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Gully erosion is a complex socio-environmental issue that has a negative influence on natural resources and has significant economic costs. This study examined the performance of two ensemble models based on multicriteria decision making (MCDM) analysis, analytic hierarchy process (AHP), weight of evidence (WoE) and random forest (RF) for spatiotemporal monitoring of gully erosion sensitivity (GES) from 1988 to 2019 as well as a projection for 2040 in a semi-arid area. The findings revealed that the vulnerable areas significantly raise between 1988 and 2040 (> 27% of the study area since 2019), in perfect alignment with a rapid deterioration of the vegetation cover (−16%), a general decrease in rainfall (−25% since 2019), and an increase in land surface temperature (LST) average (30°–37° approximatively). Finally, the area under curve (AUC) value revealed a high prediction performance for both developed models (AUC = 0.888 for WoE-RF and 0.886 for MCDM-WoE-AHP). [ABSTRACT FROM AUTHOR]

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A flash-flood event hit the northeastern part of Mallorca on 9 October 2018, causing 13 casualties. Mallorca is prone to catastrophic flash floods acting on a scenario of deep landscape transformation caused by Mediterranean tourist resorts. As global change may exacerbate devastating flash floods, analyses of catastrophic events are crucial to support effective prevention and mitigation measures. Field-based remote-sensing and modelling techniques were used in this study to evaluate rainfall–runoff processes at the catchment scale linked to hydrological modelling. Continuous streamflow monitoring data revealed a peak discharge of 442 m 3 s -1 with an unprecedented runoff response. This exceptional behaviour triggered the natural disaster as a combination of heavy rainfall (249 mm in 10 h), karstic features and land cover disturbances in the Begura de Salma River catchment (23 km 2). Topography-based connectivity indices and geomorphic change detection were used as rapid post-catastrophe decision-making tools, playing a key role during the rescue search. These hydrogeomorphological precision techniques were combined with the Copernicus Emergency Management Service and "ground-based" damage assessment, which showed very accurately the damage-driving factors in the village of Sant Llorenç des Cardassar. The main challenges in the future are to readapt hydrological modelling to global change scenarios, implement an early flash-flood warning system and take adaptive and resilient measures on the catchment scale. [ABSTRACT FROM AUTHOR]

Concentrated erosion, a major feature of land degradation, represents a serious problem for soil and water resources management and a threat to ecosystems. Understanding the internal mechanisms (de‐)coupling sediment pathways can improve the management and resilience of catchments. In this study, concentrated erosion and deposition forms were mapped accurately through field and aerial unmanned aerial vehicle (UAV) campaigns, in order to assess the evolution of connectivity pathways over a series of three contrasted and consecutive flood events occurring between October 2016 and January 2017 (return period ranging from 0.5 to 25 years) in a small Mediterranean agricultural catchment (Can Revull, Mallorca, Spain; 1.4 km2). In addition, a morphometric index of connectivity (IC) was used to identify the potential trajectories of different concentrated erosion forms and deposition areas. IC predictions were calibrated by identifying the optimal critical thresholds, i.e. those most consistent with field observations after each of the events studied. The results found that the index performed well in predicting the occurrence and the length/area of the different type of landforms, giving kappa (κ) coefficients of variation ranging between 0.21 and 0.92 and linear correlations R2 between 0.33 and 0.72. The type of landform affected the correspondence of IC predictions and field observations, with lower thresholds the greater the magnitude of their associated geomorphic processes. Rainfall magnitude proved to be a very important factor controlling the development of erosion and deposition landforms, with large differences in length/area between the contrasted events. The evolution of the observed trajectories revealed feedback dynamics between the structural and functional connectivity of the catchment, in which morphological changes determined the spatial distribution of the processes' activity in the successive events and vice versa. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The investigation of form and processes in geomorphology and ecology is highly dependent on topographic data: a reliable digital terrain representation is in fact a key issue across environmental and earth sciences. In many cases, the processing of high‐resolution topographic data (e.g., light detection and ranging (LiDAR), structure from motion) has to face issues such as void filling, vegetation/feature removal and interpolation accuracy that are usually related to (i) intrinsic limitations of the adopted technology, (ii) local conditions affecting the survey or (iii) specific design scenario. In this paper, we develop a methodology to test the accuracy of an image inpainting algorithm to fill data voids in complex mountain areas. The devised experiment exploits the availability of a high‐resolution, LiDAR‐derived digital terrain model and the inpainting approach accuracy is checked against some widely used interpolation techniques (natural neighbor, spline, inverse distance weighting, kriging). In order to better mimic the actual surface texture, a methodology to introduce local topographic variability to the interpolated surface is also presented. The results show a better performance of the inpainting algorithm especially in the case of complex and rugged topography. Two examples showing an effective usage and accuracy of the proposed technique are reported, highlighting the drawbacks that a poor surface representation can introduce. The whole procedure is made freely available within a Matlab® script with the addition of sample files. ©2019 John Wiley & Sons, Ltd. ©2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A flash-flood event hit in the 9th October 2018 the northeastern part of Mallorca Island, causing 13 casualties. This island is prone to catastrophic flash floods acting on a scenario that illustrates the deep landscape transformation of Mediterranean tourist resorts. As global change may exacerbate devastating flash floods, comprehensive analyses of catastrophic events are crucial to support effective prevention and mitigation measures. Field-based, remote-sense and modelling techniques were used in this study to evaluate rainfall-runoff processes at catchment scale linked to hydrological modelling. Continuous streamflow monitoring data revealed a peak discharge 442 m³ s-1 with an unprecedented runoff response (lag time, 15'). This very flashy behaviour triggered the natural disaster as a combination of heavy rainfall (246 mm in 10 h), karstic features and land cover disturbances in the Begura de Saumà River catchment (i.e., 23 km²). Topography-based connectivity index and geomorphic change detection were used as a rapid post-catastrophe decision-making tool, playing a key role during the rescue searching tasks. These hydrogeomorphological precision techniques were also applied in combination with Copernicus EMS and ground-based damage assessment illustrating with high accuracy the damage driving factors in the village of Sant Llorenç des Cardassar. The main challenges in the future are to readapt hydrological modelling to global change scenarios, implement an early flash flood warning system and apply adaptive and resilient measures at catchment scale. [ABSTRACT FROM AUTHOR]

As part of the Changing the Face of the Mediterranean Project, we consider how human pressure and concomitant erosion has affected a range of Mediterranean landscapes between the Neolithic and, in some cases, the post-medieval period. Part of this assessment comprises an investigation of relationships among palaeodemographic data, evidence for vegetation change and some consideration of rapid climate change events. The erosion data include recent or hitherto unpublished work from the authors. Where possible, we consider summed probabilities of 14C dates as well as the first published synthesis of all known optically stimulated luminescence dated sequences. The results suggest that while there were some periods when erosion took place contemporaneously across a number of regions, possibly induced by climate changes, more often than not, we see a complex and heterogeneous interplay of demographic and environmental changes that result in a mixed pattern of erosional activity across the Mediterranean. [ABSTRACT FROM AUTHOR]

Abstract: In recent decades, the dynamics of global change in developed countries has led to significant alterations in the hydrological and sediment dynamics of terraced land. Agricultural terraces were built to control overland flow and prevent erosion, acting as buffers and barriers throughout the sediment cascading system. Their abandonment and degradation increase the sensitivity of the catchment, promoting the collapse of dry‐stone walls and the reworking of stored sediment. In this study, a geomorphometric index of connectivity—derived from high‐resolution LiDAR data (0.9 pt/m, RMSE < 0.2 m)—analysed the spatial patterns of structural connectivity in a small Mediterranean catchment (4.8 km2) characterized by a massive presence of terraces (37% of the surface area). The morphological characteristics of these anthropogenic features generated a dual effect: (a) general disconnectivity between different compartments of the catchment and (b) concentration of water and sediment flows along preferential pathways promoted by a cascade effect of collapse within the terraced areas. The fieldwork found that 73% of wall collapses were located on these pathways that showed high index of connectivity values (>Q8). This spatial matching was related to feedback dynamics between structural and functional connectivity, in which the failure of walls increases the concentration of runoff, which in turn accelerates the hydraulic processes causing their collapse. Identifying the most connected pathways within the most vulnerable structures in an integrated analysis could be a cost‐effective strategy for establishing priority areas for the management of terraced lands. [ABSTRACT FROM AUTHOR]

Abstract: Basin management demands a sound understanding of sediment dynamics, particularly in Mediterranean mountain catchments with badlands, which affect water bodies and freshwater ecosystems. Connectivity has emerged as a framework for understanding how sediments move between geomorphic zones. We analyse the feasibility of excess lead‐210 (210Pbex) to study sediment connectivity in a 4‐km2 Mediterranean mountain basin with badlands (Vallcebre research catchments, Eastern Pyrenees) by applying mass‐balance models for hypothesis generation and experimental testing. Badlands in the area are weathered by freezing during the winter and are eroded in summer by high‐intensity showers. The eroded sediments may remain deposited within the streams from months to years. Application of 210Pbex balance models in our basin suggests: (i) a saw‐tooth seasonal pattern of badland surface 210Pbex activities (increasing from October to May, and depleted in summer) and (ii) a downstream increase in sediment activity due to fallout lead‐210 accumulation in stream‐bed sediment deposits. Our experimental results (obtained during 2013 and 2014) showed low sediment 210Pbex concentrations, illustrating the fresh‐rock origin of sediments, but also hampering their study due to high measurement uncertainty (especially for sediments with d50 > 20 μm) and dependence on sampling methods. Suspended sediment 210Pbex activity reproduced the simulated seasonal activity patterns for the badland surfaces. However, sediment activity decreased downstream, suggesting that flushing of fine sediments by flooding prevents fallout lead‐210 accumulation on the stream bed. Overall, high sediment connectivity was revealed between the badlands, streams and outlet of the basin, as well as the fast transmission of 210Pbex by the finest sediment fraction. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Wildfires and agricultural activities are relevant factors affecting soil quality, hydrological cycle and sedimentary dynamics. Land abandonment leads to afforestation, which increases fire risk and land degradation. However, no studies have yet evaluated the effect of combining the two factors, which occur frequently in Mediterranean ecosystems. This study assessed the changes in soil quality caused by the abandonment of terraces in two microcatchments (<2.5 ha) affected distinctly by wildfires (once and twice burned) and in an unburned control microcatchment by analyzing soil quality parameters, biochemical indices and spatial patterns of hydrological and sediment connectivity. Soil samples were collected in thirty-six plots (25 m²) representing terraced and non-terraced areas within these microcatchments. Unburned non-terraced plots had higher organic matter content and higher microbiological and enzymatic activities than other plots. Plots in abandoned terraces had lower soil quality indices, regardless of the fire effect. Land abandonment induced changes in the spatial patterns of hydrological connectivity, leading to concentrated runoff, enhanced erosion and soil degradation. Fire also negatively affected soil quality in both terraced and non-terraced plots. However, microbiological communities had different positive post-fire recovery strategies (growth and activity), depending on the previous soil conditions and land uses, which is indicative of the resilience of Mediterranean soil ecosystems. [ABSTRACT FROM AUTHOR]

This paper investigates suspended sediment transport and dynamics of two nested agricultural lowland Mediterranean catchments with a difference of two orders of magnitude in the surface area (i.e., 1 and 264 km2). The effects of the drainage catchment area over the specific suspended sediment yield are assessed by using the nested approach over various timeframes. A detailed analysis of the rainfall-runoff-sediment transport relationships during the 2-year study period shows that the hydrological and sedimentological responses were extremely variable for both catchments. Very low or no correlations were observed between the rainfall intensity and the selected hydrological variables and sediment loads. However, remarkable or high correlations were obtained between the rainfall intensity and the maximum and average suspended sediment concentrations, indicating that rainfall per unit time has little control on the hydrological response, but that, simultaneously, its high-erosive power triggers sediment production, increasing the sedimentary response of the catchments. This study also illustrates how sediment is mainly transported during floods, producing predominantly clockwise hysteretic loops. Moreover, the small headwater catchment exerts a reduced (or even negligible) effect over the hydro-sedimentary response of the larger downstream catchment, caused by the reduced sediment availability in a landscape with an inherent disconnection of the sediment pathways. [ABSTRACT FROM AUTHOR]

Over short and long timescales, wildfires can be an important cause of hydrological and geomorphological change. Mediterranean rivers are part of a fire-prone and high-energy environment in which the timing of major storms in relation to fire influences the impact on fluvial systems; accordingly, the identification of major sources, stores and fluxes of sediments is essential for providing more effective post-fire management strategies. In this study, caesium-137 and excess lead-210 were used as tracers to quantify the proportional contributions of fine sediment from hillslope surface and channel bank sources to suspended sediment and channel bed deposits before the impact of a forest wildfire in Na Borges, a Mediterranean groundwater-dominated river. It also compared burnt and unburnt spatial sources of sediment within a single catchment and the extent to which burnt material was transported downstream. The study focused on two small and steep sub-catchments, where just one of the catchments was partially affected by a wildfire. The pre-fire dynamics indicated that surface soils were the main sediment source in these ephemeral creeks. Post-fire sediment dynamics were characterised by a single flood event with a short recurrence interval (i.e. return period ca. <1 year). Sediment generated from the burnt area contributed 12% on average to bed-stored sediments within the burnt catchment, which reduced downstream to 5% along the main channel of the Na Borges River. The findings demonstrate the potential for using fallout radionuclide tracers to understand the wider impacts of wildfires on fluvial environments located outside of the burn area. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Samples of suspended and fine channel bed sediment were used to examine the spatial and temporal variability in the amount of fine-grained sediment and associated contaminants temporarily stored in the Na Borges River (319km2) in Mallorca and the relationship of such channel storage to the fluxes of fine sediment and associated contaminant through the system. This Mediterranean groundwater-dominated river drains a predominantly agricultural catchment, although urbanisation during the twentieth century has changed the catchment hydrology. A re-suspension technique was used to obtain estimates of channel storage at monthly intervals during the 2004–2005 hydrological year at eight locations along the main stem of the stream (i.e. 26km). The estimates of fine sediment storage ranged between 0 and 13,000gm−2, with a mean value of 2400gm−2. Only Cu exceeded the critical threshold (36μgg−1), established by existing guidelines for the contaminant content of fluvial sediment. The results demonstrated significant spatial and temporal variability, in response to the influence of urban point sources, agricultural practises, seasonal groundwater interactions and the first-flush effect. The amount of fine sediment entering storage during the study period was 515.2t, representing the net increase in storage over the study period. As a result, the mean specific storage was 21tkm−1. Suspended-sediment load and temporary fine sediment storage are the two basic components of the channel sediment budget that interact to determine sediment transport through a channel system, and they can therefore be used to compute the total input of sediment and associated contaminants to the system. Accordingly, storage values were compared with estimates of suspended sediment load and associated contaminant load values at three measuring stations along the river. During the study period, storage in the main channel system represented 87% of the sediment input and 68% of the contaminant input, indicating that deposition was more important than transport. The low gradient of the main channel and the low return period (i.e. 0–2.5years) of the flood events that occurred during the study period meant that remobilised bed sediment and associated contaminants were redeposited downstream rather than being flushed to the catchment outlet as suspended sediment. Furthermore, the river bed is dry during the summer months, allowing sealing and crusting processes to stabilise the sediment deposited during the wet season and thereby reduce its availability for remobilisation at the beginning of the next wet season. Together, these factors promote sediment deposition and storage, with the result that sediment progressively accumulate over several hydrological years until a major flood event (i.e. return period≈5years) evacuates the stored sediment. [Copyright &y& Elsevier]

Mediterranean rivers are characterized by the irregularity of flow, harsh hydrological fluctuations and a profound transformation as the result of human activity. In this study, we investigate the streamflow response of a Mediterranean temporary river in which different groundwater, agriculture and urban contributions play an important role. Streamflow was measured at three nested gauging stations installed along Na Borges River, a lowland agricultural catchment (319 km2) on the island of Mallorca. Based on two hydrological years (2004/05 and 2005/06), potential evapotranspiration and surface water-groundwater interaction generated a succession of four different hydrological periods playing an important role in baseflow dynamics. The runoff coefficients were very low (<5%). At the event scale, groundwater also controlled runoff response, being very different according to hydrogeology, antecedent conditions and human impacts. During dry seasons, wastewater and karstic spring discharges maintain an influent regime into some streams. As a result, intense rainstorms in late summer generated water volumes over the impervious urban surfaces involved, with the result that quickflow was significant because the hydrological pathways were active. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the annual, seasonal and event-scale variation transport of suspended sediment (SS) in Na Borges basin, an agricultural lowland basin in the island of Mallorca, Spain. It dwells on the analysis of its transport regimes through field measurements. It conceptualizes multiple regression models of total suspended sediment concentrations (SSC) and interprets its stormflow discharge. It reveals that there is an annual average of SS transport of 17.3 mg I-1 and a maximum of 2270 mg I-1. The multiple regression analysis demonstrates that rainfall is a process that plays a most significant role in the transport of SS from hillslopes to channels.

Mediterranean-climate catchments are characterized by significant spatial and temporal hydrological variability caused by the interaction of natural as well human-induced abiotic and biotic factors. This study investigates the non-linearity of rainfall-runoff relationship at multiple temporal scales in representative small Mediterranean-climate catchments (i.e., <10 km2) to achieve a better understanding of their hydrological response. The rainfall-runoff relationship was evaluated in 43 catchments at annual and event—203 events in 12 of these 43 catchments—scales. A linear rainfall-runoff relationship was observed at an annual scale, with a higher scatter in pervious (R2: 0.47) than impervious catchments (R2: 0.82). Larger scattering was observed at the event scale, although pervious lithology and agricultural land use promoted significant rainfall-runoff linear relations in winter and spring. These relationships were particularly analysed during five hydrological years in the Es Fangar catchment (3.35 km2; Mallorca, Spain) as a temporal downscaling to assess the intra-annual variability, elucidating whether antecedent wetness conditions played a significant role in runoff generation. The assessment of rainfall-runoff relationships under contrasted lithology, land use and seasonality is a useful approach to improve the hydrological modelling of global change scenarios in small catchments where the linearity and non-linearity of the hydrological response—at multiple temporal scales—can inherently co-exist in Mediterranean-climate catchments. [ABSTRACT FROM AUTHOR]

Digital terrain models (DTMs) are a fundamental source of information in Earth sciences. DTM-based studies, however, can contain remarkable biases if limitations and inaccuracies in these models are disregarded. In this work, four freely available datasets, including Shuttle Radar Topography Mission C-Band Synthetic Aperture Radar (SRTM C-SAR V3 DEM), Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Map (ASTER GDEM V2), and two nationwide airborne light detection and ranging (LiDAR)-derived DTMs (at 5-m and 1-m spatial resolution, respectively) were analysed in three geomorphologically contrasting, small (3–5 km2) catchments located in Mediterranean landscapes under intensive human influence (Mallorca Island, Spain). Vertical accuracy as well as the influence of each dataset's characteristics on hydrological and geomorphological modelling applicability were assessed by using ground-truth data, classic geometric and morphometric parameters, and a recently proposed index of sediment connectivity. Overall vertical accuracy—expressed as the root mean squared error (RMSE) and normalised median deviation (NMAD)—revealed the highest accuracy for the 1-m (RMSE = 1.55 m; NMAD = 0.44 m) and 5-m LiDAR DTMs (RMSE = 1.73 m; NMAD = 0.84 m). Vertical accuracy of the SRTM data was lower (RMSE = 6.98 m; NMAD = 5.27 m), but considerably higher than for the ASTER data (RMSE = 16.10 m; NMAD = 11.23 m). All datasets were affected by systematic distortions. Propagation of these errors and coarse horizontal resolution caused negative impacts on flow routing, stream network, and catchment delineation, and to a lower extent, on the distribution of slope values. These limitations should be carefully considered when applying DTMs for catchment hydrogeomorphological modelling. [ABSTRACT FROM AUTHOR]

• Alteration of sediment properties during transport and storage in a temporary stream. • The spatial variability of soil properties was higher than the in-channel variability. • Colour properties showed the highest temporal and spatial stability. • Results are relevant for future sediment fingerprinting studies. Soil properties used as tracers in sediment fingerprinting studies are assumed to remain stable or vary in a predictable way in their transfer from sources to sinks, allowing a comparison with suspended sediment properties. Attention to the conservative behaviour of soil properties has largely focused on the differences in the particle size and organic matter content between sources and target sediments. However, in-channel biochemical alterations are also known to occur, and their magnitude is still poorly understood. An experiment to investigate the in-channel variations of soil properties during transport and storage was carried out with the most common soil properties used as tracers in sediment fingerprinting studies (i.e. colour, fallout radionuclides and geochemical elements). Twenty-eight soil samples collected from different land uses were introduced into an intermittent stream channel of a small Mediterranean catchment. Samples were recovered at different time intervals over one year. The changes in soil properties (average coefficient of variation 8.1 ± 8.8 %) were generally lower than the spatial variability of each source within the catchment (average coefficient of variation 16.3 ± 18.5 %). No significant differences were observed between samples from different land use types or when recovered at different time intervals. Soil properties that showed higher in-channel coefficients of variation were S, 137Cs, 210Pb ex , As, Mo and Na, with annual coefficients of variation > 19 %. Conversely, carbon (C) and colour properties were the most stable in time (average coefficient of variation 2.1 ± 0.4 % and 2.6 ± 2.2 %, respectively). The results presented will be informative with regard to performing future suspended sediment fingerprinting studies in Mediterranean catchments, providing a better understanding of which soil properties are more sensitive to in-channel biochemical alterations. [ABSTRACT FROM AUTHOR]

• Hydrology and sediment transport were compared in two intermittent rivers. • Lithology influenced the degree of flow intermittence more than rainfall. • Flow regime was the most relevant factor affecting sediment yield. • In Búger River, SSY was related to antecedent rainfall and peak discharge. • In Carapelle River, SSY was related to amount and intensity of rainfall. Flow and the sediment regime affect water quality and nutrient delivery in all river systems and are fundamental in sustaining the river ecosystem. This study aims to identify the most relevant factors affecting the flow regime and the suspended sediment transport in two Mediterranean intermittent rivers: the Búger (Spain) and the Carapelle (Italy). A set of hydrological indicators were used to characterize and classify the flow regime. High-resolution data, streamflow and suspended sediment concentration were used to quantify runoff and sediment yields at different temporal scales (annual, monthly, event). Rainfall, streamflow and sediment variables were used at the event scale to assess the rainfall-runoff-suspended sediment relationship through the Pearson correlation matrix. Hysteresis analysis provided information on sediment source dynamics. In the Búger River, the high degree of flow intermittence was mainly due to the presence of carbonate lithology and forest land use at headwaters promoting low values of runoff coefficient (2–10%) and specific suspended sediment yield (SSY; 0.5–46 t km−2 y−1). In the Carapelle River, the high values of annual runoff coefficient (14–35%), together with low flow intermittence and SSY (89–745 t km−2 y−1) were related to clay and flyschoid lithology. Most of the annual sediment yield (SY, t) was transported during floods. In Búger, SSY and maximum suspended sediment concentration (SSC max, g l−1) were checked against runoff, peak discharge and antecedent rainfall. In Carapelle, SSY and SSC max were checked against the amount and intensity of rainfall. The catchment size and the spatial distribution of rainfall, land uses and lithology played important roles in the flow regime, suspended sediment transport and hysteretic behaviour. Characterization of the flow regime linked to its main physical drivers improved understanding of the hydrological response and sediment transport variability of intermittent rivers. This study provided valuable insights into water resource management, improving the prediction of spatial patterns and of the intensity of sediment transport in river basins. [ABSTRACT FROM AUTHOR]