Uncertainty Analysis and Decision-Making in Infrastructure Systems under Climate Change

The special collection on Uncertainty Analysis and Decision-Making in Infrastructure Systems Under Climate Change is available in the ASCE Library at http://ascelibrary.org/page/ajrua6/infrastructure_systems_climate_change.

This special collection of the ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems contains three papers addressing the role of climate change in risk management for drinking water systems and structural reliability. The collection is motivated by the compelling challenge posed by climate change to infrastructure systems. Climate change presents an interdisciplinary challenge owing to large capital investments, substantial scientific uncertainty, and the political nature of infrastructure investment, planning, design, construction, and maintenance decisions.

Three aspects of this problem are addressed in this special collection. First, the effects of climate change may affect the relationship between critical infrastructure systems and the natural systems and processes supporting them. For example, many coastal drinking water systems rely on groundwater or a mixture of groundwater and surface water. If climate change leads to sea-level rise, coastal aquifers can be affected by saltwater intrusion. This may lead to treatment challenges that may not have been predicted when the treatment systems were designed and constructed. Second, the long life cycles of critical infrastructures amplify the challenge of climate change. For example, as drinking water distribution systems in the United States reach their useful design lives, the need to undertake renewal and rehabilitation to ensure continued reliability of service is becoming more urgent. Climate change makes the planning process more challenging for drinking water utilities because it may change their pipe breakage rate projections. Third, the long lifetime of most critical infrastructure system networks requires that decision makers and designers account for the impacts of climate change in their decision processes. These decision processes are made more complex owing to the fact that critical infrastructures are a mixture of new and old components. These old components may have been designed and installed before climate change threats were ascertained and may not be replaced immediately. Thus, the effects climate change has on degradation, structural reliability, and resistance may impact an infrastructure asset portfolio in ways that are difficult to predict. The three papers in this special collection highlight some of the recent advances in understanding the impacts of climate change on infrastructure systems, with a focus on drinking water systems and structural reliability.

Demissie et al. (2017) use a dynamic Bayesian network (DBN) to predict water distribution system pipe failures in Calgary, Alberta, Canada. Pipe failure models are critical to the asset management planning of drinking water systems, yet most drinking water pipe failure models do not incorporate time dependence in their environmental covariates. To evaluate the role of climate variability in pipe break prediction, Demissie et al. quantify annual and monthly effects to capture seasonality in the breakage rate, while the DBN features enable the model to incorporate time dependence in the environmental factors. While a number of studies have investigated pipe failure risk, they have assumed that the pipe break risk factors are static and not time-dependent. Clearly, it is important to be critical of this assumption under climate change. Demissie et al. address this potential shortcoming of prior models by using the DBN to obtain improved predictive accuracy of their pipe break models by incorporating the time dynamics of the freezing index, thawing index, rain deficit, and other climate-dependent environmental factors.

Kolb et al. (2017) investigate the role of sea-level rise on the formation and speciation of trihalomethanes in coastal drinking water distribution systems. The rationale for their analysis is that global mean temperatures will lead to thermal expansion in the oceans, thereby causing sea-level rise. Rising sea levels may then impact coastal aquifers by way of increased saltwater intrusion. Drinking water supplies affected by coastal aquifers may then have increased total dissolved solid (TDS) levels. TDSs are a concern in drinking water treatment works because they can lead to customer complaints or potential regulatory violations of secondary treatment standards. In addition, TDSs contain bromide. If the increased TDSs are not removed before supplies are disinfected, the increased TDSs may lead to increased formation of brominated disinfection byproducts (DBPs) owing to increased bromide levels. Brominated DBPs have been shown to be more toxic than their chlorinated analogs. In addition, brominated DBPs are heavier by mass than their chlorinated analogs. This may make it more difficult for utilities to comply with DBP regulations. Using a coastal aquifer in New Jersey as their case study, Kolb et al. show that even small increases in bromide attributable to sea-level rise can lead to increases in regulated DBP formation. Although most utilities under the influence of saltwater intrusion should have DBP concentrations that remain below the regulatory limit, the relative increase in brominated DBP formation may lead to increased risks to drinking water customers. Kolb et al. conclude that as a result of climate change, drinking water utilities may need to consider long-term capital investments to improve their capacity to utilize high TDS source waters. At the same time, utilities will need to carefully consider their source water portfolios when mixing groundwater with surface water supplies.

Saini and Tien (2017) explore the role of climate change in the assessment of structural integrity by studying the impacts of climate change on the long-term resistance and loading of infrastructure using climate projections through the year 2100. The effect is studied using a time-dependent structural aging model. When considering climate change effects on infrastructure, environmental factors such as carbon dioxide concentration and temperature may affect corrosion, and temperature changes may influence thermal loading. Moreover, extreme event occurrence distributions may also shift under climate change. Saini and Tien’s model incorporates several proposed degradation mechanisms, including temperature effects, carbonation, corrosion, and fatigue. Saini and Tien demonstrate that structural resistance is most affected by carbonation and accelerated corrosion under long-term climate change. This degradation could be pronounced for coastal structures. Saini and Tien also conclude that changes in extreme live loads due to extreme events should be accounted for in reliability studies. The combined effect of climate change on structural resistance and loading could cause failure risk to increase by two to four times. Therefore, Saini and Tien’s methodology could be used to assess the potential performance of structures under climate change throughout their life cycles.

The papers presented address various facets of risk analysis under a climate change scenario. The papers demonstrate that there is a need to accurately formulate risk problems so that decision makers can make informed decisions when trying to address climate change issues.