Hydrological regime changes in a Canadian prairie basin / Stacey Dumanski, John W. Pomeroy, and Cherie J. Westbrook.

Includes bibliographical references (pages 3903-3904).

To illustrate the hydrological impact of climate and land use change on an unregulated basin, the agriculture- and wetlanddominated
Smith Creek Research Basin (SCRB) was examined in detail. Streamflows (1975–1994) show behaviour typical of
the Canadian Prairies – generation primarily by snowmelt and cessation in May due to lack of runoff or groundwater
contributions. Depressional storage has been drained for decades, reducing the extent of ponds by 58% and increasing drainage
channel length 780%. Climate has also changed; increasing temperatures since 1942 have brought on a gradual increase in the
rainfall fraction of precipitation (no trends in total precipitation) and an earlier snowmelt by 2 weeks. The number of multiple-day
rainfall events has increased by half, which may make rainfall-runoff generation mechanisms more efficient. Annual streamflow
volume and runoff ratio have increased 14-fold and 12-fold, respectively, since 1975, with dramatically increasing contributions
from rainfall and mixed runoff regimes. Snowmelt runoff has declined from 86% in the 1970s to 47% recently while rainfall
runoff has increased from 7% to 34% of discharge. Peak discharge has tripled since 1975, with a major shift in 1994. Recent
flood volumes in SCRB have been abnormally large, and high flows in June 2012 and flooding in June 2014 were caused solely
by rainfall, something never before recorded at the basin. Changes to the observed character of precipitation, runoff generation
mechanisms and depressional storage are substantial, but it is unlikely that any single change can explain the dramatic shift in
SCRB surface hydrology. Further diagnostic investigation using process hydrology simulations is needed to explain the observed
regime changes.