Screening robust water infrastructure investments and their trade-offs under global change: A London example

Ivana Huskova,Chris Lambert,Joseph R. Kasprzyk,Evgenii S. Matrosov,Julien J. Harou

doi:10.1016/j.gloenvcha.2016.10.007

Abstract

We propose an approach for screening future infrastructure and demand management investments for large water supply systems subject to uncertain future conditions. The approach is demonstrated using the London water supply system. Promising portfolios of interventions (e.g., new supplies, water conservation schemes, etc.) that meet London’s estimated water supply demands in 2035 are shown to face significant trade-offs between financial, engineering and environmental measures of performance. Robust portfolios are identified by contrasting the multi-objective results attained for (1) historically observed baseline conditions versus (2) future global change scenarios. An ensemble of global change scenarios is computed using climate change impacted hydrological flows, plausible water demands, environmentally motivated abstraction reductions, and future energy prices. The proposed multi-scenario trade-off analysis screens for robust investments that provide benefits over a wide range of futures, including those with little change. Our results suggest that 60 percent of intervention portfolios identified as Pareto optimal under historical conditions would fail under future scenarios considered relevant by stakeholders. Those that are able to maintain good performance under historical conditions can no longer be considered to perform optimally under future scenarios. The individual investment options differ significantly in their ability to cope with varying conditions. Visualizing the individual infrastructure and demand management interventions implemented in the Pareto optimal portfolios in multi-dimensional space aids the exploration of how the interventions affect the robustness and performance of the system.

Highlights

Many urban water systems across the globe face future stresses such as reduced or shifted water availability due to climate change, increased water demands, more demanding regulatory regimes and heightened service expectations (Ferguson et al, 2013; Hallegatte, 2009; Pahl-Wostl, 2009)
In this paper we assume stakeholders are familiar with multidimensional trade-off interpretation and show plots with all dimensions of performance concurrently and focus on displaying graphically the benefits of incorporating uncertainty explicitly within investment screening
Water companies generally prefer implementing supply-side measures to plan for future deficits (Charlton and Arnell, 2011) but our results suggest that reducing demand by implementing demand management interventions increases plan robustness

Summary

Introduction

Many urban water systems across the globe face future stresses such as reduced or shifted water availability due to climate change, increased water demands, more demanding regulatory regimes and heightened service expectations (Ferguson et al, 2013; Hallegatte, 2009; Pahl-Wostl, 2009). The uncertainty in future conditions motivates novel approaches that help discover which combinations of interventions would work well under a wide range of plausible futures. Robustness as a planning goal is well suited to situations where the probabilities that govern uncertain future states are uncertain themselves. Such uncertainties are known as ‘deep’ or Knightian uncertainties (Knight, 1921). Assigning probabilities to population growth or the effects of climate change on systems is problematic (Walker et al, 2013). A robust system is one that performs well or satisfactorily well over a broad range of plausible future conditions rather than optimally in one.

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Discussion

Conclusion