Streamflow variability and hydroclimatic change at the Bear Brook Watershed in Maine (BBWM), USA.

Seasonal variations in streamflow and the associated hydrologic extremes impart significant temporal structure to watershed-scale chemical fluxes. Consequently, a careful characterization of the episodic-to-seasonal and longer-term streamflow variations is a first step toward developing a comprehensive view of the temporal dynamics of watershed processes in a changing climate. Here we analyze a nearly two-decade-long streamflow record for the East Bear subwatershed within the Bear Brook Watershed in Maine (BBWM) (USA) to understand the envelope of streamflow variability by season, with a particular focus on the high flow events that have a disproportionately large impact on the biogeochemical processes and fluxes. Interannual and longer-term variations in a number of derived statistical metrics of hydrologic variability are examined. Our analysis shows substantial interannual and longer-term variability in seasonal flow volumes and peak flows. Furthermore, a long, unimpaired streamflow record for the Narraguagus River (a proximate watershed to the BBWM) is examined with a view to understand the relative coherence in hydrologic variability, as well as quantifying the decadal and longer-term hydrologic variations in this region. We find that the streamflow variability in the two watersheds shows similarity in all seasons. A moving window analysis to assess the changing flood potential over time indicates upward trends in the recent decades. Spring season (March-May) flood estimates show a near-monotonic trend over the 1949-2008 record. Finally, empirical relationships between streamflow and large-scale atmospheric circulation patterns highlight the regional and global climatic drivers of hydrologic extremes in this region, including impacts from remnants of Atlantic hurricanes.