Flooding in the Peace-Athabasca Delta: climatic and hydrologic change and variation over the past 120 years

Over the past 120 years, major temporal variations in river flows, lake levels, flood occurrence, wildlife abundance, and vegetation communities, coupled with spatial heterogeneity, have provided fertile ground for narratives of change within the Peace-Athabasca Delta (PAD). In this paper, I show that simple cause-effect explanations and reliance on short-term datasets have misled through over-generalization and have failed to account for the ecosystem’s natural range of variation. Spring break-up discharge correctly predicts 71 to 90% of the binary outcomes (floods, no floods), but break-up discharge is weakly-related to flood magnitude. River regulation has not reduced Peace River spring flood frequency or magnitude. Contrary to popular belief, spring break-up discharge to the PAD from the Peace River’s point of regulation at Hudson Hope has increased, not decreased, since regulation. Conversely, suppression of early May to late August discharge is the most noteworthy effect of Peace River regulation, but its ecological impacts remain poorly documented. Flows of the Peace and Athabasca Rivers are strongly correlated and exhibit similar daily, annual, and decadal patterns. An 8-year highstand of Lake Athabasca occurred just prior to river regulation. Lake Athabasca levels prior to the 1960s and after reservoir-filling did not differ significantly but were 60–80 cm lower than during the 1960–1967 highstand. Climatic changes have been complex. The clearest trends are winter warming and a PDSI regime shift from wet and variable to drier and less variable conditions since 1980. Spring flooding is preceded by greater winter precipitation upstream of the PAD and colder winters at the PAD. Spring ice-run floods without ice jams can recharge portions of the PAD including perched basins. I describe two water management approaches that would recharge large areas. Ecosystem complexity and cognitive biases hamper greater understanding of the dynamics of this globally significant ecosystem.