Trading‐off tolerable risk with climate change adaptation costs in water supply systems

Abstract

Choosing secure water resource management plans inevitably requires trade-offs between risks (for a variety of stakeholders), costs, and other impacts. We have previously argued that water resources planning should focus upon metrics of risk of water restrictions, accompanied by extensive simulation and scenario-based exploration of uncertainty. However, the results of optimization subject to risk constraints can be sensitive to the specification of tolerable risk, which may not be precisely or consistently defined by different stakeholders. In this paper, we recast the water resources planning problem as a multiobjective optimization problem to identify least cost schemes that satisfy a set of criteria for tolerable risk, where tolerable risk is defined in terms of the frequency of water use restrictions of different levels of severity. Our proposed method links a very large ensemble of climate model projections to a water resource system model and a multiobjective optimization algorithm to identify a Pareto optimal set of water resource management plans across a 25 years planning period. In a case study application to the London water supply system, we identify water resources management plans that, for a given financial cost, maximize performance with respect to one or more probabilistic criteria. This illustrates trade-offs between financial costs of plans and risk, and between risk criteria for four different severities of water use restrictions. Graphical representation of alternative sequences of investments in the Pareto set helps to identify water management options for which there is a robust case for including them in the plan.

National-scale analysis of low flow frequency: historical trends and potential future changes

“…Non-climatic factors like population increase and economic development can place further strain on water resources by increasing water demand, alongside potential decreases in water supply caused by both climatic and non-climatic factors (Jiménez Cisneros et al 2014). Studies investigating the potential future balance of supply and demand, like that of Arnell and Lloyd-Hughes (2014) based on a simple threshold of annual per capita water availability, are thus important, as is more detailed water resource system modelling (Borgomeo et al 2016). The flows from the hydrological modelling described here are also being used to investigate potential future impacts on river ecology and agricultural production.…”

Risk, Robustness and Water Resources Planning Under Uncertainty

“…In water resources management, this has been interpreted as the probability of not meeting a desired frequency of water use restrictions of different levels of severity (Hall et al, ). This probability is estimated by counting the frequency of water use restrictions and their severity over a range of future time horizons simulated with a water system model (Borgomeo et al, , ).…”

Assessment of Risks to Public Water Supply From Low Flows and Harmful Water Quality in a Changing Climate

“…WATHNET was selected for the following reasons: (1) the efficient computation time and capability of running on parallel nodes; (2) the availability of the source code allowed for its adaptation to the new requirements of this study; (3) the scripting feature that facilitates introducing any rules or constraints; and (4) its architecture facilitates the implementation of multi‐objective optimization and handling optionality. WATHNET has been successfully used in many studies of water supply systems (Borgomeo et al, ; Mortazavi‐Naeini et al, ; Mortazavi‐Naeini et al, ; Mortazavi et al, ).…”