Hydrological Behaviour Research Articles

Analysis of heat transfer and water flow with phase change in saturated porous media by bond-based peridynamics

A wide range of natural and industrial processes involve heat and mass transport in porous media. In some important cases the transported substance may undergo phase change, e.g. from liquid to solid and vice versa in the case of freezing and thawing of soils. The predictive modelling of such phenomena faces physical (multiple physical processes taking place) and mathematical (evolving interface with step change of properties) challenges. In this work, we develop and test a non-local approach based on bond-based peridynamics which addresses the challenges successfully. Our formulation allows for predicting the location of the interface between phases, and for calculating the temperature and pressure distributions within the saturated porous medium under the conditions of pressure driven water flow. The formulation is verified against existing analytical solutions for 1D problems, as well as finite element transient solutions for 2D problems. The agreement found by the verification exercise demonstrates the accuracy of the proposed methodology. The detailed coupled description of heat and hydraulic processes can be considered as a critical step towards a thermo-hydro-mechanical model, which will allow, for example, description of the hydrological behaviour of permafrost soils and the frost heave phenomenon.

Parameter Design for Group Method Data Handling (GMDH) using Taguchi in Software Effort Estimation

Recently, the use of data-driven models is becoming increasingly impactful but has proven to offer best prediction with less knowledge of the geological, hydrological, and physical process behaviour and criteria. A Group Data Handling Model (GMDH) is one of the sub-model common neural network data driven. It was first developed for complex systems with a modelling and recognition algorithm. GMDH is known as a self-organizing heuristic modelling approach. For solving modelling issues involving multiple inputs to single output data, it is very successful. While the GMDH model has been implemented in many modelling fields, some modifications in terms of parameter design have been given little attention. In other respects, Dr. Genichi Taguchi suggested that the Taguchi method for improving the process or product design with the help of significant parameter levels that influence the delivery of the product. In this paper, we evaluated the behaviour of GMDH model based on numbers of neuron per layer, hidden layer, alpha, and train ratio parameters using Taguchi method. Cocomo and Kemerer datasets are used to test our hypothesized scenarios. The result shows that number of neurons, layer and train ratio are the important parameters that affects the performance of the GMDH model.

Big Data and sustainable functioning of geotechnical systems

The authors use the theory of Big Data to discuss the stages of induced transformation in the Earth’s interior. The amount of data on the mining sector exponentially grows with its digital transformation. Mining sciences call for efficient processing and integration of data acquired from numerous digital systems. Such data reach the amount of hundreds terabytes annually at a scale of a single company. This article gives grounds for the fact that the mining sector data belong to Big Data. The current world’s mining industry uses a few hundreds of different digital technologies. The amount of incoming data is colossal as a consequence. At the same time, digital technologies are unequally distributed among the mining companies. Based on the data-flow analysis, the problem on systematization of sources and amounts of information on a geotechnical system is formulated and solved. The systematization allows demonstrating the scale of the information received and used, and discloses the principle of the data processing and storage. The trends of research in the sphere of Big Data towards sustainable functioning of geotechnical systems in correlation with the environment and society. Creation of the efficient processing methods for Big Data of a geotechnical systems can help reveal more general nature-and-technology interactions in the future. This can help studying transformation of the structure and properties of the Earth’s interior under the manmade impact. Later on, Big Data can become a tool for the analyses of hydrological behavior and gas dynamics, environment, social aspects of subsoil use, etc.The study was carried out under state contracts between the Geophysical Center, IPKON RAS and the Ministry of Science and Higher Education of Russia. The authors appreciate participation of Associate Professor, Candidate of Engineering Sciences D. N. Radchenko and Head of Laboratory, Candidate of Engineering Sciences D. A. Klebanov from the Academician Melnikov Research Institute of Comprehensive Exploitation of Mineral Resources – IPKON RAS in this study.

Assessing the potential value of the regionalised input constraint indices for constraining hydrological model simulations in the Congo River Basin

The regionalised characteristics of a sub-basin's long-term hydrological behaviour are used as multiple constraint filters for constraining hydrological model simulations in the Congo Basin using the monthly time step Pitman model. The results suggest that the constraints are appropriate in many sub-basins (≥ 20 gauging stations), but not all. Detailed examination of these results suggested that the effects of high slopes (> 7%) could increase the runoff ratio and Q90/MMQ (low flow index) constraint values and that implementing an adjustment factor based on slope did improve some of the very poor results. The percentage points on the FDC falling within the simulated uncertainty band has increased from 0% to 59.6% and 2.4% to 39.9% for the Rift valley and Batéké plateaux regions, respectively. Future studies ideally need a range of different rainfall products to quantify the uncertainties related to the inappropriateness of the CRU rainfall data in some parts of the Congo Basin.

Daily flow duration curve model for ungauged intermittent subbasins of gauged rivers

In this study, we develop a daily flow duration curve model for ungauged intermittent subbasins of gauged rivers. The long-term mean streamflow of the river basin, one of the central parts in the model, is calculated with a regression model of annual precipitation and physical characteristics of the river basin; e.g., drainage area, basin relief, topographical slope, drainage density. The input data of the model are normally accesible, and this makes the model applicable to ungauged points within the river basin. Another central part of the model is the cease-to-flow point which makes the model significant for intermittent rivers. The daily streamflow discharge recorded in gauging stations over the river basin is nondimensionalized by dividing each with their own long-term mean, and their collection is transformed to fit the normal probability distribution; i.e., the normalized nondimensional daily streamflow data are used in the model. The streamflow data are inverted back to the original distribution for any given exceedance percentage by incorporating the cease-to-flow point, and are dimensionalized finally by using the empirically-derived long-term mean streamflow discharge. The model is applied on hundreds of thousands station-day daily streamflow data from three river basins in different geographical regions in Turkey. Results of the case studies are found promising to propose the model as a good foundation for the daily flow duration curve at an ungauged intermittent subbasin of gauged rivers: However, it is noticeable that the model might have low performance in some particular gauging stations where the hydrological behavior deviates from the general characteristics of the river basin. This can be overcome by developing empirical models better approaching the observed long-term mean streamflow, which is a key issue of the model.

Event-based analysis of wetland hydrologic response in the Prairie Pothole Region

Previous studies in the Prairie Pothole Region mainly assessed wetland hydrologic function at seasonal, annual and decadal scales. While many studies have looked at water balance dynamics and local flow generation processes in wetlands, no study looked at hydrological dynamics in response to individual rainfall events in prairie pothole wetlands (here after referred as wetlands) across a gradient of alteration. The present study aimed to investigate: (1) the most important metrics needed to characterize the spatial variability of wetland hydrologic response to rainfall-runoff events; (2)the temporal variability of individual wetland hydrologic response; (3) the spatial and temporal variability of wetland-stream interaction; and (4) the temporal persistence of various spatial controls on individual wetland hydrologic response characteristics. High-frequency water level data was collected over two years for ten intact, three consolidated, and seven drainage ditches associated with fully drained wetland(s), as well as a creek located in southwestern Manitoba, Canada. The hydrologic response of the studied wetlands to individual rainfall-runoff events was characterized using a range of metrics. Several data analysis methods were used, including principal component analysis, graphical assessments of wetland-stream hysteresis dynamics, and correlations analyses between wetland response metrics and spatial characteristics. Results suggested that wetland alteration status (i.e., drained versus intact, open-water wetlands) plays an important role in explaining differences in the event-scale hydrologic behaviour of wetlands. Climatic and antecedent storage conditions (i.e., surface and subsurface storage in wetland basin) also had a strong influence on the hydrologic responses of wetlands during individual rainfall-runoff events and appeared to override the influence of spatial controls such as wetland area, volume or catchment area. Antecedent storage also seemed to be the driving factor of wetland-stream interactions. A lack of persistent correlations between wetland spatial characteristics and response metrics was observed and suggested nonstationary wetland hydrological behaviours and controls, a conclusion that has significant implications for wetland classification and modelling.

Coupling of a subsurface drainage model with a soil reservoir model to simulate drainage discharge and drain flow start

The environmental impact of subsurface drainage and agricultural activities has been widely studied in the literature. Agricultural subsurface drainage modifies the hydrological behavior and accelerates the transfer of pollutants of agricultural origin into surface water during the drain flow period, which is often limited to winter. The main objective of this study is to present a modeling approach allowing an accurate modeling of subsurface drainage discharge and prediction of drain flow start times, by integrating a new conceptual soil reservoir, managing the water flow in the unsaturated zone, to the SIDRA model. A comparison of the model results with field measurements of drainage discharge at the “La Jaillière” site (France) shows that such a model can efficiently simulate drainage discharge (KGE values >0.75) and predict, with good accuracy, the drain flow start time (with a median value of 5 days and a standard deviation of 10 days). The split simple test conducted for the model calibration and validation shows that the model is temporally robust. A sensitivity analysis conducted using the Sobol method on the five model parameters reveals that the drainage discharge simulation is mainly sensitive to the hydraulic conductivity and drainable porosity parameters. On the other hand, the date delimiting drain flow start is sensitive to the soil reservoir parameters. The model's ability to accurately predict the start of drain flow serves to avoid the application of farm inputs (pesticides or fertilizers) during this critical period in order to limit their transfer to surface waters.

Hydrological behavior of natural springs/streams in mid hills of Chakrata Himalaya, India

<p>The present study was carried out to understand the hydrological behavior of natural springs/streams in Semalta watershed, Kalsi block, Dehradun. The surface catchment areas of springs/streams were delineated using Survey of India Toposheet (1:50,000 scale) whereas drainage, slope, and land use maps of the watershed were prepared using open source ILWIS GIS software. The drainage map of the watershed indicated the ephemeral, intermittent and perennial nature of streams and the slope map of the watershed indicated that the majority of the area falls under scrubland. The discharge trend at different gauging sites from October 2015 to March 2016 indicated that the flow rate of the stream gradually decreased from post-monsoon to pre-monsoon period. The geohydrological and geomorphological study indicated that most of the springs/streamflow were controlled by fracture/joints with slate/phyllite/limestone/quartzite as country rock. The pH of most of the stream water was mildly alkaline (7.85-8.82) whereas EC was non-saline (0.087-0.425) and temperature varied from 14-23°C. Results on major ions indicated that a higher percentage of NH4+ together with NO3- was possible because of anthropogenic influence. In addition, the higher percentage of SO4- and F- was due to lithological pyrite whereas the higher percentage of HCO3- was due to pyrite weathering of slate. Results on the isotopic variation of δ18O showed that samples were collected with a total height difference of 700 m with a variation of -0.21‰ per 100 m for stream water and -0.5‰ for rainwater. On higher altitudes mainly narrow subsurface pathways are found and therefore only small size of structures are required for recharging and vice versa for the recharge of springs located in lower altitudes. The present study discusses various sampling techniques to ascertain the altitude of recharge of springs which would form the basis for taking appropriate on field activities for spring/stream rejuvenation.</p>

Isotopic analysis to quantify the role of the Indian monsoon on water resources of selected river basins in the Himalayas

AbstractWestern disturbances (WDs) and Indian summer monsoon (ISM) led precipitation play a central role in the Himalayan water budget. Estimating their contributions to water resource is although a challenging but essential for hydrologic understanding and effective water resource management. In this study, we used stable water isotope data of precipitation and surface waters to estimate the contribution of ISM and WDs to the water resources in three mountainous river basins ‐ Indus, Bhagirathi and Teesta river basins of western, central and Eastern Himalayas. The study reveals distinct seasonality in isotope characteristics of precipitation and surface waters in each river basin is due to changes in moisture source, hydrometeorology and relief. Despite steady spatial variance in the slope and intercept of regression lines from the Teesta to Indus and the Bhagirathi river basins, the slope and intercept are close to the global meteoric water line and reported local meteoric water line of other regions in the Himalayas and the Tibetan Plateau. The two‐component end‐member mixing method using d‐excess as tracer were used to estimate the contribution from ISM and WD led precipitation to surface water in aforementioned river basins. The results suggest that the influence of the ISM on the water resources is high (>72% to annual river flow) in Teesta river basin (eastern Himalayas), while as the WDs led precipitation is dominantly contributing (>70% average annual river flow) to the surface waters in the Indus river basin (western Himalayas). The contribution of ISM and WD led precipitation in Bhagirathi river basin is 60% and 40%, respectively. The findings demonstrate that the unusual changes in the ISM and WD moisture dynamics have the potential to affect the economy and food security of the region, which is dependent on the availability of water resources. The obtained results are of assistance to policy makers/mangers to make use of the information for better understanding hydrologic response amid unusual behaviour of the dual monsoon system over the region.

Prediction of Streamflow Recession Curves in Gauged and Ungauged Basins

AbstractPrediction of the time for perennial outflow from a natural basin to recede from the mean to some low flow value is an important practical and difficult problem in water resource management. This study aims to gain further understanding of this complex problem and to put forward new practical and accurate methods for predicting flow recessions between nominated limits in both gauged and ungauged basins. For a gauged basin, a three parameter recession model is employed to estimate the recession time, from day‐to‐day, as flow recedes from mean flow using previously measured site recession curves and a library of recession curve shapes generated by the RObust Parameter Estimation algorithm. The model is tested using data from 10 New Zealand basins which are diverse in low flow hydrological behavior and yields a Median Absolute Error (MAE) of 1 day. Another new model is also developed to predict recession time in an ungauged basin using catchment characteristics and information from master recession curves in a suite of 10 reference basins geologically and hydrologically similar to the ungauged basin, as assessed by a Random Forest model. Model performance is robust with a MAE of 1 day and the models advance the use of past flow records to enable more accurate predictions to be obtained. They can be applied elsewhere with confidence although further testing is desirable.

A multiple changepoint approach to hydrological regions delineation

Hydrologic regionalization consists of regrouping stations and catchments in pools based on a similarity measure. Regionalization is commonly used to extract a robust signal that can be used to describe the hydrology of the region or extrapolated to a location without measured information. Obviously, the similarity measure used affects the type of hydrological behavior one would expect from stations within a region. Most regionalization methods assume a stable and/or linear relationship between parameters of interests while it is well known that the physical processes driving the behavior of hydrometeorological variables are inherently non-linear and non-stationary. In this paper, we propose a similarity measure that is based on the location of changepoints in hydrological time series. The proposed method has the unique advantage over other hydrological region delineation methods to detect regions where hydrological member stations are non-linearly correlated, and where the strength of the relation varies with time. It therefore has the potential to uncover similarities that would not have been detected by existing regionalization techniques. The proposed method is applied to the Tensift watershed located in Morocco, North Africa. The coherence of the detected regions is checked using wavelet coherence.

Internal structure of a large, complex rock glacier and its significance in hydrological and dynamic behavior: A case study in the semi‐arid Andes of Argentina

AbstractThis paper presents an analysis of the internal structure, hydrogeology and dynamics of a large, complex, multilobate and multiroot rock glacier combining electrical resistivity tomography (ERT), hydrochemical data and differential interferometry synthetic aperture radar (DInSAR). The rock glacier consists of a series of overlapping lobes that represent different advancing stages with different degrees of conservation. The ERT surveys characterize the active layer and the upper part of the permafrost layer, the latter showing a heterogeneous geometry and electrical resistivity values ranging from 7 to 142 kΩm. Hydrochemical data argue for both the existence of different disconnected water flow pathways inside the rock glacier and the remarkable ionic concentrator effect of this landform. The horizontal displacement from October 2014 to April 2017 shows greatest magnitudes in the upper sector of both tongues, reaching speeds of up to 150 cm/year. The active frontal sector shows a displacement rate of 2–4.5 cm/year. This study contributes to knowledge of the material properties of rock glaciers, which are considered to represent important reservoirs/water resources, and their influence on the distribution of mountain permafrost, hydrology, and dynamics. Finally, to the best of our knowledge, the possible influence of the metal content of the ground on the resistivity values recorded for mountain permafrost is highlighted for the first time.

Stormflow generation in a humid forest watershed controlled by antecedent wetness and rainfall amounts

Understanding the meanings and identifying the controls for the stormflow generation with complex and nonlinear behaviors is essential for the development of threshold-based hydrological theory, as well as accurate assessment and prediction for flash flood risks. However, the study of catchment emergent patterns with three-linear threshold behaviors associated with hydrological connectivity has received little attention. Therefore, utilizing soil water storage, rainfall, and streamflow data spanning 3 years in a humid forest experimental watershed, Dujiangyan city, China, we elucidated how and where stormflow was generated with nonlinear behaviors, which were affected by antecedent wetness and rainfall amounts. Stormflow threshold behavior was taken as a function of combined gross precipitation and antecedent soil water storage, which was isolated using piecewise regression analysis with the identification of two breakpoints (i.e., generation threshold, Tg and rising threshold, Tr). It was found that the initial emergent behavior of rainfall-runoff was generally activated at the Tg, and then an abrupt shift from slow to fast flood response was possibly triggered at the Tr. These processes are important to understand the formation and development of flash floods at the watershed scale. It was noted that, above the Tr, considerably higher stormflow amounts generally occurred due to the lateral-connectivity extension of runoff contributing area from stream to neighboring hillslopes. Meanwhile, gravity-driven water movements in soil and better hydrological connectivity during the above-Tr phase readily triggered the huge flash flood disasters. The above-Tr flash floods with abrupt shifts were predominantly controlled by rainfall amounts, while initial below-Tg stormflow generation was mainly controlled by unsaturated soil water storage. More noteworthy, under heavy rainstorm conditions, the above-Tr stormflow was dominantly generated by subsurface flow, as was demonstrated at hillslope and watershed scales. These findings contribute to increasing our understanding of the controls on three-linear threshold-based hydrological behaviors, as well as of subsurface stormflow generation mechanism associated with hydrological connectivity in humid forest watersheds.

Clays Are Not Created Equal: How Clay Mineral Type Affects Soil Parameterization

AbstractClay minerals dominate the soil colloidal fraction and its specific surface area. Differences among clay mineral types significantly influence their effects on soil hydrological and mechanical behavior. Presently, the soil clay content is used to parameterize soil hydraulic and mechanical properties (SHMP) for land surface models while disregarding the type of clay mineral. This undifferentiated use of clay leads to inconsistent parameterization, particularly between tropical and temperate soils, as shown herein. We capitalize on recent global maps of clay minerals that exhibit strong climatic and spatial segregation of active and inactive clays to consider spatially resolved clay mineral types in SHMP estimation. Clay mineral‐informed pedotransfer functions and machine learning algorithms trained with datasets including different clay types and soil structure formation processes improve SHMP representation regionally with broad implications for hydrological and geomechanical Earth surface processes.

Development and Evaluation of a Chinook Salmon Smolt Swimming Behavior Model

Hydrologic currents and swimming behavior influence routing and survival of emigrating Chinook salmon in branched migratory corridors. Behavioral particle-tracking models (PTM) of Chinook salmon can estimate migration paths of salmon using the combination of hydrodynamic velocity and swimming behavior. To test our hypotheses of the importance of management, models can simulate historical conditions and alternative management scenarios such as flow manipulation and modification of channel geometry. Swimming behaviors in these models are often specified to match aggregated observed properties such as transit time estimated from acoustic telemetry data. In our study, we estimate swimming behaviors at 5 s intervals directly from acoustic telemetry data and concurrent high-resolution three-dimensional hydrodynamic model results at the junction of the San Joaquin River and Old River in the Sacramento-San Joaquin Delta, California. We use the swimming speed dataset to specify a stochastic swimming behavior consistent with observations of instantaneous swimming. We then evaluate the effect of individual components of the swimming formulation on predicted route selection and the consistency with observed route selection. The PTM predicted route selection fractions are similar among passive and active swimming behaviors for most tags, but the observed route selection for some tags would be unlikely under passive behavior leading to the conclusion that active swimming behavior influenced the route selection of several tagged smolts.

Streamflow regime of a lake‐stream system based on long‐term data from a high‐density hydrometric network

AbstractNorthern landscapes are dominated by a mosaic of lakes and streams, yet only a limited number of studies have explored how these lake‐stream networks influence streamflow regimes. In order to gain further insight into the hydrologic behaviour of lake‐stream systems, we conducted a study using long‐term streamflow data to investigate the annual‐, seasonal‐ and event‐scale streamflow regimes of a lake‐stream network at the Turkey Lakes Watershed (TLW) in central Ontario, Canada. Streamflow metrics were compared for seven lake and 12 no‐lake catchments within the TLW, in addition to 14 no‐lake catchments from other forested landscapes. It was difficult to attribute patterns in annual streamflow regimes to the influence of lakes due to the confounding influence of catchment size; however, streamflow regimes appeared to be less flashy at locations with more lake influence. In addition, lake catchments showed high similarity in streamflow regimes across seasons, whereas no‐lake catchments showed more similarity to lake catchments during wet seasons but less similarity during dry seasons. Event‐scale streamflow regimes further downstream from lake outlets were associated with greater increases in peakflow response and hydrograph rise rate following rain events than locations closer to lake outlets. Antecedent conditions were also important for both the peakflow response and rise rate, but less so than the amount of rainfall during the event. Variability in streamflow across lake‐stream networks appears to be driven by interactions between delayed contributions from lakes and relatively rapid runoff contributions from hillslopes and tributaries without lakes. In addition, streamflow regimes are influenced by temporal changes in lake storage deficits, which are a function of lake and catchment properties, as well as hydrometeorological conditions. Our results highlight that a network‐scale perspective that incorporates lakes and streams is needed to understand how these landscapes will hydrologically respond to environmental change.

Original

The morphometric analysis of any drainage basin is considered useful for water resource studies such as flood assessment, water quality sampling, water use reporting, watershed management etc. Drainage basin is generally defined as the areal extent of land from which the surface runoff flows to a defined drain, channel, stream or river. It is mainly governed by the topography of the terrain. Geographical Information System and Image Processing Techniques can be used for the identification of morphological features and analyzing properties of the basin. The morphometric parameters include linear, areal and relief aspects. ‘Watershed Atlas of India’ (2014) on 1:50,000 scale is an important digital database for planning and monitoring of development programs on a watershed basis. It serves as a uniform baseline for developing a hydrological unit-based data bank to be used for the management of water resources in the country. Run-off, sedimentation, water balance, evapotranspiration and several other catchment characterization related studies may be taken up on a watershed basis. The present study deals with morphometric parameters such as stream order (Nu), stream length (Lu), bifurcation ratio (Rb), drainage density (D) and stream frequency (Fs) of the Betwa drainage basin. Geographically the basin (77° 30′ to 80° 12′ east longitudes and 23°30′ to 25°55′ north latitudes) is located in two states i.e. Madhya Pradesh and Uttar Pradesh occupying an area of 43780 km2. The length of the stream segment is maximum for the first-order stream and decreases as the stream order increases. This study would help in understanding the hydrological behaviour of the basin. This, in turn, may enable the local people to utilize the resources of the basin for the sustainable development of the area.

Modified hydrologic regime of upper Ganga basin induced by natural and anthropogenic stressors

Climate change and anthropogenic activities pose serious threats to river basin hydrology worldwide. The Ganga basin is home to around half a billion people and has been significantly impacted by hydrological alterations in the last few decades. The increasing high-intensity rainfall events often create flash flooding events. Such events are frequently reported in mountainous and alluvial plains of the Ganga basin, putting the entire basin under severe flood risk. Further, increasing human interventions through hydraulic structures in the upstream reaches significantly alter the flows during the pre-and post-monsoon periods. Here, we explore the hydrological implications of increasing reservoir-induced and climate-related stressors in the Upper Ganga Basin (UGB), India. Flow/sediment duration curves and flood frequency analysis have been used to assess pre-and post-1995 hydrological behaviour. Our results indicate that low and moderate flows have been significantly altered, and the flood peaks have been attenuated by the operation of hydraulic structures in the Bhagirathi (western subbasin). The Alaknanda (eastern subbasin) has experienced an increase in extreme rainfall and flows post-1995. The downstream reaches experience reservoir-induced moderate flow alterations during pre-and post-monsoon and increasing extreme flood magnitudes during monsoon. Furthermore, substantial siltation upstream of the reservoirs has disrupted the upstream–downstream geomorphologic linkages.

Partial exclusion of precipitation: throughfall, stemflow and canopy interception in Eucalyptus plantations in southern Brazil

Hydrological behavior in reforested watersheds is different from that under other forms of cover. The variation may be related to aspects intrinsic to species, planting density, physiological maturity, management system and climatic conditions. Periodically, climatic anomalies such as the case of La Ninã are observed, and these are responsible for the alteration of the rainfall regime and consequently generate water deficits in the southern region of Brazil. Water deficit is responsible for reducing growth and productivity for the Eucalyptus genus, in addition to causing changes in hydrological behavior in reforested watersheds. Accordingly, this study compared the partition of rainfall in throughfall, stemflow and canopy interception of eucalyptus trees submitted or not to partial exclusion of precipitation. In the open field, 3 rainfall collectors were installed, and in the stand, for each rain exclusion treatment, 9 throughfall collectors and 9 stemflow collectors were installed. Every two weeks for 12 months, the volume of the collectors was measured. The quantified precipitation was 1627 mm over a year. In the treatment without exclusion, 84.8, 2.9 and 12.3% referred to throughfall, stemflow and canopy interception, respectively, while in the treatment excluding rainfall 80.6, 2.3 and 17.2% referred to throughfall, stemflow and canopy interception. The regression adjustments for throughfall and stemflow showed satisfactory R2 coefficients.

Nonlinear response of hydrodynamic and soil erosive behaviors to biocrust coverage in drylands

In dryland ecosystems, soil erosion poses severe threats to ecosystem productivity and human well-being. Biological soil crusts (biocrusts) are ubiquitous living covers in these ecosystems and play an important role in soil stabilization and erosion prevention. However, the quantitative relationship between biocrust coverage and soil water erosion as well as the driving mechanism have not yet been fully discussed, which hinders the development of soil erosion models that consider the effect of biocrusts. Accordingly, we set up 19 biocrust plots (10 m × 2.1 m) with coverage ranging from 9.3% to 80.0% on the Loess Plateau of China and conducted a series of simulated rainfall experiments. The quantitative relationship between runoff and sediment yield and biocrust coverage was assessed, and further complex correlations among these variables were analyzed using structural equation modeling (SEM). We found that (1) the runoff rates and sediment yield were significantly related to biocrust coverage. The runoff rates and sediment yield decreased with increasing biocrust coverage via a logarithmic function and an exponential function, respectively. The runoff rate and sediment yield rate from the plot with 9.3% biocrust coverage were 3.2 and 51.5 times higher, respectively, than those from the plot with 78.4% biocrust coverage. (2) The flow pattern and regime of overland flow were significantly affected by biocrust coverage. The overland flow was shifted from tranquil flow to supercritical flow when the biocrust coverage declined to 12.3%. The flow velocity, stream power, Darcy-Weisbach resistance coefficient, Froude number, and Reynolds number were strongly correlated with biocrust coverage (R2 = 0.548–0.830). (3) Biocrust coverage both directly and indirectly affected sediment yield. The anchoring effect of biocrusts directly protected the surface soil from raindrop impacts and runoff scouring (direct effect = −0.59). Additionally, biocrust cover had an indirect negative effect (−0.38) on sediment yield by decreasing the flow velocity and runoff rate with path coefficients of −0.81 and −0.78, respectively. Our results confirm that soil hydrological and erosive behavior have nonlinear relationships with biocrust coverage at the hill-slope scale, and they also reveal that variation in biocrust coverage is one of the main driving factors affecting soil hydrological and erosive behaviors. These results would improve soil water erosion estimation on biocrust-covered slopes and provide guidance for revising soil erosion models to include the effectiveness of biocrusts.