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In the context of the Sustainable Development Goals (SDG), understanding landscape evolution is essential to design long-term management plans. In agricultural fields, such as the vineyards on steep slopes, the terraces offer one of the most important morphological changes. However, it is not clear if the poorly managed agricultural terraces are optimal to reduce soil erosion and overland flow, although the trafficability is improved. Therefore, the main aim of this research is to compare the differences between initial soil erosion processes on poorly managed terraced vineyards and sloping vineyards at the pedon scale, considering the key role of the SSC (Soil Surface Components). To achieve this goal, twenty-six rainfall simulations were performed, considering the inclination, vegetation and stone covers, and surface roughness. Our research was carried out in the sloping vineyards (>20°) of the Almachar municipality, in the Montes de Malaga (Spain). Those vineyards are characterized by bare soils, low organic matter and high rock fragment contents. Our results showed that higher soil losses (42.2 g m−2 vs 9.4 g m−2) and runoff (4.9 l m−2 vs 1.6 l m−2) were detected in the plots of the poorly managed terraced vineyard than in the sloping one. Moreover, the time to runoff generation was lower in the poorly conserved terraces (232 s) than in the sloping vineyard (679 s), showing a faster saturation capacity. The SSC considered as the key factors were the reduction of the stone cover and an increase of roughness. As a conclusion, we confirm that the imminent transformation from sloping vineyards into terraced fields could lead several land degradation processes if a poor management is carried out, and no control measures are applied during the process, such as the conservation of stone walls or vegetation cover above the embankment, which is not in compliance with the SDG.

A sound understanding of erosive processes at different scales can contribute substantially to the design of suitable management strategies. The main aim of this work was to evaluate key factors at the pedon scale that cause soil erosion to occur. To achieve this goal, we quantified infiltration, permeability, soil losses and runoff volumes in a small Southern Spanish catchment cultivated with olive orchards. To assess which factor contributed most to speeding up soil erosion, a Spearman rank coefficient and principal components analysis were carried out. The results confirmed low infiltration values (11.8 mm h−1) in the surface soil layers and high permeability values (24.6 mm h−1) in the sub-surface soil layers, and produced an average soil loss of 19.7 g m−2 and average runoff coefficients of 26.1%. Statistical analyses showed that: i) the generation of runoff was closely correlated with soil loss; and, ii) an increase in the vegetation cover helped reduce soil erosion. In comparison to larger areas such as a catchment, the pedon scale produced lower or similar soil losses and runoff coefficients in rainfall simulation conditions, although the influence of vegetation cover as a control factor was also detected.

It is well known that rainfall causes soil erosion in sloping German vineyards, but little is known about the effect of age of plantation on soil erosion, which is relevant to understand and design sustainable management systems. In the Ruwer-Mosel valley, young (1- to 4-years) and old (35- to 38-years after the plantation) vineyards were selected to assess soil and water losses by using two-paired Gerlach troughs over three years (2013-2015). In the young vineyard, the overland flow was 107 L m-1 and soil loss 1000 g m-1 in the year of the plantation, and decreased drastically over the two subsequent years (19 L m-1; 428 g m-1). In the old vineyard, soil (from 1081 g m-1 to 1308 g m-1) and water (from 67 L m-1 to 102 L m-1) losses were 1.2 and 1.63 times higher, respectively, than in the young vineyard.

Las unidades geomorfologicas estan relacionadas con ciertos procesos y con la historia de su formacion. Ademas, se definen por sus formas y materiales. En este estudio se investigan los procesos de erosion en diferentes unidades de relieve. Simulaciones de lluvia, experimentos en rigolas y seguimientos a traves de fotografia aerea se llevaron a cabo en dunas, glacis, rellenos holocenos, taludes y terrazas franco-arcillosos de origen cuaternario, con el objeto de conocer la variacion en la intensidad de los procesos. Para ello, se evaluaron el impacto de las gotas de lluvia, la generacion de escorrentia, la erosion en inter-rigolas y rigolas durante varios anos. Las areas de estudio se situaron en el NE y SE de Espana, sur de Marruecos y norte de Burkina Faso. Los resultados muestras claramente que los procesos medidos son muy diferentes entre si segun la formacion de las propias unidades de relieve. Las dunas y los rellenos holocenos en los valles son altamente susceptibles a la erosion por el impacto de las gotas de lluvia y la formacion de regueros. Por el contrario, las terrazas sobre materiales franco-arcillosos muestran baja susceptibilidad a los procesos de erosion. Por lo tanto, se puede concluir que las distintas unidades de relieve muestran diferentes dominancia e intensidad de procesos. Las diferencias son mas significativas con el incremento de la escala y la complejidad del proceso erosivo: el crecimiento de las carcavas varia mucho mas entre diferentes unidades que los efectos del impacto de la gota de lluvia y la formacion de rigolas.

In this introductory article to the special issue “Experiments in geomorphology”, the fundamentals of experiments in science, and especially in earth science and geomorphology, are discussed. This is of special interest, as geomorphological sciences crosses scales and thus, different types of experiments are applied for highly variable tasks: (i) Real experiments: to test hypotheses on the process interaction of well defined landscape components; (ii) Quasi experiments: the integrated response of pre-defined morphological units is quantified here; (iii) Hybrid experiments: spatial stratification of the landscape according to statistically evaluable characteristics.A short review on different types of experiments in geomorphology is given, focusing on the processes relevant for soil erosion: splash, inter-rill and linear erosion. Finally, the contributions to the special issue are classified according to the classification of experiments given.

German vineyards are one of the land uses most prone to soil erosion. Due to their placement on mainly steep slopes and non-conservative cultivation practices, runoff and soil loss are a serious problem for wine growers. In the Saar-Mosel valley (Rhineland-Palatinate, Germany), there is a tendency towards organic management of vineyards with protective grass cover in the inter-rows. Since there is a lack of information about organic-conventional tillage in German vineyards related to soil erosion processes, this study presents a comparison between these two soil management practices. For this purpose, 22 rainfall simulations were performed as well as a medium-term monitoring by using 4-paired Gerlach troughs in two experimental sites in the Saar-Mosel valley. The mean simulated runoff coefficient and suspended sediment load in conventional vineyards amounted up to 23.3% and 33.75 g m -2 , respectively. In the organic site, runoff and soil loss were only recorded in one out of the 11 simulations. Runoff and sediment was collected in the Gerlach troughs for 33 natural rainfall events. In the conventional vineyard, the total measured soil loss was 3314.63 g m -1 and 6503.77 g m -1 and total runoff volumes were 105.52 L m -1 and 172.58 L m -1 . In the organic site, total soil losses reached 143.16 g m -1 and 258.89 g m -1 and total runoff was 21.65 L m -1 and 12.69 L m -1 . When soil loss was measured without corresponding runoff or precipitation, soil erosion was activated by tillage or trampling. Finally, the conventional vineyard showed a higher variability in soil loss and runoff suggesting less predictable results.

Conventional Mediterranean vineyards from the Montes de Malaga (Axarquia region, Spain) are characterized by high average temperatures, extreme rainfall events during autumn and winter, elevated stoniness and steep slopes (20–50°). Traditionally, several problems of high soil loss, rill and ephemeral gully generation, and elevated runoff are observed by farmers, which are increasing land degradation processes and a decrease of the productivity. According to this, the main aims of this paper were: i) to quantify the initial soil loss, surface flow and infiltration processes; ii) to characterize and describe the hydrological and geomorphological dynamics; iii) to detect the key factors, which control the soil erosion processes. For this purpose, a combined methodology was applied, using soil analysis, a small portable rainfall simulator and a Guelph permeameter on one experimental plot cultivated with vineyards with steep slopes. Results showed a high variability of soil erosion and permeability processes. Soil analysis showed an elevated concentration of silt particles and stoniness, with higher contents of sand particles between 0 and 5 cm, and clays from 5 cm. With a Guelph permeameter, high average of permeability and saturated hydraulic conductivity with elevated standard deviation were observed. Furthermore, an increase of these parameters from the upper to the foot slope was registered. By using rainfall simulations, on the upper and the foot slope positions the highest runoff coefficient and soil loss were registered. The most elevated peak of sediment concentration was obtained on the middle slope. In general, high infiltration coefficients between 66.5 and 100% were observed. In conclusion it was observed that the activation of the soil erosion processes was due to the distribution of the surface soil components (high roughness, several cracks and high stoniness and silt content), the steep slopes and the impact of the soil traditional tillage practices. These Mediterranean hillslope vineyards registered a mixed Hortonian-Hewlettian model, which combines surface and sub-surface flow conditioned by the micro-topographical changes and its saturation degree.

The movement of stones is important in a variety of disciplines such as geomorphology or hydraulic engineering. Plenty of different sensors, visual, active or passive tracers exist to capture movements in various ways. However, none of them is sufficiently small to be implanted in pebbles with a longest axis of approx. 60 mm. In this article, a sufficiently small probe is introduced: the Smartstone probe. It consists of a metal cylinder (diameter 8 mm, length 55 mm) with a flexible antenna and contains a Bosch BMX055 sensor composed of a triaxial accelerometer, magnetometer and gyroscope, respectively. Additional components inside the probe are memory to store data, active RFID (Radio-frequency identification) technique to transmit data and two button cells as power supply. Mounted into a pebble, the applicability of this probe was tested in laboratory flume experiments by determining the pebble movement using the Smartstone measurements and comparing them to the movement pattern captured by a high-speed camera. The derived orientations and positions in these test experiments resulted in deviations of 32.4% compared to the visual footage. The different reasons for deviations are noise, quantization error, integration error, orientation error and clipping. The error sources were divided with supplementary experiments resulting in mean absolute deviation (MAE) of 3.3% due to noise, quantization, and integration errors; orientation errors result in an increased MAE of 13.7% in natural environment and 21.7% in laboratory. The MAE of all experiments containing clipping was 63.2%. These deviations will be reduced in future by application of methods like Kalman filtering or Markov models, which are established in other disciplines like computer science, robotics or (pedestrian) navigation.

Knowledge about connectivity and what affects it, through space and time, is needed for taking appropriate action at the right place and/or time by stakeholders. Various conceptual frameworks for hydrological and sediment connectivity have been developed in recent years. For most of these frameworks, the objective was to conceptualise connectivity, not necessarily to infer it from measurements. Studies focussing on measurements of connectivity have so far not been done often. Because of lack of data on connectivity, few real-world data have been used in recent connectivity modelling studies. The aim of this study was to demonstrate that existing data can be used to assess governing factors of connectivity, and how these change over time. Data from three catchments in Navarre, Northern Spain, were used to assess factors that influence hydrologic and sediment connectivity. These factors were used as components in a linear model for discharge and suspended-sediment yield. Three components of connectivity were distinguished: topographical, biological and soil. Changes in the topographical component for the studied periods were considered relatively small, and, therefore, kept constant. Changes in the biological component were determined using the Normalised Difference Vegetation Index. Changes in the soil component were assessed using an Antecedent Precipitation Index. Nash–Sutcliffe model efficiency coefficients were between 0·49 through 0·62 for the discharge models and between 0·23 through 0·3 for the sediment-yield models. We recommend applying the model at smaller spatial scales than catchment scale to minimise the lumping of spatial variability in the components. Copyright © 2016 John Wiley & Sons, Ltd.

For a long time, studies concerning erosion caused by concentrated overland flow mainly dealt with the erosion and the transport of fine material. More recent studies have shown that rock fragments reduce the intensity of soil erosion processes on the one hand, but on the other hand rock fragment movements also have been observed both in the rill- and interrill erosion processes. However, there is little knowledge about the movement process of rock fragments in shallow channel flow. Are certain movement patterns typical for different shapes? Are there relationships between movement patterns and slope and flow velocity? Are all these patterns and relationships reproducible? To answer these questions, we performed laboratory channel experiments. With these experiments, we could obtain information about movement patterns of pebbles, by varying the following parameters: shape (flat, ellipsoidal, nearly spherical), size (diameter between 1.97 and 4.0 cm) and channel slope (5°, 10°). During the experiments, a high-speed camera was used to capture the motion of eight specially painted pebbles. The resulting image sequences were processed using both automatic image processing and manual visual inspection. Besides the movement patterns, the pebbles velocity, the water velocity and the water depth were estimated. We could show that there were different movement patterns depending on the shape and the slope. For the 5° experiments, the big, flat pebbles lie at the beginning of the tests. After the following yawing, the pebbles mainly showed the movement form rolling around the longest axis. For the 10° experiments the big, flat pebbles showed the same movement pattern firstly, but later in the sequence, they started to roll around their shortest axis and in the end this movement form was combined with saltation. These patterns are described using a simple symbolic language: sequences of pictograms describe the consecutive movement forms. Furthermore, we detected five different velocity groups of the pebbles for each slope: different cross-section shapes of the pebbles result in different acceleration behavior. The methodology is limited to clear water in laboratory use. Even a larger water depth restricts the image processing. Thus, in the future the experiments will be combined with a small sensor that is implanted in the pebbles and measures forces (acceleration), compass (magnetic flux density) and rotations (gyroscope).

The set-up and characterisation of an indoor nozzle-type rainfall simulator (RS) at Wageningen University, the Netherlands, are presented. It is equipped with four Lechler nozzles (two nr. 460·788 and two nr. 461·008). The tilting irrigation plot is 6 m long and 2·5 m wide. An electrical pump supplies the constant flow during the experiments. The spatial distribution of the rainfall was measured with 60 rain gauges equally distributed on the experimental plot. Thies® Laser Precipitation Monitor was used to measure the size and falling velocity of the raindrops. Four different flow rates were applied (Q1–4). From the collected data, spatial rainfall intensity and spatial kinetic energy distribution maps were created; Christiansen uniformity coefficient was calculated for each flow rate. The results of the experiments revealed that the rainfall parameters (spatial rainfall intensity, kinetic energy, raindrop size distribution and fall velocity) in the RS are not homogeneous (Christiansen uniformity ranges from 68·5% to 83·2%). Accordingly, the whole plot can only be irrigated irregularly applying a wide range of intensities and rainfall energies. The RS offers a good opportunity to study great variety of process intensities such as splash erosion, runoff generation, soil aggregate stability, organic matter migration and scaled landscape development.

Summary Rainfall erosivity is a key component in soil erosion by water. While kinetic energy and momentum are used to describe the erosivity of rainfall, and both are derived from mass and velocity of raindrops, it is not clear how different substrates transform this energy. In our study we conducted rainfall simulation experiments to determine splash detachment amounts of five substrates (coarse sand, medium sand, fine sand, PE balls, silt) for seven different rainfall intensities (52–116 mm h−1). We used linear mixed-effect modeling (LME) to calculate erosivity predictors for each substrate. Additionally, we separated drop-size-velocity relationship into lower left and upper right quarter to investigate the effect of small and slow just as big and fast raindrops on splash detachment amounts. We suggest using momentum divided by drop diameter as a substrate-independent erosivity predictor. To consider different substrates specific erosivity parameters are needed. Heavier substrates like sand are best described by kinetic energy multiplied by diameter whereas lighter substrates like silt point to momentum divided by diameter to the power of 1.5. Furthermore, our results show that substrates are differently affected by the size and velocity of drops. While splash detachment of light substances can be reliably predicted by drop size and velocity for small and slow drops, drop size and velocity loses its predictive power in heavier substrates like sand.

The Mosel Wine region has suffered during the last decades a decrease in productive area, mostly on steep sloping vineyards. To avoid the spread of diseases, the extraction of grapevines on abandoned vineyards is mandatory in Rhineland-Palatinate. At the same time, the organic production of wine is growing slowly, but well established in the area. We assess in this paper the degree of the land-use changes, as well as their effect on runoff generation and sediment production, depending on the age of the abandonment, as well as the type and age of the land management, whether organic or conventional. Land use data were obtained to identify land-use change dynamics. For assessment of runoff generation and soil erosion, we applied rainfall simulation experiments on the different types of vineyard management. These were organically managed, conventionally managed and abandoned ones, all of varying ages. During the last decades of the last century, a decrease of around 30% of vineyard surface could be observed in Germany&rsquo, s Mosel Wine Region, affecting mostly the steep sloping vineyards. Despite a high variability within the types of vineyard management, the results show higher runoff generation, and soil erosion associated with recently installed or abandoned vineyards when compared to organic management of the vineyards, where erosion reached only 12%. In organic management, runoff and erosion are also reduced considerably, less than 16%, after a decade or more. Thus, organic vineyard management practices show to be very efficient for reduction of runoff and erosion. Consequently, we recommend to adopt as far as possible these soil management practices for sustainable land management of steep sloping vineyards. In addition, soil protection measures are highly recommended for vineyard abandonment according to the law.

The relative impact of water and wind on total erosion was investigated by means of an experimental-empirical study. Wind erosion and water erosion were measured at five different sites: (1) Mediterranean fallow, (2) Mediterranean orchard, (3) wheat field, (4) vineyard and (5) sand substrate. Mean erosion rates ranged from 1.55 to 618 g&middot, m&minus, 2&middot, h&minus, 1 for wind and from 0.09 to 133.90 g&middot, 1 for rain eroded material over all tested sites. Percentages (%) of eroded sediment for wind and rain, respectively, were found to be 2:98 on Mediterranean fallow, 11:89 on Mediterranean orchard, 3:97 on wheat field, 98:2 on vineyard and 99:1 on sand substrate. For the special case of soil surface crust destroyed by goat trampling, the measured values emphasize a strong potential impact of herding on total soil erosion. All sites produced erosion by wind and rain, and relations show that both erosive forces may have an impact on total soil erosion depending on site characteristics. The results indicate a strong need to focus on both wind and water erosion particularly concerning soils and substrates in vulnerable environments. Measured rates show a general potential erosion depending on recent developments of land use and climate change and may raise awareness of scientist, farmers and decision makers about potential impact of both erosive forces. Knowledge about exact relationship is key for an adapted land use management, which has great potential to mitigate degradation processes related to climate change.

In the framework of the EU-INTERREG-IVb-project ForeStClim (Transnational Forestry Management Strategies in Response to Regional Climate Change Impacts) a combination of experimental methods has been applied for the investigation of the spatial and temporal variation and intensity of overland flow generation and soil erosion processes. In the presented study, the influences of land-use type and land-management practices on overland flow generation and soil erosion are investigated for three low mountain range catchments in Luxembourg and in Rhineland-Palatinate, Germany. The key questions of the study can be summarized as follows: Can Hortonian overland flow generation be observed on all land-use types in the investigated areas in the Central European low mountain range? How can the contribution of forested areas to the flood and erosion dynamics be evaluated under humid climate conditions in Central Europe and what are the most important factors of influence? The results of the presented study show that forest areas can also be sources for overland flow and sediment, particularly artificial linear structures like unpaved roads and harvester tracks, where runoff coefficients between 41.2 and 97.1%, and erosion values between 2.6 and 122.5 g m− 2 were determined using rainfall experiments. Another important factor is soil water repellency, this factor can pre-eminently be observed under rather dry soil moisture conditions in summer and can have severe influence on overland flow generation particularly in forested areas. The results of the rainfall experiments in coniferous forests show runoff coefficients ranging from 0 to 86.9%, here the high values can all be traced back to water repellency influence, as the field observations suggest. In the context of flood generation, it is becoming more and more important to improve knowledge on overland flow generation and soil erosion processes occurring in forested catchments, particularly considering the expected climate change.

28 páginas, 6 figuras, 2 tablas.- The definitive version is available on: http://www.sciencedirect.com/science/article/pii/S0341816213001252, [EN] Small-scale portable rainfall simulators are an essential research tool for investigating the process dynamics of soil erosion and surface hydrology. There is no standardisation of rainfall simulation and such rainfall simulators differ in design, rainfall intensities, rain spectra and research questions, which impede drawing a meaningful comparison between results. Nevertheless, these data become progressively important for soil erosion assessment and therefore, the basis for decision-makers in application-oriented erosion protection. The artificially generated rainfall of the simulators used at the Universities Basel, La Rioja, Malaga, Trier, Tübingen, Valencia, Wageningen, Zaragoza, and at different CSIC (Spanish Scientific Research Council) institutes (Almeria, Cordoba, Granada, Murcia and Zaragoza) was measured with the same methods (Laser Precipitation Monitor for drop spectra and rain collectors for spatial distribution). Data are very beneficial for improvements of simulators and comparison of simulators and results. Furthermore, they can be used for comparative studies, e.g. with measured natural rainfall spectra. A broad range of rainfall data was measured (e.g. intensity: 37–360 mm h− 1; Christiansen Coefficient for spatial rainfall distribution: 61–98%; median volumetric drop diameter: 0.375–6.5 mm; mean kinetic energy expenditure: 25–1322 J m− 2 h− 1; mean kinetic energy per unit area and unit depth of rainfall: 0.77–50 J m− 2 mm− 1). Similarities among the simulators could be found e.g. concerning drop size distributions (maximum drop numbers are reached within the smallest drop classes < 1 mm) and low fall velocities of bigger drops due to a general physical restriction. The comparison represents a good data-base for improvements and provides a consistent picture of the different parameters of the simulators that were tested., The research for this study was funded by the Deutsche Forschungsgemeinschaft (DFG) project number Ri-835/6-1. We would like to thank the anonymous reviewers for their remarks.

This paper tackles two main questions by linking observations, determination of hydraulic parameters and measurement of sediment transport with the formulae used in soil erosion models. First, do constant shear stress values in different rills with constant soil parameters result in the same soil detachment values? Secondly, deterministic soil erosion models make the assumption that there is a relationship (often further assumed to be linear) between shear stress and soil detachment; is this suitable for representing real erosion process combinations in natural rills? Following most process based deterministic soil erosion models, derived hydraulic and erosion parameters should be similar. However, the results from the different experiments showed clear differences in sediment concentration, transport rates and other measured as well as calculated values. In contrast to our experimental results, a model simulation would produce erosion parameters with low variations, represented by the relative measurement error and the empirical variation coefficient. This reveals the general problems of using process based deterministic models for erosion in shallow rills. While soil erosion models simulate the processes resulting from the shear forces of flowing water on the soil surface, other processes like side wall failure, headcut retreat and plunge pool dynamics are not taken into account. Our results suggested that these other processes may contribute substantially to rill erosion processes. The results of this study strongly suggested that the model concept of most physical based soil erosion models is inadequate for modeling rill erosion processes. Measured total rill erosion rates were the sum of erosion rates caused by a combination of different soil erosion processes with different spatial and temporal distribution. This combination cannot be described by a single equation.

The present paper is based on several field investigations (monitoring soil and rill erosion by aerial photography, rainfall simulations with portable rainfall simulators, and manmade rill flooding) in southern Spain. Experiments lead now to a closer understanding of the dynamics and power of different soil erosion processes in a gully catchment area. The test site Freila (Andalusia, Spain) covers an area of 10.01 ha with a rill density of 169 m ha−1, corresponding to a total rill length of 1694 m. Assuming an average rill width of 0.15 m, the total rill surface can be calculated at 250 m2 (0.025 ha). Given that, the surface covered by rills makes up only 0.25% of the total test site. Since the rill network drains 1.98 ha, 20% of the total runoff comes from rills. The rills’ sediment erosion was measured and the total soil loss was then calculated for detachment rates between 1685 g m−2 and 3018 g m−2. The interrill areas (99.75% of the test site) show values between 29 and 143 g m−2. This suggests an important role of rill erosion concerning runoff and soil detachment.

The importance of distinguishing and discretely studying the subprocesses of runoff generation and erosion has led to the development of rainfall simulations on small plots. We methodically upgraded a small portable rainfall simulator with particular respect to (1) rainfall characteristics that include homogeneous spatial rainfall distribution and drop spectrum, (2) handling, and (3) control of test conditions. We measured simulator characteristics with rain gauges, calibration plate and Laser Precipitation Monitor by Thies (LPM). The upgraded small rainfall simulator, and measurements of the improved rainfall characteristics are presented in this paper.The upgraded configuration shows the desired improvements: regarding drop size distribution, a close relationship to natural rainfall (Marshall & Palmer Distribution) can be observed. Due to low fall heights, measured drop fall velocities are slow; maximum velocities range between 3.4 and 5 m s1. Mean kinetic energy expenditure, mean kinetic energy per unit area and unit depth of rainfall and mean momentum are 214 J m2 h1, 5.8 J m2 mm1 and 0.016 kg m s1, respectively. The spatial rainfall distribution of the upgraded simulator is homogenous with a Christiansen-Uniformity Coefficient of 91%. The measured variables show extremely low variation throughout all tests and should therefore be reproducible in field investigations at any time.

The Pyrenean and Pre-Pyrenean mountain areas have been intensively used at least since roman times, but nowadays depopulation has lead to widespread land abandonment without a steering land-management. Vegetation recovery is weak in most abandoned fields. Soil formation and characteristics are conditioned by this fact, and for this, soils show past degradation processes and are mostly predominant factors for continuing land degradation or restoration. Three study areas were set up along a climatic gradient with increasing summer water deficit in the sub-humid zone between the Central Pyrenees and Pre-Pyrenees. Soil survey combined with experiments for the determination of infiltration, runoff and erosion were applied for understanding the degradation history and the future development of the soils. All areas are dominated by Entisols, but also Inceptisols and Alfisols are found, and even soils with hydromorphic features. The soils show signs of heavy erosion. The parental material determines the nutrient supply and the general chemical properties. All sites show a weak water storing capacity, as a result of the removal of fine material by erosion and due to the depletion of soil organic matter. In addition, infiltration capacity and runoff generation are high within the studied areas, averaging between 27 and 37 per cent. The driest area studied shows an ongoing trend to degradation, with high erosion rates combined with a high degradations status of the soil. The other areas are characterised by a patchy pattern of soil degradation and regradation processes. Copyright © 2008 John Wiley & Sons, Ltd.

Rainfall simulations at different scales have been used for understanding the influence of different factors on runoff generation and erosion. They are an accepted method for calibrating and validating physically based rainfall and erosion models. Nevertheless, it is proven that not only the patterns of rainfall are highly variable over space and time. Soil parameters responsible for runoff generation and erosion – e.g. infiltration capacity, soil moisture, aggregate stability – are highly variable, too. The results of more than 100 plot scale rainfall simulations on abandoned fields in different areas of Spain are analysed for identifying and quantifying factors affecting runoff and erosion processes. The variability of superficial runoff and suspended sediment yield is very high within most of the test areas, reaching values up to a runoff coefficient of 1 and yielding 130 g per experiment. Only within the semi-arid areas we can find a significant and high correlation between vegetation cover and sediment yield (and sediment concentration), whereas most of the other investigated surface parameters show no influence on runoff and erosion. For this, even in simulations on small plots more complex processes can be assumed. The factors controlling them have to be searched, even at detailed scales, within the geo-ecological characteristics of the investigated areas at chorological scales.

Within this Editorial, we put the articles included in the Special Issue into a historical and actual context of experimental research in Earth system sciences.

We present a comparison study on how well capacitance and time domain reflectometry water content sensors can estimate average water content values in non-uniformly wetted soils. This ability is important in studies where accurate average values are crucial. The averaging behavior of two capacitance water content sensors in nonuniform wetted sand samples was assessed and compared with the averaging behavior of a time domain reflectometry (TDR) water content sensor in identical samples. Four different nonuniform wetting situations were assessed. In one of the four experiments, the orientation of the capacitance sensor was altered, while in another the sensitivity along the length of the sensor was tested. For one of the tested sensor types, the overestimation of the volumetric water content (VWC) was 0.034 compared with the value determined by drying, while the corresponding TDR value deviated 0.009. The conclusion is that in a nonuniform wetted soil profile, the capacitance sensors tested weigh the wet parts more heavily than the dry parts, resulting in an overestimation of the average VWC. Therefore we conclude that the capacitance sensors tested are less suitable for applications in situations where both nonuniform wetted profiles are encountered and accurate VWC measurements are required.