Identification of Seasonal Streamflow Regimes and Streamflow Drivers for Daily and Peak Flows in Alaska

Alaska is among northern high-latitude regions where accelerated climate change is expected to impact streamflow properties, including seasonality and primary flow drivers. Evaluating changes to streamflow, including flood characteristics, across this large and diverse environment can be improved by identifying the distribution and influence of flow drivers. Using metrics of mean monthly streamflow data from 253 streamgages, seasonal flow regimes were clustered to guide identification of seasonal flow drivers and form hydrologic groups for identification of peak-flow populations. Nine seasonally distinct subclasses described variability within three classes dominated by (mostly fall) rainfall, (spring) snowmelt, and (summer) high-elevation melt. The most glacierized basins exclusively grouped into high-elevation melt subclasses, and less glacierized basins sometimes exhibited seasonal patterns aligned with rainfall-dominated and snowmelt-dominated regimes. Peak-flow populations varied by subclass from dominant rainfall or dominant snowmelt to mixed rainfall-snowmelt or mixed rainfall, snowmelt, and high-elevation melt. Within subclasses, rainfall generated higher mean peak flows (relative to mean annual flow) than snowmelt or high-elevation melt. Seasonal flow regimes showed clear but complex associations with basin characteristics, primarily elevation and winter temperature, and with geographic location. These dependencies provided elevation-based analogies for changes associated with warming and insights for seasonal flow regime prediction and hydrologic region delineation. These results provide a spatially comprehensive perspective on seasonal streamflow drivers across Alaska from historical data and serve as an important historical basis for analysis.