Sanford Dam in Michigan, US, several months after failing in 2020. Research has indicated an increased risk of similar events due to more intense rainfall under a changing climate.

Canada has a long history of recurrent flooding. Seven of the ten most costly flood events occurred between 1980 and 2019, and after 2010. This upward trend in flood risk is posing significant threats to critical structure such as dams and levees. However, as Islam et al suggest in recent research published by Discover Applied Sciences, national-level guidance on integrating resilience-based frameworks, and addressing climate risks and uncertainties in existing design flood estimation methodologies for dams and levees, are lacking.

The changes in the frequency and intensity of floods anticipated with climate change will be a challenge for conventional design flood estimation methods. As the authors explain, ageing dams in Canada also create an increasing risk. With approximately half of the country’s dams over 50 years of age, many were designed and well-maintained to withstand extreme events but weren’t designed with climate change in mind. In addition, it is claimed that some have deteriorated beyond repair and are vulnerable to failure even during moderate rainstorms and associated overland flows. Such vulnerability is now being exacerbated by the increasing occurrence of massive deluges, often following severe drought, which is a trend projected to intensify over time under climate change.

However, as Islam et al state, there currently is a lack of comprehensive and unambiguous guidance on climate-resilience-based frameworks, leading to confusion among engineers and policymakers. The authors wanted to address this gap by reviewing design flood estimation procedures, the potential impact of climatic trends and regional vulnerabilities to climate change, and the barriers and opportunities for advancing a climate-resilience framework. By studying the vulnerability of Canadian dams and levees to flooding in light of changing regional climatic patterns and associated hydrologic design criteria, the authors have tried to identify areas where interventions are necessary to enhance the climate-resilience of such assets.

The increasing trend of destructive floods across different parts of Canada and the projections of rising frequencies of higher return period floods in a changing climate, have highlighted the need for new regional and national initiatives to update design flood estimates. The authors say the conventional approaches which utilise stationary climatic assumptions are no longer adequate for calculating design values, and therefore new strategies must be developed to not only account for the dynamic behaviour of the climate system, but also alleviate undesirable consequences of future climate change. It is imperative, they add, to continuously update estimates of various risk components, including hydrologic loads, and monitor system response in order to enhance climate-resilience and inform the decision-making process.

Islam et al highlighted the various challenges for estimating climate-informed design floods for dams and levees. These include:

Constraints of sample size and event identification difficulties

Design flood estimation for dams relies heavily on historical records of peak discharge and extreme precipitation events. A shorter record and incomplete information about storm characteristics introduce uncertainties. To overcome this, regional approaches are preferred for estimating frequency-based flood magnitudes and transposition of climatic variables and storm characteristics for estimating PMP-based floods.

Multi-variate analysis

Integrating copula-based multi-variate frequency analysis with the current design flood estimation guidance is crucial to address dependency between various flood characteristics (eg, flood peak, volume, and duration) and compound flooding (eg, joint occurrence of fluvial, pluvial, and coastal foods) in a realistic way.

Incorporating climate change and addressing non-stationarity

Global warming is likely to augment the amount of water vapour in the atmosphere and consequently, changes in precipitation characteristics and extreme weather patterns are expected. This makes it important to explore non-stationary techniques for estimating design floods for both small and large dams, levees, and embankments and to develop associated design guidance.

Quantifying uncertainty

The conventional design flood estimation approaches fall short in addressing the full extent of deep uncertainty. It is imperative to take steps to identify underlying those present at various stages of the design flood estimation process. This can be achieved by leveraging new understandings and statistical methods, such as by employing the Bayesian approaches to quantitatively capture the uncertainty, or performing sensitivity experiments across a plausible range of perception

Climate-resilience framework

Infrastructure designed by considering the impacts of climate change can offer increased service delivery and reliability, longer productive lifespan, and prolonged investment returns. Climate-resilience is a continuous process that must extend throughout the asset’s lifespan. There is documented evidence that investing in climate-resilience can result in benefits that can outpace costs by several folds.

In their work, Islam et al introduce a climate-resilience framework tailored for dams and levees. In this, the essence of resilience is encapsulated by threshold capacity, coping capacity, recovery capacity, and adaptive capacity of flood control structures.