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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

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

Abstract. Drought is a major driver of vegetation activity in Spain, with
significant impacts on crop yield, forest growth, and the occurrence of
forest fires. Nonetheless, the sensitivity of vegetation to drought
conditions differs largely amongst vegetation types and climates. We used a
high-resolution (1.1 km) spatial dataset of the normalized difference
vegetation index (NDVI) for the whole of Spain spanning the period from 1981 to
2015, combined with a dataset of the standardized precipitation
evapotranspiration index (SPEI) to assess the sensitivity of vegetation types
to drought across Spain. Specifically, this study explores the drought timescales at which vegetation activity shows its highest response to drought
severity at different moments of the year. Results demonstrate that – over
large areas of Spain – vegetation activity is controlled largely by the
interannual variability of drought. More than 90 % of the land areas
exhibited statistically significant positive correlations between the NDVI
and the SPEI during dry summers (JJA). Nevertheless, there are some
considerable spatio-temporal variations, which can be linked to differences
in land cover and aridity conditions. In comparison to other climatic regions
across Spain, results indicate that vegetation types located in arid regions
showed the strongest response to drought. Importantly, this study stresses
that the timescale at which drought is assessed is a dominant factor in
understanding the different responses of vegetation activity to drought.

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

48 Pags.- 1 Tabl.- 18 Figs. The definitive version is available at: http://link.springer.com/journal/382 ; In this study, we analyzed the influence of El Niño–Southern Oscillation (ENSO) on the spatio-temporal variability of droughts in Ecuador for a 48-year period (1965–2012). Droughts were quantified from 22 high-quality and homogenized time series of precipitation and air temperature by means of the Standardized Precipitation Evapotranspiration Index. In addition, the propagation of two different ENSO indices (El Niño 3.4 and El Niño 1 + 2 indices) and other atmospheric circulation processes (e.g., vertical velocity) on different time-scales of drought severity were investigated. The results showed a very complex influence of ENSO on drought behavior across Ecuador, with two regional patterns in the evolution of droughts: (1) the Andean chain with no changes in drought severity, and (2) the Western plains with less severe and frequent droughts. We also detected that drought variability in the Andes mountains is explained by the El Niño 3.4 index [sea surface temperature (SST) anomalies in the central Pacific], whereas the Western plains are much more driven by El Niño 1 + 2 index (SST anomalies in the eastern Pacific). Moreover, it was also observed that El Niño and La Niña phases enhance droughts in the Andes and Western plains regions, respectively. The results of this work could be crucial for predicting and monitoring drought variability and intensity in Ecuador. ; This work was supported by the EPhysLab (UVIGO-CSIC Associated Unit) and the research projects I-COOP H2O 2013CD0006: "Test multisectorial y actividades demostrativa sobre el potencial desarrollo de sistemas de monitorización de sequías en tiempo real en la región del oeste de Sudamérica" financed by the Spanish National Research Council, CGL2011-27574-CO2-02, 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. Arturo Sanchez-Lorenzo was supported by the JCI-2012-12508 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. E. Aguilar was funded by the Grant CCI-009-ATN/OC-12439-RG-2012 from the Banco Iberoamericano de Desarrollo. ; Peer reviewed

This study links tree-ring growth and gross primary production for a variety of forest types under different environmental conditions across Spain. NOAA-AVHRR satellite imagery data were combined with dendrochronological records and climate data at a fine spatial resolution (1.21 km2) to analyze the interannual variability of tree-ring growth and vegetation activity for different forest biomes from 1981 to 2015. Specifically, we assessed the links between tree-ring width indices (TRWi), the Normalized Difference Vegetation Index (NDVI) and a variety of environmental conditions, represented by climatic variables (air temperature, precipitation, evapotranspiration and water balance) and elevation. The impact of these variables on tree growth was assessed by means of the Predictive Discriminant Analysis (PDA). Results reveal a general positive and significant relationship between inter-annual variability of the NDVI at a high spatial resolution (1.21 km2) and tree-ring growth. Maximum correlations between NDVI and tree-ring growth were recorded when cumulative NDVI values were considered, in some cases covering long time periods (6–10 months), suggesting that tree growth is mainly related to Gross Primary Production (GPP) at annual scale. The relationship between tree-ring growth and inter-annual variability of the NDVI, however, strongly varies between forest types and environmental conditions. ; Research projects CGL2014-52135-C03-01, CGL2015-69186-C2-1-R, CGL2015-69985-R, CGL2013-48843-C2-1-R, AGL2014-53822-C2-1-R, (BFU2010-21451), PCIN-2015-220, CGL2016-81706-REDT, CGL2017-82216-R, 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, IMDROFLOOD, Water Works 2014, co-funded call of the European Commission, CROSSDRO financed by the AXIS (Assessment of Cross(X) – sectorial climate Impacts and pathways for Sustainable transformation) JPI-Climate co-funded call of the European Commission and INDECIS, part of ERA4CS, an ERA-NET initiated by JPI Climate, FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR), co-funding by the European Union (Grant 690462). Spanish Commission of Science and Technology and FEDER, 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), Aragon Regional Government, Spanish Ministry of Economy and Competitiveness, Spanish Ministry of Education, Culture and Sport, IJCI-2015-25845, MINECO-FPDI 2013-16600, FJCI 2016-30121, FEDER funds. Xunta de Galicia (PGIDIT06PXIB502262PR, GRC GI-1809, ROCLIGAL-10MDS291009PR), INIA (RTA2006-00117), and Interreg V-A POCTEFA (CANOPEE, 2014-2020-FEDER funds) projects.