Increasing dam failure risk in the USA due to compound rainfall clusters as climate changes

A changing climate, with intensifying precipitation may contribute to increasing failures of dams by overtopping. We present the first analysis of rainfall sequences and events associated with recent hydrologic failures of 552 dams in the United States. We find that the maximum 1-day rainfall associated with failure was often not extreme compared to dam spillway design criteria, even when accounting for rainfall statistics changing with time at each site. However, the combination of the total rainfall 5 to 30 days prior and the maximum 1-day rainfall associated with dam failure is rare. Persistent atmospheric circulation patterns that lead to recurrent rainfall events, rather than just more moisture in the atmosphere is a possible reason. The probability of these compound precipitation risks has increased across much of the country. With over 90,000 aging dams still in service, the increasing likelihood of intense rainfall sequences raises concerns about future dam failures.