ESTIMATING EVAPORATION USING STABLE ISOTOPES - QUANTITATIVE RESULTS AND SENSITIVITY ANALYSIS FOR 2 CATCHMENTS IN NORTHERN CANADA

The stable isotope-mass balance method can provide useful water balanc e information in ungauged catchments. The method has been used to eval uate evaporation and water balance at two contrasting sites in norther n Canada. Areally weighted evaporative discharge from an 850 km2 tundr a catchment in south-central District of Keewatin is estimated to be a bout 7 % of total water discharge (almost-equal-to 16 mm/yr), compared to about 19 % (almost-equal-to 65 mm/yr) from a 300 km2 forested wate rshed in the Upper Mackenzie Valley. Lakes in both watersheds exhibit broad ranges of evaporation/inflow ratios related to local water balan ce. The potential errors in the estimates are evaluated through consid eration of possible variations in basin storage, humidity, and the iso topic composition of atmospheric vapour.