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6 páginas, 4 figuras. ; The changing spatial patterns of the North Atlantic Oscillation (NAO) dipole and the changing correlations between the NAO and European precipitation were analyzed using the AOGCM CGCM3.1(T63) model provided by the Canadian Centre for Climate Modelling and Analysis (CCCma). Four output scenarios were considered: the IPCC pre-industrial (PI) scenario, the 20th century (20C) scenario, and the B1 and A2 emission scenarios for the 21st century. We detected some differences in the spatial patterns of the NAO-precipitation relationship among the four scenarios. Moreover, there were large differences in the temporal stability of the NAO pressure pattern, and also in the NAO-precipitation relationship among the four scenarios. Under increased greenhouse gas emissions the stability of the NAO-precipitation correlations is enhanced due to the lower variability in the pattern of the NAO dipole. ; This work has been supported by the research project CGL2005-04508/BOS, financed by the Spanish Commission of Science and Technology and FEDER, and ''Programa de grupos de investigación consolidados'' financed by the Aragón Government. ; Peer reviewed

24 páginas, 15 figuras. ; In this study, droughts are analyzed using the standardized precipitation index (SPI) at different time scales for all of Europe over the period 1901–2000. The SPI is calculated at different time scales (1–12 months), as are the average values that correspond to negative and positive phases of the North Atlantic Oscillation (NAO). The responses of droughts to the phases of the NAO vary spatially, but the response also depends on the month of the year and the time scale of the analysis. During the positive/negative phases, negative/positive SPI values are generally recorded in southern Europe, with the opposite pattern recorded in northern Europe. In certain regions, significant differences in the SPI are also recorded during spring, summer, and even autumn. In several regions, the magnitude of the average SPI anomalies is noticeably different for the positive and negative phases of the NAO, indicating the asymmetric response of droughts to the NAO. The unstable response of drought occurrence is also demonstrated, at different time scales, to positive and negative phases of the NAO throughout the twentieth century. During the second half of the twentieth century, there is a strengthening of the influence of the positive phases of the NAO on droughts. In contrast, the negative phases show a weaker influence on the SPI during the second half of the twentieth century. This pattern is related to changes in the wintertime sea level pressure fields associated with positive and negative phases of the NAO. ; This work has been supported by the following projects: CGL2005-04508/BOS (financed by the Spanish Commission of Science and Technology and FEDER), PIP176/2005 (financed by the Aragón Government), and "Programa de grupos de investigación consolidados" (BOA 48 of 20-04-2005), also financed by the Aragón Government. Research of the first author was supported by postdoctoral fellowship by the Ministerio de Educación (Spain). ; Peer reviewed

27 páginas, 15 figuras, 6 tablas.-- El documento se encuentra en su versión post-print. ; This paper analyses the spatial and temporal variability of winter droughts in a semi-arid geographic gradient in Northeast Spain, from the Pyrenees in the north to the Mediterranean coastland in the south. Droughts that occurred between 1952 and 1999 were analysed by means of the Standardised Precipitation Index (SPI). The influence of the weather-type frequency and of the general North Atlantic atmospheric circulation patterns was analysed. The results indicate that winter droughts show an important spatial variability in the study area, differentiating three well-defined patterns. These correspond to the Pyrenees, the centre of the Ebro Valley, and the Mediterranean coastland. General negative trends in winter SPI have been found, which are indicative of the increase in winter drought conditions in the study area. Nevertheless, important spatial differences have also been recorded. Dominant north–south gradients in the influence of weather types are shown. Moreover, the negative trends in winter-SPI values agree with the negative trend in the frequency of the weather types prone to cause precipitation, such as the C, SW and W weather types and the increase in the frequency of A weather types. Nevertheless, in the Mediterranean coastland, the positive trend in SPI values agrees with the increase in the frequency of weather types of the east (E, SE), which are prone to cause precipitation in this area. Interannual variations in the frequency of the different weather types have been highly determined by different general atmospheric circulation patterns, mainly the North Atlantic Oscillation (NAO). Nevertheless, the correlation between the time series of weather-type frequency and the winter SPI is higher than that found between the SPI and the NAO. Thus, although the interannual NAO variability explains a high percentage of the interannual differences in the frequency of different weather types, it is not sufficient to explain the spatial and temporal variability of droughts, which respond better to atmospheric variability at more detailed (synoptic) spatial scales. ; This work has been supported by the projects: 'Caracterización espacio-temporal de las sequías en el valle medio del Ebro e identificación de sus impactos' (BSO2002-02743), 'Variabilidad climática y dinámica forestal en ecosistemas de ecotono' (REN2003-07453), Procesos hidrológicos y erosivos en cuencas pirenaicas en relación a cambios de usos de suelo y variabilidad climática (PIRIHEROS, REN2003-08678/HID) 'Caracterización y modelización de procesos hidrológicos en cuencas aforadas para predicción en cuencas no aforadas' (CANOA, CGL 2004-04919-c02-01), all funded by the Spanish Commission of Science and Technology (CICYT) and FEDER, and 'Programa de grupos de investigación consolidados' (grupo Clima, Cambio Global y Sistemas Naturales, BOA 48 of 20-04-2005), financed by the Aragón Government. We want to thank to the National Institute of Meteorology (INM) for providing the data used in this work. Research of the second author was supported by postdoctoral fellowships by the Ministerio de Educación, Cultura y Deporte (Spain). ; Peer reviewed

11 páginas, 7 figuras, 1 tabla.-- This work is licensed under a Creative Commons License. ; At present, the Standardized Precipitation Index (SPI) is the most widely used drought index to provide good estimations about the intensity, magnitude and spatial extent of droughts. The main advantage of the SPI in comparison with other indices is the fact that the SPI enables both determination of drought conditions at different time scales and monitoring of different drought types. It is widely accepted that SPI time scales affect different sub-systems in the hydrological cycle due to the fact that the response of the different water usable sources to precipitation shortages can be very different. The long time scales of SPI are related to hydrological droughts (river flows and reservoir storages). Nevertheless, few analyses empirically verify these statements or the usefulness of the SPI time scales to monitor drought. In this paper, the SPI at different time scales is compared with surface hydrological variables in a big closed basin located in the central Spanish Pyrenees. We provide evidence about the way in which the longer (>12 months) SPI time scales may not be useful for drought quantification in this area. In general, the surface flows respond to short SPI time scales whereas the reservoir storages respond to longer time scales (7–10 months). Nevertheless, important seasonal differences can be identified in the SPI-usable water sources relationships. This suggests that it is necessary to test the drought indices and time scales in relation to their usefulness for monitoring different drought types under different environmental conditions and water demand situations. ; The authors want to acknowledge financial support from the following projects: BSO2002-02743, REN2003-07453, CGL2005-04508/BOS, PIRIHEROS (REN2003- 08678/HID) and CANOA (CGL 2004-04919-c02-01), funded by Ministerio de Ciencia y Tecnología (Spain) and UE-FEDER, and "Programa de grupos de investigación consolidados" (BOA 48 of 20-04-2005), funded by Aragon Government. Research of the first author was supported by postdoctoral fellowship by the Ministerio de Educación y Ciencia (Spain). ; Peer reviewed

In this study, we assess the role of altitude in determining the relative performance of temperature and precipitation as predictors of snowpack variability in Switzerland. The results indicate a linear relationship between altitude and the correlation of temperature (precipitation) with snowpack depth and duration. We identify a threshold altitude of approximately 1400 m a.s.l. (± 200 m, depending on the snow index considered), below which temperature is the main explanatory variable and above which precipitation is a better predictor of snowpack variability. The results also highlight that as climate warms, the altitude at which temperature is the main constraint on snow accumulation increases. This has important implications for the future viability of snow-dependent economic sectors in Switzerland, where projections indicate a continuous warming during the course of the 21st century. ©2013. American Geophysical Union. All Rights Reserved. ; This study was made possible thanks to financial support from the Spanish Government (Ministry of Education) through the postdoctoral program "Ayudas de movilidad postdoctoral en centros extranjeros (Orden EDU/2728 /2011, de 29 de septiembre)" and the project CGL2011-27536/HID: "Hidrologia nival en el Pirineo central español: variabilidad espacial, importancia hidrológica y su respuesta a la variabilidad y cambio climático", funded by the Spanish Commission of Science and Technology, and FEDER. ; Peer Reviewed

25 pages, 8 figures, 3 tables. ; [EN] In recent decades many authors have adopted the Penman- Monteith formula as the standard way to estimate reference evapotranspiration from climate data. The main drawback associated with the Penman-Monteith method is the relatively high data demand: temperature, solar radiation, relative humidity and wind speed are the minimum inputs required by the formula. In the Spanish Pyrenees historical databases usually consist of temperature and rainfall only, although an improvement in data acquisition is expected in terms of parameters monitored. Under situations of data scarcity, some authors recommend the use of less data intensive methods, such as the empirical Hargreaves equation. Other authors suggest that it is better to estimate the missing parameters and to apply the Penman-Monteith equation. This paper presents a study on the accuracy of the Penman-Monteith method for a situation where some parameters have to be estimated from available temperature, and wind speed data must be replaced by a constant value. The results have been compared with the information available for a location in the central Spanish Pyrenees (period 1999-2003) where parameters required by the Penman-Monteith method have been monitored. A comparison is then made with the Hargreaves model in order to assess the most appropriate method for calculation of the reference evapotranspiration. The results indicate that the use of the Penman-Monteith formula results in errors in reference evapotranspiration ETo estimation of different magnitude and sign throughout the year. However, in general, it offers a more accurate estimation of reference evapotranspiration than the Hargreaves formula. ; [ES] En los últimos años, diferentes autores han adoptado el método de Penman-Monteith para estimar la evapotranspiración potencial mediante datos climáticos. El principal inconveniente de este método es que precisa de un gran número de variables para ser calculado: temperatura, radiación solar, humedad relativa y velocidad del viento. En el Pirineo español las bases de datos climáticas a menudo solamente muestran disponibilidad de datos térmicos y pluviométricos. Bajo estas carencias, algunos autores recomiendan el uso de métodos que precisan de menos datos, como es el caso de la ecuación empírica de Hargreaves. Otros autores sugieren que resulta preferible estimar los datos no disponibles necesarios para aplicar la ecuación de Penman –Monteith a partir de los datos disponibles de temperatura y velocidad del viento. Los resultados de ambos procedimientos han sido comparados con la información disponible en una estación del Pirineo central español (1999-2003) donde están disponibles los parámetros para aplicar la ecuación de Penman-Monteith. Se han comparado los resultados con el modelo de Hargreaves para valorar el método más apropiado de cálculo. Los resultados muestran errores estacionales muy diferentes mediante la fórmula de Penman-Monteith, sin embargo, este procedimiento muestra una aproximación mejor para obtener la evapotranspiración potencial que aplicando la fórmula de Hargreaves. ; This work has been supported by the research projects CGL2008-01189/BTE, CGL2006-11619/HID and CGL2008-1083/CLI financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7- ENV-2008-1-226487) and ACQWA (FP7-ENV-2007-1- 212250) financed by the VII Framework Programme of the European Commission, "Las sequías climáticas en la cuenca del Ebro y su respuesta hidrológica" and "La nieve en el Pirineo aragonés: Distribución espacial y su respuesta a las condiciones climática" Financed by "Obra Social La Caixa" and the Aragón Government and "Programa de grupos de investigación consolidados" financed by the Aragón Government. ; Peer reviewed

9 Pag., 5 Fig. ; We discuss here shortcomings of the PDSI in adequately modeling the soil water balance, and its limited ability to quantify and monitor droughts of different types. Conversely, we describe the advantages of statistically based drought indices in analyzing the spatial and temporal variability of drought, identifying drought impacts in a variety of systems, and monitoring drought conditions in real time. ; This work has been supported by the research projects CGL2006‐11619/HID, CGL2008‐01189/BTE, CGL2011‐27574‐ CO2‐02 and CGL2011‐27536 financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7‐ENV‐2008‐1‐ 226487) and ACQWA (FP7‐ENV‐2007‐1‐ 212250) financed by the VII Framework Programme of the European Commission, "Efecto de los escenarios de cambio climático sobre la hidrología superficial y la gestión de embalses del Pirineo Aragonés" financed by "Obra Social La Caixa" and the Aragón Government and "Influencia del cambio climático en el turismo de nieve", CTTP01/10, Financed by the Comisión de Trabajo de los Pirineos. ; Peer reviewed

We propose a new climatic drought index: the Standardized Precipitation Evapotranspiration Index (SPEI). The SPEI is based on precipitation and temperature data, and has the advantage of combining a multi-scalar character with the capacity to include the effects of temperature variability on drought assessment. The procedure to calculate the index is detailed, and involves a climatic water balance, the accumulation of deficit/surplus at different time scales, and adjustment to a Log-logistic probability distribution. Mathematically, the SPEI is similar to the Standardized Precipitation Index (SPI), but includes the role of temperature. As the SPEI is based on a water balance, it can be compared to the self-calibrated Palmer Drought Severity Index (sc-PDSI). We compared time series of the three indices for a set of observatories with different climate characteristics, located in different parts of the world. Under global warming conditions only the sc-PDSI and SPEI identified an increase in drought severity associated with higher water demand due to evapotranspiration. Relative to the sc-PDSI, the SPEI has the advantage of being multi-scalar, which is crucial for drought analysis and monitoring. ; This work has been supported by the research projects CGL2006-11619/HID, CGL2008- 01189/BTE, and CGL2008-1083/CLI financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7-ENV-2008-1-226487) and ACQWA (FP7- ENV-2007-1-212250) financed by the VII Framework Programme of the European Commission, "Las sequías climáticas en la cuenca del Ebro y su respuesta hidrológica" and "La nieve en el Pirineo Aragonés: distribución espacial y su respuesta a las condiciones climáticas" Financed by "Obra Social La Caixa" and the Aragón Government and the "Programa de grupos de investigación consolidados" financed by the Aragón Government.ÿ ; Peer reviewed

16 páginas, 6 figuras, 8 tablas. ; This paper compares different procedures for mapping reference evapotranspiration (ETo) by means of regression-based techniques and geographical information systems (GIS). ETo is calculated following the method of Hargreaves (HG) from a dense database of meteorological stations in the northernmost semi-arid region of Europe, the Ebro valley. The HG method requires the calculation of estimates of extraterrestrial radiation (Ra). We calculated this parameter using two approaches: (1) the common approach that assumes a planar surface and determines the parameter as a function of latitude and (2) using a digital terrain model (DTM) and GIS modelling. The maps were made on a monthly basis using both approaches. We also compared possible propagations of errors in the map calculations for maps derived from modelled layers of maximum and minimum temperatures with those modelled using previously determined local ETo calculations. We demonstrate that calculations of Ra from a DTM and GIS modelling provide a more realistic spatial distribution of ETo than those derived by only considering latitude. It is also preferable to model in advance the variables involved in the calculation of ETo (temperature and Ra) and to subsequently calculate ETo by means of layer algebra in the GIS rather than directly model the local ETo calculations. The obtained maps are useful for the purposes of agriculture and ecological and water resources management in the study area. ; This work has been supported by the project CGL2005- 04508/BOS financed by the Spanish Comission of Science and Technology (CICYT) and FEDER, PIP176/2005 financed by the Aragón Government, and 'Programa de grupos de investigación consolidados' (BOA 48 of 20-04-2005), also financed by the Aragón Government. Research of the third author was supported by postdoctoral fellowship by the Ministerio de Educación, Cultura y Deporte (Spain). ; Peer reviewed

27 Pag., 2 Tabl., 5 Fig. The definitive version is available at: http://www.informaworld.com/smpp/title~content=t911751996 ; This paper analyses the evolution of high flows in the central Spanish Pyrenees during the period 1955-1995. The method applied makes it possible to assess whether the contribution of the largest daily discharge and rainfall events to the total annual runoff and precipitation remains stationary or shows any temporal trend. The results show a general negative trend in flood intensity in the last decades, together with an increase in the importance of low flows in the total annual contribution. However, a change in the frequency distribution of precipitation events has not been detected. The different behaviour shown by runoff and precipitation could only be explained as being due to the increase in vegetation cover that is a consequence of the farmland abandonment and reforestation that occurred during the 20th century. ; This study was supported by the following research projects: "Hydrologic and erosive processes in Pyrenean catchments, related to land use changes and climate variability" (PIRIHEROS, REN 2003-08678/HID) and "Characterisation and modelling of hydrological processes in gauged basins for the prediction of ungauged basins" (CANOA, CGL 2004-04919-c02-01), both funded by the CICYT, Spanish Ministry of Science and Technology. Personal support for S.B. was provided by the Spanish Government Secretary for Education and Universities and the European Social Fund. We thank the Ebro River Hydrographic Administration (Confederación Hidrográfica del Ebro) for providing the river discharge data. ; Peer reviewed

Winter tourism is the main source of income and the driving force of local development in many mountain areas. However, in recent years, the industry has been identified as being extremely vulnerable to future climate change. Although the Pyrenees has the largest ski area in Europe after the Alps, there are few detailed climate change vulnerability assessments on the ski resorts based in this region. This paper analyzes the vulnerability of the Pyrenean ski resorts to projected changes in the snowpack under various future climate scenarios. In addition, the study analyzes the sustainability of the snowmaking systems to offset the climate variability of natural snow cover. On average, the study predicts a shorter ski-season length, especially in low-altitude ski resorts in a moderate climate change scenario and for all ski resorts in a more intensive climate change scenario. However, a significant regional variability has been identified for the projected impacts at very short geographical distances within the studied area. Moreover, this paper shows that snowmaking cannot completely solve the problem for all ski resorts in the Pyrenees, as the measure can only act as a robust adaptation strategy in the region provided climate change is limited to +2 °C snowmaking. © 2015, Springer Science+Business Media Dordrecht. ; This work was supported by the research projects Hidrología nival en el Pirineo Central Español: Variabilidad espacial, importancia hidrológica y respuesta a la variabilidad y cambio climático (CGL2011-27536/HID, Hidronieve), financed by the Spanish Commission of Science and Technology and FEDER, the CTTP1/12 "Creació d' un model d' alta resolució espacial per quantificar l'esquiabilitat i l'afluència turística al Pirineu sota diferents escenaris de canvio climàtic," financed by the Governmet of Aragon and ACTP011-AND/2010 and ACTP017-AND/2012 projects financed by the Government of Andorra in the framework of the research grants of Working Community of the Pyrenees. The first author acknowledges also a predoctoral grant from the Andorran Government [BTC2010/2013-0006-AND]. ; Peer Reviewed

A procedure for classifying daily summer temperature extremes in northeastern Spain into homogenous regions has been presented and evaluated. This procedure employed daily temperature series from a dense network of 128 weather stations spanning the period from 1960 to 2006. Characteristics of temperature extremes included temperature frequency (e.g., warm days), intensity (e.g., warmest day), and duration (e.g., maximum length of hot spell). Following the results of the principal components analysis and Ward's method of clustering, the study area was divided into four homogenous sub-regions in terms of both the geographic and climatic meanings: the Mediterranean region, the mainland and the Cantabrian region, the moderately elevated areas westward and southward, and the mountainous region. Based on an internal cluster validation measure (Silhouette width), the quality of clustering was evaluated and ensured. The temporal evolution of the long-term (1960-2006) temperature extremes clearly showed a different behavior amongst these sub-regions. The Mediterranean and the highly elevated regions revealed the strongest signals in both daytime and nighttime extremes. For mainland areas, considerable differences in the behavior of the daytime and nighttime temperature extremes were evident. The influence of atmospheric circulation on spatial and temporal variability of temperature extremes was also explored. The variability of summer temperature extremes in NE Spain appears to be mainly driven by the Scandinavian (SCA), the Western Mediterranean Oscillation (WeMO), and the East Atlantic (EA) patterns, with a tendency toward increasing during the positive (negative) phases of the EA (WeMO and SCA) circulation modes. In such a region with complex geography and climate, regionalization of summer temperature extremes can be advantageous for extracting finer-scale information, which may prove useful for the vulnerability assessments and the development of local adaptation strategies in areas such as health, ecosystems and agriculture. © 2012 Springer-Verlag Wien. ; We would like to thank the Spanish Meteorological State Agency for providing the temperature database used in this study. This work has been supported by the research projects CGL2008-01189/BTE, CGL2011-27574-CO2-02, and CGL2011-27536 financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7-ENV-2008-1-226487), and ACQWA (FP7-ENV-2007-1-212250) financed by the VII Framework Programme of the European Commission "Efecto de los escenarios de cambio climático sobre la hidrología superficial y la gestión de embalses del Pirineo Aragonés" financed by "Obra Social La Caixa" and the Aragón Government and Influencia del cambio climático en el turismo de nieve, CTTP01/10, financed by the Comisión de Trabajo de los Pirineos. ; Peer Reviewed

30 Pags., 2 Tabls., 10 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/09218181 ; The study examines climate change scenarios of precipitation extremes over the western, central and part of the eastern Mediterranean region for the late 21st century (2070–99) in an ensemble of high-resolution regional climate model (RCM) simulations from the ENSEMBLES project. Precipitation extremes are considered at a wide range of time scales from hourly to multi-day amounts and in individual seasons (DJF, MAM, JJA, SON). We focus on (1) the dependence of the results on the time scale of precipitation aggregation, (2) seasonal differences, (3) uncertainties of the scenarios related to differences amongst the RCM simulations, and (iv) identification of regions and seasons in which the projected changes in precipitation extremes are particularly large and/or robust in the RCM ensemble. The examined ensemble of RCM simulations captures basic precipitation patterns for the recent climate (1961–90), including seasonal changes. Climate change scenarios for the late 21st century differ substantially for short-term (hourly) and multi-day (5-day and 15-day) precipitation extremes, mainly in the western Mediterranean. Projected increases in short-term extremes exceed those of daily and multi-day extremes, and occur even in regions and seasons in which mean precipitation is projected to decline. This change in the patterns of extreme precipitation may have important hydrological consequences, with increases in the severity of flash floods in a warmer climate in spite of the overall drying projected for the region. However, uncertainty of the scenarios of precipitation extremes related to within-ensemble variability is large. Consistency of the projected changes amongst the RCMs is highest in winter and lowest in summer, and generally it is higher for short-term than multi-day extremes. ; The study was supported by the Czech Science Foundation under project P209/10/2265 and by CGL2011–24185 financed by the Spanish Commission of Science and Technology (CICYT) and FEDER. Parts of the work were carried out during the stay of the first author at Estación Experimental de Aula Dei, Zaragoza, Spain, funded by Consejo Superior de Investigaciones Científicas (CSIC) and the Czech Science Foundation. The research team benefited also through interactions and support within the KLIMATEXT project (CZ.1.07/2.3.00/20.0086) funded by the European Social Fund, and Grupo de Excelencia E68 financed by the Aragón Government and FEDER. The RCM and E-OBS data were produced by the EU-FP6 project ENSEMBLES (contract number 505539). ; Peer reviewed

21 páginas, 13 figuras. ; [EN] Spatial and temporal characteristics of extreme temperature events in northeastern Spain have been investigated. The analysis is based on long-term, high-quality, and homogenous daily maximum and minimum temperature of 128 observatories spanning the period from 1960 to 2006. A total of 21 indices were used to assess changes in both the cold and hot tails of the daily temperature distributions. The presence of trends in temperature extremes was assessed by means of the Mann-Kendall test. However, the autocorrelation function (ACF) and a bootstrap methodology were used to account for the influence of serial correlation and cross-correlation on the trend assessment. In general, the observed changes are more prevalent in hot extremes than in cold extremes. This finding can largely be linked to the increase found in the mean maximum temperature during the last few decades. The results indicate a significant increase in the frequency and intensity of most of the hot temperature extremes. An increase in warm nights (TN90p: 3.3 days decade−1), warm days (TX90p: 2.7 days decade−1), tropical nights (TR20: 0.6 days decade−1) and the annual high maximum temperature (TXx: 0.27 °C decade−1) was detected in the 47-yr period. In contrast, most of the indices related to cold temperature extremes (e.g. cold days (TX10p), cold nights (TN10p), very cold days (TN1p), and frost days (FD0)) demonstrated a decreasing but statistically insignificant trend. Although there is no evidence of a long-term trend in cold extremes, significant interdecadal variations were noted. Almost no significant trends in temperature variability indices (e.g. diurnal temperature range (DTR) and growing season length (GSL)) are detected. Spatially, the coastal areas along the Mediterranean Sea and the Cantabrian Sea experienced stronger warming compared with mainland areas. Given that only few earlier studies analyzed observed changes in temperature extremes at fine spatial resolution across the Iberian Peninsula, the results of this work can improve our understanding of climatology of temperature extremes. Also, these findings can have different hydrological, ecological and agricultural implications (e.g. crop yields, energy consumption, land use planning and water resources management). ; We are indebted to the anonymous reviewers for their constructive comments which were most helpful in improving the paper. We would like to thank the "Agencia Estatal de Meteorolog´ıa" for providing the temperature data used in this study. This work has been supported by the research projects CGL2008-01189/BTE and CGL2006-11619/HID financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7-ENV-2008-1-226487) and ACQWA (FP7- ENV-2007-1- 212250) financed by the VII Framework Programme of the European Commission, "Las sequ´ıas clim´aticas en la cuenca del Ebro y su respuesta hidrol´ogica" and "La nieve en el Pirineo aragon´es: Distribuci´on espacial y su respuesta a las condiciones clim´atica" Financed by "Obra Social La Caixa" and the Arag´on Government. ; Peer reviewed