Transcript A Geo-Referenced Database for Surface Roughness Parameters over Greater Manchester M.G.D.

A Geo-Referenced Database for Surface Roughness Parameters over Greater Manchester
M.G.D. Carraça and C.G. Collier
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2
(1) Dep. Física, CGE, Universidade de Évora, Portugal (2) CESR, University of Salford, UK
Contacts: [email protected] and [email protected]
1. Establishment of the land-use categories for Greater
Manchester.
2. Mapping the surface roughness parameters over a rectangular grid of 1x1km2 resolution, for
the Greater Manchester study area (24 x 24 km2)
In order to establish typical land-use categories for Greater Manchester urban area and
Rectangular
grid
to attribute reference morphologic parameters to each land-use category, an exploratory study
(not shown here) was carried out for a sample area of Salford and Manchester considered
being representative of the Greater Manchester urbanised area (Figure 1).
Map
Digitised georeferenced data of the surface elements (Cities Revealed Building Heights
Based
essentially
on
maps
and
aerial
photographs
the
Data and Environment Agency data), aerial photography, maps and field surveys allow
identification of the different land use categories was extended to the
mapping buildings, car parks, rivers, roads, railways, vegetated areas, etc... , and were used
entire study domain (24 x 24 km2). Using Arc View 3.2 tiles of similar
for the surface characterisation of Greater Manchester.
morphology and surface cover were delimited forming a non regular
Aerial
photo
The distribution of the buildings over the sample area of Salford and Manchester is
polygonal grid over the study area. These tiles were classified according
mapped on Figure 1, where buildings are projected on the terrain level horizontal plan as
to the reference categories previously established in section 1, and the
obtained from CR data.
380500
381000
381500
382000
382500
383000
383500
384000
384500
385000
Land-use
categories
399500
398500
399000
398500
398000
399500
399000
400000
400000
W
E
Height
(m) S
Nwgrd3
398000
0-2
2-5
5-8
8 - 12
12 - 16
16 - 20
20 - 30
30 - 50
50 - 76
no data
397500
397500
Figure 1 - Distribution of buildings, obtained from CR data, covering a sample area of 2.5km x 5km
of Salford and Manchester. The axes labels represent the U. K. National grid co-ordinates of the area
of interest (Ordnance Survey national grid system), X: 380000m - 385000 m; Y: 398000m- 400500m.
The legend shows the values of the buildings mean height associated with the different colours.
380000
380500
381000
381500
382000
382500
383000
383500
384000
384500
Figure 3, which refers to a selected area of Greater Manchester (4 x 2
N
400500
400500
380000
respective roughness parameters were assigned according to Table 1.
al
n
o
g
y
l
d
Po gri
Mean Buildings Height (m)
385000
379399
380399
381399
382399
379398
380398
381398
382398
km2), illustrates the procedure used to identify and mark the different
Green
CI
Res
Road
Trees
Water
Res_mix
Cemit
RailW
Uni
RailS
Centre
Baren
ResH
CentreN
CentreP
categories over the entire study area
Figure 3 - Illustration of the procedure used to identify and mark the
different categories over the entire study domain. The number centred
in each square cell (1x1 km2) gives the U.K. National grid coordinates
(in km) of the cell inferior left corner; the first three digits are the
latitudinal coordinate and the last three are the longitudinal coordinate.
Study Domain: Greater Manchester, 24x24 km2
Fraction
ofof Urbanised
Area
Fraction
urbanised area
Based on an exploratory study of this sample area, a classification of 15 land-use categories
was established for Greater Manchester and reference morphologic parameters, such as
1
surface elements height, zH, the plan area index, λP, and frontal area index, λF, were
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each category in each domain cell of 1x1 km2. The sum of the
and water surfaces.
areal percentages of the urban categories (Res, ResH, Res_mix,
Many of the surface properties are strongly related to, but not necessarily directly associated
CI, Centre, CentreN, CentreP, RailS, Uni, and Road) in each
395
390
domain cell gives the fraction of urbanised area. These estimates
0.3
385
degree of urbanisation for the present Greater Manchester study
Airport
weighted averages of the values attributed to each land-use
396
395
15
study area, over a rectangular grid of 1x1
are shown on
ste
r
395
ch
e
0.14
0.11
11
9
390
0.08
7
5
385
Figure 5.
1
380
376
381
0.05
385
3
Airport
Note the difference between the rural areas to the east and
0.17
13
390
km2,
0.20
400
17
results for a particular cell will reflect the characteristics of the
predominant land-use category.
0.23
an
present in the cell. Thus the values of zH and λF for each cell
depend on the percent of each land-use area present, and the
19
r
400
ste
category (Table 1), considering the percentage of each category
Frontal
area
index, λF
Frontal
Area Index
21
The estimates of zH and λF obtained for Greater Manchester
While for urbanized zones zH , λP and λF are
391
23
he
0.56
0.26
(e)
0.39
0.08
(e)
0.47
0.14
(e)
0.35
0.06
(e)
0.49
0.16
(e)
0.46
0.13
(e)
0.35
0.06
(e)
0.42
0.10
(e)
0.35
0.06
(e)
0.18 (R)
0.01*
0.01*
0.01*
0.01*
0.001*
(m )
2401
942
1581
1718
6584
142
736
715
1628
zH, and frontal area index, λF, for each grid cell are area-
an
c
0.26
0.51
0.08
0.17
0.14
0.29
0.06
0.21
0.16
0.63
0.13
0.19
0.06
0.18
0.10
0.12
0.06
0.16
0.18
0.45 (R)
(R)
0.01*
0.01*
0.01*
0.01*
0.001*
(m )
0.56
2401(e)
0.39
942(e)
0.47
1581(e)
0.35
1718(e)
0.49
6584(e)
0.46
142(e)
0.35
736(e)
0.42
715(e)
0.35
1628(e)
2
M
2
386
Surface
zH
Surface elements
Elements Height, ZHheight,
(m)
rd
H.Area
The estimates of the mean height of the surface elements,
lfo
zDAλ/zFFH z HH.Area
AzPD/zH
λλFP
381
Figure 4 - Fraction of urbanised area for the Greater Manchester study domain.
The coordinates X and Y are the U.K. National Coordinates. The total study
area is 24 x 24 km2 and the area of each grid square 1x1 km2. The legend on
the right-hand side refers to the values of the fraction of urbanised area.
Sa
Category Category
zH
λzPH
(m)
(m)
Centre
Centre
26
0.51
26
CentreN CentreN
14
0.17
14
CentreP CentreP
15
0.29
15
CI
10
CI
0.21
10
RailS
RailS
20
0.63
20
Res
Res
8
0.19
8
Res_mix Res_mix
8
0.18
8
ResH
ResH
22
0.12
22
Uni
15
Uni
0.16
15
Trees
8.7
Trees
(R)
0.45
8.7 (R)
(R)
Baren
0.05*
Baren
0.05*
Green
Green
0.15*
0.15*
RailW
0.05*
RailW
0.05*
Road
0.05*
Road
0.05*
Water
0.001*
Water
0.001*
0
380
376
M
Table 2 - Land-use categories defined for
Greater Manchester (first column) and
Urban Terrain Zones of Ellefsen
(1990/91).
0.1
area.
the United Kingdom, for example the distribution and type of buildings and green spaces.
Table 1 - Roughness parameters for each land-use
category of Greater Manchester. Mean buildings
height, zH, plan area index, λP, frontal area index, λF,
AF  z H AP .
and mean horizontal plan area of the buildings,
0.2
d
also some differences. These differences are probably due to the nature of the urban areas in
0.4
or
Comparisons with earlier published work revealed similarities to previous representations, but
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0.5
are shown in Figure 4, which reveals the spatial variation of the
major land-use categories.
0.7
Sa
lf
with, socio-economic activities. However, it was convenient to associate the tiles with some
an
ch
es
te
r
some typical values for Greater Manchester. These include built-up areas, vegetated areas
0.8
M
Arcview 3.2 software enables the estimation of the area of
Sa
lfo
attributed to each category. These categories are presented in Table 1 and Table 2 with
rd
400
386
391
396
Airport
380
376
381
0.02
386
391
396
estimated mainly from the geometric dimensions of
south compared to the urban areas. The area of high rise Figure 5 - (a) Mean building height, zH, for each cell in the study domain. The legend on the right-
the surface elements (buildings) (Figure 2), for
buildings is clearly evident.
Zero-plan displacement
height,length,
zD ZD (m)
Zero-plan displacement
roughness length for momentum, z0M, (Figure 6) are calculated
as a function of the height of the surface roughness elements, zH,
Figure 2 - Definition of some surface dimensions used
in morphometric analysis (adapted from Grimmond and
Oke, 1999a).
For built areas, zH and λP for each urban
homogeneous array are direct results from the CR
data statistics performed using ArcView 3.2. The
fraction of built up area, i. e., the quotient between
the total horizontal plan built area over an urban
array and the total area of the urban array, is taken
as an estimate of the plan area index- λP.
AP AP
(Eq. 1)
 

P
AT
AT
The frontal area index, the mean area of the
surface elements facing the wind, was estimated
AF A P
from the expression
(Eq. 2)
F 
AP AT
In this equation , AP, and AT are direct results from
the CR data statistics performed using ArcView
3.2. The mean frontal area is calculated using the
approximation that buildings are rectangular
parallelepipeds with a squared base, thus
AF  z H AP
z 0M
zH
Where
 zd
 1 
 zH
 

u
exp  k  ψ h 

 
u
*

 


u*
0.5  u * 
 min cS  c R λ F  ,   
u
 u  max 

an
ch
e
r
16
M
8
2.4
te
rd
lfo
9
11
2.2
2.0
1.8
7
1.6
6
1.4
11
5
1.2
1.0
4
(Eq. 5)
0.8
3
6
0.6
6
2
Airport
(Eq. 6)
u ≡ wind speed
u* ≡ friction velocity
zH ≡ surface elements height
cS ≡ drag coefficient for the substrate surface at height zH
in the absence of roughness elements
cR ≡ drag coefficient of an isolated roughness element
mounted on the surface at height
cdl ≡ a free parameter.
ψh ≡ roughness sublayer influence function,
Typical values specified by Raupach (1994) are used in our
model: cS=0.003, cR=0.3, cdl = 7.5, ψh=0.193 and (u*/u)max =0.3.
Taking all the roughness values over the entire study domain it
was found that zD = 5 z0M, zD = 0.4 zH , z0M = 0.08 zH (Figure 7).
0.4
Airport
1
0
1
1
6
11
16
0.2
0.0
1
21
1
6
11
16
21
Figure 6 – (a) Zero-plan displacement height, zD, for each domain cell. The legend on the righthand side refers to the values of zD expressed in m. (b) Roughness height for momentum, z0M, for
each domain cell. The legend on the right-hand side refers to the values of z0M expressed in m.
3.0
zD = 0.42 zH
14
14
zD = 5.3 z0M
12
12
R2 = 0.94
10
10
2
R = 0.95
2.5
z0M = 0.076 zH
2.0
2
R = 0.84
8
1.5
6
8
6
1.0
0.5
0.0
Grimmond and Oke 1999a).
21
10
(Eq. 4)
These results are in agreement with published literature (e.g.,
(Eq. 3)
Sa

16
z0M(m)


 exp  c d1 2λ F   1

 1 

0.5


zH
c d1 2λ F 


zD
ste
r
21
2.6
es
11
recommended by Grimmond and Oke (1999a) for urban areas,
0.5
2.8
12
and frontal area index, λF, (Figure 5) using Raupach’s (1994,
1995) method, which is one of the morphometric approaches
Roughness length for
momentum,
z0M
Roughness
length for momentum,
Z0M (m)
ch
reference tables in the published literature.
the
an
from
and
M
extrapolated
zD,
rd
are
length,
lfo
values
displacement
Sa
these
zero-plane
zD(m)
surfaces
The
zD(m)
permeable-rough surfaces with vegetation and water
hand side refers to the values of zH expressed in m. (b) Mean frontal area index, λF, for the same
study area. The legend on the right-hand side refers to the values of λF.
0
5
10
15
zH(m)
20
25
4
4
2
2
0
0
0
1
z0M(m)
2
3
Figure 7 - (a) Zero plan displacement height, zD, and roughness length for momentum, z0M, as
functions of the surface roughness elements height, zH. (b) Zero plan displacement height, zD,
versus roughness length for momentum, z0M. Each line represents the fitted linear function
between a pair of variables resulting from linear regression. R is the linear correlation coefficient.
Acknowledgements: M.G.D. Carraça acknowledges the support from the Portuguese Foundation for Science and Technology under grant SFRH/BD/4771/2001.