FOG CONTRIBUTIONS TO THE WATER-BUDGET OF FORESTED WATERSHEDS IN THE CANADIAN MARITIME PROVINCES - A GENERALIZED ALGORITHM FOR LOW ELEVATIONS

Fog contributes to the water budget of forested watersheds directly by water deposition, and indirectly by reducing potential and actual eva potranspiration. This study was designed to develop an empirical formu la for calculating fog and mist frequencies in the Maritimes, to adapt an algorithm for converting fog frequencies into water deposition rat es, and to assess the effectiveness of this algorithm for estimating t he fog and mist contributions to the water budget of forested watershe ds. Multiple regression analysis of data from 16 stations (elevations less than or equal to 145 m) distributed across the Maritimes revealed that 87% of the variance in fog-mist frequencies was explained collec tively by distance to the southern coast (the Bay of Fundy or the Atla ntic), time of rear (month) and air temperature. Fog frequencies calcu lated from the resulting multiple regression relationship were convert ed to fog water deposition using the Unsworth-Crossley model. Incorpor ating the fog algorithm into the forest hydrology model ForHyM effecti vely resolved discrepancies between simulated and recorded streamflow volumes for six forested watersheds in the Maritimes. Calculated fog w ater deposition amounted to 5-8% of recorded precipitation volumes. Si mulated evapotranspiration was reduced by 1-6% of precipitation owing to fog occurrences. These results are consistent with the fact that st reamflow volumes are about 10% higher than precipitation in the Mariti mes than in other regions in Canada where fog and mist conditions occu r infrequently.