The influence of seasonal changes in canopy structure on interception loss: Application of the revised Gash model

Interception loss from a multi-species, deciduous, broad-leaved secondary forest in Japan was derived from gross rainfall, throughfall, and stemflow. The seasonal changes in the canopy structure were expressed using the leaf area index, which ranged from 1.65 to 4.31. In addition, the relationship between leaf area index (LAI) and relative light index (RLI) was examined using the Beer-Lambert equation. We established that RLI was associated with the canopy cover fraction. The relationships between throughfall, stemflow, and interception loss and gross rainfall were approximated by a linear regression equation for the growing and dormant seasons. Spatial variability in throughfall could be estimated from the relationship between the ratios of throughfall and RLI or LAI measured at many points, and had a high coefficient of variation. For stemflow, the regression coefficient and constant were strongly related to the diameter at breast height and were approximated by exponential equations. The differences in interception loss between seasons were small despite the distinct differences in LAI (the percentages of the total gross rainfall were 17.6 and 14.3% in the growing and dormant seasons, respectively). The revised Gash model was used to estimate interception loss more precisely by dividing the calculation period into (i) the entire study period, (ii) the growing and dormant seasons, and (iii) 3-month periods. The estimated interception loss was over- and underestimated by 7.8% for (i), 1.4% for (ii), and −2.2% for (iii). Regarding the parameters in revised Gash model, the canopy storage capacity varied with changes in LAI, and the evaporation rate was related not only to meteorological conditions, but also to the canopy structure in terms of aerodynamic resistance.