lessons learnt from urban human-biometeorology of urban...

ASI1_Lecture 1_5/12/2011

1

ASI 1: URBAN CLIMATE FOR HUMAN COMFORT School of Architecture, The Chinese University of Hong Kong, Hong Kong, 5-6 Dec 2011

Lessons learnt fromurban human-biometeorology

of urban areas in Central Europe

• Helmut Mayer• full professor• Meteorological Institute /

Albert-Ludwigs-University of Freiburg,Germany

Croucher Advanced Study Institute 2011-2012Urban Climatology for Tropical & Sub-tropical Regions

Lecturer’s Photo


Location of Freiburg, Germany (I)

Freiburg


2


Location of Freiburg, Germany (II)

Freiburglocated atthe eastern borderof the southernUpper Rhine valley

≈ 220.000 inhabitants

48° 00' N, 7° 51' E269 m a.s.l.

atmospheric backgroundsituation:warmest within Germany

FR


interdisciplinary science

dealing with the impacts of

- weather

- climate

- air pollutants

on living organisms

Biometeorology: definition


3


Biometeorology: international

December 5-9, 2011


according to the target groups

- human-biometeorology

- plant-biometeorology

- agricultural meteorology

- forest meteorology

- phenology

- animal-biometeorology

Biometeorology: fields


4


- target group: citizens

- general objective

maintaining quality of life for citizens

- within urban open spaces

- indoors

even under poor atmospheric background conditions

objective requires

- identification of problematic urban spaces

- application of appropriate methods

- validation of applied methods

Urban human-biometeorology


Atmospheric background of cities (I)

Cities are embeddedinto specific atmospheric background conditions

on regional scale.


5


Atmospheric background of cities (II)

is related to

- thermal situation

- air quality

- …

dependent on

- topography

- land use

- pattern of large-scale weather

- …


urban land use, structures and processes

modification of regional atmospheric backgroundconditions by

∆ (z.B. ∆Ta, ∆VP, ∆v, ∆Tmrt, ∆NO2, …)

∆: no constant, but a function

dependent on

- weather

- time of day and the year

- urban land use (site on micro-scale)

- …

Urban climate: causes


6


consequences of ∆:

- urban climate

city is considered as a whole in contrast

to the rural surroundings

- different urban micro-climates within a city

local climate zones (Stewart and Oke, 2009)

Urban climate: features


Human-biometeorological conditions

different urban micro-climates

specific human-biometeorological conditions for citizens

characteristics:

strain for citizens

- impairment of efficiency

- limited well-being

- health hazard

- elevated morbidity

- elevated mortality


7


Regional climate change

characteristics of regional climate change:

- trends of climate variables(air temperature, precipitation, …)

- embedded severe weather atmospheric- heat waves background- drought in summer conditions- convective rainfall- severe storms (?)- …


Heat waves in Central Europe (I)

example: heat waves in southwest Germany:

2003, 2006, 2009, 2010, 2011, … in the future?

accumulation effects

Freiburg, 22-08-2011


8


Heat waves in Central Europe (II)

characteristics:

- cloudless sky high K* (daytime) and L* (night)

- high mean radiant temperature Tmrt

- high near-surface air temperature Ta

- low near-surface wind speed v

- near-surface vapour pressure VP

< 18 hPa dry heat

> 18 hPa humid heat

- high concentrations of O3 and PM10

- …


Central European cities: heat waves

significant problem currently

- urban structures in Central Europe:

not adapted to severe heat

- citizens in Central Europe:

not adapted to severe heat

- demographic development in Central European cities:

citizens become elder

elevated vulnerability of citizens to severe heat

in the future?


9


Problem in Central Europe: heat waves

projections from regional climate models for Central Europe:

severe heat waves

- more frequent

- more intense

- longer lasting

starting in about 2040/2050:

- annually heat waves in the intensity of 2003 in SW Europe

- each 6th-8th year heat waves

with the intensity of the 'Moscow heat wave' in 2010


Regional climate Change - citizens

regional climate change: changed atmospheric backgroundconditions

severe heat waves+

dynamic of cities: modified urban micro-climates- conversion of urban spaces- structural concentration- combustion processes- …

citizens: strain severe health stress


10


Measures against heat waves

- preventive on a short-term basis:

heat health warning system (e.g. German Weather Service)

- current situation:

individual behaviour of citizens

- preventive on a long-term basis:

methods of urban planning

design of urban spaces

adapted to new challenges

by regional climate change


Individual behaviour against heat (I)


11


Individual behaviour against heat (II)


Urban planning

increasing need for urban planning:

- to develop

- to apply

- to validate

methods

to mitigate the negative health effects of severe heat on citizens

possible at all and to what extend?

dry heat - humid heat

in the daytime (outdoors) - at night (indoors)


12


Assessment methods

- urban planning needs:human-biometeorologically significant assessment

of impacts of urban design on human thermal comfortduring severe summer heat

- assessments methodsbased on the human energy balance thermo-physiological assessment indices (e.g. PET)

- available- well tested- applicable


Thermal index


13


Meteorological input variables

methods to obtain the meteorological input variables

required to calculate a thermal assessment index

- experiments (point measurements)

- numeric simulations for an appropriate spatial grid

(e.g. ENVI-met model, vers. 4.0, spatial resolution: 1 m)


Experiments

human-biometeorologicalmeasuring system,

used in Freiburg


14


Investigation design

methods to obtain basic results on the impacts of

- urban design

- street geometry

on the perception of heat by citizens:

co-ordinated approach consisting of

- experiments

- questionnaires

- numeric simulations

- statistic analyses


Questionnaires


15


Numeric simulationsOrientation

E-W

N-S

NE-SW

NW-SE

Height-to-width ratio H/W

street: 8 x 1 m

2 m1.2 m

WH

0.5 1 2 43

Ali-Toudert and Mayer, 2006


Ta vs. Tmrt

- “despite the tendency of many researchersto focus on air temperature,

it is radiant exchangethat is mostly the dominant factor

affecting human thermal comfort”(Shashua-Bar et al., 2010)

mean radiant temperature Tmrt:most significant meteorological variable

for human thermal comfort during severe heatnot air temperature Ta or UHI

(but similar processes that govern Ta, UHI and Tmrt!)


16


Definition of Tmrt (ASHRAE, 2001)

Tmrt is defined as:

- uniform temperature of an imaginary enclosure

- in which the radiant heat transfer from the human body

equals

- the radiant heat transfer in the actual non-uniform enclosure

Tmrt represents the amount of radiation heat

absorbed by humans


Assessment concepts

- human-biometeorological conceptsto assess the thermal urban environment

are mostly related to a collective of citizens

- collective of citizens is representedby a standardised standing person

(cylinder-like shape)

consequences of the standing position?


17


Angle factorsconsequences of the standing position

for absorbed radiant flux densities:

definition of angle factors Wi

to estimate the radiant flux densities

received by the standing person

Wi = 0.22 for the four lateral radiant flux densities

Wi = 0.06 for the up- and downwelling radiant flux densities

increased significance of lateral radiant flux densities

manipulations of vertical walls by urban planning

impact on lateral radiant flux densities


Mean radiant temperature Tmrt

273.15σε

ST

0.25

radmrt

Tmrt: mean radiant temperature (°C)

Srad: total of all absorbed radiant flux densities (W m-2)

ε: emissivity of the human body (0.97)

σ: Stefan-Boltzmann constant (5.67 · 10-8 W m-2 K-4)


18


Radiant flux density Srad

6

1iilikirad LαKαWS

Srad: total of all absorbed radiant flux densities (W m-2)

Ki: short-wave radiant flux densities

Li: long-wave radiant flux densities

αk: short-wave absorption coefficient (0.7)

αl: long-wave absorption coefficient (0.97)

Wi: angle factors (percentage of Ki and Li,received by the human body in each direction i)


How to determine Ki and Li?

within urban street canyons and open spaces by use of

a) simulation models(e.g. RayMan, SOLWEIG)

b) measurementsof short- and long wave radiant flux densities

- from the four horizontal cardinal directions (E, S, W, N)- as well as from the upper and the lower hemisphere

paper “Different methods for estimating the mean radiant temperature in an outdoor urban setting” by Thorsson et al., 2007, IJC


19


Measurements of Ki and Li (I)

system “Freiburg” (Germany) system “Gothenburg” (Sweden)Thorsson, 2011

system “Gothenburg” (Sweden)Thorsson, 2011

system “Gothenburg” (Sweden)Thorsson, 2011Thorsson, 2011

system “Gothenburg” (Sweden)Thorsson, 2011

system “Gothenburg” (Sweden)


Measurements of Ki and Li (II)

system “Taichung” (Taiwan)

Lin, 2011


20


Globe thermometer

to measure globe temperature Tg

a) calculation of Tmrt from Tg

with the help of Ta and v

b) differentiation between

short- and long-wave radiant flux densities

is impossible

c) differentiation between the radiant flux densities

according to their directions

is impossible


Results from simulations (I)



21


Results from simulations (I)

conclusions:

- thermal stress in general:

strongest in E-W street canyon

with low aspect ratio (H/W)

- thermal stress per orientation of street canyon:

decrease with increasing aspect ratio

- thermal stress for constant aspect ratio:

in total strongest in E-W street canyonparticularly on the northern sidewalk ( oriented to S)



Results from simulations (II)

ENVI-met simulationsPET: Freiburg, Rieselfeld

(a) 15-07-2007, 12 CET

(b) „worst case“

(c) „worst case“ + 30 a

Huttner and Bruse, 2009


22


Case study in Freiburg

Germany: Freiburg, Vauban

WNW-ESE street canyonNNE oriented sidewalk


Ki, typical summer dayFreiburg, Vauban, 15-07-2007

0

200

400

600

800

1000

8 10 12 14 16 18 20 22

CET (hrs)

K

(W

m-2

)

K

K

K(S)

K(W)

K(E)

K(N)

WNW-ESE street canyonH/W = 0.10; SVF = 0.48 NNE oriented sidewalk


23


absorbed Ki, typical summer dayFreiburg, Vauban, 15-07-2007

0

30

60

90

120

150

8 10 12 14 16 18 20 22

CET (hrs)

Ka

bs

orb

ed

by

a s

tan

din

g p

ers

on

(

W m

-2)

KK

K(S)

K(W)K(E)

K(N)



Li, typical summer dayFreiburg, Vauban, 15-07-2007

400

430

460

490

520

550

8 10 12 14 16 18 20 22CET (hrs)

L

(W

m-2

)

L

L

L(S)

L(E)

L(W)

L(N)



24


absorbed Li, typical summer dayFreiburg, Vauban, 15-07-2007

0

30

60

90

120

8 10 12 14 16 18 20 22

CET (hrs)

La

bs

orb

ed

by

a s

tan

din

g p

ers

on

(

W m

-2)

L

L

L(S)

L(E) L(W)L(N)



absorbed K* and L* (%)

Freiburg, Vauban, 15-07-2007

0

20

40

60

80

100

8 10 12 14 16 18 20 22

CET (hrs)

K*,

L

*

(%)

L*totally absorbed by a standing person

K*totally absorbed by a standing person



25


Tmrt and PET, typical summer day

Freiburg, Vauban, 15-07-2007

10

20

30

40

50

60

70

8 10 12 14 16 18 20 22

CET (hrs)

Ta,

Tm

rt,

PE

T

(°C

);

RH

(

%)

0.2

0.6

1.0

1.4

1.8

2.2

2.6

v (m

s-1)


v

Tmrt

Ta

PET

RH


What do we learn from all data sets?


26


PET vs. Tmrt

Freiburg, typical summer days 2007

PET = 0.582*Tmrt + 8.0

R2 = 0.863

10

20

30

40

50

60

20 30 40 50 60 70Tmrt (°C)

PE

T

(°C

)


PET vs. Ta

Freiburg, typical summer days 2007

PET = 1.665*Ta - 11.5

R2 = 0.657

10

20

30

40

50

60

15 20 25 30 35 40Ta (°C)

PE

T

(°C

)


27


PET vs. VPFreiburg, typical summer days 2007

PET = 0.289*VP + 28.4

R2 = 0.014

10

20

30

40

50

60

10 15 20 25 30

VP (hPa)

PE

T

(°C

)


PET vs. vFreiburg, typical summer days 2007

10

20

30

40

50

60

0.0 0.5 1.0 1.5 2.0 2.5v (m/s)

PE

T

(°C

)


28


Tmrt vs. SVF90-270

Freiburg, 2007-2009, typical summer days

Tmrt = 0.378*SVF90-270° + 32.6

R2 = 0.764

20

30

40

50

60

70

0 20 40 60 80 100

SVF90-270 (%)

Tm

rt

(°C

)


Cities in Central Europe (I)

severe heat:

occurs in summer daytime hours exceed night hours

double strategy of planning methodsto maintain local thermal comfort for citizens

under severe regional heat

- first priority: methods aiming at the daytime situation

- second priority: methods aiming at the night hours


29


Cities in Central Europe (II)

double strategy of planning methods:

- first priority (methods aiming at the daytime situation):

lowering of the heat input into all urban spaces

- in accordance with environmental protection goals –

- second priority (methods aiming at the night hours):

maintaining sufficient ventilation

at night: mountain wind, cold air drainage on slopes

in the daytime: sea breeze


Planning methods

lowering of the heat input into urban spaces (in the daytime)

primarily by shading:

optimised street and building design

more „green“

- green roofs and facades

- street trees

- front gardens

- large urban green areas

- …

…


30


Shading ty street tree canopy

from experimental investigationsat different sites in Freiburg

during typical Central European summer days (2007-2009):

reduction of SVF90-270 by 10% due to the shading by street tree canopies

results in:

lowering of Ta by 0.2 °C

lowering of Tmrt by 3.8 °C

lowering of PET by 1.4 °C

(mean values: 10-16 CET)


Conclusions (I)

- urban climate:

modification of the atmospheric background situation

- regional climate change (trends, extreme weather):

aggravation of the atmospheric background situation

- cities in Central Europe:

pattern of urban land use, buildings and citizens:

not adapted to severe heatdemographic development risk group “elderly people” is increasing

health stress for citizens is increasing

urgent need for methods against severe heat


31


Conclusions (II)

methods against severe heat:

- preventive on a short-term basis:

heat health warning system

- current situation:

individual behaviour of citizens

- preventive on a long-term basis:

methods of urban planning (double strategy)

design of urban spaces

adapted to new challenges

by regional climate change


Conclusions (III)

- Tmrt: most important meteorological variable

for human thermal comfort during severe heat

- several methods to measure and simulate Tmrt outdoors

- from measurements:

distinct significance of horizontal radiant flux densities

for Tmrt

particularly for the long-wave radiant flux densities

reason: standing position of reference person


32


Conclusions (IV)

- higher significance of L* compared to K* for Tmrt

L*: total of absorbed long-wave radiant flux densities from six directionsK*: total of absorbed short-wave radiant flux densities from six directions

K*/(K* + L*): ≈ 30% (sunlit)

K*/(K* + L*): ≈ 8% (shaded)

- high potential of vertical surfaces (walls)(material, colour, “green” coverage, …)

to influence Tmrt PET(maintaining of human thermal comfort during severe heat)


Conclusions (V)What should urban planning do?

- to consider and apply lessons learned fromurban climate master plans (urban climate function maps)

- to consider, adapt to cities and applylessons learned from urban human-biometeorology

- to offer advanced training to planners in urban human-biometeorology

- to challenge existing concepts of urban climate,if they are quantified in an insufficient way up to now e.g. cold air drainage on slopes, mountain wind


33


Conclusions (VI)

What should urban planning do?

- to develop, apply and validate planning methodsagainst severe heat (target group: citizens)

- suited methods from urban human-biometeorology are- developed- tested- validatedcan be applied

- necessary:permanent quality control by independent experts


Prof. Dr. Helmut MayerMeteorological InstituteAlbert-Ludwigs-University of Freiburg(Werthmannstr. 10,D-79085 Freiburg, Germany)Tel: +49/761/2033590 Email: [email protected] Website: www.meteo.uni-freiburg.de

End, Thank YouEnd, Thank You

Prof. Dr. Helmut MayerMeteorological InstituteAlbert-Ludwigs-University of Freiburg(Werthmannstr. 10,D-79085 Freiburg, Germany)Tel: +49/761/2033590 Email: [email protected] Website: www.meteo.uni-freiburg.de

lessons learnt from urban human-biometeorology of urban...

Documents