https://doi.org/10.1016/j.jhydrol.2026.135389

Whitfield, Paul H.; Burn, Donald H. (2026) Rogue and extreme floods in North America, Journal of Hydrology, https://doi.org/10.1016/j.jhydrol.2026.135389

Unusual flood events are important for understanding the nature of the flood regime of a watershed and for identifying changes to the flood regime at a location. This study presents a methodology to identify Flood-of-Record (FoR) events that are large in magnitude but occur outside the most common flood season. The method combines detection of single dimension magnitude and timing outliers, and multi-dimensional magnitude/timing density outliers. Conceptually, the flood-of-record is generally well known; the methods here identify large FoR events that are outliers in several distinct ways that are thus considered Rogue events. These events that are particularly interesting are outside the commonly observed timing of events that suggests a different generating process, i.e., they are completely different to the ‘regular’ flood-generating mechanism. An example would be a nival catchment where the annual peak is usually from snowmelt in spring/summer, but large events that occurred in fall or winter are generated by an alternate process [hurricane, atmospheric river]. The methodology is applied to more than 2100 natural streamflow hydrometric stations across North America. The spatial and temporal distributions of these events are compared. Rogue events are often associated with atmospheric phenomenon that occur outside the normal high flow period, which in North America is associated with snowmelt. The implications of these Rogue events in flood frequency analysis and in trend studies are discussed.

https://doi.org/10.1016/j.jhydrol.2026.135389