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Abstract:Evaporation from the forest floor (Ef ) of a secondary broad-leaved forest was monitored for 1 year at 30 min intervals using a closed chamber system. The diurnal and seasonal variation of Ef and forest structure were analysed for days undisturbed by rainfall. The diurnal change in Ef reached a maximum at about 14 : 00 and gradually decreased towards midnight along with the vapour pressure deficit (D). Although Ef comprised about 20% of evapotranspiration from the dry canopy (Et ), it had only a small influence on diurnal evaporation efficiency (ˇ) characteristics above the canopy because its diurnal range was much smaller than that of Et. Although leaf emergence and leaf fall clearly affected available energy (Ae) beneath the canopy, the influence was not clear with Ef. In contrast, seasonal variation in Ef was strongly correlated with D and Ae above the canopy, and the determination coefficient (R 2 ) changed with the Bowen ratio (B). At night, Et was almost equal to Ef when the friction velocity (u Ł ) ranged between 0Ð2 and 0Ð4 m s 1 . The ratio of Ef to Et was exponentially correlated with leaf area index (LAI ) when the soil was not dry. The ratio of Ef to Et was mainly influenced by LAI and soil moisture, but the existence of understory vegetation did not have a strong influence.

Abstract:To elucidate the factors involved in interception loss, we conducted experiments in which we measured environmental variables such as rainfall intensity, forest structure, and weather conditions. An artificial forest consisting of 24 vinyl trees was used to examine the influences of forest structure and rainfall conditions on interception loss. The interception rate was higher at higher plant area index (PAI) values and wind speeds and lower with greater rainfall intensity.We confirmed the factors affecting interception loss by using an interception model based on the tank model. The artificial forest simulations provide new evidence that interception loss is influenced by the PAI, rainfall intensity, saturation deficit, and wind speed. The effect of the saturation deficit on the interception rate was unclear from the experimental results, but the single-tank model revealed that wind speed strongly influences the effects of the saturation deficit on interception loss. Thus, whereas interception loss was not significantly affected by the saturation deficit at low wind speeds, it increased significantly with the saturation deficit under windy conditions. The model simulation also showed the sensitivity of each factor with regard to the interception rate. The sensitivity of rainfall intensity decreased as the PAI increased, and the sensitivity of the saturation deficit increased as the wind speed increased.The experiments and model calculations clarified the main elements affecting interception loss and their sensitivities. Compared with previous studies on interception loss, this study revealed a positive relationship between the PAI and interception loss, a negative exponential relationship with rainfall intensity, and the effects of the saturation deficit on interception loss.