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1.
ABSTRACT

The interception process impacts rainfall magnitude and intensity under the canopy. In this study, the effect of plant interception on throughfall characteristics was assessed in the deciduous Caatinga vegetation, at different canopy development stages and for temporal scales ranging from seasonal to the intra-event scale. Throughfall and stemflow percentages were slightly higher at the onset of the rainy season, when leaf area density is low, with resulting lower interception losses. However, there was no statistical difference among the variables at the seasonal scale. At the intra-event scale, average and maximum throughfall intensity at different time intervals showed statistical difference between the stages of canopy development. Regardless of leaf area density and rainfall depth, vegetation is able to retain all the water up to 2 min in the beginning of each rainfall event with accumulated rainfall smaller than 0.6 mm. Furthermore, the Caatinga vegetation attenuates the rainfall intensity by 30–40%.  相似文献   

2.
While the hydrological balance of forest ecosystems has often been studied at the annual level, quantitative studies on the factors determining rainfall partitioning of individual rain events are less frequently reported. Therefore, the effect of the seasonal variation in canopy cover on rainfall partitioning was studied for a mature deciduous beech (Fagus sylvatica L.) tree over a 2‐year period. At the annual level, throughfall amounted to 71% of precipitation, stemflow 8%, and interception 21%. Rainfall partitioning at the event level depended strongly on the amount of rainfall and differed significantly (p < 0·001) between the leafed and the leafless period of the year. Therefore, water fluxes of individual events were described using a multiple regression analysis (ra2 > 0·85, n = 205) with foliation, rainfall characteristics and meteorological variables as predictor variables. For a given amount of rainfall, foliation significantly increased interception and decreased throughfall and stemflow amounts. In addition, rainfall duration, maximum rainfall rate, vapour pressure deficit, and wind speed significantly affected rainfall partitioning at the event level. Increasing maximum hourly rainfall rate increased throughfall and decreased stemflow generation, while higher hourly vapour pressure deficit decreased event throughfall and stemflow amounts. Wind speed decreased throughfall in the growing period only. Since foliation and the event rainfall amount largely determined interception loss, the observed net water input under the deciduous canopy was sensitive to the temporal distribution of rainfall. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

3.
This study aimed at analysing the effects of biological and meteorological factors on stemflow generation in a temperate mixed oak (Quercus petraea Liebl.) and beech (Fagus sylvatica L.) stand. A statistical model was developed to predict single‐event individual stemflow volume from trunk circumference and rainfall depth allowing mechanistic stemflow parameters to be deduced from the model, namely stemflow rates (SFrate), storage of water on tree organs (St) and rainfall thresholds for stemflow (RFmin). SFrate and St increased with increasing trunk circumference while RFmin was not significantly influenced by tree size. RFmin and, for a given tree size, St were higher for oak than for beech, and inversely for SFrate. For each species, RFmin was higher for the leaved season than for the leafless period, while the opposite was found for SFrate, and St was not significantly affected by the season. Increasing wind speed during rain increased SFrate, lowered RFmin and did not influence St. In contrast, St and RFmin tended, respectively, to decrease and to increase with increasing values of the ratio between the cumulated potential evaporation during the dry period preceding the rain event and the volume of the preceding rainfall (Eva pADP/Rprevious). Stemflow volume, which results from the combined effects of the previous parameters, was higher for beech than for oak and also higher during the leafless period than during the leaved period; these differences were large for the smallest events but decreased rapidly as rainfall depth increased. In addition, an enhancing and a depressing effect on stemflow volume were shown for the average wind speed during rain and for the ratio Eva pADP/Rprevious, respectively. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

4.
The partitioning of gross rainfall into throughfall, stemflow, and interception loss and their relationships with forest structure was studied for a period of four years (October 2002–September 2006) and two years (October 2005–September 2007) in seven experimental catchments of temperate rainforest ecosystems located in the Andes of south‐central Chile (39°37′S, 600–925 m a.s.l.). The amount of throughfall, stemflow, and interception loss was correlated with forest structure characteristics such as basal area, canopy cover, mean quadratic diameter (MQD), and tree species characteristics in evergreen and deciduous forests. Annual rainfall ranged from 4061 to 5308 mm at 815 m a.s.l. and from 3453 to 4660 mm at 714 m a.s.l. Throughfall ranged from 64 to 89% of gross rainfall. Stemflow contributed 0·3–3·4% of net precipitation. Interception losses ranged from 11 to 36% of gross rainfall and depended on the amount of rainfall and characteristics as well as on forest structure, particularly the MQD. For evergreen forests, strong correlations were found between stemflow per tree and tree characteristics such as diameter at breast height (R2 = 0·92, P < 0·01) and crown projection area (R2 = 0·65, P < 0·01). Stemflow per tree was also significantly correlated with epiphyte cover of trunks in the old‐growth evergreen forests (R2 = 0·29, P < 0·05). The difference in the proportion of throughfall and interception loss among stands was significant only during winter. The reported relationships between rainfall partitioning and forest structure and composition provide valuable information for management practices, which aimed at producing other ecosystem services in addition to timber in native rainforests of southern Chile. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

5.
The characteristics of stemflow were observed in a tall stewartia (Stewartia monadelpha) deciduous forest on a hillslope in central Japan, revealing new findings for a previously unreported type of deciduous forest. Using 2-year observations of 250 rainfall events, we analyzed seasonal and spatial variations in stemflow for several trees, and applied additional data sets of throughfall and plant area index (PAI) to produce a rough estimate of seasonal variations in rainfall redistribution processes and canopy architecture for a single tree. Compared to previous findings for other deciduous tree species, the ratios of throughfall, stemflow, and interception to open-area rainfall obviously varied with PAI changes for tall stewartia. Meteorological conditions of rainfall amount, rainfall intensity, wind speed, and wind direction had little effect on stemflow generation, which was mainly affected by variation in canopy architecture. Three novel characteristics of stemflow were identified for several tall stewartia trees. First, the yearly stemflow ratio at the forest-stand level for tall stewartia (12%) was high compared to previous findings on beech and oak stands, indicating tall stewartia has considerably high potential to generate a great amount of stemflow. Second, stemflow tended to be 1.3–2.0 times greater in the leafed period than in the leafless period. Third, the amount of stemflow was 12–132 times greater on the downslope side of the stem than on the upslope side. It likely caused by the uneven area between the upslope and downslope sides of the canopy and by asymmetrical stemflow pathways between the upslope and downslope sides of the trunk due to downslope tilting of the tree trunk.  相似文献   

6.
ABSTRACT

Trees concentrate rainfall to near-stem soils via stemflow. When canopy structures are organized appropriately, stemflow can even induce preferential flow through soils, transporting nutrients to biogeochemically active areas. Bark structure significantly affects stemflow, yet bark-stemflow studies are primarily qualitative. We used a LaserBark to compute bark microrelief (MR), ridge-to-furrow amplitude (R) and slope (S) metrics per American Society of Mechanical Engineering standards (ASME-B46.1–2009) for two morphologically contrasting species (Fagus sylvatica L. (European beech), Quercus robur L. (pendunculate oak)) under storm conditions with strong bark water storage capacity (BWSC) influence in central Germany. Smaller R and S for F. sylvatica significantly lowered BWSC, which strongly and inversely correlated to maximum funnelling ratios and permitted stemflow generation at lower rain magnitudes. Larger R and S values in Q. robur reduced funnelling, diminishing stemflow drainage for larger storms. Quercus robur funnelling and stemflow was more reliant on intermediate rain intensities and intermittency to maintain bark channel-dependent drainage pathways. Shelter provided by Q. robur’s ridged bark also appears to protect entrained water, lengthening mean intrastorm dry periods necessary to affect stemflow. Storm conditions where BWSC plays a major role in stemflow accounted for much of 2013’s rainfall at the nearest meteorological station (Wulferstedt).
Editor M.C. Acreman; Associate editor not assigned  相似文献   

7.
Rainfall interception loss plays an important role in ecohydrological processes in dryland shrub ecosystems, but its drivers still remain poorly understood. In this study, a statistical model was developed to simulate interception loss based on the mass balance measurements arising from the partitioning of rainfall in 2 dominant xerophytic shrub (Hippophae rhamnoides and Spiraea pubescens) communities in the Loess Plateau. We measured throughfall and stemflow in the field under natural rainfall, calculated the canopy storage capacity in the laboratory, and identified key factors controlling these components for the 2 shrubs. We quantified and scaled up the stemflow and the canopy storage capacity measurements from the branches and/or leaves to stand level. The average interception loss, throughfall, and stemflow fluxes account for 24.9%, 72.2%, and 2.9% of the gross rainfall for H. rhamnoides, and 19.2%, 70.7%, and 10.1% for S. pubescens, respectively. Throughfall increased with increasing rainfall for both shrubs; however, it was only correlated with the leaf area index for S. pubescens. For stemflow measured from individual branches, we found that the rainfall amount and basal diameter are the best predictors for H. rhamnoides, whereas rainfall amount and branch biomass appear to be the best predictors for S. pubescens. At the stand level, stemflow production is affected by the rainfall amount for H. rhamnoides, and it is affected by both the rainfall amount and the leaf area index for S. pubescens. The canopy storage capacity of H. rhamnoides (1.07–1.28 mm) was larger than S. pubescens (0.88–1.07 mm), and it is mainly determined by the branches and stems of H. rhamnoides and the leaves of S. pubescens. The differences in interception loss between the 2 shrub stands are mainly attributed to different canopy structures that induced differences in stemflow production and canopy storage. We evaluated the effects of canopy structure on rainfall interception loss, and our developed model provides a better understanding of the effects of the canopy structure on the water cycles in dryland shrub ecosystems.  相似文献   

8.
Knowledge of exchanges of energy and water over terrestrial surfaces is the first step towards understand the ecohydrological mechanisms, particularly in water-limited ecosystems in dryland environments. However, patterns of energy exchange and evapotranspiration (ET) are not well understood in the oasis-desert ecotone, which plays an important role in protecting oases against the threat of desertification in arid regions of northwestern China. Here, the continuous measurements of surface energy fluxes were made using eddy covariance in conjunction with auxiliary measurements for 2 years (2014–2015) in an oasis-desert ecotone mainly covered by phreatophyte shrubs Haloxylon ammodendron, Nitraria tangutorum/sphaerocarpa, and Calligonum mongolicum in arid northwestern China. Based on the collated data for 2 years, statistical analysis on a 30-min time scale indicated that approximately 50% of daytime net radiation (Rn) in the ecotone was dissipated as H on average, and one-third of Rn was consumed by soil heat flux (G). Only 9% of Rn was consumed for latent heat flux (λE), which peaked in summer (21% in 2014 and 16% in 2015), corresponding to the highest rainfall season. Daily mean ET was approximately 1 mm days−1 during the growing season of the shrub species. Accumulated annual ET was 195 and 181 mm in 2014 and 2015, respectively, exceeding the corresponding precipitation (P) by approximately 87 and 77 mm, indicating that groundwater may be another important source of water for ET in the ecotone aside from rainfall. Results within provide valuable insights into the mechanisms responsible for sustaining energy and water balance in the ecotone, a potentially groundwater-dependent ecosystem. These results also offer a foremost ecohydrological implication for water and land resources management and ecotone conservation, such as avoiding heavy groundwater pumping for extensive agricultural irrigation use to sustain groundwater availability for these shrub species in the ecotone.  相似文献   

9.
An increasing number of studies have examined the effects of various biotic and abiotic factors on stemflow production. Of those that have ascribed the importance of canopy structure to stemflow production, there has been a bias towards field studies. Coupling Bayesian inference with the NIED (National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan) large-scale rainfall simulator, this study leveraged a unique opportunity to control rainfall amounts and intensities to pinpoint the canopy structural metrics that differentially influence stemflow funnelling ratios for three common tree species between leafed and leafless canopy states. For the first time, we examined whether canopy structure metrics exert a static control on stemflow funnelling ratios or whether different elements of canopy structure are more or less important under leafed or leafless states, thereby allowing us to determine if tacit assumptions about the static influence of canopy structure on stemflow production (and funnelling) are valid (or not). Rainfall simulations were conducted at 15, 20, 30, 40, 50, and 100 mm h−1 under both leafed and leafless tree conditions (12 simulations in total) to detect any differential effects on the presence or absence of foliage on stemflow funnelling ratios. For leafed conditions, the highest percentages of best-fitting models (ΔDIC ≤2) indicated that stemflow funnelling ratios were mainly controlled by total dry aboveground biomass (Ball), diameter at breast height (DBH), total dry foliar biomass (Bf), tree height (H), and woody to foliar dry biomass ratio (BR). Whilst for the leafless state, the highest percentages of best-fitting models (ΔDIC ≤2) indicated that total dry branch biomass (Bbr) was relatively dominant as was the interaction effects between crown projection area and species (CPA:species). These results compel us to reject any assumption of a static effect of different elements of canopy structure on stemflow funnelling.  相似文献   

10.
Stemflow of xerophytic shrubs was monitored on event basis within a revegetated sand dune. Quantity of stemflow showed a clear species‐specific dependence in combination with the rainfall characteristics. Results obtained revealed that for ovate‐leaved C. korshinskii with an inverted cone‐shaped canopy and smooth bark, the quantity of stemflow in depth accounted for 7.2% of the individual gross rainfall, while it was 2.0% for needle‐leaved A. ordosica with a cone‐shaped canopy and coarse bark. There were significant positive linear relationships between stemflow and individual gross rainfall and rainfall intensity for the two shrubs. An individual gross rainfall of 1.4 and 1.8 mm was necessary for stemflow generation for C. korshinskii and A. ordosica, respectively. Multiple regression analysis showed that the abiotic and biotic variables including the individual gross rainfall, mean windspeed (WS), canopy height, branch length, and canopy volume have significant influence on stemflow for C. korshinskii, whereas for A. ordosica, the notable influencing variables were individual gross rainfall, stem diameter, and leaf area index. Generally, WS has less effect on stemflow than that of rainfall for A. ordosica. The correlation relationship between individual gross rainfall and funneling ratio showed that the funneling ratio attains its peak when the gross rainfall is 13 and 16 mm for C. korshinskii and A. ordosica, respectively, implying that the canopy morphology emerged as determining factors on funneling ratio decrease when the individual gross rainfall exceeds these values. In comparison, higher WS increased the funneling ratio remarkably for C. korshinskii than A. ordosica due partly to the greater branch length and canopy projection area in C. korshinskii. Funneling ratio can be used as an integrated variable for the effects of canopy morphology and rainfall characteristics on stemflow. The implication of stemflow on water balance and its contribution to sustain the shrubs and the revegetation efforts was discussed. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

11.
A total of 144 free-field ground motions with closest site-to-rupture distances (Rrup) less than 200 km recorded during the 2010 Mw 7.2 El Mayor–Cucapah earthquake are used to investigate predictive capabilities of the next generation attenuation (NGA) ground-motion prediction equations (GMPE). The NGA GMPEs underpredict observed spectral accelerations at sites with shear wave velocity in the upper 30 m of the site (Vs30) between 180 and 366 m/s with Rrup from about 10 to 50 km and overpredict at sites with Rrup from about 50 to 200 km. Intra-event residuals of the NGA GMPEs exhibit a noticeable negative trend for peak ground acceleration and 0.3, 1.0, and 2.0 s periods. Comparison of the inter-event residual between the 2010 Mw 7.2 El Mayor–Cucapah earthquake and the NGA dataset reveals that short-period inter-event residuals from the 2010 Mw 7.2 El Mayor–Cucapah earthquake is within the scatter of inter-event residuals from the NGA dataset but long-period inter-event residuals do not appear within of the scatter of inter-event residuals from the NGA dataset. Spectral accelerations predicted by the NGA GMPEs are generally unbiased against Vs30 and periods of less than 4.0 s. Observed spectral accelerations show a stronger Vs30 dependence for both short and long periods compared with the NGA GMPEs. The Boore and Atkinson (Earthq Spectra 24(1):99–138, 2008) and Chiou and Youngs (Earthq Spectra 24(1):173–215, 2008) GMPEs perform better in predicting observed short-period spectral accelerations at the sites with Vs30 between 180 and 250 m/s than the Abrahamson and Silva (Earthq Spectra 24(1):67–97, 2008) and Campbell and Bozorgnia (Earthq Spectra 24(1):139–171, 2008) GMPEs.  相似文献   

12.
The incidence of large rain events in Mediterranean ecosystems vary among years. Summer aridity is interpreted as a resetting event, eliminating previous soil‐moisture dynamics. The dynamics of soil moisture and retention are critical to tree survival, particularly in dry regions. This study examines the long‐term soil water content (θV) dynamics in two distinct locations within the forest, under the canopy and forest clearing, within two diverse oak forests: subhumid mixed oak forests (MG) and semiarid monospecific oak woodlands (YE). Plots were established at small‐scale catchments and soil water contents were measured during 2010–2013, at three depths in the two different locations. Cumulative rainfall was used as an independent proxy for θV analysis. A novel bell‐bilogistic mathematical model of wetting, saturation, and drying arms was developed. We aimed to study the θV distribution differences between soil profiles giving the large climatic gradient between the two forested sub basins, the differences in vegetation traits along with soil attributes. We further aimed at determining the role of an individual tree in regulating soil‐moisture dynamics. We hypothesized the occurrence of distinct responses between sites in all soil‐moisture indices with higher θV at the wetter site. We tested the hypothesis that seasonal cumulative rainfall dictates the variations in soil‐moisture regimes throughout contiguous years. Annual rainfall was higher than long‐term average throughout the study. Soil profiles under the canopies at both sites were consistently wetter. Infiltration and depletion constants were higher at MG whereas maximum soil moisture was higher at YE. Homogenous recharge patterns were seen at MG although YE evinced more variation. Oaks had no effect on recharge at MG compared with the forest clearing. Soil properties primarily affected the wetting arm whereas vegetation composition regulated the drying arm. Mixed‐stands characterized by ever‐green and deciduous species may maintain favourable soil‐moisture conditions, in comparison with other mixed stand morphologies. The increasing role of slacking forces in infiltration process may alter the interaction between trees and herbaceous vegetation.  相似文献   

13.
Gerard Govers  Jan Diels 《水文研究》2013,27(25):3777-3790
Experimental work has clearly shown that the effective hydraulic conductivity (Ke) or effective infiltration rate (fe) on the local scale of a plot cannot be considered as constant but are dependent on water depth and rainfall intensity because non‐random microtopography‐related variations in hydraulic conductivity occur. Rainfall–runoff models generally do not account for this: models assume that excess water is uniformly spread over the soil surface and within‐plot variations are neglected. In the present study, we propose a model that is based on the concepts of microtopography‐related water depth‐dependent infiltration and partial contributing area. Expressions for the plot scale Ke and fe were developed that depend on rainfall intensity and runon from upslope (and thus on water depth). To calibrate and validate the model, steady state infiltration experiments were conducted on maize fields on silt loam soils in Belgium, with different stages and combinations of rainfall intensity and inflow, simulating rainfall and runon. Water depth–discharge and depth–inundation relationships were established and used to estimate the effect of inundation on Ke. Although inflow‐only experiments were found to be unsuitable for calibration, the model was successfully calibrated and validated with the rainfall simulation data and combined rainfall–runon data (R²: 0.43–0.91). Calibrated and validated with steady state infiltration experiments, the model was combined with the Green–Ampt infiltration equation and can be applied within a two‐dimensional distributed rainfall–runoff model. The effect of water depth–dependency and rainfall intensity on infiltration was illustrated for a hillslope. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

14.
Stemflow is an important hydrological process of rainfall partitioning, but it has rarely been studied in the alpine riparian shrub Myricaria squamosa in the Qinghai–Tibet Plateau. This study aimed to measure and model the stemflow of the unstudied M. squamosa and to identify the key controlling factors of stemflow yield. Correlations and stepwise regression analysis between stemflow and five meteorological and ten biological factors indicated that the rainfall amount and the aboveground biomass were the best variables for modelling and predicting stemflow. We used the best model to estimate annual and stand stemflow, as well as rainfall threshold for stemflow generation. Annual stemflow accounted for 2.3 to 10.2% of the annual rainfall amount, varying with different vegetation coverage and leaf area index. The annual stemflow percentage increased linearly with the annual total rainfall amount of events > 7.3 mm. For M. squamosa stands, branches with diameters of 10 to 25 mm were less frequent but contributed much more stemflow than branches with diameters smaller than 10 mm. The stemflow percentage increased sharply with increasing rainfall amounts when the rainfall amounts were less than 4, 8 or 13 mm for the M. squamosa stands with coverage of 32.6, 47.6 or 56.1%, respectively, but increased gently when the rainfall amounts were greater than these values. The rainfall threshold for stemflow generation decreased as the branch aboveground biomass increased, and the estimated median value of the rainfall threshold was 0.8 mm for M. squamosa stands, with a range of 3.0 to 0.4 mm for branches weighing 10 to 300 g, respectively. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

15.
Laboratory rainfall simulation experiments using a small artificial olive tree are used to show that the fraction of rain falling at a constant intensity that becomes stemflow rises from 9% at 2.5 mm/h to 36.1% at 35 mm/h. Natural rainfall events commonly exhibit wide fluctuations of intensity. Simulated rainfall events each having a mean intensity of 10 mm/h, but containing short intensity peaks of 20 to 100 mm/h at varying intra‐event positions, were used to explore the effect of varying intensity profiles. Results demonstrate that changes in rainfall event profile are associated with wide variation in stemflow flux, stemflow volume and stemflow fraction. When applied to an initially dry plant, rainfall events with a late intensity peak yielded an average peak stemflow flux up to 188% larger than events of contrasting profile, such as early peak events. The increase was smaller, up to 141%, when rain was applied to plants that were already partially wet, but was again found in events with a late intensity peak. Moreover, such events yielded a peak stemflow flux up to approximately seven times larger than comparable events of uniform intensity. Likewise, changing event profile with no change in rainfall depth was associated with a maximum stemflow fraction that was 31% larger than theminimum stemflow fraction, and a maximum stemflow volume that was nearly 37% larger than the minimum stemflow volume. These results suggest that rainfall event profile exerts a significant effect on all of the studied stemflow parameters. It is hypothesized that this is a consequence of the way in which intensity profile affects the rate of wetting‐up of trickle pathways on the plant, and variation in the time taken for these pathways to become fully connected. Event profile must therefore be considered along with plant architecture in seeking to understand stemflow. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

16.
To investigate the impacts of the invasion by bamboo on fluxes of nutrients and pollutants, the nutrient/pollutant fluxes and canopy interactions, including neutralization of acidity, leaching and uptake of nitrogen (N), were characterized in conjunction with rainfall partitioning in a Moso‐bamboo (Phyllostachys pubescens) forest. Measurements of precipitation volume, pH, major ions, and silicate (SiO2) in rainfall, throughfall and stemflow were collected weekly in a Moso‐bamboo forest located in Munakata City, Western Japan for 1 year. Results showed that rainfall partitioning into stemflow was larger than that for other types of forest, which may be due to the properties of Moso‐bamboo forest structure, such as a straight and smooth culm. Inorganic N (NO3− + NH4+) and S (SO42−) fluxes of throughfall and stemflow were approximately 1·6 and 1·3 times higher than that of rainfall, respectively. Contribution of stemflow flux to inorganic N and S fluxes to the forest floor was high. This could be due to lower uptake of inorganic N through culm and a higher rainfall partitioning into stemflow than that for other types of forest. The Moso‐bamboo canopy neutralized rainfall acidity, reducing the fluxes of potentially acidifying compounds via throughfall and stemflow. Canopy leaching of K+ was distinctly higher than that of Mg2+ and Ca2+ and could be related to the high mobility of K+ in plant tissues. Cl− and SiO2 were readily leached as for K+. The impact of the invasion by bamboo on nutrient cycling was discussed. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

17.
David Dunkerley 《水文研究》2014,28(22):5469-5482
This paper presents the first experimental study of how rainfall intensity and event profile affects stemflow behaviour on the rigid branches and stems of leafless, woody plants. Constant intensity rainfall simulation experiments showed that stemflow fraction rises with intensity. Varying intensity experiments showed that the stemflow fraction and stemflow flux vary with the rainfall event intensity profile and peak intensity. Stemflow fraction tends to be larger when intensity peaks occur early in the rainfall event, and variable intensity events exhibited peak stemflow fluxes >3 times those seen in constant intensity events. Moreover, experiments in which incident drop energy was reduced by a mesh screen suspended above the test plant commonly showed increases of >100% (and exceeding 300% under particular intensity profiles) in stemflow fraction, depth and peak stemflow flux. The results suggest that the development of trickle pathways along woody branches is facilitated by rain of moderate intensity and that splash dislodgement of attached water progressively reduces the adhesion of drops during intense rainfall. Thus, in plants with extensive woody branches, it is not merely rainfall intensity that determines stemflow fraction but the temporal variations in rainfall intensity. This offers a new explanation for increased stemflow production when trees are leafless, than when foliage is present, in terms of the reduced intensity peaks during rain in the dormant season. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

18.
Summary The scale-value switch (Fig. 1) makes it possible to calibrate even the older Askania tidal equipment with a galvanometer at a reduced scale-value. If resistors R 2 and R 3 are selected as shown in Eqs(4) and(5), the ratio of reduction of the scale value1/n does not depend on the internal resistance of the photo-cell in the gravimeter. The resistance of the recording galvanometer R 4 must be determined with an accuracy of±1% in order to obtained an accuracy of±0.5%. Together with the reduction in scale value also the damping is considerably decreased, which enables the time, required for calibration, to be cut down considerably.  相似文献   

19.
Understanding the isotopic composition of precipitation in a forested catchment is critical for ecohydrological studies. Changes in the water isotopes of rainfall were assessed during its passage through the canopy in throughfall, and the effect of different forest stands on the isotope composition of throughfall. In a cool temperate forest in Korea, rainfall and throughfall samples collected under Pinus densiflora (red pine), Castanea crenata (chestnut), Robinia pseudoacacia (black locust) and mixed stands (mix of these three species) were analysed for oxygen and hydrogen isotopes. Throughfall δ18O and δD were enriched compared to rainfall. A difference of δ18O and δD among throughfall may be related to the difference in interception–storage capacity of different species due to dissimilar canopy characteristics. Since isotopic composition of throughfall and rainfall are different due to canopy isotopic effects, use of rainfall isotopic signatures for ecohydrological studies in forested ecosystem can lead to biases.  相似文献   

20.
Tropical rainforest canopy trees that have large projected areas of upwardly inclined branches are capable of funnelling large volumes of rainwater down their trunks. During periods of prolonged heavy rainfall on Mount Bellenden Ker in northeast Queensland, Australia, stemflow volumes were found to be as much as two orders of magnitude greater than the volume of incident rainfall expected in a rain gauge occupying an area equal to the trunk basal area. Stemflow totals ranging from 6000 to 70000 litres were generated by individual trees from 7800 mm of rainfall over two successive wet seasons. The combination of high intensity rainfall and the funnelling effect results in significant quantities of infiltration-excess at the ground surface. Stemflow fluxes as high as 31.4 cm3 min?1 per cm2 of basal area (i.e. the equivalent of 314 mm min?1) were recorded when rainfall intensity was only 2 mm min?1. The mean infiltration capacity of the topsoil was determined to be 6.2 mm min?1. The areas over which the stemflow would have had to spread in order to infiltrate were computed to be as much as 3 m2 around the bases of individual canopy trees. Approximations of the distances that the infiltration-excess would have travelled away from the tree bases were calculated by assuming that the infiltration area either expands radially outward in the form of an annulus or extends straight downslope from the tree base.  相似文献   

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