg on 19
June 2007
From regression analyses performed for sites, which are not influenced by sea breezes,
it is known that on typical summer days the physiologically equivalent temperature PET
has the strongest correlation with Tmrt. Therefore, the similarity of the patterns for Tmrt
and PET (Fig. 11) is not surprising. PET exceeded the 40 °C level during the whole
afternoon at the sunny stationary micro-site, which can be interpreted as strong heat
stress. In contrast, at the shaded MP1 PET was in the same period between 25 and 30
°C, which indicates a mean thermal sensation of “slightly warm”. This distinct microscale reduction of the perceived heat level by citizens resulted mainly from the lower
radiation heat, which characterised the shaded situation.
5.
Conclusions
Thermal comfort represents an indispensable prerequisite for the quality of life within
cities. It is essential for efficiency, well-being and health of citizens. Human thermal
comfort within urban structures depends on the large-scale meteorological background
conditions, which are modified within cities by their specific meteorological features in
a way that the thermal level is enhanced. Based on simulations of the regional climate in
SW Germany, the likelihood of longer lasting, more intense and more frequent heat
waves has a pronounced reliability. This changed background conditions lead to more
thermal stress situations for citizens, which can be quantified by the application of
thermal indexes. Elevated thermal stress represents an important challenge for town
planning to develop concepts, which enable human thermal comfort in urban structures
despite of thermal background stress and limited possibilities for town planning due to
widely existing urban structures in central European cities. The joint research project
KLIMES is integrated in the way how to solve this problem.
Acknowledgement
The authors are indebted to the Federal Ministry of Education and Research (BMBF) for funding the sub research projects KLIMES ALUF-1 and KLIMES ALUF-2 (FZK: 01LS05020),
which are part of the joint research project KLIMES; within the scope of the research initiative
klimazwei.
References
Bruse, M., 2007: Simulating human thermal comfort and resulting usage patterns of urban open
spaces with a multi-agent system. Proc. 24rd Int. Conf. Passive and Low Energy Architecture
(PLEA) 2007, 491-498.
Bruse, M., H. Fleer, 1998: Simulating surface-plant-air interactions inside urban environments
with a three dimensional numerical model. Environ. Modell. Softw. 13, 373-384.
Eliasson, I., 2000: The use of climate knowledge in urban planning. Landscape Urban Plan. 48,
31-44.
Grimmond, C.S.B., 2006: Progress in measuring and observing the urban atmosphere. Theor.
Appl. Climatol. 84, 3-22.
Höppe, P., 1992: Ein neues Verfahren zur Bestimmung der mittleren Strahlungstemperatur im
Freien. Wetter und Leben 44, 147-151.
Knez, I., S. Thorsson, 2006: Influences of culture and environmental attitude on thermal, emotional and perceptual evaluations of a public square. Int. J. Biometeorol. 50, 258-268.
Meehl, G.A., C. Tebaldi, 2004: More intense, more frequent, and longer lasting heat waves in
the 21st century. Science 305, 994-997.
Oke, T.R., 2006: Towards better scientific communication in urban climate. Theor. Appl. Climatol. 84, 179-190.
Thorsson, S., F. Lindberg, I. Eliasson, B. Holmer, 2007: Different methods for estimating the
mean radiant temperature in an outdoor urban setting. Int. J. Climatol. 27, 1983-1993.
Authors’ address:
Prof. Dr. Helmut Mayer (helmut.mayer@meteo.uni-freiburg.de)
Meteorological Institute, Albert-Ludwigs-University of Freiburg
Werthmannstr. 10, D-79085 Freiburg, Germany
Prof. Dr. Lutz Katzschner (katzschn@uni-kassel.de)
Department of Environmemntal Meteorology, University Kassel
Henschelstr. 2, D-34127 Kassel, Germany
Prof. Dr. Michael Bruse (m.bruse@geo.uni-mainz.de)
Institute of Geography, Johannes-Gutenberg-University of Mainz
Johann-Joachim-Becher Weg 21, D-55099 Mainz