Further diagnostic investigation using process hydrology simulations is needed to explain the observed regime changes.
Changes to the observed character of precipitation, runoff generation mechanisms and depressional storage are substantial, but it unlikely that any single change can explain the dramatic shift in SCRB surface hydrology. Recent flood volumes in SCRB have been abnormally large and high flows in June 2012 and flooding in June 2014 was caused solely by rainfall, something never before recorded at the basin. Peak discharge has tripled since 1975, with a major shift in 1994.
Snowmelt runoff has declined from 86% in the 1970s to 47% recently whilst rainfall runoff has increased from 7% to 34% of discharge. 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. The number of multiple day rainfall events has increased by half, which may make rainfall-runoff generation mechanisms more efficient. 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. Depressional storage has been drained for decades, reducing the extent of ponds by 58% and increasing drainage channel length 780%. 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. To illustrate the hydrological impact of climate and land use change on an unregulated basin, the agriculture and wetland dominated Smith Creek Research Basin (SCRB) was examined in detail.
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