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.     

Raindrop impact and water flow on the vegetative surfaces of trees and the effects on stemflow and throughfall generation

The physical processes of raindrop impact and water flow on the leaves and branches of selected tropical tree species were examined under laboratory conditions using simulated rainfall. Inclined branches were found to be particularly efficient in detaining impacting water droplets. This efficiency in raindrop detention increases linearly as a function of branch inclination on branches that are initially dry. On branches that have been thoroughly wetted, this increase in raindrop detention with branch inclination is best expressed as a logarithmic function. At branch inclinations of 60° above the horizontal, the quantity of branchflow was found to be > 80 per cent of the total quantity of impacting rainfall, indicating that < 20 per cent was lost to rainsplash. The strong positive relationship between branchflow and branch inclination explains why trees with large projected areas of steeply inclined upthrust branches have significant quantities of intercepted water draining from their branches and trunks under heavy rainfall conditions. This drainage from the woody frame of trees influences surficial processes by generating both stemflow and large throughfall droplets.     

Spatial variability of throughfall and stemflow in an exotic pine plantation of subtropical coastal Australia

Large‐scale exotic pine plantations have been developed for timber production in subtropical Australia. Few studies investigate the spatial variability of both throughfall and stemflow in such managed pine plantations despite their acknowledged effects on the heterogeneity of hydrological and biochemical processes of forested ecosystems. To examine the spatial variability of rainfall under a 12‐year‐old pine plantation in a subtropical coastal area of Australia, we observed gross rainfall, throughfall and stemflow over a 1‐year period. Our results show that the spatial variability of gross rainfall within a 50 m × 50 m plot is minimal. Throughfall is significantly different among three tree zones (midway between rows, west and east side of trunks), particularly for rainfall <50 mm, with the highest throughfall on the east side of the tree trunks (sum = 85% of gross rainfall) and the lowest in the midway between tree rows (sum = 68% of gross rainfall). These spatial patterns persist among 84% of recorded rainfall events. Spatial variability and time stability of throughfall are better explained by canopy interception of the inclined rainfall resulting from the prevailing easterly wind direction throughout the experiment. The annual stemflow is different among individual sample trees, which is mainly ascribed to the difference in tree size (e.g. projected canopy area and stem diameter). The outcomes of this study would help future investigators better design appropriate sampling strategies in these pine plantations under similar climate conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Precipitation interception in Australian tropical rainforests: I. Measurement of stemflow,throughfall and cloud interception

Methods for measuring throughfall, stemflow and, hence, interception in the tropical rainforests of the Wet Tropics region of North Queensland, Australia, were tested at three sites for between 581 and 787 days. The throughfall system design was based on long troughs mounted beneath the canopy and worked successfully under a range of rainfall conditions. Comparison of replicated systems demonstrated that the methodology is capable of capturing the variability in throughfall exhibited beneath our tropical rainforest canopies. Similarly, the stemflow system design which used spiral collars attached to sample trees worked well under a range of rainfall conditions and also produced similar estimates of stemflow in replicated systems. Higher altitude rainforests (>1000 m) in North Queensland can receive significant extra inputs of water as the canopy intercepts passing cloud droplets. This additional source of water is referred to as ‘cloud interception’ and an instrument for detecting this is described. The results obtained from this gauge are compared with cloud interception estimates made using a canopy water balance method. This method is based on stemflow and throughfall measurements and provides an alternative means to fog or cloud interception gauge calibration techniques used in the literature. Copyright © 2007 John Wiley & Sons, Ltd.     

Hydrochemical characteristics of throughfall and stemflow in a Moso‐bamboo (Phyllostachys pubescens) forest

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.     

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.     

Spatial variations in throughfall in a Moso bamboo forest: sampling design for the estimates of stand‐scale throughfall

We investigated the spatial and seasonal variations in throughfall (Tf) in relation to spatial and seasonal variations in canopy structure and gross rainfall (Rf) and assessed the impacts of the variations in Tf on stand‐scale Tf estimates. We observed the canopy structure expressed as the leaf area index (LAI) once a month and Tf once a week in 25 grids placed in a Moso bamboo (Phyllostachys pubescens) forest for 1 year. The mean LAI and spatial variation in LAI did have some seasonal variations. The spatial variations in Tf reduced with increasing Rf, and the relationship between the spatial variation and the Rf held throughout the year. These results indicate that the seasonal change in LAI had little impact on spatial variations in Tf, and that Rf is a critical factor determining the spatial variations in Tf at the study site. We evaluated potential errors in stand‐scale Tf estimates on the basis of measured Tf data using Monte Carlo sampling. The results showed that the error decreases greatly with increasing sample size when the sample size was less than ～8, whereas it was near stable when the sample size was 8 or more, regardless of Rf. A sample size of eight results in less than 10% error for Tf estimates based on Student's t‐value analysis and would be satisfactory for interception loss estimates when considering errors included in Rf data. Copyright © 2009 John Wiley & Sons, Ltd.     

Chemistry of rainfall,throughfall and stemflow in a eucalypt forest and a pine plantation in south-eastern Australia: 1. Rainfall

Rainfall samples were collected from several hundred rainfall events. Up to nine samples per event were collected from sites 3–500 m apart. They differed substantially in both concentration and composition, even though great care was taken to wash all collectors beforehand. Dryfall, storage and analytical procedures could not explain the variation. When data for rainfall events of similar size (but very different cation inputs) were examined, the major differences were associated with the prevailing wind direction. Events leading to high concentrations were associated with easterly winds and showed the influence of a marine source. Chemical concentration and composition were not altered by the occurrence of a drought year followed by a very wet year. The mean pH was 5·3 and ranged from 4·6 to 5·8. For a given event, a difference of 0·5 often occurred between collection sites. Regular seasonal variations in the concentration of NO₃-N and the NO₃/NH₄ ratio occurred, with the ratio being higher in summer due primarily to bush fires. Organic nitrogen comprised 14% of total nitrogen.     

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.     

Isotopic variations in precipitation at Bangkok and their climatological significance

The stable isotopic composition of precipitation from low to mid latitudes contains information about changes of some climatic factors, such as temperature, precipitation and atmospheric circulation patterns. However, the isotopic variations in the area are very complicated because of the combined influences of these factors. Proper interpretation of the patterns of isotopic variations for palaeoclimate reconstructions in this area requires a detailed understanding of these complex stable isotope controls. The isotopic data (δ¹⁸O and δ²D) in precipitation at the International Atomic Energy Agency–World Meteorological Organization Bangkok station were collected and analysed because of the relatively long and unbroken isotopic records and the particular geographical location. The isotopic variations at Bangkok have strong seasonal patterns owing to distinct source regions in different seasons. In summer, the remote sources of water there can influence the δ¹⁸O values significantly, which is verified by the simple Rayleigh model. In winter, the mixing of isotopically distinct air masses with different origins, i.e. the continental and oceanic air masses, accounts for the isotopic variations. In the transition periods of the Asia–Australia monsoon, namely in May and October, the local vapour contribution may play a role in the isotopic ratios. On the interannual time‐scale, the influences of El Niño–southern oscillation (ENSO) and the Indian Ocean dipole (IOD) on isotopic composition are examined. The indications are that both the ENSO and IOD indices have a significant correlation with the δ¹⁸O ratios, and that the δ¹⁸O ratio in summer rains is significantly more enriched (depleted) during the warm (cold) phase of ENSO/IOD events. All the results suggest that it is useful for us in understanding the water cycling process and may be helpful in palaeoclimate reconstruction in this monsoon region. Copyright © 2006 John Wiley & Sons, Ltd.     

Investigating young water fractions in a small Mediterranean mountain catchment: Both precipitation forcing and sampling frequency matter

The proportion of water younger than 2–3 months (young water fraction, F_yw) has become increasingly investigated in catchment hydrology. F_yw is typically estimated by comparing seasonal tracer cycles in precipitation and streamflow, through water sampling. However, some open research questions remain, such as: (i) whether part of the summer precipitation should be discarded because the high evapotranspiration demand, (ii) how well F_yw serves as a metric to compare catchments, and (iii) how sampling frequency affects F_yw estimates. To address these questions, we investigated F_yw in soil-, ground- and stream waters for the small Mediterranean Can Vila catchment. Rainfall was sampled at 5-mm intervals. Mobile soil water and groundwater were sampled fortnightly. Stream water was sampled depending on flow at variable time intervals (30 min to 1 week). Over 58 months, this sampling provided 1,529 δ¹⁸O determinations. Isotopic analyses results led us to include summer precipitation in the input signal. We found the highest F_yw in mobile soil waters (34%), while this was almost zero for groundwater except during wet periods. For stream waters, F_yw depended on the discharge variations, so that the flow-weighted young water fraction () was 22.6%, whereas the time-weighted F_yw was just 6.2%. Both and its discharge sensitivity (S_d) varied when different 12-month sampling periods were investigated. The young water fraction that would be obtained from a virtual thorough sampling () was estimated from the S_d and the observed stream flow. This showed an underestimation of by 25% for the frequent dynamic sampling and 66% for weekly sampling, due to missing high flows. Our results confirm that F_yw and its discharge sensitivity are metrics very sensitive to meteorological forcing during the analysed period. Thus, comparisons between catchments need long-term mean annual values and their variability. Our findings also support the dependence of F_yw estimates on the sampling rate and show the advantages of flow-weighted analysis. Finally, catchment water turnover investigations should be accompanied by the analysis of flow duration curves.     

Effect of urbanization on the winter precipitation distribution in Beijing area

According to the urbanization extent of Beijing area, and with 1980 as a turning point, the duration from 1961 to 2000 is divided into two periods: one is defined as the slow urbanization period from 1961 to 1980, and other one as the fast urbanization period from 1981 to 2000. Based on the 40-year’s precipi-tation data of 14 standard weather stations in Beijing area, the effect of urbanization on precipitation distribution is studied. It is found that there has been a noticeable and systematic change of wi...     

Understory and small trees contribute importantly to stemflow of a lower montane cloud forest

Stemflow (Sf) measurements in tropical rain and montane forests dominated by large trees rarely include the understory and small trees. In this study, contributions of lower (1‐ to 2‐m height) and upper (>2‐m height and <5‐cm diameter at breast height [DBH]) woody understory, small trees (5 < DBH < 10 cm), and canopy trees (>10‐cm DBH) to Sf per unit ground area (Sf_a) of a Mexican lower montane cloud forest were quantified for 32 days with rainfall (P) during the 2014 wet season. Rainfall, stemflow yield (Sf_y), vegetation height, density, and basal area were measured. Subsequently, stemflow funneling ratios (SFRs) were calculated, and three common methods to scale up Sf_y from individual trees to the stand level (tree‐Sf_y correlation, P‐Sf_y correlation, and mean‐Sf_y extrapolation) were used to calculate Sf_a. Understory woody plants, small trees, and upper canopy trees represented 96%, 2%, and 2%, respectively, of the total density. Upper canopy trees had the lowest SFRs (1.6 ± 0.5 Standard Error (SE) on average), although the lower understory had the highest (36.1 ± 6.4). Small trees and upper understory presented similar SFRs (22.9 ± 5.4 and 20.2 ± 3.9, respectively). Different Sf scaling methods generally yielded similar results. Overall Sf_a during the study period was 22.7 mm (4.5% of rainfall), to which the understory contributed 70.1% (15.9 mm), small trees 10.6% (2.4 mm), and upper canopy trees 19.3% (4.4 mm). Our results strongly suggest that for humid tropical forests with dense understory of woody plants and small trees, Sf of these groups should be measured to avoid an underestimation of overall Sf at the stand level.     

Isotopic temporal and spatial variations of tropical rivers in Thailand reflect monsoon precipitation signals

Stable isotopic compositions (δ¹⁸O and d-excess) from 25 rivers in Thailand were analysed monthly during 2013–2015. Results indicated that monsoon precipitation fundamentally influences the river isotopes. The overland flow supplied from monsoon precipitation and human-altered flow regimes produces considerable isotopic variability. Spatial and temporal variations were observed among four principal geographical regions. The seasonality of monsoon precipitation in mountainous Thailand produced large variations in isotopic compositions because most rainfall occurred during the southwest monsoon, and dry conditions prevailed during the northeast monsoon. The northern and northeastern regions are mountainous, highland areas. Low δ¹⁸O values were found in these regions, likely because of altitude effects on precipitation. Conversely, monsoonal precipitation continually supplies rivers in southern Thailand all year round, producing higher and more consistent δ¹⁸O values than in the other regions. The Chao Phraya plain in the central region experienced enrichment of δ¹⁸O river runoff related to evaporation in irrigation systems. Larger catchment areas and longer residence times resulted in more pronounced evaporation effects, producing lower values of d-excess and local river water line slopes compared with precipitation. The isotopic differences between river waters and precipitation were utilized to determine river recharge elevations and water transit time. The methods presented here can be used to explore hydrological interactions in other tropical river basins.     

Isotopic characteristics of precipitation in Slovenia and Croatia: Comparison of continental and maritime stations

The stable isotopic composition of hydrogen and oxygen (δ²H and δ¹⁸O) and tritium activity (³H) were monitored in monthly precipitation at two continental stations (Ljubljana, Zagreb) and six stations along the eastern Adriatic coasts of Slovenia and Croatia in the period 2001–2003. Mean air temperatures and amount of precipitation were also recorded.

Distinct differences in both meteorological and isotopic data between the continental and maritime stations were observed. Seasonal variations in δ¹⁸O are smaller at the maritime stations than at the continental ones due to smaller seasonal temperature variations. A good correlation between δ¹⁸O and δ²H was obtained for each station, and the local meteoric water lines are close to the Global Meteoric Water Line, with a decreasing trend of slope for the south-Adriatic stations. Good correlations between δ¹⁸O in monthly precipitation and mean monthly air temperature were observed at all stations. The slope of δ¹⁸O vs. T varied between 0.37‰ °C⁻¹ and 0.15‰ °C⁻¹. Mean ³H activity and seasonal variation of ³H activity are smaller at maritime stations than at continental ones. Additionally, ³H activity decreases in the NW–SE direction of the Adriatic coast.

The study of spatial variations over this relatively small area rich in geographical and climatic diversities showed the complexity of the isotopic composition of precipitation and the isotopic data obtained for eight stations, most of them in the karstic area along the Adriatic coast, and gave valuable information for regional hydrological investigations and modelling of isotope variability over the Mediterranean basin.     

Effects of rainfall on the spatial distribution of the throughfall kinetic energy on a small scale in a rubber plantation

This study evaluated the spatial distribution of the throughfall kinetic energy (TKE) on a small scale in a rubber plantation. The experiments used Tübingen splash cups with natural rainfall. The results indicate that the leaf area index did not significantly affect the TKE during the foliated season. There was no significant correlation between the TKE and the distance from the trunk. However, the lateral translocation of the throughfall in the canopy significantly affected the spatial distribution of the TKE, and high TKE points appeared in the middle and at the edge of the canopy. The results also show that the spatial distribution of the volume-specific TKE values was similar in different rainfall and rainfall intensity groups. The variogram of the spatial variability demonstrates that the TKE exhibited a strong spatial autocorrelation. We confirm that the rainfall redistribution is important for the spatial distribution of the TKE in a rubber plantation.     

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.     

The effect of uncertainties in precipitation global datasets on the estimates of terrestrial water balance components

The results of simulation of terrestrial water balance components are analyzed. The simulation involved six alternative datasets on precipitation and four land surface models SWAP, NSIP, NOAH, and SSiB. The calculations have been carried out for the entire land surface (except for the Antarctic Continent) with one-degree step in the space grid and three-hour time step over 1982–1995. The extent of the influence of uncertainties in the specification of precipitation and the choice of the model on simulated water balance characteristics is revealed.     

Measured effects of new lake surfaces on regional precipitation

Abstract

Although often modelled, empirical evidence for regional water balance shifts, due to local land-use changes, is rare. The same holds for the quantification of such effects by measurement. The flooding of former open-cast mining areas in Lusatia, eastern Germany, delivers a unique opportunity to address this topic in a well-gauged region. During two decades, flooding changed about 60 km² of lignite pits to lake surfaces. To quantify possible shifts in the regional precipitation pattern, the background of general precipitation dynamics within the research area was separated from all raingauge records using principal component analysis (PCA). Linear models with the dominating PCA component as independent variable were fitted to the single station records. The residuals of these fits represent the local deviations from the general dynamics, and they contain the signals of climate alterations within the region. The analysis of these residuals revealed a shifting precipitation pattern with significant increases (up to 10% of the former mean annual precipitation, which is approximately 650 mm) on the lee side of the developing lake area. Further analysis showed that most of the observed changes are due to more frequent and intense convective storms. Water balance estimations indicate that the additional evaporation approximately equals the precipitation increase.