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To predict hydrologic responses to inputs and perturbations, it is important to understand how precipitation is stored in catchments, released back to the atmosphere via evapotranspiration (ET), or transported to aquifers and streams. We investigated this partitioning of precipitation using stable isotopes of water (18O) at the Can Vila catchment in the Spanish Pyrenees mountains. The isotope data covered four years of measurements, comprising >550 rainfall and >980 stream water samples, capturing intra-event variations. They were complemented by fortnightly plant water isotope data sampled over eight months. The isotope data were used to quantify how long it takes for water to become evapotranspiration or to be discharged as streamflow using StorAge Selection (SAS) functions. We calibrated the SAS functions using a conventional approach fitting the model solely to stream water isotope data and a multi-objective calibration approach in which the model was simultaneously fitted to tree xylem water isotope data. Our results showed that the conventional model-fitting approach was not able to constrain the model parameters that represented the age of water supplying ET. Consequently, the ET isotope ratios simulated by the conventionally calibrated model failed to adequately simulate the observed xylem isotope ratios. However, the SAS model was capable of adequately simulating both observed stream water and xylem water isotope ratios, if those xylem water isotope observations were used in calibration (i.e., the multi-objective approach). The multi-objective calibration approach led to a more constrained parameter space facilitating parameter value identification. The model was tested on a segment of data reserved for validation showing a Kling-Gupta Efficiency of 0.72 compared to the 0.83 observed during in the calibration period. The water-age dynamics inferred from the model calibrated using the conventional approach differed substantially from those inferred fro

Rainfall is the key factor to understand soil erosion processes, mechanisms, and rates. Most research was conducted to determine rainfall characteristics and their relationship with soil erosion (erosivity) but there is little information about how atmospheric patterns control soil losses, and this is important to enable sustainable environmental planning and risk prevention. We investigated the temporal and spatial variability of the relationships of rainfall, runoff, and sediment yield with atmospheric patterns (weather types, WTs) in the western Mediterranean basin. For this purpose, we analyzed a large database of rainfall events collected between 1985 and 2015 in 46 experimental plots and catchments with the aim to: (i) evaluate seasonal differences in the contribution of rainfall, runoff, and sediment yield produced by the WTs; and (ii) to analyze the seasonal efficiency of the different WTs (relation frequency and magnitude) related to rainfall, runoff, and sediment yield. The results indicate two different temporal patterns: the first weather type exhibits (during the cold period: autumn and winter) westerly flows that produce the highest rainfall, runoff, and sediment yield values throughout the territory; the second weather type exhibits easterly flows that predominate during the warm period (spring and summer) and it is located on the Mediterranean coast of the Iberian Peninsula. However, the cyclonic situations present high frequency throughout the whole year with a large influence extended around the western Mediterranean basin. Contrary, the anticyclonic situations, despite of its high frequency, do not contribute significantly to the total rainfall, runoff, and sediment (showing the lowest efficiency) because of atmospheric stability that currently characterize this atmospheric pattern. Our approach helps to better understand the relationship of WTs on the seasonal and spatial variability of rainfall, runoff and sediment yield with a regional scale ba

Recent virtual and experimental investigations have shown that the young water fraction Fyw (i.e. the proportion of catchment outflow younger than circa 2–3 months) increases with discharge in most catchments. The discharge sensitivity of Fyw has been defined as the rate of increase in Fyw with increasing discharge (Q) and has been estimated by the linear regression slope between Fyw and Q, hereafter called DS(Q). The combined use of both metrics, Fyw and DS(Q), provides a promising method for catchment inter-comparison studies that seek to understand streamflow generation processes. Here we explore the discharge sensitivity of Fyw in the intensively sampled small Mediterranean research catchment Can Vila. Intensive sampling of high flows at Can Vila allows young water fractions to be estimated for the far upper tail of the flow frequency distribution. These young water fractions converge toward 1 at the highest flows, illustrating a conceptual limitation in the linear regression method for estimating DS(Q) as a metric of discharge sensitivity: Fyw cannot grow with discharge indefinitely, since the fraction of young water in discharge can never be larger than 1. Here we propose to quantify discharge sensitivity by the parameter of an exponential-type equation that expresses how Fyw varies with discharge. The exponential parameter (Sd) approximates DS(Q) at moderate discharges where Fyw is well below 1; however, the exponential equation and its discharge sensitivity metric better capture the non-linear relationship between Fyw and Q and are robust with respect to changes in the range of sampled discharges, allowing comparisons between catchments with strongly contrasting flow regimes.

The young water fraction (Fyw), the proportion of water younger than 2-3 months, was investigated in soil-, ground- and stream waters in the 0.56 Km2 sub-humid Mediterranean Can Vila catchment. Rain water was sampled at 5-mm rainfall intervals. Mobile soil water and groundwater were sampled fortnightly, using suction lysimeters and two shallow wells, respectively. Stream water was dynamically sampled at variable time intervals (30 minutes to 1 week), depending on flow. A total of 1,529 18O determinations obtained during 58 months were used. The usual hypothesis of rapid evapotranspiration of summer rainfall could not be maintained, leading to discard the use of an “effective precipitation” model. Soil mobile waters had Fyw up to 34%, while in ground and stream were strongly related to water table and discharge variations, respectively. In stream waters, due to the highly skewed flow duration curve, the flow-averaged young water fraction (F*yw) was 22.6%, whereas the time-averaged Fyw was 6.2%. Nevertheless, both F*yw and its exponential discharge sensitivity (Sd) showed relevant changes when different 12-month sampling periods were investigated. The availability of Sd and a detailed flow record allowed us to simulate the young water fraction that would be obtained with a virtual thorough sampling (F**yw). This showed that underestimation of F*yw is associated with missing the sampling of highest discharges and revealed underestimations of F*yw by 25% for the dynamic sampling and 66% for the weekly sampling. These results confirm that the young water fraction and its discharge sensitivity are metrics that depend more on precipitation forcing than on physiographic characteristics, so the comparisons between catchments should be based on mean annual values and inter-annual variability. They also support the dependence of the young water fraction on the sampling rate and show the advantages of flow-weighted F*yw. Water age investigations should be accompanied by the ana

Rainfall is the key factor to understand soil erosion processes, mechanisms, and rates. Most research was conducted to determine rainfall characteristics and their relationship with soil erosion (erosivity) but there is little information about how atmospheric patterns control soil losses, and this is important to enable sustainable environmental planning and risk prevention. We investigated the temporal and spatial variability of the relationships of rainfall, runoff, and sediment yield with atmospheric patterns (weather types, WTs) in the western Mediterranean basin. For this purpose, we analyzed a large database of rainfall events collected between 1985 and 2015 in 46 experimental plots and catchments with the aim to: (i) evaluate seasonal differences in the contribution of rainfall, runoff, and sediment yield produced by the WTs; and (ii) to analyze the seasonal efficiency of the different WTs (relation frequency and magnitude) related to rainfall, runoff, and sediment yield. The results indicate two different temporal patterns: the first weather type exhibits (during the cold period: autumn and winter) westerly flows that produce the highest rainfall, runoff, and sediment yield values throughout the territory; the second weather type exhibits easterly flows that predominate during the warm period (spring and summer) and it is located on the Mediterranean coast of the Iberian Peninsula. However, the cyclonic situations present high frequency throughout the whole year with a large influence extended around the western Mediterranean basin. Contrary, the anticyclonic situations, despite of its high frequency, do not contribute significantly to the total rainfall, runoff, and sediment (showing the lowest efficiency) because of atmospheric stability that currently characterize this atmospheric pattern. Our approach helps to better understand the relationship of WTs on the seasonal and spatial variability of rainfall, runoff and sediment yield with a regional scale ba

Ecosystems experience natural disturbances and anthropogenic impacts that affect biological communities and ecological processes. When natural disturbance modifies anthropogenic impacts, current widely used bioassessment metrics can prevent accurate assessment of biological quality. Our aim was to assess the ability of biomonitoring metrics to detect anthropogenic impacts at both perennial and intermittent sites, and in the latter including both flowing and disconnected pool aquatic phases. Specifically, aquatic macroinvertebrates from 20 rivers were sampled along gradients of natural flow intermittence (natural disturbance) and anthropogenic impacts to investigate their combined effects on widely used river biomonitoring metrics (i.e. taxonomic richness and standard biological indices) and novel functional metrics, including functional redundancy (i.e. the number of taxa contributing similarly to an ecosystem function, here a trophic function) and response diversity (i.e. how functionally similar taxa respond to natural disturbance and anthropogenic impacts). Only the widely used IBMWP index (Iberian Biological Monitoring Working Party) was able to detect anthropogenic impacts in intermittent rivers when used during flowing phases. Several functional metrics also detected anthropogenic impacts regardless of flow intermittence. Besides, functional redundancy of the entire community remained effective even in disconnected pools. Synthesis and applications . Our results show that natural flow intermittence can confound river bioassessment, and that a set of new functional metrics could be used as effective alternatives to standard metrics in naturally disturbed intermittent rivers. Our findings suggest that water managers should incorporate alternative functional metrics in the routine biomonitoring of naturally disturbed rivers.

Traditional cultivation terraces are one of the most ancient and conspicuous agricultural landscapes in mountain and hilly regions of the Mediterranean basin. Spreading out from Asia, the first terraces in the Mediterranean region date from the Bronze Age and the classical Hellenic and Roman periods, reaching their greatest spatial extent during the eighteenth and nineteenth centuries. Under optimum management, these systems contribute to the conservation of soil and water resources by increasing infiltration and decreasing sediment yield. However, traditional management and cultivation ceased on many terraced landscapes of the northern-shore Mediterranean countries during the twentieth century, with variable results. An extensive bibliographic review and meta-analysis was carried out to explore the main effects of land abandonment of Mediterranean agricultural terraces on local hydrological and geomorphological processes. Our results point to the development of vegetation cover and degradation of terraced structures (e.g., walls, terrace risers, channels) as the main critical factors controlling the hydrological behaviour (i.e., runoff production and hydrological connectivity) of abandoned terrace systems. Severe geomorphological problems, in the form of intense surface erosion, aggressive piping and gullying, occurred under special climatic (semi-arid climate), lithologic (dispersive marls) and structural (high vertical hydraulic gradient) conditions. Dense colonization by vegetation proved to be of major importance for controlling surface erosion. Vegetation, however, showed a limited capacity to control the activity of mass movements in most cases. Mass movements in the form of small soil slips primarily affected long-abandoned terraces in hillslope concavities and valley bottom positions that concentrate (surface and subsurface) water fluxes and show recurrent soil saturation. In humid terraced landscapes characterized by high hillslope gradients and terrace ri

Soil water-content (SWC) variability in forest ecosystems is affected by complex interactions between climate, topography, forest structure and soil factors. However, detailed studies taking into account the combined effects of these factors are scarce. This study's main aims were to examine the control that throughfall exerts on local spatial variation of near-surface soil water-content and to combine this information with forest structure and soil characteristics, in order to analyze all their effects together. Two stands located in the Vallcebre Research Catchments (NE Spain) were studied: one dominated by Quercus pubescens and the other by Pinus sylvestris. Throughfall and the related shallow SWC were monitored in each plot in 20 selected locations. The main characteristics of the nearest tree and soil parameters were also measured. The results indicated that mean SWC increment at the rainfall event scale showed a strong linear relationship with mean throughfall amount in both forest plots. The % of locations with SWC increments increased in a similar way to throughfall amount in both forest plots. The analyses considering all the effects together indicated again that throughfall had a significant positive effect in both forest plots, while soil litter depth showed a significant negative effect for the oak plot but lower statistical significance for the pine plot, showing a comparable –although more erratic– influence of the organic forest floor for this plot. These results, together with lower responses of SWC to throughfall than expected in rainfall events characterized by low preceding soil water-condition and high rainfall intensity, suggest that litter layer is playing an important role in controlling the soil water-content dynamics. The biometric characteristics of the nearest trees showed significant but very weak relationships with soil water-content increment, suggesting that stemflow and throughfall may act at lower distances from tree trunk than those

Obtaining representative hydrometric values is essential for characterizing extreme events, hydrological dynamics and detecting possible changes on the long-term hydrology. Reliability of streamflow data requires a temporal continuity and a maintenance of the gauging stations, which data are affected by epistemic and random sources of error. An assessment of discharge meterings' and stage-discharge rating curves' uncertainties were carried out by comparing the accuracy of the measuring instruments of two different hydrometric networks (i.e., one analogical and one digital) established in the same river location at the Mediterranean island of Mallorca. Furthermore, the effects of such uncertainties were assessed on the hydrological dynamics, considering the significant global change impacts beset this island. Evaluation was developed at four representative gauging stations of the hydrographic network with analogic (≈40 years) and digital (≈10 years) data series. The study revealed that the largest source of uncertainty in the analogical (28 to 274%) and in the digital (17–37%) networks were the stage-discharge rating curves. Their impact on the water resources was also evaluated at the event and annual scales, resulting in an average difference of water yields of 183% and 142% respectively. Such improvement on the comprehension of hydrometric networks uncertainties will dramatically benefit the interpretation of the long-term streamflow by providing better insights into the hydrologic and flood hazard planning, management and modelling. © 2019

The isotopic composition of precipitation (D and 18O) has been widely used as an input signal in water tracer studies. Whereas much recent effort has been put into developing methodologies to improve our understanding and modelling of hydrological processes (e.g., transit-time distributions or young water fractions), less attention has been paid to the spatio-temporal variability of the isotopic composition of precipitation, used as input signal in these studies. Here, we investigated the uncertainty in isotope-based hydrograph separation due to the spatio-temporal variability of the isotopic composition of precipitation. The study was carried out in a Mediterranean headwater catchment (0.56 km2). Rainfall and throughfall samples were collected at three locations across this relatively small catchment, and stream water samples were collected at the outlet. Results showed that throughout an event, the spatial variability of the input signal had a higher impact on hydrograph separation results than its temporal variability. However, differences in isotope-based hydrograph separation determined preevent water due to the spatio-temporal variability were different between events and ranged between 1 and 14%. Based on catchment-scale isoscapes, the most representative sampling location could also be identified. This study confirms that even in small headwater catchments, spatio-temporal variability can be significant. Therefore, it is important to characterize this variability and identify the best sampling strategy to reduce the uncertainty in our understanding of catchment hydrological processes. © 2018 John Wiley & Sons, Ltd.

This paper presents the main results obtained from the study of hydrological processes in the Vallcebre Research Catchments since 1988. Distributed hydrometric measurements, environmental tracers and hydrological modelling were used to understand Mediterranean catchment behaviour and to provide new data to help assess the global change effects on these catchments' water resources. Thirty years of hydrological processes observation in the Vallcebre Research Catchments have increased understanding not only of their hydrological response, but also of the main hydrological and erosion processes characteristic of Mediterranean mountain catchments. This paper briefly summarises the main results obtained since 1988 on ecohydrological processes, hydrological response, runoff generation processes, erosion and sediment transport. Some of the main findings from this research are (i) the importance of temporal variability in precipitation to determine the hydrological processes; (ii) the paramount role played by forest cover in reducing soil water content; (iii) the marked influence of antecedent wetness conditions on runoff generation that determine different runoff responses; (v) the dominant contribution of pre-existing water during floods; (vi) the importance of freezing-thawing processes in badland areas on erosion and the role of summer convective storms in controlling sediment transport., Este trabajo presenta los principales resultados sobre el estudio de los procesos hidrológicos obtenidos en las cuencas de investigación de Vallcebre desde 1988. Se han utilizado aproximaciones metodológicas complementarias, tales como mediciones hidrométricas distribuidas, trazadores ambientales y modelización hidrológica con la finalidad de mejorar la comprensión de la respuesta de las cuencas mediterráneas y proporcionar nuevos conocimientos válidos para evaluar los efectos de cambio global en los recursos hídricos de estas cuencas. Treinta años de observaciones de los procesos hidrológicos en las cuencas de investigación de Vallcebre han permitido comprender no sólo su respuesta hidrológica, sino también los principales procesos hidrológicos y de erosión propios de las cuencas mediterráneas. Este artículo resume los principales resultados obtenidos desde 1988 sobre los procesos ecohidrológicos, la respuesta hidrológica, los procesos de generación de escorrentía, la erosión y el transporte de sedimentos. Algunos de los principales resultados de estas investigaciones son (i) la crucial importancia de la variabilidad temporal de las precipitaciones en los procesos hidrológicos; (ii) el papel fundamental de la cubierta forestal en la reducción del contenido hídrico del suelo; (iii) la marcada influencia de las condiciones de humedad antecedentes en la generación de escorrentía y su efecto en las diferentes respuestas hidrológicas; v) la contribución dominante de las aguas preexistentes durante las crecidas; vi) la importancia que tienen sobre la erosión los procesos de hielo-deshielo en las áreas de badlands y el papel de las tormentas convectivas de verano en el transporte de sedimentos.

This paper presents the main results obtained from the study of hydrological processes in the Vallcebre Research Catchments since 1988. Distributed hydrometric measurements, environmental tracers and hydrological modelling were used to understand Mediterranean catchment behaviour and to provide new data to help assess the global change effects on these catchments' water resources. Thirty years of hydrological processes observation in the Vallcebre Research Catchments have increased understanding not only of their hydrological response, but also of the main hydrological and erosion processes characteristic of Mediterranean mountain catchments. This paper briefly summarises the main results obtained since 1988 on ecohydrological processes, hydrological response, runoff generation processes, erosion and sediment transport. Some of the main findings from this research are (i) the importance of temporal variability in precipitation to determine the hydrological processes; (ii) the paramount role played by forest cover in reducing soil water content; (iii) the marked influence of antecedent wetness conditions on runoff generation that determine different runoff responses; (v) the dominant contribution of pre-existing water during floods; (vi) the importance of freezing-thawing processes in badland areas on erosion and the role of summer convective storms in controlling sediment transport., Este trabajo presenta los principales resultados sobre el estudio de los procesos hidrológicos obtenidos en las cuencas de investigación de Vallcebre desde 1988. Se han utilizado aproximaciones metodológicas complementarias, tales como mediciones hidrométricas distribuidas, trazadores ambientales y modelización hidrológica con la finalidad de mejorar la comprensión de la respuesta de las cuencas mediterráneas y proporcionar nuevos conocimientos válidos para evaluar los efectos de cambio global en los recursos hídricos de estas cuencas. Treinta años de observaciones de los procesos hidrológicos en las cuencas de investigación de Vallcebre han permitido comprender no sólo su respuesta hidrológica, sino también los principales procesos hidrológicos y de erosión propios de las cuencas mediterráneas. Este artículo resume los principales resultados obtenidos desde 1988 sobre los procesos ecohidrológicos, la respuesta hidrológica, los procesos de generación de escorrentía, la erosión y el transporte de sedimentos. Algunos de los principales resultados de estas investigaciones son (i) la crucial importancia de la variabilidad temporal de las precipitaciones en los procesos hidrológicos; (ii) el papel fundamental de la cubierta forestal en la reducción del contenido hídrico del suelo; (iii) la marcada influencia de las condiciones de humedad antecedentes en la generación de escorrentía y su efecto en las diferentes respuestas hidrológicas; v) la contribución dominante de las aguas preexistentes durante las crecidas; vi) la importancia que tienen sobre la erosión los procesos de hielo-deshielo en las áreas de badlands y el papel de las tormentas convectivas de verano en el transporte de sedimentos.

La utilidad de los estudios en pequeñas (< 10 km2) cuencas ha sido reiteradamente reconocida a lo largo de la historia de la investigación hidrológica. Este prólogo al número especial de Cuadernos de Investigación Geográfica – Geographical Research Letters sobre investigaciones hidrológicas a largo plazo en pequeñas cuencas en Europa destaca las principales razones para fomentar los estudios en pequeñas cuencas y revisa su creciente uso, empezando por los estudios de cuenca llevados a cabo en Suiza con fines de gestión del territorio, seguidos por el desarrollo de programas de investigación más interdisciplinares que utilizaron las cuencas como laboratorios de campo, observatorios a largo plazo, lugares para validar métodos y modelos, y para formar a jóvenes investigadores. Este volumen incluye nueve contribuciones sobre estudios llevados a cabo en sitios instrumentados a largo plazo en varios países europeos y pretende mostrar la relevancia del uso de pequeñas cuencas en la investigación hidrológica en Europa., The usefulness of small (< 10 km2) catchments has been repeatedly recognized during the recent history of hydrological research. This foreword to the special issue of Cuadernos de Investigación Geográfica – Geographical Research Letters devoted to long term hydrological research in small catchment in Europe highlights the main reasons for promoting the small catchment approach and revises its growing use, starting with the first catchment studies in Switzerland for management purposes, and followed by the development of more interdisciplinary research programs that used small catchments as field laboratories, long-term observatories, sites for method and model validation, and places for training young researchers. The volume includes nine contributions concerning studies carried out in long term monitoring sites in several European countries and aims at showing the relevance of the small catchment approach in hydrological research in Europe.

Even though throughfall is the dominant input of water to forests, many questions remain about the temporal fine-scale mechanisms controlling the redistribution of rainfall by forest canopies. Hydrologists must therefore combine different methods in novel way to achieve breakthroughs in our understanding of rainfall partitioning and its interactions with pre-event water storage on tree surfaces. Here, we apply a combination of isotopes (oxygen and hydrogen) and laser disdrometers to quantify the isotopic composition of free, splash, and release throughfall at the sub-event timescale. For individual events, isotopic differences between throughfall and open rainfall may indeed vary in magnitude and direction as a result of evaporation, exchange or selection processes. Our working hypothesis is that relating the sub-event timescale throughfall measurements with that of drop size distribution and of isotopic variations will provide an unprecedented understanding of the throughfall generation process. Such an understanding would be required to fully and accurately track the transfer of moisture from the canopy to the forest floor. This work performed in a Scots pine forest under Mediterranean conditions is based on the continuous (5min data) measurement of open rainfall and throughfall amounts (by means of tipping-buckets) and of drop size distributions (laser disdrometers) at the same two locations. In addition, rainfall and throughfall passing through the laser disdrometers and the tipping buckets are finally collected sequentially by means of automatic samplers. This presentation will show preliminary findings on the relationship between throughfall drop size and isotopic composition for several rainfall events of different magnitudes and intensities, helping to reveal how water moves through flowpaths and storage reservoirs in the canopy.

Although temporary rivers are very common in many regions of the world, there has been a general failure to understand, protect and manage this type of freshwater ecosystems. In Europe, the implementation of the Water Framework Directive has been unable to provide a solution to determine the ecological status of temporary water bodies. The first reason for this failure is the lack of attention to and knowledge of the hydrological regime of these rivers that includes diverse phases relevant to aquatic life such as flow, stagnant pools and dry stream bed. The second reason is that quality assessment tools using biological quality indicators have been developed primarily for perennial rivers and therefore are inadequate for rivers with hydrological regimes as complex as temporary rivers undergo. In order to tackle these challenges, the LIFE+ TRivers project (LIFE13 ENV/ES/000341) has addressed the following targets: - Development and implementation of operational methods for obtaining information on the temporal patterns of the diverse states and phases that characterize the hydrological regime of temporary rivers. - Classification of temporary river regimes on the basis of updated concepts beyond flow measurements, critical for the development of aquatic life. - Categorization of the diverse regime features that help to assess the degree of hydrological alteration of the natural regimes and obtain an hydrological status. - Design of calendars and protocols for monitoring the characteristics of bio indicators according to the diverse aquatic phases of the river regime. - Test and improvement of biological quality indicators for their application to temporary rivers. - Development of the TREHS software tool that includes all the former features. TREHS has been tested for hydrology in over 100 test water bodies and for all the developments in 25 pilot river sites. - Public participation and proposal of measures for improving both the hydrological and biological status of

(1) Mediterranean Ecogeomorphological and Hydrological Connectivity Research Team (http://medhycon.uib.cat), Department of Geography, University of the Balearic Islands, Carretera de Valldemossa Km 7.5 07122, Palma, Spain, (2) Institute of Agro-Environmental and Water Economy Research –INAGEA, University of the Balearic Islands, (3) Institute of Earth and Environmental Science, University of Potsdam, Karl-Liebknecht-Straße 24/25, 14476 Potsdam-Golm, Germany, (4) Institute of Environmental Assessment and Water Research (IDAEA), Spanish Research Council (CSIC), Jordi Girona 18, 08034 Barcelona, Spain Mediterranean catchments are characterized by high inter-intra annual precipitation variability and summer drought. The hydrological regime is characterized by ephemeral behaviour due to the direct rainfall-runoff relationship. Furthermore, extreme precipitations can generate an amount of rainfall higher than 200 mm in 24 hours with short response time. These events occurred normally under wet soil moisture conditions. The Mediterranean catchment morphology is a favourable factor for flash floods: short catchments with a high gradient slope. Others factor that condition the hydrological regime are the presence of limestone lithology and the impact of human activities on fluvial systems as geomorphological changes in channels and flood plains. The aim of this study is analyse the hydrological response of five hydrological years (2012-17) in an agricultural headwater catchment (i.e. < 4 km2) at different time scales. Rainfall-runoff relationship was carried out at annual and seasonal scale through the flow duration computation, the variability index, 30/70 ratio, quick flow response ratio and base flow index. The rainfall-runoff relationship at event scale was carried out through a Pearson correlation matrix using different variables extracted from the hyetograph and hydrograph. These variables were placed into two groups: a) antecedent conditions and b) event conditions. T

[EN] Mediterranean catchments are characterized by strong nonlinearities in their hydrological behaviour. Properly simulating those nonlinearities still represents a great challenge and, at the same time, an important issue in order to improve our knowledge of their hydrological behaviour. The main aim of this work is find out diverse modelling approaches to reproduce the observed nonlinear hydrological behaviour in a small Mediterranean catchment, Can Vila (Vallcebre, NE Spain). To this end, three hydrological models were considered: two lumped models called LU3 and LU4 of increasing complexity, and a distributed model called TETIS. The structures of these different models were used as hypotheses, which could explain and reproduce the observed nonlinear behaviour at the outlet. Four analyses were carried out: (i) goodness-of-fit criteria analysis, (ii) residual errors analysis, (iii) sensitivity analysis and (iv) multicriteria analysis based on the concept of Pareto Optimal. These analyses showed the higher capability and robustness of the distributed model to reproduce the observed complex hydrological behaviour in this catchment.

To improve understanding of DOC dynamics in seasonal Mediterranean environments, rainfall, soil water, groundwater and stream water samples were taken during a 27-month period in the Can Vila catchment (northeast Spain). Using these data, we characterized DOC dynamics in the different hydrological compartments and analysed the factors affecting them. We also analysed DOC dynamics during storm events and the factors that control DOC delivery to the stream. The results show some seasonality in rainwater and soil water DOC concentrations, while no clear seasonality was observed in stream water and groundwater, where DOC dynamics were strongly related to discharge and water table variations. For storm events with several discharge peaks, the slope of the discharge–DOC concentration relationship was higher for the first peak. The rather similar dynamics of stream water DOC concentration in all floods contrast with the observed diversity of hydrological processes. This raises the question of the origin of the observed rapid DOC increase.

Aim: Mediterranean terrestrial ecosystems serve as reference laboratories for the investigation of global change because of their transitional climate, the high spatiotemporal variability of their environmental conditions, a rich and unique biodiversity and a wide range of socio-economic conditions. As scientific development and environmental pressures increase, it is increasingly necessary to evaluate recent progress and to challenge research priorities in the face of global change. Location: Mediterranean terrestrial ecosystems. Methods: This article revisits the research priorities proposed in a 1998 assessment. Results: A new set of research priorities is proposed: (1) to establish the role of the landscape mosaic on fire-spread; (2) to further research the combined effect of different drivers on pest expansion; (3) to address the interaction between drivers of global change and recent forest management practices; (4) to obtain more realistic information on the impacts of global change and ecosystem services; (5) to assess forest mortality events associated with climatic extremes; (6) to focus global change research on identifying and managing vulnerable areas; (7) to use the functional traits concept to study resilience after disturbance; (8) to study the relationship between genotypic and phenotypic diversity as a source of forest resilience; (9) to understand the balance between C storage and water resources; (10) to analyse the interplay between landscape-scale processes and biodiversity conservation; (11) to refine models by including interactions between drivers and socio-economic contexts; (12) to understand forest-atmosphere feedbacks; (13) to represent key mechanisms linking plant hydraulics with landscape hydrology. Main conclusions: (1) The interactive nature of different global change drivers remains poorly understood. (2) There is a critical need for the rapid development of regional- and global-scale models that are more tightly connected with larg