Frameworks for assessing and improving urban water supply security planning under climate change.

Abstract

There exist large uncertainties in projecting future climate and understanding how climate change projections relate to water supply. Non-traditional water sources (e.g., stormwater harvesting), which are emerging as adaptation options to augment stressed water supply systems, further complicate the simulation of these systems. However, in assessing a city’s water supply security, there is no framework explicitly acknowledging and accounting for both the additional complexities and uncertainties associated with non-traditional water sources and climate change impacts. Furthermore, mitigation and adaptation measures to climate change should be considered. However, minimising GHG emissions (and thus considering mitigation) is likely to conflict with other objectives of water supply system planning. Hence, a multi-objective evolutionary algorithm (MOEA) approach is necessary to balance multiple objectives, as well as to efficiently search many feasible alternatives to find Pareto-optimal solutions. However, for cities, MOEA studies incorporating GHG emissions and thus focussing on both mitigating and adapting to climate change do not exist. The main aim of this thesis is to develop methods for assessing and improving urban water supply security planning under climate change to better understand: (1) the relative magnitudes of uncertainty sources in assessing climate change impacts; (2) enhanced simulation complexity of non-traditional water sources and increased uncertainty of climate change impacts; and (3) adaptation and mitigation responses to climate change. Consequently, major contributions of this research include: (1) developing a scenario-based sensitivity analysis to understand the relative magnitudes of uncertainty sources in assessing the impacts of climate change on water supply systems; (2) developing a generalised framework for a city's water supply system that outlines the additional complexities due to the incorporation of non-traditional water sources and the additional uncertainties due to climate change impacts; and (3) incorporating GHG emissions as an objective function within a MOEA framework to take into consideration both adaptation and mitigation responses to climate change. Furthermore, while these frameworks could readily be applied to any city, Adelaide’s southern water supply system is used as a real-life case study to illustrate the practical management implications. The methods developed in the thesis were found to be effective when applied to Adelaide’s southern water supply system. Results indicate that studies analysing the impact of climate change on water supply security should consider uncertainties other than those associated with climate change and hydrological modelling, as these could have as great, if not greater, impacts on water supply security projections. Furthermore, trade-offs exist between cost and supply security for solutions that use desalination and harvested stormwater to augment water supply; however, use of rainwater tanks is undesirable, as they are an expensive source. In terms of the trade-off between economic cost and GHG emissions, the main drivers are the presence of rainwater tanks and the desalination plant – rainwater tanks are an expensive option, while desalination is a GHG emission intensive option. Consequently, while desalination may be a good adaptation option, other water sources may be better mitigation measures. Accounting for GHG emissions is thus important to ensure mitigation measures are considered.