e urban green volume — how to calculate

e urban green volume — how to calculate
Clemens Deilmann, Guenter Arlt, Iris Lehmann
Leibniz Institute of Ecological and Regional Development, Germany
e urban environmental quality depends very much on the ecological performance of urban green. Key
factor for the microclimatic situation of cities is the green ‘volume’. e volume can be differentiated into
three basic layers of green which are of importance to urban planning. For example low vegetation (lawns)
does have good assimilation values. High vegetation (trees) is favorable to improving air-temperature and
moisture. Parks, where all layers of vegetation exist, do have high bioclimatic impact for the overall city
balance. e Leibniz Institute of Ecological and Regional Development (IOER) analyzed empirically 116
cities in Germany to discover relations between urban green and the different land use categories. is
was done with help of GIS-tools (feature recognition). Important factors for the green volume situation
of cities as a whole are sealed surfaces, forest, water and minimizing areas. e results are cause-effect
relations and models for urban green. ese models can be helpful to develop planning strategies and
management tools.
It was possible to identify 5 characteristic clusters of cities within the 116 cases. e ecological quality
and quantity of green volume and connectivity could be linked to the 5 clusters with average values and
indicators. e clusters take into account the land use structure, the land use density, the green volume
and its spatial distribution. e information does support decisions in urban planning especially when it
comes to deciding on how and where to use brown field areas.
Keywords: cluster-analyses, environmental quality, green volume
1
Context and Goal of the Study
Urban greenery is a quality factor in the ecology of cities. In particular, the supply
of urban green spaces strongly influences climatic conditions and air hygiene. e
type, level, and spatial distribution of urban vegetation are determined by the uses
to which land is put. Land-use structures interact with ecological production,
living-environment, and regulatory functions. Knowledge about causes and effects
is required if land-use patterns are to shape ecological quality in the city. Urban
ecological quality is part of environmental quality. It is a measure of the extent to
which the status of the urban environment deviates from the environmental
protection and nature conservation targets set by society.
Green space in cities exhibits various spatial patterns. Its positive ecological
impact depends largely on how much of the urban territory it occupies, its spatial
distribution, and the biomass of total vegetation (vegetation or “green” volume).
e study investigated the proportion of green space and vegetation volume,
which, together with ground sealing, interconnectivity, and ecological quality
levels, providing a basis for ensuring the differentiated internal development of
urban ecological quality. Within cities, the findings permit conclusions to be
drawn about deficiencies in the supply of green spaces at the district or
neighbourhood level.
2
Urban Green Space as Indicator of Ecosystem
services
Ecosystem services refer to the degree to which functions are performed in the
context of land use (Arlt et al. 2001).
e supply of urban vegetation influences ecosystem services. It is thus also an
indicator of certain environmental situations.
Fig. 1: Indicator function of urban green space for selected ecological functions
(source: Arlt et al. 2005 after Baeseler et al.1974)
Basically, the type and extent of landcover influences ecological performance. To
quantify the impact of various types of landcover on the environment, selected
ecological land functions and landcover types of sealed, unsealed vegetation-free
areas and unsealed vegetated areas were analysed and assessed (Heber, Lehmann
1996). e assessment procedure assigned dimensionless ecological performance
parameters to types of landcover. e ecological performance of an area is
assessed on an ordinal scale from 0 (no ecological performance) and 1 (very high
ecological performance).
e functions climatic compensation, dust filtration, pollutant retention, porosity
and permeability, groundwater replenishment, rainwater infiltration, and biotope
formation were assessed for lawn, meadow, and perennial cover as well as trees
and shrubs and open ground as vegetationless land.
Low to high ecological performance was recorded for all vegetated areas and open
ground areas. Vegetated areas are most efficient in climatic compensation,
porosity and permeability of the soil, rainwater infiltration, pollutant retention,
and biotope formation (except for lawn surfaces). Lawn, meadow, and perennial
cover showed low to medium performance in binding dust and replenishing
groundwater. Areas with tree and shrub cover contribute least to groundwater
intake but are the most efficient when it comes to dust filtration.
3
Empirical Studies
3. 1
Subject of Study
A research project at the Leibniz Institute of Ecological and Regional Development
addressed the empirical-deductive determination and assessment of green space
and volume in cities and urban regions. e basis was a GIS vegetation structure
analysis of 116 urban districts and selected surrounding communities.
e empirical investigation focused on an impact analysis of relations between
land use structure and the proportion of green space and area-specific vegetation
volume. Regional statistical procedures were used.
e fundamental methodological tool was the comparative city study. It addressed
ordinal scaled measurement of vegetation levels (low, medium, and high) on the
basis of the proportion of green space and area-specific green volume. is
involved urban typology studies on the basis of cluster analysis with the aim of
identifying city types. Cities belonging to the same type show comparable
proportions of green space and area-specific vegetation volume, which can be
interpreted as ecosystem services and quality levels. ey have largely similar use
structures (for example, in settlement and traffic infrastructure, settlement density,
area per inhabitant).
3. 2
Spatial Levels and Data Base
e vegetation structure analysis of 116 German cities addressed three spatial
levels: the core city, the urban region, and open space.
e term core city refers to the city within its administrative boundaries.
e urban region includes the core city and selected surrounding communities.
e data base for determining vegetation structure in German urban districts is
generated by the 1993 and 1999 Dresden urban biotope type maps, the 1997 urban
structure type maps of the 116 urban districts, and land cover maps.
Fig. 2: Mapping of urban structure types, open space and surface water
bodies. The example of the Stuttgart urban region (source: Arlt et al.
2005)
3. 3
Method for Determining Green Space and Vegetation
Volume
Of key importance in determining the proportion of green space and vegetation
volume in German urban districts and urban regions are the urban biotope type
and urban structure type approaches. For practical planning purposes, they enable
a workable definition of vegetation structures and their assessment by type
(classified units of public and private green space), dimensions (size and geometry
of green spaces), and location (compactness and interconnectivity of green
spaces).
From a biological point of view, the city consists of a mosaic-like multiplicity of
biotopes. As a rule, they are clearly demarcated and internally relatively
homogeneous. Urban biotope mapping provides a good overview of the biotope
types and vegetation structures in a city. Vegetation structures were analysed and
vegetation patterns determined on the basis of the urban biotope mapping of
Dresden. 52 biotope types were identified, on the basis of which vegetation
structures and volumes were assessed.
Fig. 3: Matrix of vegetation structure: example of the urban biotope
type 1 (residential development, mixed uses, industrial, commercial and
special purpose areas)and schematic flowchart of vegetation structural
analysis (Arlt, et al., 2002)
e vegetation structure of urban biotope types was analysed in representative
areas, analysis including the physiognomic identification of areas with low (≤ 1m),
medium (≥ 1m to ≤ 3m), high vegetation levels ((> 3m), and vegetation less areas
(built-up land, other sealed and open ground, water bodies).
4
Results of the Study of 116 German urban districts
and their regions
In the context of the empirical studies, the vegetation structure analysis shows the
proportion of green space and specific vegetation volume differentiated in terms of
vegetation layer for the 116 German urban districts and their regions. e
proportion of green space and specific vegetation volume are parameters which,
on a medium scale (1: 25 000 to 1: 50 000), assist practical city-wide or urban
regional planning. At the same time they serve to pinpoint deficiencies in the
supply of green spaces at the district or neighbourhood level. In a model
abstraction, green spaces and their cubature are two and three dimensional
components of the physical urban space and, in interaction with sealed areas,
surface water, and buildings, fundamentally affect the material, energetic, and
informational state of the urban living environment. Physical urban structures are
influenced by land-use structures.
4.1
Proportion of Green Space and Specific Vegetation Volume
e proportion of green space refers to the percentage share of vegetated areas in
the core city, the urban region, the settlement area, and open spaces as a whole
and differentiated by layer as “low,” “medium,” and “high.”
Specific vegetation or “green” volume refers to the volume of vegetated areas in
relation to given units of area (as a rule 1 m²) in the core city, urban region,
settlement area, or open space. It is differentiated by vegetation layer into “low,”
“medium,” and “high” and expressed in m³ per m² for the sum of vegetation layers.
Data on the urban ecological parameters green space and vegetation volume
differentiated by spatial level and vegetation stratification are available for 116
German urban districts and as mean values for all cities.
Tab. 1: German urban districts – mean proportion of green space and specific
vegetation volume differentiated by spatial level and vegetation layer (source: Arlt
et al. 2005)
Against a backdrop of progressive land take for settlement and transport purposes,
the quality of the living environment is increasingly reflected in the type and
extent of green space in settlement areas. Owing to the long period people spend
in the settlement area and its relatively poor experience value, the ecological and
psycho-social functions of green space in urban settlement areas are more greatly
appreciated than those of open terrain.
In the settlement areas of core cities, the average proportion of green space is
about 25 %. e proportions by vegetation layer are 5 % (“low”), 5 % (“medium”),
and 15 % (“high”). In the settlement areas of urban regions, there is a markedly
higher proportion of green space, on average 60 %; 35 % with a “low” vegetation
coverage, 10 % with “medium” coverage, and 15 % with “high” coverage.
Vegetation volume relative to a square metre unit and the spatial units core city
and urban region is not a sensitive indicator. Changes in green volume caused by
urban development measures at the neighbourhood or plot level are hardly shown
by city-wide or urban regional statistics, although the micro-climatic impact of
such changes can be considerable. Specific vegetation volume on the medium
spatial scale is rather to be seen as a basic municipal indicator which – generally in
connection with soil sealing – provides a “rough” pointer of urban ecological
quality.
4.2 Interaction between Urban Structure, Green Space and
Vegetation Volume
Impact analysis was based on regional statistics research, and selected structural
and phenomenological parameters were included. Sub-studies were conducted
within the circular causal connection between processes, structures, and
phenomena. ey addressed interaction between urban and land-use structures
and green spaces and vegetation volumes differentiated in terms of vegetation
layer. Correlations were shown and incorporated in stochastic models. Relevant
regional statistical methods were used in the studies on interaction between urban
and land-use structures, green space and volume. e regional statistics
programme was developed against a backdrop of accepted and plausible
circumstances.
Stochastic models were developed on the basis of factors and parameters to
calculate the proportion of green space and vegetation volume in both core cities
and urban regions. e high coefficients of determination make the models highly
relevant for planning practice. Taking the land cover data (for the 5 parameters) as
input for the model will be sufficient to calculate the green volume and proportion
of green space for any German city. It might be possible to adapt the model for
other countries.
Fig. 4: Analytical parameter models “proportion of green space” for
core cities and “specific green volume” for urban regions (source: Arlt
et al. 2005)
5
City Clusters
City clusters enable complex circumstances to be structured and substance lent to
complex concepts like “sustainable urban development.” rough cluster analysis
as a multivariate procedure, the parent population of urban districts was divided
in terms of several characteristic variables into types (clusters) in such a way as to
make the similarities between cities of a given type and the differences between
cities of any two types as great as possible.
Such cluster analysis takes account of the proportion of green space, vegetation
volume, degree of surface sealing, and the proportion of surface water bodies –
use-structural parameters that relate to selected elements of the physical urban
space. Apart from these statistical parameters of land-use structure, function
performance and efficiency depend very strongly on the spatial structure of urban
land.
e analysis identified clusters of cities with characteristic quality standards and
attribute structures. is permits land-use structures to be identified, described,
and assessed from a qualitative perspective.
Fig. 5: City clusters from an ecological perspective – characteristic vegetation
patterns with vegetation volumes and the proportion of green space and surface
water for clusters I to V (source: own processing)
6
Conclusion
Green and open spaces perform ecological functions.
e type and extent of green space and vegetation volume in cities and urban
regions interact with land-use structures and the spatial structuration of uses.
Urban vegetation volume is a highly aggregated indicator of many aspects of
ecosystem services in the urban living environment (especially in bioclimatic
balance and air hygiene), whose function is to be seen as providing a rough
intimation of city-wide ecological quality.
Cognizance of interaction within the structure of uses enables action to be taken
to influence ecological performance and quality in urban settlement areas.
Differentiated preferences in urban development create differences in land-use
structure and thus in the characteristic ecological setting of a city. ese
framework conditions require a range of strategies and the differentiated use of
tools and programmes to secure and develop the supply of urban green spaces and
ecological quality.
7
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8
Figures and Tables
Fig. 1: Indicator function of urban green space for selected ecological
functions (source: Arlt et al. 2005 after Baeseler et al.1974)..................2
Fig. 2: Mapping of urban structure types, open space and surface water
bodies. e example of the Stuttgart urban region (source: Arlt et al.
2005).....................................................................................................................3
Fig. 3: Matrix of vegetation structure: example of the urban biotope type 1
(residential development, mixed uses, industrial, commercial and
special purpose areas)and schematic flowchart of vegetation
structural analysis (Arlt, et al., 2002)..........................................................4
Fig. 4: Analytical parameter models “proportion of green space” for core cities
and “specific green volume” for urban regions (source: Arlt et al.
2005).....................................................................................................................6
Fig. 5: City clusters from an ecological perspective – characteristic vegetation
patterns with vegetation volumes and the proportion of green space
and surface water for clusters I to V (source: own processing)...............7