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PLEA 2020 A CORUÑA
P lanni ng P o st Car bo n C ities
Natural Capital Impact Assessment
for New Urban Developments
PEPE PUCHOL-SALORT
1
, MAARTEN VAN REEUWIJK
2
, ANA MIJIC
3
1,2,3
Civil and Environmental Engineering Department, Imperial College London, London, United Kingdom
ABSTRACT: Under pressures of climate change and population growth, it is crucial to address water security and
sustainable urban development in our cities. This challenge is particularly important for London, where a shortage
of housing has been experienced during last decades and the region is considered highly vulnerable to water
shortages and floods. According to the Greater London Authority (GLA), an average of 66,000 new homes per year
should be built until 2041. However, assessing impacts of such urban growth on environmental management and
protection is complex and difficult to evaluate.
This creates a need to determine the extent to which Ecosystem Services (ES), or the benefits provided by the
functioning natural environment in the form of Urban Natural Capita (UNC), are essential to the wellbeing of
current and future urban dwellers and how costly it may be to provide them. This research aims to create an impact
assessment framework for Urban Natural Capital (UNC) for new urban developments, which will provide crucial
indicators to assess sustainability at an urban development scale. The results will be used to inform improved
urban design in the context of water and environmental management, including Blue Green Infrastructure (BGI)
solutions, and showcase the benefits that lead to better decisions and sustainable urban development.
KEYWORDS: Urban Natural Capital, Sustainability, Urban Developments, Ecosystem Services
1. INTRODUCTION
Under the increasing pressures of climate change
and population growth at the global level, it is crucial
to address water security and sustainable urban
development. Urban Infrastructure Systems (UIS)
involve multiple sectors, including water, land,
transport and housing. These infrastructures interact
with each other and put constant pressures on their
surrounding environment and human wellbeing in the
form of flood risk, water shortages, air and water
pollution, and Urban Heat Island (UHI) effect [1].
Nowadays, more than 50% of the world's
population live in urban areas, and this is predicted to
reach 66% by 2050 [2]. This level of growth will be
particularly critical in London, where population is
projected to increase by 70,000 people every year,
reaching 10.8 million citizens in 2041 [3].
The capital is one of the most at-risk UK’s urban
areas to future climate change, being particularly
vulnerable to water scarcity, heat waves, flooding and
air quality problems [3, 4, 5]. According to the Greater
London Authority (GLA) and their new London Plan, an
average of 66,000 new homes per year should be built
in the city until 2041 [3].
However, the relationship between urbanisation
and environmental management is very complex and
has not been sufficiently addressed yet. Urbanisation
is a difficult spatiotemporal process that influences
areas beyond the urban cores, being a difficult process
to control, quantify and plan [6]. Increased
urbanisation can be detrimental to natural
environment’s connectivity and condition, which are
key components of resilience to climate change [7, 1].
Ecosystem Services (ES) and Natural Capital (NC)
assessment is growing in popularity as an innovative
and powerful method to evaluate the level of
sustainability for new urban developments. The
results from this type of assessment are generally
presented as a series of numerical scores (positive or
negative), but little evidence is available about their
combination with spatial representation of the urban
development. Hence, a valuable method that
combines Urban Natural Capital (UNC) values with
graphical Geographical Information Systems (GIS)
maps is performed in this study, making the process
for sustainable urban design more effective and
reliable, which may ultimately lead to better planning
decisions.
1.2 Sustainable urban infrastructure solutions
Nature Based Solutions (NBS) are broadly defined
as solutions inspired and supported by nature that
simultaneously provide environmental, social and
economic benefits to citizens [8]. They also have a
series of co-benefits, such as improving health and
quality of life, and the attractiveness of the place [8].
The NBS concept includes Blue Green Infrastructure
(BGI) and other sustainable concepts such as
Sustainable Drainage Systems (SuDS), Ecological
Engineering and Water Sensitive Urban Design
(WSUD). Some examples of BGI include: street trees;
parks and open spaces; permeable paving; engineered
stormwater controls (bioswales, rain gardens or
retention ponds); green roofs; green facades;
waterways and wetlands; or, urban gardens [9].
In parallel to this, Ecosystem Services (ES) are
understood as all the benefits that citizens and human
beings obtain from natural ecosystems [10]. In
economic terms, natural ecosystems are also
understood as a Natural Capital (NC), accounting for all
the assets that the natural environment provides in
the context of ES. These include soil, air, water and all
living organisms [11].
BGI benefits can outweigh those of traditional hard
infrastructure based on reinforced concrete, also
known as grey infrastructure [12]. In order to achieve
a good level of urban sustainability and a large number
of ES, it would be necessary to evaluate the optimal
combination of BG vs grey interventions to be
implemented in our cities.
1.3 Complexity of urban interactions
Despite the fact that numerous investigations
recently tried to integrate urban planning design with
water and housing systems, many challenges still
remain. These challenges are very clear if we analyse
London’s urban environment, which is currently in
danger of critical deterioration due to climate change
and a wide variety of constant pressures [3].
Figure 1: Systems thinking diagram that interlinks Urban
Infrastructure Systems (UIS) with Urban Ecosystem Services
(UES) and the relationship of sustainable design solutions to
the design and operation of UIS.
More housing growth requires more water to be
abstracted, which is finally converted into wastewater
once it is treated, stored and consumed. This
wastewater discharges from sewage treatment plants
are released back to the natural environment and
affect the final amount of ES provided to citizens. In
order to maintain a sustainable process and to manage
urban water efficiently, it will be necessary to re-think
the urban design concept from a systems perspective
(see Fig. 1).
Although Urban Infrastructure Systems (UIS) might
include transport or energy production, in this study
they are comprised of the three main elements seen in
Figure 1: 1) Housing, 2) Land, and 3) Water Services
Infrastructure (WSI). These three urban elements are
always interconnected and depend on, and affect each
other. Land includes all the Blue and Green assets that
are internal part of the system, that is the Urban
Natural Capital (UNC); while housing includes all the
building infrastructure and any impervious surface
necessary to support it, such as parking, roads or
paths. As conceptualised in Figure 1, UIS directly affect
the Urban Ecosystem Services (UES), which at the
same time also add value to the urban infrastructure
(UIS). Therefore, the sustainable design solutions
proposed for landscape and building areas will directly
affect the performance and operation of the UIS.
1.4 CAMELLIA research project
This research is a key element of the Community
Water Management for a Liveable London (CAMELLIA)
research programme, which is focused on sustainable
urban water management in London. CAMELLIA has
four London-based case studies (Mogden, Enfield,
Southwark and Thamesmead), each reflecting
different key issues of urban water management (see
Fig. 2). Among them, Thamesmead will be this work’s
main case study, where a major redevelopment plan is
expected to emerge during the next 20 years [3].
CAMELLIA is supported by communities,
policymakers and industry; it aims to transform
collaborative water management to support the
provision of lower cost and better performing water
infrastructure in the context of significant housing
development, whilst improving people's local
environments and their quality of life.
Figure 2: Case study areas inside CAMELLIA research project
(London map with Thamesmead highlighted in red) and
partners involved (logos around the map). (Source:
CAMELLIA)
2. METHODOLOGY
2.1 Thamesmead as main case study area
Thamesmead is a 750-ha neighbourhood located in
Shout-East London where around 150 ha are
considered blue or green space. Following a report
conducted by Vivid Economics, the total NC potential
value provided by Thamesmead’s blue and green-
space is estimated to be at least £306 million or £257
per person per year [3]. Despite this abundant natural
value, this blue and greenspace is not appropriately
used by their citizens and large areas are even
inaccessible.
As mentioned in Section 1.4, this district is
undergoing a large urban regeneration programme
and its major development will be Thamesmead
Waterfront Development Plan (TMWDP). This scheme
will include more than 11,500 new homes and a
contemporary renovated masterplan carried out by
the Peabody Housing Association. TMWDP, which
comprises a total area of 100 ha and embraces almost
3 km of underdeveloped river waterfront, will be our
main case study area to test our different urban design
proposals.
2.2 Natural Capital impact assessment
Engineers and scientists need to determine the
extent to which certain ES are essential to the welfare
of current and future generations and how costly it
may be to protect and conserve them. Accounting for
the Urban Natural is a crucial indicator of our cities’
level of sustainability and finding the most reliable
type of assessment is a challenging task that needs to
be analysed.
As already explained in previous sections, NC
accounting will be this study’s starting point in order
to understand the environmental impact created by
new housing developments. At this stage, the studies
are focused only on the design aspect, leaving the
operation of the system mentioned in Section 1.3 for
future stages of the work (see Fig. 1).
There are different tools that evaluate Natural
Capital (NC), two of the most commonly used being
NCPT (Natural Capital Planning Tool; Hölzinger et al.,
2019) and InVEST (Integrated Valuation of Ecosystem
Services and Trade-offs; Sharp et al., 2018). Between
them, NCPT is chosen because it is more appropriately
designed for urban developments and fits within the
general design process explained in Figure 1.
Despite its appropriate functionality, the NCPT only
provides numerical scores for Ecosystem Services (ES)
and lacks a graphical representation of land uses.
Therefore, an important innovation presented in this
work is the ability to link the pre- and post-
development land-use areas of the site with a GIS
software. For this, QGIS (Cavallini et al., 2019) is used
because it is a free-open source platform and can be
easily shared with a range of professionals.
2.3 Urban design scenarios
Three different urban design scenarios of land uses
are suggested in order to compare different levels of
environmental impact. But, before presenting these
three urban design scenarios, it is necessary to
understand the pre-development land-use map, which
will act as the initial baseline for all of them. This is
represented based on research data previously
collected and supplemented by OpenStreetMap and
Google satellite maps.
Figure 4: Pre-development land-use map for Thamesmead
Waterfront Development Plan.
As seen in Fig. 4, most of the land at the pre-
development state is currently developable
brownfield land and hazardous waste land fill. The
latter cannot be used for building, but it might be
transformed into a natural reserve. On the other hand,
the blue space (lakes and canals), the amenity
grassland and the protected wetland must be
preserved [7]. Apart from an existing and functioning
water-pump station, all the existing buildings will be
removed and redesigned in all three design options.
Figure 5: Post-development Land-Use map for Thamesmead
Waterfront Development Plan. Scenario 1 – “Adverse”.
Based on initial constraints previously explained
such as the hazardous waste land fill areas or the
protected wetlands, and in order to find a realistic but
“adverse scenario”, the first urban layout is proposed
(see Fig. 5). Scenario 1 represents a traditional way of
building [14] and does not consider any sustainable
urban form, such as appropriate orientation or green
roofs. In this case, some land uses are transformed,
such as developable brownfield or hazardous waste
land; new ones emerge, such as built-up areas (high,
medium and low density), gardens, mixed parkland or
pond. These built-up areas with different types of
densities are built with traditional ways of
construction, being considered non-sustainable
buildings.
As aforementioned, in Scenario 1 the blue space,
protected wetland and intertidal mud-sand are
preserved and have not been changed. Other land-
uses, such as mixed woodland and amenity grassland,
have been decreased in some parts but augmented
elsewhere, especially where there is currently
hazardous waste land fill.
The next scenario, called “intermediate”, has the
same number of built-up hectares as Scenario 1, but
instead of being high-, medium-, or low-density built-
up areas, those are replaced by “buildings covered
with green roofs” or “buildings with green walls” land
uses. These two land uses are the only sustainable
building options given by the NCPT. This is therefore
seen as an important limitation of the tool, as BGI
option cannot be implemented in the design properly.
In the same way, the previous “roads” have been
replaced by “local green roads”; while “paved areas
(car parks, etc.)” are transformed into “gardens”
(including the Thames path). NCPT does not give
options for BGI land uses, such as “permeable paving”
or “swales”, which constitutes another important
limitation of the tool.
Figure 6: Post-development Land-Use map for Thamesmead
Waterfront Development Plan. Scenario 3 – “Favourable”.
The third option, called “favourable”, is based on a
completely new urban layout design (see Figure 6). In
this case, instead of keeping the same areas and
changing only the “building typologies” (which would
not be possible due to the already explained NCPT
constraints); more green, blue and recreation spaces
are arranged around the built-up areas to increase the
ES received. This scenario is based on compact
densities and BGI around them, which is proven to be
a more sustainable option for future cities than low-
density layouts [14].
Additionally, a series of further planning decisions
is taken in Scenario 3: a) most existing woodland is
preserved; b) more woodland and pond areas are
added inside the parkland; c) gardens (which
represent BGI) are placed around most of the building
blocks; and, d) blue space is considerably increased
with new lakes and a new canal network.
2.4 Densities for built-up areas
In terms of number of houses, the building
developer, Peabody Housing Association, has a clear
target of 11,500 new homes for this large urban
development of TMWDP. It is demonstrated inside the
literature that the concept of density is quite critical
and is based on specific thresholds. Therefore, the
values for high-, medium- or low-density can be
defined differently depending on the author and
always will depend on the particular context of the
development and its surroundings [14].
Table 1. Estimated densities for the built-up areas for every
urban design scenario studied and compared to Peabody’s
target of 11,500 new homes.
Hence, the number of dwellings per hectare inside
these built-up areas has been estimated in order to
achieve Peabody’s target for each urban design
scenario previously presented (Table 1). These
estimated densities provide a general idea of the
housing typologies that might be included in every
urban design scenario.
3. RESULTS
The NCPT analyses ten Urban Ecosystem Services
(UES), providing NC impact scores for each of them.
These ten UES evaluated by the NCPT are: 1) harvested
products, 2) biodiversity, 3) aesthetic values, 4)
recreation, 5) water quality regulation, 6) flood risk
regulation, 7) air quality regulation, 8) local climate
regulation, 9) global climate regulation and, 10) soil
contamination.
Additionally, NCPT also gives the number of ES
achieving Environmental Net Gain (ENG), which
represents the environmental impacts of habitat
change. It is important to highlight that, although
these scores might be highly valuable indicators, they
should always be deployed alongside with some
expert knowledge in the field.
As explained in Section 2.3, the pre-development
land-use map will be the initial baseline for all three
scenarios. Once all the land-use data are processed
using QGIS and the number of hectares for every land
use are quantified in every scenario, these are
introduced into the NCPT. This is combined with other
types of data such as heat exposure, proportion of
built-up area, flood risk zone, drinking water safeguard
zone, air quality management area, accessibility, size
of greenspace site, and soil drainage. At the end, the
tool provides NC Impact Scores for every UES analysed
and NC Net-gains for each designed urban scenario. At
this point, it is remarkable to see how small changes in
urban layout and land uses are able to provide
significant variations in the NC impact assessment (see
results in Table 2).
Table 2: NC Impact Scores and NC Net-gains for every ES
analysed for the 3 different scenarios. (Source: NCPT)
As seen in Table 2, only two ES, Recreation and
Global Climate Regulation, achieve NC net-gain for
Scenario 1. The positive score achieved in Recreation
in this scenario is easily explained because the
Waterfront Development Plan site is currently
inaccessible greenspace and the new urban design will
directly provide new leisure and outdoor activity space
to citizens. Regarding Scenario 2, Table 2 reveals that
five ES achieve the NC net-gain. This indicates a
significant improvement compared to Scenario 1, but
there are still some ES in negative values.
Finally, in Scenario 3 most ES are positive and
achieve NC net-gains. Harvested Products and
Biodiversity are now the only ES with negative scores,
although this is almost certainly due to the limitations
discussed of the NCPT. Hence, it is seen that “gardens”
(in this case understood as BGI) have a negative impact
on biodiversity (compared to “poor grassland”).
Recreation again has the highest positive score. This
can be explained firstly because the space was before
inaccessible and, secondly, because there is an
increase in green and blue space in this third urban
design. As mentioned in Section 2.2, these scores are
based only on the design aspect, although future
studies on system operation will be conducted too.
3.1 Need for further methodological improvements
The analysis presented in previous sections, based
on the TMWDP area and using the NCPT and QGIS
tools, showed that the NCPT does not adequately
account for important land uses to evaluate the
benefits of BGI. For instance, the land use named
“gardens” was introduced as the only form of BGI, but
this generated negative scores of Biodiversity.
Therefore, it is suggested that new BGI typologies
should be introduced in the NCPT land uses, for
instance: “Permeable paving”, “Detention basins”,
“Retention ponds”, “Buildings with rainwater
harvesting” or “Swales”. It would also be useful to
differentiate between “intensive green roofs” (deeper
substrate and shrubby vegetation or even trees) and,
“extensive green roofs” (thin layer of soil medium and
plants like succulents, grasses or other low
maintenance, low growing vegetation), as they might
affect the final environmental performance of the
buildings [14] . Additionally, “Buildings – area covered
with green roof” and “Buildings - green walls” land
areas should differentiate three different levels of
density (high, medium and low). All of this will
definitely deliver new and more accurate scores.
Finally, the tool is also lacking a systems thinking
approach because it calculates each ES independently
without considering interconnections between the
three UIS elements (land, housing and water)
presented in Figure 1. For all these reasons and the
need for monetary valuation, a prototype for an
Integrated Modelling Tool is introduced next.
3.2 New Integrated Modelling Tool
B£ST (Benefits Estimation Tool; CIRIA, 2019) is a
tool that provides an estimation of the profits that BGI
can generate from an economic perspective; however,
it also presents some limitations, such as not including
sustainable building valuation side. A new Integrated
Modelling Tool (IMT) which solves all the limitations
presented in the NCPT and B£ST, and also links their
numerical results with a spatial representation of the
development, is proposed. It will improve the vision
and accuracy for suitable sustainable urban design
solutions and enable more collaboration between
urban design stakeholders. See the software
architecture diagram of this Integrated Modelling Tool
(IMT) and its functionality in Figure 7.
Both the NCPT and B£ST are based on spreadsheet
interface and the IMT will act as a software wrapper
with Python code, enabling the user to design a new
urban development layout and relate its spatial
representation with ES assessment and monetary
prediction. The outputs of the tool will ultimately be
compared against approved certification criteria, such
as BREEAM Communities or LEED-ND.
Figure 7: Integrated Modelling Tool (IMT) diagram to
understand the software architecture of the prototype.
4. DISCUSSION
London needs to cope with its increasing housing
demand to fulfil the expanding economic and social
interests, but at the same time it must preserve its
natural environment in order to be resilient and
adapted to future climate change impacts. Its built
environment should provide healthy and secure living-
conditions to future generations and considerably
reduce the risk of natural catastrophes, such as
flooding and droughts. Sustainable urban
development is considered crucial to tackle these
stresses and its different types of sustainability
assessment are still not sufficiently understood.
UIS (Urban Infrastructure Systems) are an
interconnected entity and one of the best indicators of
their functionality and impact into the environment is
the evaluation of UES (Urban Ecosystem Services). This
work starts from a systems approach concept in order
to define a novel assessment framework for new
urban developments, which has been initially outlined
in Figure 1. The future steps should improve and
redefine this framework and provide a quantitative
evidence for optimal urban design solutions. This will
require studying BGI and its multiple benefits, as well
as the effects of urban form and vegetation within the
context of Urban Ecosystem Services (UES) and Urban
Natural Capital (UNC).
4. CONCLUSION
Urban Natural Capital (UNC) assessment is crucial
to analyse the impacts of new urban developments on
the environment. It will help housing developers,
urban planners and policy-makers to make better
decisions, especially at the early stages of the design.
However, initial studies that combine NCPT numerical
results with QGIS maps have shown that these tools
are still lacking some important functionalities and
there remains a need for a revised method. Hence, the
next steps in this research work will focused on
developing a new and integrated modelling tool for
Urban Natural Capital (UNC) and Urban Ecosystem
Services (UES) assessment in order to provide more
accurate and valuable results, all mapped from an
overarching systems thinking perspective.
ACKNOWLEDGEMENTS
This work would not have been possible without
funding from the Engineering and Physical Sciences
Research Council (EPSRC) Centre for Doctoral Training
(CDT) in Sustainable Civil Engineering. The research
reported in this paper was taken as part of the
CAMELLIA project (Community Water Management
for a Liveable London), funded by the Natural
Environment Research Council (NERC) under grant
NE/S003495/1.
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