Department Urban Water Management

Decision Analysis

Introduction to the social science and decision analysis modules

by Judit Lienert

In the project “Sustainable Water Infrastructure Planning” (SWIP), Multi-Criteria Decision Analysis (MCDA) was used to integrate all available data: “hard facts” derived from the engineering modules and “soft preferences” of stakeholders. MCDA provides a consistent framework that allows active participation of stakeholders throughout the process.

Qualitative, non-monetary sustainability goals

MCDA allows the explicit formulation of all objectives (criteria, performance indicators) that are important to decision makers in characterizing a “good water infrastructure system”. This enlarges the scope of current infrastructure planning to non-monetary and qualitative sustainability objectives.

Current planning approaches are usually based on few objectives. For example, implicit goals of good water infrastructures are the continuous provision of high-qualtity water for potable (drinking, cooking) and non-potable uses (e.g. washing, firefighting). Goals are also the safe disposal of household wastewater and stormwater. MCDA makes these implicit objectives explicit and allows to find trade-offs between the different objectives to come up with good compromise solutions. In SWIP, a generic objectives hierarchy for water supply and wastewater infrastructures was developed, based on intensive collaboration with local, cantonal, and national actors. It includes the six fundamental objectives in Figure 1.

Figure 1: The six fundamental objectives of good water supply and wastewater infrastructure

The objectives were operationalized with the help of attributes (indicators) that allow quantifying how well each objective is achieved. The SWIP objectives hierarchy was constructed in such a way that it can be easily adapted to other applications (more details see Lienert et al., 2014).

Different types of water supply and wastewater systems

MCDA allows comparing the performance of very different types of decision alternatives. Expanding current planning in the water sector, which is usually based on the status quo, a broad range of alternatives was created in SWIP, together with stakeholders. These include “business-as-usual” upgrades of the central water supply and wastewater system, but also semi- to fully decentralized alternatives.

For instance, rain water might be collected for firefighting or household usage, and drinking water bought in the supermarket. The wastewater system might include conventional sewers in urban centers, but on-site wastewater treatment systems in peripheral settlements. The most extreme decentralized alternative has on-site wastewater disposal systems in every house. SWIP also considered different organizational forms, which include stronger regionalization and mergers of utilities that use the underground.

What will the world look like in 2050?

We do not know and there is no way of knowing! Despite uncertainty, it is possible to make far-reaching planning decisions today. The idea of scenario planning is to create images of different possible futures. These narratives must neither be highly probable, nor especially desirable. However, they should be internally consistent and plausible. Each scenario should tell a convincing story about a future world.

In SWIP, four future scenarios were adapted to the local situation in a stakeholder workshop. They characterize how the region of “Mönchaltorfer Aa” might look like in 2050. In the Boom scenario, there is high population growth from todays’ 24’200 inhabitants to 200’000. There is also high economic and technological development. Opposed to this, the Doom scenario is characterized by a difficult economic situation and a slight population decline. The attractive Quality of Life scenario strongly focuses on sustainable development, and prosperity goes hand in hand with high environmental awareness. The Status Quo scenario is a projection of the current boundary conditions to the year 2050 (details see Lienert et al., 2014).

These scenarios were used in the MCDA to test the robustness of each decision alternative. An alternative is considered less robust if it performs well in one scenario, for example in the Status Quo scenario, but especially poorly in another. Our results indicate that the Boom scenario with massive population growth is especially sensitive affecting the ranking of some decision alternatives (see results of the MCDA for water supply, sub-project3  and wastewater disposal, sub-Project4)

Combining hard facts with stakeholder preferences

The decision alternatives are not directly evaluated by the decision makers. Rather, the MCDA analyzes how well each decision alternative achieves each of the objectives. Hereby, the performance of each alternative (for each scenario) is estimated. For instance, how well wastewater is cleaned or how much this costs per person and year. Some predictions require the input from models, e.g. the performance of aging water supply pipes. For other predictions expert estimates are needed.

To be able to combine the performance predictions with the subjective preferences of each decision maker, 31 interviews with important stakeholders were carried out. MCDA thus acknowledges that different people might have different priorities and allows integrating both aspects on equal footing.

The hard facts are combined with the stakeholder preferences with help of a mathematical model. In SWIP, the model includes the uncertainty of the predictions as well as the decision makers’ uncertainty. For example, the number of combined sewer overflows might be uncertain, but also the preferences of the decision maker if she has to state trade-offs between objectives. The model was replicated for each stakeholder and future scenario. Sensitivity analyses were performed to evaluate whether the results would change under changed assumptions.

Finding compromise solutions

The result of the MCDA is a ranking of the alternatives for each decision maker under each future scenario. Alternatives that perform well for most decision makers under all scenarios are potentially robust and attractive choices. Their advantages and disadvantages should then again be discussed with the decision makers (see results of the MCDA for water supply , sub-project3 and wastewater disposal, sub-project4)

In many cases, an MCDA might reveal that supposed conflicts between different actors are not as fundamental as presumed. Ideally, a decision alternative can be identified that performs reasonably well despite different priorities of stakeholders. In other cases, thanks to the transparency of the decision making process, it might be possible to identify shortcomings of the proposed alternatives and construct a compromise alternative that overcomes main deficits.

The Multi-Criteria Decision Analysis (MCDA) framework

MCDA as applied in SWIP consists of following steps (see Lienert et al., 2014):

  1. Clarify decision context, set boundaries, define who to include in the decision making process. Who is important to make the decision or affected by it? Who interacts with whom? For this, a stakeholder analysis was combined with a social network analysis. To enlarge the boundary conditions and incorporate uncertain future socio-demographic development, MCDA was combined with scenario planning.
  2. Define objectives. What is important to the decision makers/ to society/ to future generations? Define attributes (indicators) that make objectives measurable.
  3. Develop socio-economic future scenarios. How could the world look like in the year 2050 and in which way might this affect the water infrastructures?
  4. Develop alternatives. How can water be supplied to households and wastewater be disposed of? How can the infrastructures be maintained, repaired, or replaced? How can the water utilities be organized?
  5. Estimate consequences. How well does each decision alternative (step 4) achieve the objectives (step 2) under each future scenario? For example, the performance of water supply pipes under different rehabilitation strategies was estimated with help of engineering models. A hydraulic model supported predicting the number of combined sewer overflows for different alternatives under climate change. Or expert estimates helped to quantify the quality of management and operations under different organizational forms.
  6. Elicit the preferences of stakeholders. Which objectives are most important? Can the achievement of one objective be traded off with another objective? For example can increased costs be justified by achieving higher water quality standards?
  7. Integrate the predictions (step 5) with preferences of stakeholders (step 6) to evaluate trade-offs and propose robust alternatives for water supply and wastewater infrastructures. Can we find one or several alternatives that perform reasonably well for most stakeholders under the different future scenarios? If not, can a compromise alternative be constructed? Do the suggestions appeal to the stakeholders?
  8. Implement, monitor and review. Real-world implementation was not goal of this research project. However, it is intended to bridge the gap between theory and practice application in follow-up projects after SWIP.

More information

  • Sub-project 1: Stakeholder and social network analysis by Judit Lienert, Florian Schnetzer, Karin Ingold.
  • Sub-project 3: Dissertation by Lisa Scholten: Multi-criteria decision analysis for water supply infrastructure planning under uncertainty.
  • Sub-project 4: Postdoctorate by Jun Zheng: Incorporating stakeholders’ preferences into wastewater infrastructure planning with multi-criteria decision analysis.
  • Lienert, J., Scholten, L., Egger, C., Maurer, M. (2014) Structured decision making for sustainable water infrastructure planning and four future scenarios. EURO Journal on Decision Processes, special issue on Environmental Decison Making: in press.


Dr. Judit LienertGroup Leader, Cluster: DA (Decision Analysis)Tel. +41 58 765 5574Send Mail