Discharge Regimes of North American High-Latitude Rivers

Abstract

Regimes of river discharge, characterized by the timing and magnitude of seasonal and stochastic flow variation, are changing in northern rivers due to warming climate. However, spatial heterogeneity in discharge regimes across high-latitude regions has made it difficult to predict flows under accelerated warming. We quantified seasonal and stochastic variation in mean daily discharge from 172 rivers of Alaska and northern Canada over 2000–2022 and compared flow regimes of rivers across ecoregions, climate gradients, and cryospheric conditions. Floods were shorter and occurred later in the year, on average, in Marine West Coast Forest compared to other ecoregions. Strongest seasonal relative to stochastic variation in flows occurred in the snowmelt-dominated Northwestern Forested Mountains ecoregion. Discharge in glacial watersheds was more strongly seasonal than in non-glacial watersheds, likely due to production of meltwater in summer. Greater rainfall in the watershed was correlated with weaker seasonal variation in flow and earlier annual occurrence of high-flow anomalies. In contrast, greater snowfall resulted in strongly seasonal regimes with anomalous high flows later in the year. We also contrasted discharge regimes of 72 rivers between ∼1970–1992 and 2000–2022, finding less seasonal relative to stochastic variation in recent decades and contemporary anomalous high flows occurring later in the year relative to historic regimes. Discharge from glacial rivers was relatively resistant to change, suggesting buffering by seasonal glacial melt. Shrinking of the cryosphere and shifts in the precipitation regime due to continued warming will increase stochasticity and decrease seasonality in the flows of high-latitude rivers.