Interannual variability and interdecadal trends in Hudson Bay streamflow

This study investigates the interannual variability and interdecadal trends in streamflow input to Hudson Bay (including James Bay) over 1964–2008. The 23 rivers chosen for this study span a maximum gauged area of 2.54 × 106 km2 and collectively transport 522 km3 of freshwater to Hudson Bay each year. Adjusting this value for the missing contributing area yields a total annual freshwater flux of 760 km3 into Hudson Bay. The standard deviation and coefficient of variation in annual streamflow to Hudson Bay reach 48.5 km3 and 0.09, respectively. The monotonic trend assessed with a Kendall–Theil Robust Line shows no detectable (|signal-to-noise ratio| < 1) change in total discharge into Hudson Bay over 1964–2008. A 5-year running mean in total Hudson Bay streamflow, however, reveals a downward trend from the mid-1960s to the mid-1980s, followed by relatively high flows in the mid-1980s, and then an upward trend, marked by a record annual discharge of 635 km3 in 2005, until the end of the study period. There is a notable shift in the seasonality of Hudson Bay discharge over time, with a detectable positive (negative) trend in winter (summer) streamflow from 1964 to 2008. Annual hydrographs for regulated and natural rivers over two periods suggest these changes arise from the storage of water in reservoirs during spring and summer that is later released for the generation of hydroelectricity in fall and winter. The naturally-flowing rivers show a marked decline in the variability of daily streamflow input to Hudson Bay in recent years while the opposite trend is found in the regulated systems. The fall 2009 diversion of 14.5 km3 yr− 1 or 48% of the total annual streamflow from the Rupert River northward into La Grande Rivière for enhanced power production further exacerbates the streamflow timing shifts observed in Hudson Bay. The potential impacts of flow regulation on the Hudson Bay marine environment are then discussed.

Research Highlights
► This study finds no detectable trend in annual Hudson Bay streamflow for 1964-2008.
► Total annual Hudson Bay streamflow reached a record value of 635 km3 in 2005.
► There is a shift from summer to wintertime streamflow driven by water regulation.
► The recent regulation of the Rupert River further alters the Hudson Bay streamflow.
► The observed changes in streamflow input affect the Hudson Bay marine environment.