Fog contributions to the water budget of forested watersheds in the Canadian Maritime Provinces: A generalized algorithm for low elevations

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Abstract
Fog contributes to the water budget of forested watersheds directly by water deposition, and indirectly by reducing potential and actual evapotranspiration. This study was designed to develop an empirical formula for calculating fog and mist frequencies in the Maritimes, to adapt an algorithm for converting fog frequencies into water deposition rates, and to assess the effectiveness of this algorithm for estimating the fog and mist contributions to the water budget of forested watersheds. Multiple regression analysis of data from 16 stations (elevations ≤ 145 m) distributed across the Maritimes revealed that 87% of the variance in fog‐mist frequencies was explained collectively by distance to the southern coast (the Bay of Fundy or the Atlantic), time of year (month) and air temperature. Fog frequencies calculated from the resulting multiple regression relationship were converted to fog water deposition using the Unsworth‐Crossley model. Incorporating the fog algorithm into the forest hydrology model ForHyM effectively resolved discrepancies between simulated and recorded streamflow volumes for six forested watersheds in the Maritimes. Calculated fog water deposition amounted to 5–8% of recorded precipitation volumes. Simulated evapotranspiration was reduced by 1–6% of precipitation owing to fog occurrences. These results are consistent with the fact that streamflow volumes are about 10% higher than precipitation in the Maritimes than in other regions in Canada where fog and mist conditions occur infrequently.