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27 Pags.- 10 Figs.- 7 Tabls. © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). ; 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. ; This work was supported by the research project CGL2017-88200-R "Functional hydrological and sediment connectivity at Mediterranean catchments: global change scenarios –MEDhyCON2" funded by the Spanish Ministry of Science, Innovation and Universities, the Spanish Agency of Research (AEI) and the European Regional Development Funds (ERDF). The contribution of Jérôme Latron was supported by the research project PCIN-2017-061/AEI also funded by the Spanish Government. Josep Fortesa has a contract funded by the Ministry of Innovation, Research and Tourism of the Autonomous Government of the Balearic Islands (FPI/2048/2017). Julián García-Comendador is in receipt of a pre-doctoral contract (FPU15/05239) funded by the Spanish Ministry of Education, Culture and Sport. Miquel Tomàs-Burguera acknowledges the support from the project CGL2017-83866-C3-3-R financed by the European Regional Development Funds (ERDF) and the Spanish Ministry of Science, Innovation and Universities. Jaume Company is in receipt of Young Qualified Program fund by Employment Service of the Balearic Islands and European Social Fund (SJ-QSP 48/19). Aleix Calsamiglia acknowledges the support from the Spanish Ministry of Science, Innovation and Universities through a pre-doctoral contract (BES-2013-062887). ; Peer reviewed

12 Pags.- 6 Figs.- 1 Tabl. © The Author(s) 2018. Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. ; The purpose of this research was to identify major drought events on the Spanish mainland between 1961 and 2014 by means of two drought indices, and analyze the spatial propagation of drought conditions. The indices applied were the standardized precipitation index (SPI) and the standardized evaporation precipitation index (SPEI). The first was calculated as standardized anomalies of precipitation at various temporal intervals, while the second examined the climatic balance normalized at monthly scale, incorporating the relationship between precipitation and the atmospheric water demand. The daily meteorological data from Spanish Meteorological Archives (AEMet) were used in performing the analyses. Within the framework of the DESEMON project, original data were converted into a high spatial resolution grid (1.1 km2) following exhaustive quality control. Values of both indices were calculated on a weekly scale and different timescales (12, 24 and 36 months). The results show that during the first half of the study period, the SPI usually returned a higher identification of drought areas, while the reverse was true from the 1990s, suggesting that the effect from atmospheric evaporative demand could have increased. The temporal propagation from 12- to 24-month and 36-month timescales analyzed in the paper seems to be a far from straightforward phenomenon that does not follow a simple rule of time lag, because events at different temporal scales can overlap in time and space. Spatially, the propagation of drought events affecting more than 25% of the total land indicates the existence of various spatial gradients of drought propagation, mostly east–west or west–east, but also north–south have been found. No generalized episodes were found with a radial pattern, i.e., from inland to the coast. ; This work is supported by the projects CGL2014-52135-C03-01, CGL2014-52135-C3-3-R and PCIN-2015-220, financed by the Spanish Government, Ministry of the Economy and Finance and FEDER, IMDROFLOOD financed by the Water Works 2014 co-funded call of the European Commission, INDECIS, financed by the ERA-NET Cofund for Climate Services of the European Research Area for Climate Services, and the Regional Government of Aragón DGA-FSE (Grupo de Investigación Consolidado 'Clima, Agua, Cambio Global y Sistemas Naturales'). Celia Salinas is a FPI-PhD student supported by the Ministry of the Economy and Finance. Miquel Tomas-Burguera was supported by the predoctoral FPU program 2013 (Ministry of Education, Culture and Sport). ; Peer reviewed

14 Pags.- 5 Figs. Under Creative Commons License CC BY-NC-ND ; The standardized precipitation evapotranspiration index (SPEI) is one of the well‐established drought metrics worldwide. It is simply computed using precipitation and atmospheric evaporative demand (AED) data. Although AED is considered a key driver of drought variability worldwide, it could have less impact on drought in specific regions and for particular times as a function of the magnitude of precipitation. Specifically, the influence of the AED might overestimate drought severity during both normal and humid periods, resulting in "false alarms" about drought impacts on physical and human environments. Here, we provided a global characterization of the sensitivity of the SPEI to changes of the AED. Results demonstrate that the contribution of AED to drought severity is largely impacted by the spatial and temporal variability of precipitation. Specifically, the impact of AED on drought severity was more pronounced during periods of low precipitation, compared to wet periods. Interestingly, drought severity in humid regions (as revealed by SPEI) also showed low sensitivity to AED under drier conditions. These results highlight the skill of SPEI in identifying the role of AED in drought evolution, especially in arid and semiarid regions whose climate is characterized typically by low precipitation. This advantage was also evident for humid environments, where SPEI did not overestimate drought severity due to the increased AED. These findings highlight the broader applicability of SPEI to accurately characterize drought severity worldwide. ; This work was supported by the research projects CGL2017‐82216‐R and PCI2019‐103631, financed by the Spanish Commission of Science and Technology and Fondo Europeo de Desarrollo Regional (FEDER); CROSSDRO project financed by the AXIS (Assessment of Cross(X)—sectoral climate Impacts and pathways for Sustainable transformation), JPI‐Climate cofunded call of the European Commission and INDECIS which is part of ERA4CS, an ERA‐NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), and ANR (FR) with cofunding by the European Union (Grant 690462). Dhais Peña‐Angulo received a "Juan de la Cierva" postdoctoral contract (FJCI‐2017‐33652 from Spanish Ministry of Economy and Competitiveness, MEC). ; Peer reviewed

2 .pdf files: 1) Article (18 Pags.- 2 Tabls.- 10 Figs.); 2) Supplement (20 Pags.- 19 Figs.). © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0/). ; Assessing the probability of occurrence of drought is important for improving current drought assessment, management and mitigation measures, and strategies across Spain. This study employed two well-established drought indices, the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI), to characterize drought duration and magnitude at different timescales over Spain. In order to map the drought hazard probability, we applied the extreme value theory and tested different thresholds to generate peak-over-threshold (POT) drought duration and magnitude series. Our results demonstrate that the generalized Pareto (GP) distribution performs well in estimating the frequencies of drought magnitude and duration. Specifically, we found a good agreement between the observed and modelled data when using upper percentiles to generate the POT series. Spatially, our estimations suggest a higher probability of extreme drought events in southern and central Spain compared to the northern and eastern regions. Also, our study found spatial differences in drought probability estimations as a function of the selected drought index (i.e. SPI vs. SPEI) and timescale (i.e. 1, 3, 6, and 12 months). Drought hazard probability maps can contribute to the better management of different sectors (e.g. agriculture, water resources management, urban water supply, and tourism) at national, regional, and even local scale in Spain. ; This work was supported by the following research projects: CGL2014-52135-C03-01 and PCIN-2015-220 financed by the Spanish Commission of Science and Technology and FEDER, 1560/2015; Herramientas de monitorización de la vegetación mediante modelización ecohidrológica en parques continentales financed by the Red de Parques Nacionales; IM-DROFLOOD financed by Water Works 2014; a co-funded call of the European Commission and INDECIS, which is part of ERA4CS; and an ERA-NET initiated by JPI Climate, funded by MINECO with co-funding by the European Union (grant 690462). Marina Peña-Gallardo was funded by the Spanish Ministry of Economy and Competitiveness, Miquel Tomas-Burguera was supported by a doctoral grant by the Spanish Ministry of Education, Culture and Sport, and Ahmed El Kenawy was supported by a postdoctoral Juan de la Cierva contract. ; Peer reviewed

33 Pags.- 1 Tabl.- 16 Figs. Creative Commons Attribution License. ; We analyzed potential land degradation processes in semiarid regions worldwide using long time series of remote sensing images and the Normalized Difference Vegetation Index (NDVI) for the period 1981 to 2011. The objectives of the study were to identify semiarid regions showing a marked decrease in potential vegetation activity, indicative of the occurrence of land degradation processes, and to assess the possible influence of the observed drought trends quantified using the Standardized Precipitation Evapotranspiration Index (SPEI). We found that the NDVI values recorded during the period of maximum vegetation activity (NDVImax) predominantly showed a positive evolution in the majority of the semiarid regions assessed, but NDVImax was highly correlated with drought variability, and the trends of drought events influenced trends in NDVImax at the global scale. The semiarid regions that showed most increase in NDVImax (the Sahel, northern Australia, South Africa) were characterized by a clear positive trend in the SPEI values, indicative of conditions of greater humidity and lesser drought conditions. While changes in drought severity may be an important driver of NDVI trends and land degradation processes in semiarid regions worldwide, drought did not apparently explain some of the observed changes in NDVImax. This reflects the complexity of vegetation activity processes in the world's semiarid regions, and the difficulty of defining a universal response to drought in these regions, where a number of factors (natural and anthropogenic) may also affect on land degradation. ; This work was supported by the research projects CGL2011-27574-CO2-02, CGL2011-24185, CGL2014-52135-C03-01 and Red de variabilidad y cambio climático RECLIM (CGL2014-517221-REDT) financed by the Spanish Commission of Science and Technology and FEDER and "LIFE12 ENV/ES/000536-Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (LIFE MEDACC)" financed by the LIFE programme of the European Commission. Cesar Azorin-Molina was supported by the JCI-2011-10263 grant. Miquel Tomas-Burguera was supported by a doctoral grant by the Ministry of Economy and Competitiveness and Natalia Martin-Hernandez was supported by a doctoral grant by the Aragón Regional Government. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI). ; Peer reviewed

Abstract. Assessing the probability of occurrence of drought is important for improving current drought assessment, management and mitigation measures, and strategies across Spain. This study employed two well-established drought indices, the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI), to characterize drought duration and magnitude at different timescales over Spain. In order to map the drought hazard probability, we applied the extreme value theory and tested different thresholds to generate peak-over-threshold (POT) drought duration and magnitude series. Our results demonstrate that the generalized Pareto (GP) distribution performs well in estimating the frequencies of drought magnitude and duration. Specifically, we found a good agreement between the observed and modelled data when using upper percentiles to generate the POT series. Spatially, our estimations suggest a higher probability of extreme drought events in southern and central Spain compared to the northern and eastern regions. Also, our study found spatial differences in drought probability estimations as a function of the selected drought index (i.e. SPI vs. SPEI) and timescale (i.e. 1, 3, 6, and 12 months). Drought hazard probability maps can contribute to the better management of different sectors (e.g. agriculture, water resources management, urban water supply, and tourism) at national, regional, and even local scale in Spain.

18 Pags.- 8 Tabls.- 9 Figs. ; We analysed recent evolution and meteorological drivers of the atmospheric evaporative demand (AED) in the Canary Islands for the period 1961–2013.We employed long and high-quality time series of meteorological variables to analyse current AED changes in this region and found that AED has increased during the investigated period. Overall, the annual ETo, which was estimated by means of the FAO- 56 Penman–Monteith equation, increased significantly by 18.2mmdecade1 on average, with a stronger trend in summer (6.7mmdecade1). In this study we analysed the contribution of (i) the aerodynamic (related to the water vapour that a parcel of air can store) and (ii) radiative (related to the available energy to evaporate a quantity of water) components to the decadal variability and trends of ETo. More than 90% of the observed ETo variability at the seasonal and annual scales can be associated with the variability in the aerodynamic component. The variable that recorded more significant changes in the Canary Islands was relative humidity, and among the different meteorological factors used to calculate ETo, relative humidity was the main driver of the observed ETo trends. The observed trend could have negative consequences in a number of water-depending sectors if it continues in the future. ; This work was supported by the research projects PCIN-2015-220, CGL2014-52135-C03-01, and Red de variabilidad y cambio climático RECLIM (CGL2014-517221-REDT), financed by the Spanish Commission of Science and Technology and FEDER; "IMDROFLOOD-Improved Drought and Flood Early Warning, Forecasting and Mitigation using real-time hydroclimatic indicators", supported through the Water Joint programme Initiative "Water Challenges for a Changing World"; and Water Works 2014 Cofunded call and "LIFE12 ENV/ES/000536-Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (LIFE MEDACC)", financed by the LIFE programme of the European Commission. Cesar Azorin-Molina (JCI-2011-10263), Arturo Sanchez-Lorenzo (JCI-2012-12508) and Marina Peña-Gallardo received grants from the Spanish Ministry of Economy and Competitiveness; Natalia Martin-Hernandez was supported by a doctoral grant by the Aragón Regional Government; and Miquel Tomas-Burguera was supported by a doctoral grant by the Ministerio de Educación, Cultura y Deporte. ; Peer reviewed

23 Pags.- 13 Figs. © Author(s) 2018. This work is distributed under the Creative Commons Attribution 3.0 License. ; We analyzed changes in surface relative humidity (RH) at the global scale from 1979 to 2014 using both observations and the ERA-Interim dataset.We compared the variability and trends in RH with those of land evapotranspiration and ocean evaporation in moisture source areas across a range of selected regions worldwide. The sources of moisture for each particular region were identified by integrating different observational data and model outputs into a Lagrangian approach. The aim was to account for the possible role of changes in air temperature over land, in comparison to sea surface temperature (SST), but also the role of land evapotranspiration and the ocean evaporation on RH variability. The results demonstrate that the patterns of the observed trends in RH at the global scale cannot be linked to a particular individual physical mechanism. Our results also stress that the different hypotheses that may explain the decrease in RH under a global warming scenario could act together to explain recent RH trends. Albeit with uncertainty in establishing a direct causality between RH trends and the different empirical moisture sources, we found that the observed decrease in RH in some regions can be linked to lower water supply from land evapotranspiration. In contrast, the empirical relationships also suggest that RH trends in other target regions are mainly explained by the dynamic and thermodynamic mechanisms related to the moisture supply from the oceanic source regions. Overall, while this work gives insights into the connections between RH trends and oceanic and continental processes at the global scale, further investigation is still desired to assess the contribution of both dynamic and thermodynamic factors to the evolution of RH over continental regions. ; This work was supported by the EPhysLab (UVIGO-CSIC Associated Unit), PCIN-2015-220, CGL2014-52135-C03-01, and CGL2014-60849-JIN financed by the Spanish Commission of Science and Technology, and FEDER, IMDROFLOOD financed by the Water Works 2014 co-funded call of the European Commission and INDECIS, which is part of ERA4CS, an ERA-NET initiated by JPI Climate. This study was also funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), and ANR (FR) with co-funding from the European Union (grant 690462). ; Peer reviewed

40 Pags.- 8 Figs.- 3 Tabls. The definitive version is available at: https://rmets.onlinelibrary.wiley.com/journal/10970088 ; Although the mean environmental lapse rate (MELR) value (a linear decrease of −6.5 °C/km) is the most widely used, near‐surface (i.e., non‐free atmosphere) air temperature lapse rates (NSLRs; measured at ~1.5 m height) are variable in space and time because of their dependence on topography and meteorological conditions. In this study we conducted the first analysis of the spatial and temporal variability of NSLRs for continental Spain and their relationship to synoptic atmospheric circulation (circulation weather types [CWTs]), focusing on major mountain areas including the Pyrenees, Cantabrian, Central, Baetic, and Iberian ranges. The results showed that the NSLR varied markedly at spatial and seasonal scales and depended on the dominant atmospheric conditions. The median NSLR values were weaker (less negative) than the MELR for the mountain areas (Pyrenees −5.17 °C/km; Cantabrian range −5.22 °C/km; Central range −5.78 °C/km; Baetic range −4.83 °C/km; Iberian range −5.79 °C/km) and for the entire continental Spain (−5.28 °C/km). For the entire continental Spain the steepest NSLR values were found in April (−5.80 °C/km), May (−5.58 °C/km), and October (−5.54 °C/km) because of the dominance of northerly and westerly advections of cold air. The weakest NSLR values were found in July (−4.67 °C/km) and August (−4.78 °C/km) because of the inland heating, and in winter because of the occurrence of thermal inversions. As the use of the MELR involves the assumption of large errors, we propose 1 zonal, 12 monthly, 11 CWTs, and 132 hybrid monthly–CWTs NSLRs for each of the mountain ranges and for the entire continental Spain. More regional studies are urgently needed to accurately assess the NSLR as a function of atmospheric circulation conditions. ; This study was funded by the research projects CGL2014‐52599‐P "Estudio del manto de nieve en la montaña española y su respuesta a la variabilidad y cambio climatico" and CLIMPY "Characterization of the evolution of climate and provision of information for adaptation in the Pyrenees" (FEDER‐POCTEFA). F.N.‐S. and M.T.‐B. are granted with a pre‐doctoral FPU grant (Spanish Ministry of Education, Culture and Sports) and C.A.‐M. has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska‐Curie grant agreement no. STILLING project‐703733. ; Peer reviewed

15 Pags.- 9 Figs.- 2 Tabls. ; We analyzed the relationships between meteorological drought and hydrological drought using very dense and diverse network of gauged natural drainage basins across the conterminous U.S. Specifically, this work utilized a dataset of 289 gauging stations, covering the period 1940–2013. Drainage basins were obtained for each gauging station using a digital terrain model. In addition to meteorological data (e.g., precipitation, air temperature and the atmospheric evaporative demand), we obtained a number of topographic, soil and remote sensing variables for each defined drainage basin. A hydrological drought index (the Standardized Streamflow Index; SSI) was computed for each basin and linked to the Standardized Precipitation Evapotranspiration Index (SPEI), which was used as a metric of climatic drought severity. The relationships between different SPEI time-scales and their corresponding SSI were assessed by means of a Pearson correlation coefficient. Also, the general patterns of response of hydrological droughts to climatic droughts were identified using a principal component analysis. Overall, results demonstrate a positive response of SSI to SPEI at shorter time-scales, with strong seasonality and clear spatial differences. We also assessed the role of some climatic and environmental factors in explaining these different responses using a predictive discriminant analysis. Results indicate that elevation and vegetation coverage are the main drivers of the diverse response of SSI to SPEI time-scales. Similar analyses were made for three sub-periods (1940–1964, 1965–1989 and 1989–2013), whose results confirm considerable differences in the response of SSI to SPEI over the past eighty years. ; This work was supported by the research project I-Link1001 (Validation of climate drought indices for multi-sectorial applications in North America and Europe under a global warming scenario) financed by CSIC, PCIN-2015-220 and CGL2014-52135-C03-01 financed by the Spanish Commission of Science and Technology and FEDER, IMDROFLOOD financed by the Water Works 2014 co-funded call of the European Commission and INDECIS, which is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462). Marina Peña-Gallardo was granted by the Spanish Ministry of Economy and Competitiveness. Miquel Tomas-Burguera was supported by a doctoral grant by the Spanish Ministry of Education, Culture and Sport. Jamie Hannaford was supported by the Belmont Forum project 'DrIVER', NERC Grant Number (grant NE/L010038/1). Marco Maneta acknowledges support from the USDA NIFA grant 2016-67026-25067. ; Peer reviewed

23 Pags.- 12 Figs.- 4 Tabls. ; This article developed and implemented a new methodology for calculating the standardized evapotranspiration deficit index (SEDI) globally based on the log-logistic distribution to fit the evaporation deficit (ED), the difference between actual evapotranspiration (ETa) and atmospheric evaporative demand (AED). Our findings demonstrate that, regardless of the AED dataset used, a log-logistic distribution most optimally fitted the ED time series. As such, in many regions across the terrestrial globe, the SEDI is insensitive to the AED method used for calculation, with the exception of winter months and boreal regions. The SEDI showed significant correlations (p < 0.05) with the standardized precipitation evapotranspiration index (SPEI) across a wide range of regions, particularly for short (<3 month) SPEI time scales. This work provides a robust approach for calculating spatially and temporally comparable SEDI estimates, regardless of the climate region and land surface conditions, and it assesses the performance and the applicability of the SEDI to quantify drought severity across varying crop and natural vegetation areas. ; This work was supported by the re-search projects PCIN-2015-220 and CGL2014-52135-C03-01 financed by the Spanish Commission of Science and Technology and FEDER. IMDROFLOOD financed by the Water Works 2014 co-funded all of the European Commission and INDECIS, which is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (Sweden), DLR (Germany), BMWFW (Austria), IFD (Denmark), MINECO (Spain), and ANR (France), with co-funding by the European Union (Grant 690462). Diego G. Miralles acknowledges support from the European Research Council (ERC) under Grant Agreement 715254 (DRY–2–DRY). Marina Peña-Gallardo was supported by the Spanish Ministry of Economy and Competitiveness and Miquel Tomás-Burguera was sup-ported by a doctoral grant by the Ministerio de Educación, Cultura y Deporte. ; Peer reviewed

19 Pags.- 5 Figs.- 2 Tabls. © 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ; Drought monitoring is essential to determine, at short time intervals, the main characteristics of drought events, such as their duration, severity, and spatial distribution. To ensure that drought monitoring represents a useful tool for governmental plans aimed at preventing or minimizing drought impacts, up-to-date information must be instantaneously accessible and it must provide high spatial and temporal resolution. This study presents a system that allows the automatic tracking of meteorological droughts in the Spanish territory, based on an open and easy-to-use online platform (https://monitordesequia.csic.es/monitor). This drought monitoring system provides two drought synthetic indices: the Standardised Precipitation Index (SPI) and the Standardised Precipitation Evapotranspiration Index (SPEI). Information is provided on a quasi-weekly basis, in a grid format, with a spatial resolution of 1.1*1.1 km, and with data from 1961 to the present time. This drought monitor is updated based on the real-time information gathered from automatic stations, which in turn requires historic information to identify and track drought events. The drought indices are obtained from data processing (quality control, temporal series reconstruction, homogenisation, interpolation, and validation) using climatic variables (maximum and minimum temperatures, solar radiation, rainfall, dew point, and wind speed) which are provided by the Spanish Meteorology Agency and the Ministry of Agriculture of the Spanish Government. We performed a validation of the drought indices for the whole historical period (1961–2020). This allowed us to observe a strong spatial agreement between the indices obtained with the historical dataset and the indices from the monitoring dataset, especially for mainland Spain and the Balearic Islands (Pearson's r, SPI and SPEI >0.99). The presented real-time drought monitoring system represents a relevant and useful tool that allows for quick and effective actions to prevent and mitigate the effects of drought on society and ecosystems. ; This work was supported by projects PCI2019-103631 financed by the Spanish Ministry of Science and Technology and FEDER and CROSSDRO project funded by AXIS (Assessment of Cross (X) - sectoral climate Impacts and pathways for Sustainable transformation), JPI-Climate co-funded call of the European Commission. ; Peer reviewed

11 Pags.- 1 Tabl.- 4 Figs. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. ; We present a long-term assessment of precipitation trends in Southwestern Europe (1850–2018) using data from multiple sources, including observations, gridded datasets and global climate model experiments. Contrary to previous investigations based on shorter records, we demonstrate, using new long-term, quality controlled precipitation series, the lack of statistically significant long-term decreasing trends in precipitation for the region. Rather, significant trends were mostly found for shorter periods, highlighting the prevalence of interdecadal and interannual variability at these time-scales. Global climate model outputs from three CMIP experiments are evaluated for periods concurrent with observations. Both the CMIP3 and CMIP5 ensembles show precipitation decline, with only CMIP6 showing agreement with long term trends in observations. However, for both CMIP3 and CMIP5 large interannual and internal variability among ensemble members makes it difficult to identify a trend that is statistically different from observations. Across both observations and models, our results make it difficult to associate any declining trends in precipitation in Southwestern Europe to anthropogenic forcing at this stage. ; This work was supported by the research projects CGL2017-82216-R, CGL2017-83866-C3-3-R and PCI2019-103631, financed by the Spanish Commission of Science and Technology and FEDER; CROSSDRO project financed by the AXIS (Assessment of Cross(X)—sectoral climate Impacts and pathways for Sustainable transformation), JPI-Climate co-funded call of the European Commission and INDECIS which is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462). Dhais Peña-Angulo received a 'Juan de la Cierva' postdoctoral contract (FJCI-2017-33652 Spanish Ministry of Economy and Competitiveness, MEC). Conor Murphy was supported by the Irish Environmental Protection Agency (Grant Nos. 2019-CCRP-MS.60). Marco Turco has received funding from the Spanish Ministry of Science, Innovation and Universities through the project PREDFIRE (RTI2018-099711-J-I00), which is co-financed with the European Regional Development Fund (ERDF/FEDER). ; Peer reviewed

20 Pags.,- 13 Figs.- 3 Tabls. Supplementary data associated with this article can be found, in the online version. © 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the license Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ; Study region: The Segre basin (northeastern Spain). Study focus: The Segre basin is extensively regulated, through a dense network of dams, during the second half of the 20th century. This study assessed the impact of river regulation on the evolution of hydroclimatological extreme events across the basin during the past six decades (1950–2013). We assessed whether the occurrence of floods and hydrological droughts has changed, and whether these changes have differed spatially between the headwaters and lower areas ofthe basin. For this purpose, we employed a set of hydroclimatological indices in order to quantify the evolution of the amount as well as the frequency of quantiles of high precipitation and flood events. Changes in these variables were assessed by means of the nonparametric Mann–Kendall Tau coefficient. New hydrological insights: Results reveal a general reduction in the occurrence of extreme precipitation events in the Segre basin from 1950 to 2013, which corresponded to a general reduction in high flows measured at various gauged stations across the basin. While this study demonstrates spatial differences in the decrease of streamflow between the headwaters and the lower parts of the basin, mainly associated with changes in river regulation, there was no reduction in the frequency of the extraordinary floods. Changes in water management practices in the basin have significantly impacted the frequency, duration, and severity of hydrological droughts downstream of the main dams, as a consequence of the intense water regulation to meet water demands for irrigation and livestock farms. Nonetheless, the hydrological response of the headwaters to these droughts differed markedly from that of the lower areas of the basin. ; This work was supported by the research project PCIN-2015-220, CGL2014-52135-C03-01, Red de variabilidad y cambioclimático RECLIM (CGL2014-517221- REDT) financed by the Spanish Commission of Science and Technology and FEDER, "LIFE12 ENV/ES/000536-Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (LIFE MEDACC)" financed by the LIFE programme of the European Commission and IMDROFLOOD financed by the Water Works 2014 cofunded call of the European Commission. Marina Peña-Gallardo and Esteban Alonso-González were granted by the Spanish Ministry of Economy and Competitiveness; Natalia Martin-Hernandez was supported by a doctoral grant by the Aragón Regional Government; and Miquel Tomas-Burguera was supported by a doctoral grant by el Ministerio de Educación, Cultura y Deporte. Arturo Sanchez-Lorenzo was supported by a postdoctoral fellowship JCI-2012-12508 financed by the Spanish Ministry of Economy and Competitiveness. ; Peer reviewed