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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]

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]

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]

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]

• Colour parameters tracing suspended sediment sources after a wildfire. • Scanner and spectrometer derived colour tracers showed a high correlation. • Ash content discriminated burned and unburned sources. • Colour and fallout radionuclides provided analogous results. After a wildfire, total or partial removal of vegetal biomass and changes in physicochemical soil properties lead to an increase in overland flow and sediment yield. Eventual damage must be counteracted urgently by identifying erosion hotspots and by implementing post-fire management programmes and sampling campaigns. In this context, the sediment source fingerprinting technique is widely used to determine the origin of suspended sediments in catchments and to evaluate the effectiveness of sediment management programmes. It traditionally relies on the use of physical, biochemical and geochemical properties as tracers. However, measuring these tracers in the laboratory is often expensive and time-consuming. Colour tracers have been shown to greatly reduce time and cost, especially if a normal office scanner is used for measurements. Here we explored whether colour parameters can be used to investigate suspended sediment origin in burned catchments. To this end, sediment and ash were mixed artificially to verify colour linear additivity and ash influence on colour parameters. Colour parameters were then used for source ascription of suspended sediment samples (n = 9) collected during two years after a fire in a small Mediterranean catchment (Mallorca, Spain). In addition, reflectance-derived colour parameters were compared with those obtained using a normal office scanner. The close correlation between most chromatic indexes (obtained using both methods; p < 0.01) suggested that scanning is a good alternative for measuring soil and sediment colour. A Bayesian tracer mixing model (MixSIAR) determined the relative contribution of each source. The type of mixing model enables appropriate representation of natural and sampling uncertainty in tracer data. During the first events, suspended sediment originated mainly in burned surfaces, whereas the contribution of these decreased throughout the study period. Tracing results obtained using colour parameters were compared with calculations using 137Cs and 210Pb ex , as recognized tracers to discriminate between surface and subsurface sediment sources after wildfires. Estimated source ascriptions with both methods (i.e. reflectance-derived colour parameters and radionuclides) coincided in predicting the dominant source in 7 of the 9 samples measured. Colour tracers proved useful in discriminating between burned and unburned sources, making them suitable for suspended sediment source ascription and monitoring as part of post-fire management strategies. [ABSTRACT FROM AUTHOR]

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]

The influence of the sea and topography are vital factors in the atmospheric processes affecting any island, as they introduce peculiarities in the hydrosedimentary response of fluvial systems. In view of that, the relationship between the surface atmospheric conditions (weather types, WTs), rainfall, runoff and erosion dynamics in three small catchments located in Mallorca were analysed. The catchments are representative in terms of geomorphology and land use but also due to their location within the major rainfall areas previously identified in the island by (Sumner et al., 1993). Data of rainfall, runoff and sediment variables, coupled with calculated WTs were used for the 2013–2017 period. WTs frequency and distribution during this period were compared to the last climatic period reference (1981–2010) to test the climate validity of the study period. The results illustrated how hydrosedimentary response was mostly caused by eco-geographical patterns but also by differences in the response of each catchment to WTs, related to the intrinsic geographical position in the island and different exposures to humid winds. Anticyclonic WT was the most frequent, despite it being only involved in one flood event at the eastern catchment. Conversely, eastern and northeastern WTs generated more than 85% of the total runoff and sediment, representing only 39% of flood events. The understanding of the specific role of WTs on the island's hydrology was improved, considering that freshwater resources are scarce and eco-sociologically crucial. • Weather types, rainfall, and hydrosedimentary assessment in a Mediterranean island. • Three small contrasting catchments located in different rainfall areas of Mallorca. • Eastern and northeastern weather types generated >85% of runoff and sediment. • Low runoff and erosion values in Mediterranean standards by karstic features. • Sediment transport was extremely ephemeral due low frequency of easterly flows. [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]

In this study, a low-cost unmanned aerial vehicle was used to obtain multi-spectral high-resolution imagery (1.4 cm px−1) from 2 microcatchments (3.3 ha) with burned Mediterranean shrubland and pine forests. This imagery was used to calculate the blue normalized differential vegetation index and to generate digital elevation models for estimating the sediment connectivity index. Both indices enabled an integrated approach for deciphering how hydrological and sediment connectivity interact with vegetation as well as soil conservation structures. The application of spatial analysis improves our understanding of the feedback between biological and geomorphological processes. Local spatial data analysis established a significant link between local geomorphological and biological factors, enabling a precise identification of homogeneous areas at micro-catchment scale and the minimal size of vegetation units reacting to geomorphology as natural groups at plot-scale where management strategies and efforts should be applied. Establishing this local relationship between sediment connectivity and vegetation patterns through new and interdisciplinary methodologies represents a new strategy for the assessment of ecosystem dynamics and management. Unlabelled Image • Very high-resolution multi-spectral imagery are used to generate HR-DEM models. • Relations between sediment connectivity and post-disturbance vegetation dynamics are mapped. • Spatial data established significant links between local bio-geomorphological factors. • Hotspot areas where management strategies should be applied are identified. [ABSTRACT FROM AUTHOR]

Mediterranean humid mountains are ecological hotspots with high water availability that may accelerate their recovery after farmland abandonment, a widespread phenomenon in marginal areas of the European Mediterranean Region. This land use change led to secondary succession processes triggering changes in soil properties and soil microorganisms. This is the first study in assessing the environmental influence of both ecological succession and parent material over soil properties and soil bacterial communities in these habitats. To examine the effects of secondary succession and elucidate the role of parent material in soil bacterial communities, six soil plots were sampled from the combination of abandoned and rainfed olive groves, terraced or non-terraced, and over four parent materials in Lluc Valley, a Mediterranean hyper-humid mountainous area on the island of Mallorca, Spain. Soil bacterial diversity and taxonomic composition at phylum and family level in each field were analyzed by rRNA 16 S amplicon sequencing. In addition, a series of soil physicochemical and microbiological properties, together with enzyme activities were assessed. Results showed that secondary succession and parent material significantly affected soil physicochemical and microbiological properties, soil enzyme activities and soil bacterial communities' diversity and taxonomic composition. Secondary succession following farmland abandonment triggered higher total organic carbon (TOC), microbial biomass carbon (C mic), basal soil respiration (REB), alkaline phosphatase activity (Php) and dehydrogenase activity (DHA), thus enhancing soil quality. In contrast, parent material significantly shaped pH, specific surface area (SSA), TOC, C mic , REB and soil enzyme activities, playing a key role in land use effects modulation. According to the distance-based redundancy analysis (db-RDA), SSA, TOC, REB, C mic , urease activity (Ur) and Php were the soil properties that contributed to significant changes in bacterial communities' composition at the family level. This study evidenced that farmland abandonment led to improve soil quality in Mediterranean humid mountains, with positive feedbacks provided by parent material. • Farmland abandonment triggered higher TOC, C mic and REB, enhancing soil quality. • Lithology significantly shaped pH, SSA, TOC, C mic , REB and soil enzyme activities. • β-diversity analyses showed changes due to secondary succession and parent material. • Significant relationships were found between soil properties and bacterial families. [ABSTRACT FROM AUTHOR]