Conclusions

The predicted future climate for the Grand Forks area from the downscaled CGCM1 model will result in more recharge to the unconfined aquifer from spring to the summer season. The largest predicted increase is from day 100 to day 150, when it is predicted to increase by a factor of three or more from present levels. In the summer months, recharge is predicted to be approximately 50% greater than at present (in most zones); in the autumn season the recharge is predicted to increase (10 to 25%) or remain the same as present, and in the winter recharge is expected to decrease.

Irrigation return flow begins after day 150 causing an increase of aquifer recharge by 10 to 20% in most irrigation district zones.

The groundwater flow model is sensitive to recharge only away from the river floodplain, and the maximum change expected (within the range of recharge values between the 65 recharge zones) in water table elevation is between 10 and 50 cm, but typically about 20 cm. Areas of the aquifer where temporal variation in recharge does not significantly affect model output are along river flood-plains. There, water levels are almost entirely controlled by river water levels.

The predicted temporal shifts in river hydrographs cause changes in aquifer water levels compared to the present, if compared to the same day of year. Differences are less than 0.5 m away from floodplain, but can be over 0.5 m near the river. However, the overall hydrograph shape remains the same. As the river peak flow shifts to an earlier date in a year, the 'hydrographs' for groundwater levels also shift by the same interval. Storage rates are less than 50% of inter-zonal groundwater flux, and 15 to 20% of river-aquifer flux. The river-aquifer interaction has a maximum flow rate between 11 and 20% of river flow during spring freshet - the river puts about 15% of its spring freshet flow into storage - and within 30 to 60 days, most of that water is released back to the river as baseflow.

The hydrograph shift for the 2040-2069 climate is larger than for the 2010-2039 climate scenario, therefore the computed differences to historical climate are similarly larger. The maximum water levels associated with the peak hydrograph are very similar to present climate because the peak discharge is not predicted to change, only the timing of the peak.

Financial support for this research was provided by the Natural Sciences and Engineering Council of Canada (NSERC) in the form of an undergraduate research award for J. Scibek; Natural Resources Canada under the Climate Change Action Fund (CCAF) Program; and the BC Ministry of Water, Land and Air Protection (BC WLAP). Technical support has been provided by Environment Canada (climate change predictions for the Kettle River), and BC WLAP (water well database).

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