In order to numerically evaluate the water discharge property of the Jiulianshan river basin, we applied the hydrologic cycle model (HYCYMODEL) to the discharge response to rainfall observed in the Jiulianshan river basin. The parameters in this model were optimized by trial and error. Monthly potential transpiration rate was computed from observed air temperature, humidity, and solar radiation with Priestly-Taylor equation. The discharge response to the rainfall simulated using HYCYMODEL agreed well with the observed discharge. The estimated parameters and the result of simulation of the discharge response to the rainfall were compared with those reported for the typical Japanese temperate forest river basins. In Jiulianshan, the ratio of the impermeable area is small, and the river basin has a large capacity of water storage. As a result, it was found that the shape of hydrograph of Jiulianshan river basin is different from those of Japanese river basins, although the ratio of total base flow to the total discharge is similar to those of Japanese river basins. In Jiulianshan, the peak of discharge is smaller and the recession hydrograph is more gentle.
In this study, we developed a new method for evaluating vertical profiles of CO 2 gas diffusivity and CO 2 gas production in soil samples. The CO 2 flux at the boundary and the steady‐state CO 2 gas profile are measured under two boundary gas conditions. The differential form of Fick's second law can then be used to calculate the gas diffusion coefficients and CO 2 production rate. This method was applied to an undisturbed forest soil sample in the laboratory. Both gas diffusion coefficients and CO 2 production rates decreased with increasing depth. The relative gas diffusion coefficients ranged between 0.03 and 0.15, and the CO 2 production rates ranged between 2.1 × 10 −8 and 4.7 × 10 −8 kg CO 2 m 3 s −1 at 20°C. Unsteady changes in the CO 2 concentration profile in the soil column, and flux from the soil surface were successfully simulated with these values.
Environmental factors, such as global solar radiation, wind speed, air temperature, humidity, and CO2 concentration, were measured above and within the canopy of a tropical rainforest in Lambir Hills National Park, Sarawak, Malaysia. Few data concerning the environment of this forest have been reported. Intensive observations were carried out in 1998, 1999, and 2000 with the following results: (1) The fraction of global solar radiation reaching the upper layer of the canopy varied with global solar radiation above the canopy. Even though the global solar radiation above the canopy fluctuated, the fraction of that reaching the lower canopy and the ground was constantly approximately 5%. (2) The fraction of wind speed reaching each layer of the canopy increased with wind speed above the canopy. Little wind was usually present at the lower canopy. (3) The daytime air temperature at the canopy top was higher than that near the ground. The maximum difference between the air temperature at the canopy top and that at the ground was about 5°C, and the diurnal temperature ranges at the canopy top and those at the ground were about 8°C and about 5°C, respectively. The highest daytime water vapor pressure occurred within the canopy and particularly near the ground. Vertical gradients of water vapor pressure during the day were steep, probably because of high transpiration. (4) In the 1998 observation the minimum and the maximum CO2 concentrations were 360 ppm in the day and 450 ppm at night, while in the 2000 observation the minimum and the maximum CO2 concentrations were 350 ppm in the day and 540 ppm at night. The higher CO2 concentration in the daytime and the lower concentration at night observed during the 1998 observation period were probably due to reduced photosynthesis and soil respiration caused by exceptional dry conditions during the observation period.
Abstract Although we know that rainfall interception (the rain caught, stored, and evaporated from aboveground vegetative surfaces and ground litter) is affected by rain and throughfall drop size, what was unknown until now is the relative proportion of each throughfall type (free throughfall, splash throughfall, canopy drip) beneath coniferous and broadleaved trees. Based on a multinational data set of >120 million throughfall drops, we found that the type, number, and volume of throughfall drops are different between coniferous and broadleaved tree species, leaf states, and timing within rain events. Compared with leafed broadleaved trees, conifers had a lower percentage of canopy drip (51% vs. 69% with respect to total throughfall volume) and slightly smaller diameter splash throughfall and canopy drip. Canopy drip from leafless broadleaved trees consisted of fewer and smaller diameter drops ( D 50_DR , 50th cumulative drop volume percentile for canopy drip, of 2.24 mm) than leafed broadleaved trees ( D 50_DR of 4.32 mm). Canopy drip was much larger in diameter under woody drip points ( D 50_DR of 5.92 mm) than leafed broadleaved trees. Based on throughfall volume, the percentage of canopy drip was significantly different between conifers, leafed broadleaved trees, leafless broadleaved trees, and woody surface drip points ( p ranged from <0.001 to 0.005). These findings are partly attributable to differences in canopy structure and plant surface characteristics between plant functional types and canopy state (leaf, leafless), among other factors. Hence, our results demonstrating the importance of drop‐size‐dependent partitioning between coniferous and broadleaved tree species could be useful to those requiring more detailed information on throughfall fluxes to the forest floor.
Evaporation of intercepted rainfall is a distinct hydrological process in forested areas. Several studies have shown that rainfall interception by forest canopies had major significances to the water budget, comparing to other vegetative covers (e.g. CALDER, 1976, GASH and STEWART, 1977, PEARCE and ROWE, 1979, SUZUKI, 1991). Particularly an interception study in a flux study site, where water vapor and energy cycling are monitored and modeled, is required to quantify the confident observed amount of rainfall interception by the forest canopy. This interception amounts can be used both to parameterize and to validate the output from an evapotranspiration model, which describes the hydrological processes at a study site (CALDER et al., 1986, SHUTTLEWORTH, 1988, TANAKA et al., 2003, TANI et al., 2003,KUMAGAI et al., 2004). Furthermore, the interception data observed by LLOYED et al. (1988) in an Amazonian tropical forest were used to parameterize a land-surface model in GCM (DICKINSON and HENDERSONSELLERS, 1988) and to validate the model output (LLOYD, 1990). A number of observational studies of interception have shown that rainfall interception per individual rainfall event (hereafter event-based interception) varies remarkably. This variation in event-based interception presumably supports the understanding of unclear interception processes (KURAJI and TANAKA, 2003). However, interception models based on the Penman-Montieth equation, e.g. RUTTER et al. (1971, 1975), cannot explain the observed variation (HATTORI et al., 1982, CALDER et al., 1986, SCHELLENKENS et al., 2000a, TANI et al., 2003). Therefore, it is significant to distinguish between systematic variations that arises from measurement errors, and true variations caused by differences in rainfall and meteorological conditions during each rainfall event. Measurement errors in interception observation consist of gross rainfall and net rainfall, i.e. throughfall and stemflow. While a measurement of net rainfall is identified to be difficult, problems in measurement of rainfall are commonly ignored (CROCKFORD and RICHARDSON, 2000, KURAJI and TANAKA, 2003). In general, it is very difficult to find or establish a wellpositioned clearing in a large forest reserve for a forest hydrological experiment. Normally any clearing used for rainfall observation is separate from interception study plots. CROCKFORD and RICHARDSON (2000) indicated that a event-based rainfall at a clearing and a study plot *1 *2 *3
