The stable isotope-mass balance method can provide useful water balance information in ungauged catchments. The method has been used to evaluate evaporation and water balance at two contrasting sites in northern Canada. Areally weighted evaporative discharge from an 850 km2 tundra catchment in south-central District of Keewatin is estimated to be about 7 % of total water discharge (≈ 16 mm/yr), compared to about 19 % (≈ 65 mm/yr) from a 300 km2 forested watershed in the Upper Mackenzie Valley. Lakes in both watersheds exhibit broad ranges of evaporation/inflow ratios related to local water balance. The potential errors in the estimates are evaluated through consideration of possible variations in basin storage, humidity, and the isotopic composition of atmospheric vapour.

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