The effect of a new zealand beech forest canopy on the kinetic energy of water drops and on surface erosion

Rain and throughfall drops were sampled during rain events in a New Zealand beech forest and the frequency distributions of drop mass and kinetic energy calculated. The kinetic energy of throughfall under the canopy was always greater than that of rainfall in the open, notwithstanding interception losses. During a typical rain event in which 51 mm fell in 36 h, the total kinetic energy of throughfail was 1.5 times greater than that of rainfall, and the mean amount of sand splashed from sample cups was 3.1 times greater under the canopy than in the open. It appears that where mineral soil is exposed at the surface, by animal trampling or burrowing for example, rates of soil detachment by splash under a forest canopy will probably exceed those in the open.     

Winter rainfall interception by two mature open‐grown trees in Davis,California

A rainfall interception measuring system was developed and tested for open‐grown trees. The system includes direct measurements of gross precipitation, throughfall and stemflow, as well as continuous collection of micrometeorological data. The data were sampled every second and collected at 30‐s time steps using pressure transducers monitoring water depth in collection containers coupled to Campbell CR10 dataloggers. The system was tested on a 9‐year‐old broadleaf deciduous tree (pear, Pyrus calleryana ‘Bradford’) and an 8‐year‐old broadleaf evergreen tree (cork oak, Quercus suber) representing trees having divergent canopy distributions of foliage and stems. Partitioning of gross precipitation into throughfall, stemflow and canopy interception is presented for these two mature open‐grown trees during the 1996–1998 rainy seasons. Interception losses accounted for about 15% of gross precipitation for the pear tree and 27% for the oak tree. The fraction of gross precipitation reaching the ground included 8% by stemflow and 77% by throughfall for the pear tree, as compared with 15% and 58%, respectively, for the oak tree. The analysis of temporal patterns in interception indicates that it was greatest at the beginning of each rainfall event. Rainfall frequency is more significant than rainfall rate and duration in determining interception losses. Both stemflow and throughfall varied with rainfall intensity and wind speed. Increasing precipitation rates and wind speed increased stemflow but reduced throughfall. Analysis of rainfall interception processes at different time‐scales indicates that canopy interception varied from 100% at the beginning of the rain event to about 3% at the maximum rain intensity for the oak tree. These values reflected the canopy surface water storage changes during the rain event. The winter domain precipitation at our study site in the Central Valley of California limited our opportunities to collect interception data during non‐winter seasons. This precipitation pattern makes the results more specific to the Mediterranean climate region. Copyright © 2000 John Wiley & Sons, Ltd.     

Interception loss from eucalypt forest: Lysimeter determination of hourly rates for long term evaluation

Analyses of the response by a weighing lysimeter in Kioloa State Forest during and after rainfall provided values of interception loss rate. The derived rates for time scales between 0.1 and 1.0mm h^?1 were generally similar throughout storm events to losses determined from throughfall and stemflow observations. During post-rainfall periods of canopy drying, enhanced rates of lysimeter evaporation were consistent with micrometeorological determinations of the partitioning of available radiant energy, based on atmospheric gradients of humidity and temperature. Interception losses from the eucalypt forest, deduced from the lysimeter response, varied between 10 and 15 per cent of gross rainfall in three consecutive 12 month periods whereas the corresponding rainfall ranged between 590 and 1530 mm yr^?1. Daytime losses accounted for about two-thirds of total interception loss with a similar fraction occurring during rain periods. Storage capacity of the evergreen forest canopy was inferred to be 0.35 mm. Hourly loss rates during rainfall ranged up to 0.8 mm h^?1 but with decreasing mean values and variability with increasing time scale resulting in a monthly mean value computed for the total number of hours of rain of approximately 0.1 mm h^?1. A preliminary analysis of loss rate in terms of storm windspeed and rainfall intensity explained about half of its variation in statistically derived relationships. Improved time resolution of the order of seconds was considered a prerequisite to the physical understanding of turbulent transport from saturated canopies. The small value of interception storage capacity was considered in relation to that for pine forest as a basis for explaining observed differences in interception behaviour between eucalypt forest and coniferous plantations in the same area. Large differences in interception losses between the Kioloa site and evergreen forest in the South Island of New Zealand and also eucalypt forest in Western Australia were attributed to dissimilar meteorological conditions at the various sites.     

Rainfall interception in three contrasting lowland rain forest types in Central Kalimantan, Indonesia

Rainfall interception was quantified and modeled for a Lowland Evergreen Rain Forest (LERF) and two Heath Forests (HF) of contrasting stature during a one-year period at a remote site in Central Kalimantan, Indonesia. Throughfall was measured using a roving gauge approach using 18–20 gauges per forest type. Throughfall was 82.8% of incident rainfall in the LERF vs. 89.1% in tall HF and 76.7% in stunted HF. Corresponding stemflow fractions were 0.8%, 1.3% and 2.0% of rainfall, respectively. Interception losses derived for the LERF (16.4%) and the tall HF (9.6%) were close to findings obtained for similar forest types elsewhere but the high interception loss for the stunted HF (21.3%) was unexpected. On the basis of canopy structural characteristics and wet canopy evaporation modeling it is concluded that throughfall in the stunted HF was underestimated and that the specific nature of the HF required a more intensive sampling arrangement. Throughfall sampling schemes in tropical forests, associated errors and hydrological implications are discussed.     

Rainfall interception by a young Acacia auriculiformis (a. cunn) plantation forest in West Java,Indonesia: Application of Gash's analytical model

Measurements are reported of rainfall, throughfall, stemflow, and derived interception losses made on a daily basis during two consecutive rainy seasons in a 4–5 year old and rapidly growing plantation forest of Acacia auriculiformis in a humid tropical environment. During the first observation period throughfall, stemflow, and interception loss amounted to respectively 81, 8, and 11 per cent of gross precipitation, whilst corresponding values for the second observation period were 75, 7, and 18 per cent. All three components correlated strongly with amounts of daily rainfall, but slopes of linear regression equations differed significantly between seasons for each component. Such differences are thought to reflect a 20 per cent increase in foliar mass as well as a certain instrumental bias introduced by the use of a fixed grid of throughfall troughs that differed between seasons. Tests did not reveal any effects of differences in rainfall characteristics although the two observation periods differed markedly in this respect. Although the present results fell within the (lower part of the) range reported for other sites in Southeast Asia application of Gash's analytical model suggested the results obtained during the second observation period to be anomalous. The model was tested with data from the second halves of the two observation periods, using parameters derived from the corresponding first halves. Discrepancies between estimated and observed losses were +9·4 and ?14·3 per cent for the two periods respectively. The bulk of the interception loss consisted of evaporation from a saturated canopy (69–80 per cent) and of evaporation after rainfall had ceased (25 and 15 per cent for the two periods respectively). Although the results were encouraging it would seem that a major difficulty in applying the analytical model to the humid tropics lies in obtaining a reliable estimate of the evaporation rate from a saturated canopy.     

Partitioning of rainfall in a eucalypt forest and pine plantation in southeastern australia: IV the relationship of interception and canopy storage capacity,the interception of these forests,and the effect on interception of thinning the pine plantation

A study of partitioning of rainfall into throughfall, stemflow, and interception was conducted in a dry sclerophyll eucalypt forest and an adjacent pine plantation over a period of seven years, on a rainfall event basis. The following three issues are discussed: (1) the relationship between canopy storage capacity and interception of continuous events, (2) interception, throughfall, and stemflow, and (3) the effect on interception of thinning the pine plantation.

• 1 The canopy storage capacity/interception interaction for the eucalypt forest was assessed by comparing a gravimetric estimate of canopy storage capacity with interception. The maximum possible value for canopy storage capacity was found to be a small proportion of interception for events of all sizes. This suggests that evaporation of intercepted water during the continuous events was responsible for most of the interception. This ‘within event’ evaporation appears to be responsible also for the net rainfall/gross rainfall estimate of canopy storage capacity being four times the gravimetric value. For the pines the regression estimate was more closely related to interception.
• 2 Interception, throughfall, and stemflow of these forests were measured for four years. Data are presented for each year with overall average interception being 11-4 per cent of precipitation for the eucalypt forest and 18-3 per cent for the pine plantation. Topography and rainfall event type are considered in the comparison.

Species composition and tree type are considered when comparing these results with published studies from similar forest types in southeastern Australia. The periodic (annual) variations of interception in this and the other studies makes comparison difficult.

• 3 The effect of thinning on the throughfall, stemflow, and interception in a Pinus radiata plantation is examined. Throughfall increased, interception decreased but not in proportion to the removed biomass; stemflow decreased on an area basis, but increased on a per tree basis. A positive relationshiip is established between interception and stemflow on the thinned plantation but not in the unthinned. Reasons for this are suggested. The results are compared to those reported from similar experiments in other forests.
• 4 The periodic variations in interception and errors inherent in its estimation suggest that caution should be exercised when using average interception figures in water balance studies.

     

Simulation of the size distribution and erosivity of raindrops and throughfall drops

This paper presents a model that simulates the size distribution and erosivity of raindrops and throughfall drops. It utilizes existing models of rainfall drop size distribution and fall velocity and combines them with newly collated evidence of throughfall drop size distributions. A sensitivity analysis reveals that the model is sensitive to parameters that are easily measured or estimated: rainfall intensity, the mean volume drop diameter of the intercepted throughfall, canopy cover, and canopy height. The results of the model may be used at two levels. Firstly, to calculate specifically the size and fall velocity of individual drops, parameters that are needed in studies examining the response of soil surfaces to forces applied by rainfall. Secondly, to produce erosivity indices, based on rainfall intensity but which take account of the effects of a vegetation canopy. The paper shows that while the kinetic energy of rainfall (E(0), J mm^?1 m^?2) may be calculated from an equation of the familiar form: the kinetic energy of throughfall under any canopy may be calculated by combining this equation with another that relates the energy of drops under a 100 per cent canopy cover (E(100)) and the canopy height: .     

Rainfall interception from a lowland tropical rainforest in Brunei

Results from a programme of throughfall measurements in a lowland tropical rainforest in Brunei, northwest Borneo, indicate that interception losses amount to 18% of the gross incident rainfall. The high annual rainfall experienced by the study area results in annual interception losses of around 800 mm, which may result in total annual evapotranspiration losses significantly higher than in other rainforest locations. An improved version of Gash's analytical interception model is tested on the available data using assumed values for the “forest” parameters, and is found to predict interception losses extremely well. The model predictions are based on an estimated evaporation rate during rainfall of 0.71 mm h⁻¹. This is significantly higher than has been reported in other tropical studies. It is concluded that these results are distinctive when compared with previous results from rainforests, and that further, detailed work is required to establish whether the enhanced evaporation rate is due to advective effects associated with the maritime setting of the study area.     

Characterization of differential throughfall drop size distributions beneath European beech and Norway spruce

Forest canopies present irregular surfaces that alter both the quantity and spatiotemporal variability of precipitation inputs. The drop size distribution (DSD) of rainfall varies with rainfall event characteristics and is altered substantially by the forest stand properties. Yet, the influence of two major European tree species, European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst), on throughfall DSD is largely unknown. In order to assess the impact of these two species with differing canopy structures on throughfall DSD, two optical disdrometers, one above and one below the canopy of each European beech and Norway spruce, measured DSD of both incident rainfall and throughfall over 2 months at a 10‐s resolution. Fractions of different throughfall categories were analysed for single‐precipitation events of different intensities. While penetrating the canopies, clear shifts in drop size and temporal distributions of incoming rainfall were observed. Beech and spruce, however, had different DSD, behaved differently in their effect on diameter volume percentiles as well as width of drop spectrum. The maximum drop sizes under beech were higher than under spruce. The mean ± standard deviation of the median volume drops size (D50) over all rain events was 2.7 ± 0.28 mm for beech and 0.80 ± 0.04 mm for spruce, respectively. In general, there was a high‐DSD variability within events indicating varying amounts of the different throughfall fractions. These findings help to better understand the effects of different tree species on rainfall partitioning processes and small‐scale variations in subcanopy rainfall inputs, thereby demonstrating the need for further research in high‐resolution spatial and temporal properties of rainfall and throughfall.     

Precipitation interception in Australian tropical rainforests: II. Altitudinal gradients of cloud interception,stemflow, throughfall and interception

This article presents a comprehensive study of canopy interception in six rainforests in Australia's Wet Tropics for periods ranging between 2 and 3·5 years. Measurements of rainfall, throughfall, stemflow and cloud interception were made at sites characterized by different forest types, canopy structure, altitude, rainfall and exposure to prevailing winds. Throughfall at these sites ranged between 64 and 83% of total precipitation inputs, while stemflow ranged between 2 and 11%. At sites higher than 1000 m, cloud interception was found to contribute up to 66% of the monthly water input to the forest, more than twice the rainfall at these times. Over the entire study period, cloud interception accounted for between 4 and 30% of total precipitation inputs, and was related more to the exposure of sites to prevailing winds than to altitudinal differences alone. Over the duration of the study period, interception losses ranged between 22 and 29% of total water input (rainfall and cloud interception) at all sites except the highest altitude site on Bellenden Ker, where interception was 6% of total water input. This smaller interception loss was the result of extremely high rainfall, prolonged immersion in cloud and a sparser canopy. On a monthly basis, interception losses from the six sites varied between 10 and 88% of rainfall. All sites had much higher interception losses during the dry season than in the wet season because of the differences in storm size and rainfall intensity. The link between rainfall conditions and interception losses has important implications for how evaporative losses from forests may respond to altered rainfall regimes under climate change and/or large‐scale atmospheric circulation variations such as El Niño. Copyright © 2007 John Wiley & Sons, Ltd.     

Intra‐storm evaporation as a component of canopy interception loss in dryland shrubs: observations from Fowlers Gap,Australia

Interception losses from the canopies of dryland plant taxa remain poorly understood, especially the relative contributions of intra‐storm and post‐storm evaporative losses. Employing a new measuring apparatus, this study uses low‐intensity simulated rain, matched to the properties of local rain, to explore interception processes in bluebush shrubs at an Australian dryland site. Five shrub specimens were exposed to simulated rain for 60–90 min. Experiments were repeated at three rainfall intensities (10, 15, and 20 mm h^?1). Canopy evaporation was found from the difference between the flux of water delivered to the shrub and the flux of throughfall, once equilibrium had been established. The results show that evaporation from the wet foliage during rain proceeds at an average rate of 3·6 mm h^?1. This figure is for relatively cool spring‐season conditions; evaporation rates in hot summer conditions would be larger. Intra‐storm evaporation is shown to exceed post‐rain evaporation from interception storage on the shrubs, and this differentiates dryland shrub interception processes from those of the better‐studied wet forest environment. Implications of the high dryland shrub canopy evaporation rates for aspects of dryland ecology are highlighted. Copyright © 2007 John Wiley & Sons, Ltd.     

How much water do Chilean forests use? A review of interception losses in forest plot studies

After several years of decreased annual rainfall and water shortages, the Chilean society is demanding that forest plantations take accountability of their role in consuming scarce water resources. Evidence has shown that interception losses are considerable when determining water production in watersheds. The aim of this study was to determine if site and stand variables explain interception losses by Chilean forests for the development of an empirical model that could predict the potential impacts of forest management practices and land‐use change. A total of 127 data from annual water balance plot studies in Chile were compiled to derive relationships between interception and precipitation, species composition, plantation age and other stand and site variables. The reviewed data indicated that annual interception losses are mainly explained by annual rainfall and basal area of the forest stands, with a clear difference between the northern (dryer) and southern (wetter) regions of Chile. For a wide latitudinal gradient, forest composition and age, annual interception accounted for approximately 21% of incoming precipitations. Broadleaved forest stands (including native broadleaved and eucalypt forests) generally presented higher interception losses than conifers. Interception was higher in northern zones, indicating that forests have greater impacts on water resources in dryer regions. Our results were compiled in empirical models, which can be used to estimate forest interception in a latitudinal gradient in Chile and to support policy making. These results are also proposed as an approximate analogue of the changes in forest interception losses, which may occur as vegetation belts shift latitudinally as a result of the impact of climate change. Copyright © 2016 John Wiley & Sons, Ltd.     

Seasonal and annual throughfall and stemflow in Andean temperate rainforests

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.     

INTERCEPTION AND RECHARGE PROCESSES BENEATH A PINUS ELLIOTII FOREST

Interception and recharge processes beneath a Pinus elliotii forest were considered in an integrated study. In the study area, annual rainfall was divided into throughfall (74.45%), stemflow (9.37%) and interception (16.28%). Throughfall and stemflow infiltrate into the soil in different ways. The results show that trees can affect the recharge characteristics by providing throughfall as a non-point source and stemflow as a point source, and also through their influence on infiltration processes by making the hydraulic conductivity of soil heterogeneous. In the root zone there was a divergent zero flux plane recharged by macropore flow during heavy rain and a convergent zero flux plane caused by transpiration during dry periods.     

Distribution of throughfall and stemflow in multi‐strata agroforestry,perennial monoculture,fallow and primary forest in central Amazonia,Brazil

The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi‐strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuaçu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open‐area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuaçu monoculture and 3·1% in the fallow. With more than 20% of the open‐area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright © 1999 John Wiley & Sons, Ltd.     

Rainfall partitioning into throughfall,stemflow, and interception within a single beech (Fagus sylvatica L.) canopy: influence of foliation,rain event characteristics,and meteorology

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 (r_a² > 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.     

Interception losses of rainfall from Cashew trees

The rainfall interception losses from Cashew trees were quantified, based on the records of 105 selected storms within the range 25.0 mm, occurring in a humid tropical region at Kottamparamba, India.

The storage capacity of the Cashew trees was worked out as 0.8 mm and the throughfall coefficient as 0.391. The trees under observation were 15–20 years of age with a leaf area index of 1.0–1.25.

About 31% of the storm rainfall for storms 25.0 mm was intercepted by the Cashew trees and lost to the atmosphere.

The measured interception losses from the trees were compared with the estimated interception losses using the analytical model of Gash (1979). The predicted interception losses from the Cashew trees were within ± 10% for storms with total rainfall 10.0 mm and within ± 22% for storms with a rainfall of 10.1–25.0 mm.     

Drop size distribution and kinetic energy load of rainstorms in Hong Kong

Data on drop size distribution and kinetic energy load of rainstorms are basic for rainfall erosivity indices. A simple and relatively inexpensive instrument was used to asses the instantaneous intensity and kinetic energy load of rainstorms in Hong Kong. Both the drop size and the instantaneous kinetic energy load of rainfall in Hong Kong are greater than in temperate and subtropical climates. The high kinetic energy results from the large size and greater number of raindrops falling per unit time. A high correlation between the kinetic energy of rainfall and the amount of rainfall allows for a convenient estimate of the energy load of storms from the amount of rainfall. Of more significance to the erosion process is the determination that about 74% of the total annual rainfall is erosive, containing about three‐quarters of the total annual energy load of the rains. The variability of rainfall parameters within a rainfall and from storm to storm is shown. The energy–intensity relationship, seasonal and annual distributions of rainfall erosivity are presented. Copyright © 2000 John Wiley & Sons, Ltd.     

Estimating winter evaporation in boreal forests with operational snow course data

Snow course measurements from 11 sites located in eastern and northern Finland were used to estimate the total interception evaporation of a winter season for different forest categories. We categorized the sites based on forest density and tree species. Results showed that interception loss from gross precipitation increased with forest density and approached 30% for a forest with the highest density class. Interception loss for the most common forest density class was 11%. Interception losses were slightly larger in spruce forests than in pine, deciduous, or mixed forests. We provide suggestions as to how to design snow surveys to estimate wintertime interception evaporation better. Rough terrain and transition zones between forest and open areas should be avoided. Since evaporation fraction was strongly dependent on tree crown characteristics, snow course data should include direct estimates of canopy closure. Qualitative observations made by different observers should be given a reference frame to ensure comparability of records from different sites. Copyright © 2003 John Wiley & Sons, Ltd.