Interception and Fog Drip Estimates in Fragmented Mountain Forests

Abstract

Forest interception is a major loss of water balance in mountain catchments, reducing the recharge of water resources. Fog precipitation occurring at higher elevations can reduce this loss by saturating the vegetative surface and dripping down to the soil surface. In 2015–2017, detailed observations of canopy throughfall and fog drip were performed in the upper plain of the Jizera Mountains (North Bohemia, Czech Republic). In the warm season (May–October), the interception loss of 106 mm was found in investigated mature spruce stand at 975 m a.s.l., i.e., 16% of the gross precipitation (662 mm). In 51 days a year, the forest interception was affected by a canopy fog drip. Hypothetically, by a negligible fog drip, the mean seasonal interception calculated by the Gash analytical model (225 mm) was 34% of the ‘open field’ rainfall. The fog drip volume (119 mm) was confirmed by the Slinn model (128 mm, + 9%), while the relatively simple models of Gallagher and Vermeulen significantly underestimated results by −23 and − 38%. Therefore, the Slinn model was employed to calculate daily fog drip over an annual cycle in heavy fragmented forest stands over 1 km2 of an experimental catchment. We found only slightly increased fog drip (up to 10%) within 30 m of the forest edge, reflective of the relatively high forest fragmentation (an absence of large homogenous stands and sharp edges). Four basic canopy classes (from mature spruce stands to herbaceous cover) were distinguished. The mean annual fog drip was PF = 81 mm (i.e., 7% of the gross precipitation) and fog drip reached 7–8% of the mean annual gross precipitation, or 10–12% of the mean annual runoff. In addition, the winter fog drip of up to 60% confirmed previous findings from this area.