The Observed Diversity and Distribution of Flow Regimes and Streamflow Drivers across Alaska

Abstract:

Anticipating streamflow response to climate change in Alaska is a critical water resources management need and is challenged by the diverse range of seasonality generated by the variable influences of rainfall, snowmelt, and glacier melt. The historical character and distribution of streamflow regimes, which display the respective contributions of these processes, are not well understood across the wide range of temperate to polar and coastal plain to mountainous environments in Alaska. As a foundation for regional hydrologic investigations, the objective of this study was to classify seasonal flow regimes from streamflow data to facilitate identification of daily and peak streamflow drivers. Classification of historical streamflow patterns for 253 Alaska streamgages that had at least 5 years of daily streamflow data identified nine seasonally distinct flow regimes that nested into three major groups dominated by rainfall, snowmelt, and high-elevation snowmelt or icemelt, respectively. Fall-rainfall flow regimes generated mostly fall and winter peak flows. In snowmelt flow regimes, prominent spring snowmelt modes generally coincided with the highest density of peak flows. High-elevation flow regimes had a high summer-flow seasonality supported by delayed snowmelt, sometimes by rainfall, and, for glacierized basins, by additionally delayed glacier meltwater runoff. Seasonal differences in peak streamflow timing differentiated 1-3 driver-based peak populations, depending on flow regime. Flow regimes showed associations with basin characteristics, particularly mean basin elevation and mean minimum winter temperature. Spatial coherence of flow regime members complicated by spatial overlap with other flow regimes limited definitive regional boundaries based on geography alone. These results suggest potential flow regime trajectories with warming temperatures, depending on flow regime, and indicate that coupling mean basin elevation with geographic location might improve partitioning of streams into hydrologically relevant regions. This classification provides the first systematic investigation of observed Alaska flow regimes and identifies subsets for more targeted examination of hydrologic patterns and sensitivity to changes in streamflow drivers.