Rainfall and cloud-water interception in tropical montane forests in the eastern Andes of Central Peru

Cloud-water and rainfall interception are hydrological processes of particular interest in Tropical Montane Cloud Forests (TMCF). Studies in these systems have shown important contributions of cloud/fog water to the hydrological balance. To evaluate the importance of cloud/fog water to montane forests of the western slope of the Cordillera Yanachaga in the eastern Andes of central Peru, we monitored bulk precipitation (gross rainfall), cloud water and net precipitation weekly over one year at two elevations, 2468 and 2815 masl. Bulk precipitation was greater at the upper site (2753 mm) than at the lower site (2222 mm). Annual net precipitation was 92.4% and 70.4% of rainfall at the upper and lower sites, respectively. Net precipitation was primarily composed of throughfall; stemflow was negligible, contributing less than 0.2% of annual rainfall at both sites. Apparent annual rainfall interception losses by the canopy were 7.7% and 29.6% of the bulk precipitation at the upper and lower sites, respectively. Apparent weekly rainfall interception at the upper site was sometimes negative and lower compared to that of the lower site. Apparent cloud-water interception occurred at least during weeks when negative rainfall interception was recorded, a contribution of 21 mm (0.8% of the annual rainfall) at the upper site. However, the apparent low rainfall interception losses at the upper site suggest that canopy wetting and subsequent saturation by cloud/fog water during periods with apparent positive rainfall interception may have contributed a difference of ca. 22% of apparent rainfall interception losses between sites. These contributions were supported by maximum apparent fog interception recorded by a fog gauge at the upper site. Although other equally important factors like topography, crown exposure and mossiness were not evaluated, the quantity of apparent fog interception at the upper site was found related to the canopy leaf area index. This important relationship has been previously described but mostly overlooked in studies of TMCF.