Rainfall Interception Loss Research Articles

Global canopy rainfall interception loss derived from satellite earth observations

AbstractInformation on global canopy rainfall interception loss is essential for understanding the dynamics of land surface processes and the water cycle. In addition, large uncertainty remains regarding the global variation in this factor. The development of satellite earth observations has provided a great opportunity for the estimation of global rainfall interception loss to reveal the spatiotemporal variations. In the current study, the analytical Gash model was adapted and applied to estimate global rainfall interception loss from 2001 to 2015 on the basis of satellite remote‐sensing products, for example, gross rainfall amount and rate and leaf area index. The Dalton‐type equation was adopted to estimate the wet canopy evaporation rate in the revised Gash model. The estimation on the basis of the Dalton‐type equation showed better agreement with the ground observations than the classical Penman–Monteith equation in terms of estimated rainfall interception loss and its ratio to gross rainfall. Large spatial variations in global rainfall interception loss were found, and high values appeared in the regions with dense vegetation cover and high gross rainfall amounts, for example, tropical rainforests, whereas high rainfall interception to gross rainfall ratios occurred in the regions with low rain rates and high vegetation cover. This study constitutes a significant step forward in understanding global hydrological cycle on the basis of earth observation products.

Modeling rainfall interception loss components of forests

Interception loss, I, the amount of precipitation intercepted by forests and evaporated back to the atmosphere plays important roles in the water balance and the climate system by removing approximately one quarter of the annual precipitation from the terrestrial hydrologic cycle. Models are critical for simulating I and its components; the canopy storage, S, and the evaporation rate during the storm, Er. The energy and the water balance methods commonly yield different Er assessments. Hence, there is an urgent need for further model development, testing, and simplification in order to independently evaluate I, S, and Er. The objectives of this study were to: (i) develop an independent model to assess I, S and Er; (ii) compare the model based on its fitness to cumulative and event based measured data of I; and (iii) identify the strengths and limitations of the proposed model. By breaking the linear and power regression equations commonly fitted to the I vs. P, gross precipitation, relationship, the model analytically isolates S and Ep (L L−1) as a function of P. Field measurements of 44 I case studies collected from Mexico and classified into arid & semi-arid, A&S (N = 13), tropical montane cloud, TMC (N = 6), temperate, T (N = 4), and tropical dry, TD (N = 21), forests were used to calibrate the model. Results showed that even though the model was constructed independently of the common equations; it isolates S, Er and Ep and reproduces remarkably well the conventional empirical linear and power regression equations of I vs. P; and simulates unbiased cumulative and individual-storm I values. When coupled with the function of rainfall duration, the model projects lower Er rates than previously anticipated using other empirical approaches. Statistical analysis revealed the likely oscillation of the I vs. P relationship between the linear and power functions depending on rainfall, canopy and climate conditions. The model represents an important advancement in forest hydrology by analytically isolating S, Er, Ep and simulating compatible I values for individual as well as for assemblages of storms. It further clarifies the large variability of Er and helps to explain the role of forests in the water budget and the climate system.

The modelling of rainfall interception in growing and dormant seasons for a pine plantation and a black locust plantation in semi-arid Northwest China

Interception loss can remove a significant portion of rainwater from forested ecosystems. Therefore, the quantification and modelling of interception loss are of significant importance if human and ecosystem water demands are to be balanced under a future changing climate. This is particularly true for semi-arid/arid regions, where afforestation has become an important ecological restoration measure to tackle desertification, poverty and climate change. However, quantification and modelling of interception loss of plantations in these regions have rarely been reported. In the present study, rainfall interception loss was quantified and modelled over a one-year period (January-December 2016) for a deciduous broad-leafed R. pseudoacacia plantation and an evergreen needle-leaf P. tabuliformis plantation (common afforestation tree species) situated in the semi-arid Loess Plateau of China. The stand age, density, canopy cover and leaf area index of R. pseudoacacia during the study period were 15 years, 2000 tree ha−1, 0.48 and 1.41 m2 m−2, respectively. The corresponding values for Pinus tabuliformis were 17 years, 1200 tree ha−1, 0.62 and 2.53 m2 m−2. The measured throughfall, stemflow and derived estimates of interception loss for R. pseudoacacia were 81.1%, 1.3% and 17.6%, respectively. The corresponding values for P. tabuliformis were 75.4%, 0.7% and 23.9%. Given that the weather conditions experienced by the two forest stands were similar, the observed higher interception loss for P. tabuliformis can be explained by the higher canopy storage capacity and wet canopy evaporation rate of this species. The revised Gash analytical model of rainfall interception was well calibrated and validated against field measurements and was able to simulate the cumulative interception loss at two forest stands accurately, and it also effectively captured the seasonal variation (leafed growing and leafless dormant seasons), provided that the optimized wet-canopy evaporation rates were used. The revised model was highly sensitive to the canopy storage capacity and changes in the ratio of mean wet canopy evaporation to mean rainfall intensity and less sensitive to canopy cover, but it was found to be fairly insensitive to the trunk storage capacity.

The effect of rainfall interception loss by Palm-Oil tree towards flood discharge in Seunagan watershed of Nagan Raya district of Aceh Province

Flood discharge comes from the surface run-off affected by factors such as evaporation, evapotranspiration, infiltration and interception. This research aims to predict the magnitude of interception demonstrated by a palm-oil tree and its effects toward flood discharge. This paper covers the calculations for rainfall interception loss by a palm-oil tree, designed areal rainfall, and designed flood discharge. During the calculations, the watershed is divided into two sub-watersheds. Rainfall data were obtained from Meulaboh, Beutong and Alue-Bilie station. Areal rainfall distribution obeys the pattern of Gumbel distribution. Areal rainfall of 100 years returns period for each sub-watershed are 230.81 mm and 197.59 mm before the inclusion of interception effects, while after interception effects are included the areal rainfalls are 152.94 mm and 189.09 mm. The calculated effective rainfall using the SCS (soil conservation service) method where the curve number (CN) before interception effects are 72.19 and 73.15 while 81.54 and 73.99 after the interception is accounted. Flood discharge is calculated using the method of unit hydrograph synthetic SCS. Calculation results show that designed flood discharge of 100 years return period before and after the effects of interception were 3,042.72 m3/s and 2,521.23 m3/s, respectively. It shows that rainfall interception loss by the palm-oil tree can reduce the flood discharge.

Shrub tundra ecohydrology: rainfall interception is a major component of the water balance

As shrubs expand across the Arctic, they alter all cycles in the Earth system, including the water cycle. However, the coupling of shrubs with the water cycle during summer remains poorly understood. Rainfall interception, a major cause of divergent hydrological responses between vegetated and non-vegetated environments, is particularly poorly constrained. We quantified shrub rainfall interception and redistribution in birch and alder in the Western Canadian Arctic using networks of throughfall and stemflow gauges. We find that rainfall interception losses are a major component of the water budget, as effective rainfall was reduced by 15%–30% in the birches. Underneath alders, effective rainfall was almost as large or larger than gross rainfall, but they also left a rain shadow. The spatial variability in throughfall was substantial underneath both shrub species. Stemflow was a small but non-negligible component, as the alders concentrated ∼15% of rainfall to their few vertical stems, compared to the ∼8% the birches funnelled along their numerous, predominantly skewed stems. The substantial small-scale variability in effective rainfall may create islands in which conditions for certain biogeochemical processes are particularly favourable. On larger scales, rainfall interception reduces the water yield and thus the runoff received by downstream ecosystems such as lakes. The interception losses are predicted to increase with shrub density in a way that also depends on climatic conditions, with large losses in many coastal environments. The extent to which shrub expansion leads to drier Arctic ecosystems is, however, unclear because of the complex interplay between many ecohydrological processes. Shrub rainfall interception is one major, previously overlooked piece of this puzzle.

Typhoon-induced changes in rainfall interception loss from a tropical multi-species ‘reforest’

Typhoon Haiyan made landfall in the central Philippines on 8 November 2013 as one of the strongest tropical cyclones ever. It also affected a 23-year-old multi-species ‘reforest’ at Manobo near Tacloban City on Leyte Island. As part of a larger hydrological investigation of the impacts of reforestation on streamflow response in the Tacloban area, gross rainfall (P), throughfall (TF; 24 roving collectors) and stemflow (SF; 12 trees) were monitored at Manobo between June 2013 and May 2014. Leaf Area Index (LAI) above each TF collector was measured regularly. Total rainfall interception losses (I) were determined using Gash’s revised analytical model for three consecutive periods:(i) pre-Haiyan (baseline), (ii) post–Haiyan (damaged canopy), and (iii) after initial canopy recovery. Modeled I was 18% of P before disturbance, 12% for the period with the most extensive canopy damage, and 17.5% after initial canopy recovery. Stemflow was low, and weighted mean values accounted for 2.7%, 1.3% and 2.0% of P for the respective periods. Contrasts in period-average values of I reflected changes in LAI as well as wet-canopy evaporation rates. Storm-based TF fractions at the 5 m × 5 m sub-plot scale were inversely related to LAI, especially for small storms and low rainfall intensities. Inferred hourly rates of wet-canopy evaporation showed a strong positive relationship to hourly rainfall intensity during large storms. The revised analytical model was also run using pre-disturbance parameter values for the entire year to assess the overall effect of canopy damage on I. Estimated annual losses with and without canopy disturbance were 514 mm (15% of P) and 572 mm (17%), respectively. Thus, observed and inferred changes in rainfall partitioning after canopy disturbance and initial recovery were comparatively modest, likely because the measurement site was relatively sheltered from the winds during typhoon passage and re-foliation relatively rapid. However, given the predicted increase in occurrence of ‘super-typhoons’ due to continued global warming and oceanic freshening, the structure of forests in affected regions can be expected to be modified, with potential consequences for rainfall partitioning and hydrological response.

Towards Estimating Land Evaporation at Field Scales Using GLEAM

The evaporation of water from land into the atmosphere is a key component of the hydrological cycle. Accurate estimates of this flux are essential for proper water management and irrigation scheduling. However, continuous and qualitative information on land evaporation is currently not available at the required spatio-temporal scales for agricultural applications and regional-scale water management. Here, we apply the Global Land Evaporation Amsterdam Model (GLEAM) at 100 m spatial resolution and daily time steps to provide estimates of land evaporation over The Netherlands, Flanders, and western Germany for the period 2013–2017. By making extensive use of microwave-based geophysical observations, we are able to provide data under all weather conditions. The soil moisture estimates from GLEAM at high resolution compare well with in situ measurements of surface soil moisture, resulting in a median temporal correlation coefficient of 0.76 across 29 sites. Estimates of terrestrial evaporation are also evaluated using in situ eddy-covariance measurements from five sites, and compared to estimates from the coarse-scale GLEAM v3.2b, land evaporation from the Satellite Application Facility on Land Surface Analysis (LSA-SAF), and reference grass evaporation based on Makkink’s equation. All datasets compare similarly with in situ measurements and differences in the temporal statistics are small, with correlation coefficients against in situ data ranging from 0.65 to 0.95, depending on the site. Evaporation estimates from GLEAM-HR are typically bounded by the high values of the Makkink evaporation and the low values from LSA-SAF. While GLEAM-HR and LSA-SAF show the highest spatial detail, their geographical patterns diverge strongly due to differences in model assumptions, model parameterizations, and forcing data. The separate consideration of rainfall interception loss by tall vegetation in GLEAM-HR is a key cause of this divergence: while LSA-SAF reports maximum annual evaporation volumes in the Green Heart of The Netherlands, an area dominated by shrubs and grasses, GLEAM-HR shows its maximum in the national parks of the Veluwe and Heuvelrug, both densely-forested regions where rainfall interception loss is a dominant process. The pioneering dataset presented here is unique in that it provides observational-based estimates at high resolution under all weather conditions, and represents a viable alternative to traditional visible and infrared models to retrieve evaporation at field scales.

Effects of 2,4-dichlorophenoxyacetic acid on the biochemical parameters and oxidative stress in rats: The protective role of pomegranate (punica granatum) juice

Arid pomegranate (Punica granatum) orchards are frequently rainfed. In these systems, orchard managers might be able to manipulate a stand’s canopy structure (e.g., thinning, pruning) to improve rainfall water input to the soil. The aim of this research was to determine how changes in management activities in rainfed pomegranate orchards in arid regions of Central Iran affects rainfall partitioning into throughfall, stemflow, and rainfall interception loss. We monitored gross rainfall, throughfall, stemflow and rainfall interception loss in three stands with varying levels of thinning and pruning. Management practices sufficiently altered the stand and canopy structure of pomegranate orchards to impact the quantity and pathway (throughfall v. stemflow) of rainfall reaching the ground. Decreases in tree height, canopy cover, crown length and LAI were correlated to a significant increase in rainfall reaching the forest floor. Results indicate that orchard managers may be able to prune 40% of the live crown and thin 70% of the stand if the objective it to significantly increase water inputs into the soil. Future research should focus on the impact of canopy management on soil moisture content and soil evaporation and transpiration.

Pérdidas por intercepción de lluvia en el Matorral Espinoso Tamaulipeco bajo diferentes intensidades de raleo

La cantidad de precipitación que llega a la superficie terrestre depende en gran medida de la cobertura vegetal. Está cubierta intercepta gran parte de la precipitación y la almacena temporalmente, donde es devuelta a la atmósfera por medio de la evapotranspiración. El objetivo del presente trabajo fue cuantificar y analizar las pérdidas por intercepción de lluvia bajo diferentes intensidades de raleo en un área de Matorral Espinoso Tamaulipeco (MET) en el noreste de México. En la Facultad de Ciencias Forestales dentro del municipio Linares, Nuevo León, se establecieron cuatro parcelas para la precipitación directa bajo cuatro intensidades de raleo; 75, 50, 25 y 0 %, y una parcela para la precipitación incidente. Se registraron 79 eventos de lluvia (907.6 mm) para 2016 y 2017. Los porcentajes de intercepción de lluvia fueron de 16, 29, 34 y 41 % para las intensidades de raleo de 75, 50, 25 y 0 %, respectivamente. Los análisis de regresión lineal simple señalan que la precipitación directa representa 83, 70, 65 y 58 % del total de precipitación para las intensidades de 75, 50, 25 y 0 %, respectivamente. Los coeficientes de determinación para precipitación directa e incidente fueron de r2=0.8651 y r2=0.8017 para los raleos al 25 y 0 %; esto indica que a medida que se incrementó el raleo, aumentó la precipitación directa. Las características del dosel y el follaje de las distintas especies del MET pudieron influir en el porcentaje de intercepción de lluvia.

The influence of long-term changes in canopy structure on rainfall interception loss: a case study in Speulderbos, the Netherlands

Abstract. The evaporation of intercepted water by forests is a significant contributor to both the water and energy budget of the Earth. In many studies, a discrepancy in the water and energy budget is found: the energy that is needed for evaporation is larger than the available energy supplied by net radiation. In this study, we analyse the water and energy budget of a mature Douglas fir stand in the Netherlands, for the two growing seasons of 2015 and 2016. Based on the wet-canopy water balance equation for these two growing seasons, derived interception losses were estimated to be 37 and 39 % of gross rainfall, respectively. We further scrutinized eddy-covariance energy balance data from these two consecutive growing seasons and found the average evaporation rate during wet-canopy conditions was 0.20 mm h−1. The source of energy for this wet-canopy evaporation was net radiation (35 %), a negative sensible heat flux (45 %), and a negative energy storage change (15 %). This confirms that the energy for wet-canopy evaporation is extracted from the atmosphere as well as the biomass. Moreover, the measured interception loss at the forest was similar to that measured at the same site years before (I = 38 %), when the forest was younger (29 years old, vs. 55 years old in 2015). At that time, the forest was denser and had a higher canopy storage capacity (2.4 mm then vs. 1.90 mm in 2015), but the aerodynamic conductance was lower (0.065 m s−1 then vs. 0.105 m s−1 in 2015), and therefore past evaporation rates were lower than evaporation rates found in the present study (0.077 mm h−1 vs. 0.20 mm h−1 in 2015). Our findings emphasize the importance of quantifying downward sensible heat flux and heat release from canopy biomass in tall forest in order to improve the quantification of evaporative fluxes in wet canopies.

Regional modelling of rainfall-induced runoff using hydrological model by incorporating plant cover effects: case study in Kelantan, Malaysia

The objective of this paper is to develop a spatial temporal runoff modelling of local rainfall patterns effect on the plant cover hilly lands in Kelantan River Basin. Rainfall interception loss based on leaf area index, loss/infiltration on the ground surface, and runoff calculation were considered as the main plant cover effects on the runoff volume. In this regard, a hydrological and geotechnical grid-based regional model (integrated model) was performed using Microsoft Excel® and GIS framework system for deterministic modelling of rainfall-induced runoff by incorporating plant cover effects. The infiltration process of the current model was integrated with the precipitation distribution method and rainfall interception approach while the runoff analysis of integrated model was employed based on loss/infiltration water on the ground surface with consideration of water interception loss by canopy and the remaining surface water. In the following, the spatial temporal analysis of rainfall-induced runoff was performed using 10 days of hourly rainfall events at the end of December 2014 in Kelantan River Basin. The corresponding changes in pressure head and consequent rate of infiltration were calculated during rainfall events. Subsequently, flood volume is computed using local rainfall patterns, along with water interception loss and the remaining surface water in the study area. The results showed the land cover changes caused significant differences in hydrological response to surface water. The increase in runoff volume of the Kelantan River Basin is as a function of deforestation and urbanization, especially converting the forest area to agricultural land (i.e. rubber and mixed agriculture).

Management of pomegranate (Punica granatum) orchards alters the supply and pathway of rain water reaching soils in an arid agricultural landscape

Arid pomegranate (Punica granatum) orchards are frequently rainfed. In these systems, orchard managers might be able to manipulate a stand’s canopy structure (e.g., thinning, pruning) to improve rainfall water input to the soil. The aim of this research was to determine how changes in management activities in rainfed pomegranate orchards in arid regions of Central Iran affects rainfall partitioning into throughfall, stemflow, and rainfall interception loss. We monitored gross rainfall, throughfall, stemflow and rainfall interception loss in three stands with varying levels of thinning and pruning. Management practices sufficiently altered the stand and canopy structure of pomegranate orchards to impact the quantity and pathway (throughfall v. stemflow) of rainfall reaching the ground. Decreases in tree height, canopy cover, crown length and LAI were correlated to a significant increase in rainfall reaching the forest floor. Results indicate that orchard managers may be able to prune 40% of the live crown and thin 70% of the stand if the objective it to significantly increase water inputs into the soil. Future research should focus on the impact of canopy management on soil moisture content and soil evaporation and transpiration.

Rainfall Interception by Singleleaf Piñon and Utah Juniper: Implications for Stand-Level Effective Precipitation

The expansion of piñon and juniper trees into sagebrush steppe and the infilling of historic woodlands has caused a reduction in the cover and density of the understory vegetation. Water is the limiting factor in these systems; therefore, quantifying redistribution of water resources by tree species is critical to understanding the dynamics of these formerly sagebrush-dominated rangelands. Tree canopy interception may have a significant role in reducing the amount of rainfall that reaches the ground beneath the tree, thereby reducing the amount of available soil moisture. We measured canopy interception of rainfall by singleleaf piñon (Pinus monophylla Torr. & Frém.) and Utah juniper (Juniperus osteosperma [Torr.] Little) across a gradient of storm sizes. Simulated rainfall was used to quantify interception and effective precipitation during 130 rainfall events ranging in size from 2.2 to 25.9 mm hr−1 on 19 trees of each species. Effective precipitation was defined as the sum of throughfall and stemflow beneath tree canopies. Canopy interception averaged 44.6% (± 27.0%) with no significant difference between the two species. Tree allometrics including height, diameter at breast height, stump diameter, canopy area, live crown height, and width were measured and used as predictor variables. The best fit predictive model of effective precipitation under canopy was described by stump diameter and gross precipitation (R2 = 0.744, P < 0.0001). An alternative management model based on canopy area and gross precipitation predicted effective precipitation with similar accuracy (R2 = 0.741, P < 0.0001). Canopy area can be derived from various remote sensing techniques, allowing these results to be extrapolated to larger spatial scales to quantify the effect of increasing tree canopy cover on rainfall interception loss and potential implications for the water budget.

Influence of meteorological variables on rainfall partitioning for deciduous and coniferous tree species in urban area

Rainfall partitioning is an important part of the ecohydrological cycle, influenced by numerous variables. Rainfall partitioning for pine (Pinus nigra Arnold) and birch (Betula pendula Roth.) trees was measured from January 2014 to June 2017 in an urban area of Ljubljana, Slovenia. 180 events from more than three years of observations were analyzed, focusing on 13 meteorological variables, including the number of raindrops, their diameter, and velocity. Regression tree and boosted regression tree analyses were performed to evaluate the influence of the variables on rainfall interception loss, throughfall, and stemflow in different phenoseasons. The amount of rainfall was recognized as the most influential variable, followed by rainfall intensity and the number of raindrops. Higher rainfall amount, intensity, and the number of drops decreased percentage of rainfall interception loss. Rainfall amount and intensity were the most influential on interception loss by birch and pine trees during the leafed and leafless periods, respectively. Lower wind speed was found to increase throughfall, whereas wind direction had no significant influence. Consideration of drop size spectrum properties proved to be important, since the number of drops, drop diameter, and median volume diameter were often recognized as important influential variables.

Modelling Wetland Growing Season Rainfall Interception Losses Based on Maximum Canopy Storage Measurements

This study estimates rainfall interception losses from natural wetland ecosystems based on maximum canopy storage measurements. Rainfall interception losses play an important role in water balance, which is crucial in wetlands, and has not yet been thoroughly studied in relation to this type of ecosystem. Maximum canopy storage was measured using the weight method. Based on these measurements, daily values of interception losses were estimated and then used to calculate long-term interception losses based on precipitation and potential evapotranspiration data for the 1971–2015 period. Depending mainly on the number of days with precipitation, the results show that total interception losses for the growing season as well as monthly interception losses are around 13% of gross rainfall. This value is similar to the values observed for some forests. Hence, interception losses should not be disregarded in hydrologic models of wetlands, especially because data trends in meteorological conditions (mainly number of days with precipitation) show that interception losses will increase in the future if those trends stay the same.

Remote sensing upscaling of interception loss from isolated oaks: Sardon catchment case study, Spain

Tree interception loss from two Mediterranean oak species, Quercus ilex (Q.i.) and Quercus pyrenaica (Q.p.), was estimated during 2-year period (1 October 2011 to 30 September 2013) in sparsely vegetated Sardon catchment (∼80km2, Spain) by: i) rainfall, throughfall and stemflow measurements; ii) Gash model temporal extrapolation; and iii) remote-sensing spatial upscaling. The annual, measured tree interception losses (Im) of Q.i. and Q.p. in the first year were 51% and 16% of P (335mm) and in the second, 46% and 10% of P (672mm), respectively. The revised Gash analytical model of rainfall interception loss, extrapolated well the Im temporal variability of Q.i. and Q.p., provided the throughfall-based, and not Pennman-Monteith-based, average wet canopy evaporation rates were used. Finally, a novel method of spatial upscaling of a tree-based interception loss into plot- and catchment-scale, using per-species, reference tree interception loss and object-attributes derived from satellite imagery, was proposed. The interception losses from Q.i. and Q.p. were upscaled first into two homogeneous plots (1-ha each and both with ∼20% canopy cover), one with Q.i. and the other with Q.p. oaks and then into the entire Sardon catchment with ∼7% canopy cover. The obtained annual-mean, plot interception losses were 9.5% of P in evergreen Q.i. and 2.5% of P in deciduous Q.p. plot. The annual-mean catchment interception loss was 1.4% of P. The proposed upscaling method is expected to improve catchment water balances, replacing common arbitrary or literature based tree interception loss estimates.

The influence of sugarcane crop development on rainfall interception losses

The expansion of sugarcane plantations in Brazil has raised concerns regarding its hydrological impacts. One of these impacts is related to rainfall interception, which can be expected to vary in response to substantial changes in canopy structure throughout the cropping cycle. We collected field measurements to determine interception losses and interpreted the observations using an adapted Gash model during different stages of a sugarcane ratoon cropping cycle. Cumulative gross rainfall (PG), throughfall (TF) and stemflow (SF) were measured biweekly, along with vegetation structure measurements of leaf area index (LAI) and plant height. For the first 300days after the first harvest, the cumulative PG of 1095mm was partitioned into 635mm TF (58%) and 263mm SF (24%). The inferred interception loss (IL) was 263mm (24%). There was a gradual and clear increase in IL from 3% to 46% while partitioning between TF and SF also changed during ratoon regrowth. After model parameter optimisation, observed IL was simulated satisfactorily. Model estimates suggested that evaporation from the saturated canopy is the main IL pathway, followed by evaporation after storms. Plant architecture, LAI and meteorological conditions during the cropping cycle appeared the main factors determining IL.

Modeling rainfall interception loss by two xerophytic shrubs in the Loess Plateau

AbstractRainfall 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.

Quantifying Rainfall Interception Loss of a Subtropical Broadleaved Forest in Central Taiwan

The factors controlling seasonal rainfall interception loss are investigated by using a double-mass curve analysis, based on direct measurements of high-temporal resolution gross rainfall, throughfall and stemflow from 43 rainfall events that occurred in central Taiwan from April 2008 to April 2009. The canopy water storage capacity for the wet season was estimated to be 1.86 mm, about twice that for the dry season (0.91 mm), likely due to the large reduction in the leaf area index (LAI) from 4.63 to 2.23 (m2·m−2). Changes in seasonal canopy structure and micro-meteorological conditions resulted in temporal variations in the amount of interception components, and rainfall partitioning into stemflow and throughfall. Wet canopy evaporation after rainfall contributed 41.8% of the wet season interception loss, but only 17.1% of the dry season interception loss. Wet canopy evaporation during rainfall accounted for 82.9% of the dry season interception loss, but only 58.2% of the wet season interception loss. Throughfall accounted for over 79.7% of the dry season precipitation and 76.1% of the wet season precipitation, possibly due to the change in gap fraction from 64.2% in the dry season to 50.0% in the wet season. The reduced canopy cover in the dry season also produced less stemflow than that of the wet season. The rainfall stemflow ratio ( P s f / P g ) was reduced from 12.6% to 8.9%. Despite relatively large changes in canopy structure, seasonal variation of the ratio of rainfall partitioned to interception was quite small. Rainfall interception loss accounted for nearly 12% of gross precipitation for both dry and wet seasons.

Canopy Interception for a Tallgrass Prairie under Juniper Encroachment

Rainfall partitioning and redistribution by canopies are important ecohydrological processes underlying ecosystem dynamics. We quantified and contrasted spatial and temporal variations of rainfall redistribution for a juniper (Juniperus virginiana, redcedar) woodland and a tallgrass prairie in the south-central Great Plains, USA. Our results showed that redcedar trees had high canopy storage capacity (S) ranging from 2.14 mm for open stands to 3.44 mm for closed stands. The canopy funneling ratios (F) of redcedar trees varied substantially among stand type and tree size. The open stands and smaller trees usually had higher F values and were more efficient in partitioning rainfall into stemflow. Larger trees were more effective in partitioning rainfall into throughfall and no significant changes in the total interception ratios among canopy types and tree size were found. The S values were highly variable for tallgrass prairie, ranging from 0.27 mm at early growing season to 3.86 mm at senescence. As a result, the rainfall interception by tallgrass prairie was characterized by high temporal instability. On an annual basis, our results showed no significant difference in total rainfall loss to canopy interception between redcedar trees and tallgrass prairie. Increasing structural complexity associated with redcedar encroachment into tallgrass prairie changes the rainfall redistribution and partitioning pattern at both the temporal and spatial scales, but does not change the overall canopy interception ratios compared with unburned and ungrazed tallgrass prairie. Our findings support the idea of convergence in interception ratio for different canopy structures under the same precipitation regime. The temporal change in rainfall interception loss from redcedar encroachment is important to understand how juniper encroachment will interact with changing rainfall regime and potentially alter regional streamflow under climate change.