広葉樹混交林を主体とした小流域における樹冠遮断と流域水収支の検討

Abstract

To clarify the water balance in a mixed evergreen-deciduous broadleaf forest watershed, we analyzed gross precipitation, throughfall, and stream flow in a small watershed in the Kaisho Forest, Seto City, Aichi Prefecture. First, to quantify canopy interception, we analyzed throughfall at a site with Quercus serrata in the upper layer and Camellia japonica in the lower layer. The time period was 2009-2024, and one event was defined as a 24-hour rainfall-free period. The annual interception rate ranged from 50 to 80% from 2009 to 2016, and from 10 to 30% from 2017 onward, a difference of 2 to 3 times. The rainfall at the onset of rainfall through the canopy during the period of difference is almost the same, and the difference in the interception rate during the defoliation and leaf set periods is also slight. The direct runoff was analyzed for the 2009-2011 period (Period I) and the 2021-2023 period (Period II), and the increase in direct runoff relative to gross precipitation was smaller in Period II than in Period I, suggesting that runoff suppression is occurring. Furthermore, the water balance after 2017 showed that about 30% of the annual precipitation was lost through evapotranspiration and the remaining 70% was runoff, of which 70% was basal runoff. Continued observation is necessary because the distribution of moisture in the watershed may change in the future due to forest growth and the dominance of evergreen broad-leaved trees.