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La gestión del riesgo de inundación a escala local precisa de instrumentos metodológicos que den apoyo a la toma de decisiones de forma rápida y eficiente. A partir de datos recogidos por estaciones hidrométricas, ubicadas en puntos estratégicos de las cuencas de drenaje, es posible el desarrollo de instrumentos de monitorización de la precipitación y del caudal de los ríos y torrentes. La correlación entre los datos registrados y los episodios de inundación facilitan la puesta en marcha de sistemas de alerta temprana. En este marco se trabaja en el desarrollo de instrumentos de ayuda a la gestión del riesgo a nivel municipal. La información del peligro de inundación se combina con información territorial (catastro, ocupación del suelo, infraestructuras, etc.) mediante el uso de sistemas de información geográfica para realizar una evaluación integrada de la vulnerabilidad por exposición. En este artículo se presentan resultados iniciales del análisis de la vulnerabilidad frente a inundaciones de la ciudad de Palma (Illes Balears). Los resultados muestran un elevado grado de exposición de las zonas residenciales del este de la ciudad constatando incrementos considerables en los últimos decenios., Flood risk management at the local scale requires methodological tools to support decision-making in an efficient way. Based on data collected by hydrometric stations, located at strategic points in drainage river catchments, it is possible to develop tools for monitoring their rainfall and runoff dynamics. The correlation between the data recorded and flood episodes facilitates the implementation of early warning systems. In this framework, work is ongoing to develop tools to support risk management at the municipal scale. Flood hazard information is combined with territorial one (cadastre, land use, infrastructures, etc.) through the use of geographic information systems to perform an integrated vulnerability assessment by exposure. This communication presents the initial results of the vulnerability assessment to flooding in the city of Palma (Balearic Islands). The results showed a high degree of exposure of the residential areas in the east of the city, with considerable increases in recent decades.

[EN] A flash-flood event hit the northeastern part of Mallorca on 9 October 2018, causing 13 casualties. Mal- lorca is prone to catastrophic flash floods acting on a sce- nario of deep landscape transformation caused by Mediter- ranean tourist resorts. As global change may exacerbate dev- astating flash floods, analyses of catastrophic events are cru- cial 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. Continu- ous streamflow monitoring data revealed a peak discharge of 442 m³ s¿¹ with an unprecedented runoff response. This ex- ceptional behaviour triggered the natural disaster as a com- bination of heavy rainfall (249 mm in 10 h), karstic features and land cover disturbances in the Begura de Salma River catchment (23 km²). Topography-based connectivity indices and geomorphic change detection were used as rapid post- catastrophe decision-making tools, playing a key role dur- ing the rescue search. These hydrogeomorphological preci- sion techniques were combined with the Copernicus Emer- gency Management Service and ¿ground-based¿ damage as- sessment, 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.

Soil moisture conditions play a key role in runoff and sediment load dynamics in river catchments of contrasting ecosystems. However, the highly marked seasonality of Mediterranean climate affects hydrological processes and sediment transport strongly, as evapotranspiration determines a succession of wet, transition and dry periods throughout a hydrological year. This study examines results of soil moisture, water and sediment fluxes during five hydrological years in a representative small mid-mountain Mediterranean catchment. It aims to assess the sediment load contribution and its variability at different temporal scales. Precipitation, runoff and suspended sediment load were calculated at annual, seasonal and event scales to assess inter- and intra-annual variability. A database with 45 events was used to identify the main controlling factors over sediment load thought bivariate relationships and an analysis of soil moisture-discharge and discharge-suspended sediment concentration hysteresis. At the annual scale, lithology, land use and soil conservation structures characteristic of the catchment caused low values of sediment yield, although inter-annual rates varied by up to three orders of magnitude (0.08 to 11.86 t km−2 y−1). Seasonal analysis of accumulated sediment load showed that 80% was generated during the autumn and winter seasons. At the event scale, streamflow and soil moisture were the controlling factors for the largest sediment load contributions. The highest frequency of clockwise discharge-suspended sediment concentration hysteresis revealed that most of the sediment was generated from nearby sources, although the largest sediment loads were contributed under wet antecedent conditions, as depicted by the soil moisture-discharge hysteresis assessment.

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 m3 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 km2). 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.

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.

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

(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

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.