AdApting urbAn wAter systems to climAte chAnge - IWA

20 Adapting urban water systems to climate change
A handbook for decision makers at the local level
Section 2
A strategic planning framework for adaptation
21
Further information on the
flexible solutions given in
Table 1 as well as other flexible
solutions can be found in
Modules 3 (water supply),
4 (stormwater management)
and 5 (wastewater management)
of the SWITCH
Training Kit (ICLEI European
Secretariat, 2011).
In contrast to the limitations imposed by stationarity, more flexible and sustainable
management involves making decisions and choices while considering a range of
scenarios. It leads to the selection of management options and technologies with fewer
negative impacts on the long-term sustainability of the system as a whole. For example,
solutions that target demand reductions and the use of alternative sources rather than
resource development and infrastructure expansion are less vulnerable to inaccurate
forecasts.
Choosing flexibility
Current water management infrastructure tends to be inflexible to changing circumstances,
yet projections of climate change show that variability can change capacity requirements
either regionally or across the year. More sustainable urban water management systems
are designed to cope with varying and unpredictable conditions, and achieve this through
the implementation of flexible and often decentralised options and technologies that take
into account a range of future scenarios.
A flexible system is one that is characterised by its ability to adapt to changing
requirements. Table 1 gives some examples of how a flexible urban water system would
respond to changing conditions versus how a typical system would do so. The design of a
flexible system and the choice of options and technologies can be facilitated through the
strategic planning process that will be introduced in the next section.
The flexibility of non-conventional urban water systems is often related to their
decentralised solutions. Decentralisation decreases sensitivity by spreading risk; indeed,
it is easy to understand the heightened risk faced by a city dependent on one or more
large wastewater treatment plants versus a city that operates several smaller-scale natural
treatment systems located in different areas.
In addition, decentralised solutions are often quicker to install and more cost-effective
to build and maintain. These considerations are particularly important in the face of
changing conditions, which can easily render large investments in new treatment facilities
or water supply infrastructure redundant.
COFAS - A water management decision-support tool
The selection of appropriate adaptation measures requires innovative tools that help understand
the flexibility of different options. COFAS (Comparing the Flexibility of Alternative
Solutions), for example, goes beyond the conventional multi-criteria analysis and also visualises
the inherent ability of a potential solution to respond flexibly under different scenarios.
Source: Ingenieurgesellschaft Prof. Dr. Sieker mbH, Germany
Table 1: Conventional versus flexible system responses to changing conditions (Source: ICLEI European Secretariat, 2011)
Urban water
management
aspect
Non-exhaustive examples
of climate change
impacts
Current system
response example
Potential responses to changing
conditions from a flexible system
Water supply
Wastewater
management
Stormwater
management
Reduced water supply, either
seasonally or throughout the
year
Increased inflow of pollution,
caused by flooding
Flooding of wastewater
treatment plants located near
rivers or coasts
Increased stormwater
flows and combined sewer
overflows
Increasing water supply
through additional
infrastructure such
as dams, boreholes,
desalination facilities or
bulk supply transfers
Improving treatment
technology
Construction of protective
barriers or lifting of
equipment
Improving and extending
the infrastructure
conveying stormwater
away from the city
Demand reduction through efficiency
increases, active leakage management,
behaviour change or pricing policies
Sourcing of alternative supplies for nonpotable
demand: rainwater harvesting or
treated wastewater effluent reuse
Increasing sustainable storage capacity,
for example through Aquifer Storage and
Recovery
Control of pollution at source and use of
natural treatment techniques
Use and appropriate siting of
decentralised natural treatment
techniques
Attenuation of runoff through the use
of Sustainable Urban Drainage Systems
options, for example green roofs, porous
paving, swales, rainwater harvesting, and
detention ponds and basins
Figure 2: Applying COFAS to compare two solutions for urban drainage in order
to select the most flexible one
Fostering integration across urban management sectors
As shown in Section 1, the impacts of climate change will be felt in a cross-cutting manner
across different elements of the urban water cycle, but also across all urban management
sectors. Current approaches to urban water management are often fragmented, with
the design, construction and operation of the various elements carried out in isolation
from one another, and with little coordination with other urban management sectors and
institutions.
This fragmented approach often results in unsustainable practices, for instance when
technical choices have unintended impacts in other parts of the urban system. For
example, the structural means of flood protection applied to the Elbe River in Germany
negatively affect ecosystems (Weschung et al., 2005 as cited in Kundzewicz et al., 2007).
It is also inadequate in terms of responding to the challenges posed by climate change.
Integrated Urban Water
Management (IUWM) is a
widely recognised integrated
planning approach. Further
information on IUWM can
be found in Module 1 of the
SWITCH Training Kit (ICLEI
European Secretariat, 2011).