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A long and complete series of monthly rainfall amounts corresponding to Barcelona city (Catalonia, NE Spain), exceeding two centuries (years 1786–2019), is analysed in detail. The obtained results of periodicity (annual scale), time trends (monthly, seasonal and annual scales), statistical distribution (seasonal and annual scale) and fractal/multifractal structures and self-similarity at monthly scale depict the complex structure of this pluviometric regime, which is characterized by moderate increasing and decreasing trends on rain amounts, varying from +0.08¿mm·year-1 (February) to -0.07¿mm·year-1 (September) and quite evident changes on the pluviometric trends at annual and seasonal scales when the rainfall data are analysed for segments of 50¿years from 1800 up to 2019. A good example could be the relevant change on the annual scale time trend, from +0.77¿mm·year-1 (years 1800–1850) to -0.17¿mm·year-1 (years 1950–2019). Clear evidences of decreasing pluviometry for spring, summer and autumn for the last segment (1950–2019) in comparison with the other three segments, including years 1800–1950, are also detected. Additionally, increasing rainfall patterns complexity, expected difficulties on monthly rainfall forecasting and the increasing irregularity of monthly amounts is also detected by interpreting fractal and multifractal results. Irregularity increases on the monthly rainfall series and on the rainfall regime complexity derived from multifractal parameters, could be associated with the very notable increase of CO2 emissions into the atmosphere, globally varying from 51.1¿×¿106 metric tonnes (year 1820) to 36.6¿×¿109 metric tonnes (year 2019) and the tropospheric concentration increasing from 280.8 ppm (year 1850) to 397.5 ppm (year 2014), being the probable relationship between tropospheric concentrations and changes on rainfall patterns the objective of future researches.

The study analyzes the atmospheric variability that caused the largest floods affecting the town of Tortosa in the mouth of the Ebro River (northeast Iberian Peninsula). The Tortosa flood database and flood marks in the nearby town of Xerta are used to define the more relevant flooding episodes (discharges > 2900 m3s-1) of the 1600-2005 period. We explore the atmospheric variability based on low-frequency patterns and synoptic types applying a multivariable analysis to grids at sea-level pressure and geopotential at 500 hPa provided by the 20th Century V3 Reanalysis Project for the instrumental period (since 1836). Output from the Last Millennium Ensemble Project and climate reconstructions (Luterbacher et al., 2002) were used to analyze the sea-level pressure over the pre-instrumental period (before 1836).The synoptic analysis includes 33 flood episodes since 1836. Four synoptic types are related to floods in Tortosa, characterized by low-pressure systems that interact with the Mediterranean warm air-mass and promote the atmosphere destabilization. The prevailing synoptic conditions that favor heavy rainfall explains well the hydrological reconstruction of the flood events. The synoptic types are characterized by Atlantic low-pressure systems that interact with the Mediterranean warm air mass that destabilizes the atmosphere due to temperature differences between the surface (warm and moist air from the Mediterranean Sea) and the middle levels of the troposphere. Furthermore, due to high-pressure systems located in Central Europe causing stagnation of the synoptic configuration, long-lasting rainfall can occur over the Ebro basin.We detected four clusters of high-frequency flooding in Tortosa since 1600: 1617-1643, 1710-1787, 1825-1884, and 1907-1985. Most of these are related phases of high solar variability, which highlight atmospheric and hydrological instability in periods of rapid climate change. The low-frequency atmospheric variability connected to these flood periods is related to the positive phase of the NAO, relative high values of solar activity and positive Northern Hemisphere temperature anomalies. This provides evidence that complex solar processes might provoke changes in temperature and variability in the atmospheric circulation. The NAO shows that the major floods in the region are related to the zonal atmospheric circulation. These atmospheric disturbances have a winter effect in the western part of the basin, while the Pyrenean sub-basins are affected during autumn.The major finding is that similar flood behavior is detected since 1600. Results from our study help to improve our understanding of the past, present and future climates, as well as their impacts, thereby enhancing the knowledge base for addressing some aspects and impacts of climate change in order to reduce uncertainty about future outcomes. Furthermore, future investigations seeking to detect and prevent extreme events will find it particularly useful to establish relationships between modes of low-frequency atmospheric variability, synoptic types and flooding.

Oliva, M. et. al., The Little Ice Age (LIA) is known as one of the coldest stages of the Holocene. Most records from the Northern Hemisphere show evidence of significantly colder conditions during the LIA, which in some cases had substantial socio-economic consequences. In this study we investigated the magnitude and timing of climate variability during the LIA in the mountains of the Iberian Peninsula, based on a wide range of natural records (including from glacial, periglacial, and lacustrine/peatland areas; fluvial/alluvial deposits; speleothems; and tree rings), historical documents, and early instrument data. The onset of the LIA commenced in approximately CE 1300, and cold conditions with alternating moisture regimes persisted until approximately CE 1850; the environmental responses ranged from rapid (e.g. tree rings) to delayed (e.g. glaciers). The colder climate of the LIA was accompanied by severe droughts, floods, and cold/heat waves that showed significant spatio-temporal variation across the Iberian mountains. Several phases within the LIA have been detected, including (a) 1300–1480: increasing cooling with moderate climate oscillations; (b) 1480–1570: relatively warmer conditions; (c) 1570–1620: gradual cooling; (d) 1620–1715: coldest climate period of the LIA, particularly during the Maunder Minimum, with temperatures approximately 2 °C below those at present; (e) 1715–1760: warmer temperatures and a low frequency of extreme events; (f) 1760–1800: climate deterioration and more climate extremes (i.e. cold and heat waves, floods and droughts); (g) 1800–1850: highly variable climate conditions alternating with stability (1800–1815), extreme events (1815–1835), and a slight trend of warming associated with intense hydrometeorological events (1835–1850); (h) since 1850: a gradual staggered increase in temperature of approximately 1 °C. Post-LIA warming has led to substantial changes in geo-ecological dynamics, mainly through shrinking of the spatial domain affected by cold climate processes. © 2017 Elsevier B.V., MO is supported by the Ramón y Cajal Program of the Spanish Ministry of Economy and Competitiveness (RYC-2015-17597). OLC is funded by Plan Galego I2C mod. A and Juan de la Cierva Incorporación (IJCI-2015-26864). This study was supported by the research projects CRIOINDI (CGL2015-68144-R), ESPAS (CGL2015-65569-R), DESIRÈ (HAR2013-43701-P), (CGL2014-58127-C3-1-R) and CLIMED (CGL2015-69985R) of the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER) and IMDROFLOOD (PCIN-2015-220) financed by the Water Works 2014 co-funded call of the European Commission.

In previous studies the Western Mediterranean Oscillation index (WeMOi) at daily resolution has proven to constitute an effective tool for analysing the occurrence of episodes of torrential rainfall over eastern Spain. The Western Mediterranean region is therefore a very sensitive area, since climate change can enhance these weather extremes. In the present study we selected the extreme torrential episodes (≥ 200 mm in 24 hours) that took place in Catalonia (NE Iberia) during the 1951–2016 study period (66 years). We computed daily WeMOi values and constructed WeMOi calendars. Our principal results reveal the occurrence of 50 episodes (0.8 cases per year), mainly concentrated in the autumn months. We inferred a threshold of WeMOi ≤ −2 to define an extreme negative WeMO phase at daily resolution. Most of the 50 episodes (60 %) in the study area occurred on days presenting an extreme negative WeMOi value. Specifically, the most negative WeMOi values are detected in autumn, during the second 10-day period of October (11th–20th), coinciding with the highest frequency of extreme torrential events. On comparing the subperiods, we observed a statistically significant decrease in WeMOi values in all months, particularly in late October, and in November and December. No changes in the frequency of these extreme torrential episodes were observed between both subperiods; in contrast, a displacement of the episodes is detected from early to late autumn.

Long-term drought variability and trends were assessed in Barcelona at annual and seasonal scale for the period 1787-2014 and sub-periods 1851-2014, 1901-2014 and 1951-2014 to identify changes in drought patterns across time. High quality and adjusted monthly temperature and precipitation series were required for this purpose. The Standardized Precipitation Index (SPI), based on precipitation, and the Standardized Precipitation Evapotranspiration Index (SPEI), based on the difference between precipitation and reference evapotranspiration (ET0), were calculated to describe temporal drought fluctuations. Therefore, major droughts and wet events were identified and an accurate analysis of drought severity, magnitude and duration were also carried out.Both drought indices provided similar results related to drought variability and trends in Barcelona across time, although the SPEI showed larger drought severity than SPI especially during the second half of the 20th century. Trends analysis revealed a significant drying trend at annual scale according to the SPEI since mid-19th century while the SPI did not show changes in drought patterns. At seasonal scale, both the SPI and SPEI found a clear drying trend only for summer (JJA) during the current period (1951-2014), although the SPEI was indicating the trend towards drier conditions for the whole period (1787-2014). Drought severity in SPEI series increased 13% during the second half of the 20th century compared with the whole period under study while drought magnitude and duration did not present significant changes in both the SPI and SPEI series. The increasing atmospheric evaporative demand associated to the large temperature rising experienced in Barcelona during the last decades could have played a substantial role in explaining the increase of drought severity and trends found in the SPEI series.

Detection and reconstruction of early instrumental series is an interdisciplinary activity that allows us to extend climate data records to periods prior to the mid-19th century, extending the overlapping periods with climate proxies and characterizing extreme events. In this work, the collection of several data sources corresponding to different periods and locations, obtained with a wide range of methods and instruments by institutions or private observers, provides the following results: Barcelona has a continuous rainfall series with monthly resolution since 1786 and with daily resolution since 1850. It is worth mentioning that the records from Barcelona provide the longest continuous monthly series available on rainfall in the Iberian Peninsula. The monthly records have been homogenized by using a relative homogenization approach, HOMER. The results highlight the existence of five breaks, most of them due to relocations or instrumentation changes documented in the metadata, which have been adjusted to remove non-climatic factors. The homogenized annual and winter precipitation series in Barcelona show a statistically significant increase from 1786 to 2014, although this increase is mainly due to the concentration of negative anomalies during the first half of the 19th century, which is also clearly visible in the seasonal series. Specifically, an extreme mega-drought episode was observed from the 1810s to the 1830s, which is supported by different proxy data. For a better dissemination of the homogenized monthly series developed in this study, the data set is freely available to the research community.

International audience; Los cambios climáticos durante el Cuaternario (últimos 2,6 millones de años), y en particular la sucesión de periodos glaciales e interglaciales, han tenido importantes repercusiones en los procesos superficiales (modelado del paisaje, geomorfología) y en los ecosistemas pirenaicos, incluyendo la formación de grandes artesas y circos glaciares, depósitos glaciolacustres y formas de detalle.

[1] We analyze the impact of stratospheric volcanic aerosols on the diurnal temperature range (DTR) over Europe using long-term subdaily station records. We compare the results with a 28-member ensemble of European Centre/Hamburg version 5.4 (ECHAM5.4) general circulation model simulations. Eight stratospheric volcanic eruptions during the instrumental period are investigated. Seasonal all- and clear-sky DTR anomalies are compared with contemporary (approximately 20 year) reference periods. Clear sky is used to eliminate cloud effects and better estimate the signal from the direct radiative forcing of the volcanic aerosols. We do not find a consistent effect of stratospheric aerosols on all-sky DTR. For clear skies, we find average DTR anomalies of −0.08°C (−0.13°C) in the observations (in the model), with the largest effect in the second winter after the eruption. Although the clear-sky DTR anomalies from different stations, volcanic eruptions, and seasons show heterogeneous signals in terms of order of magnitude and sign, the significantly negative DTR anomalies (e.g., after the Tambora eruption) are qualitatively consistent with other studies. Referencing with clear-sky DTR anomalies to the radiative forcing from stratospheric volcanic eruptions, we find the resulting sensitivity to be of the same order of magnitude as previously published estimates for tropospheric aerosols during the so-called “global dimming” period (i.e., 1950s to 1980s). Analyzing cloud cover changes after volcanic eruptions reveals an increase in clear-sky days in both data sets. Quantifying the impact of stratospheric volcanic eruptions on clear-sky DTR over Europe provides valuable information for the study of the radiative effect of stratospheric aerosols and for geo-engineering purposes.

Based on the daily sea level pressure (SLP) circulation catalogue obtained by Esteban, Martin-Vide and Mases, Int J Climatol 26:1501–1515, (2006) for Western Europe, high-resolution maps of daily maximum and minimum temperature, mean daily precipitation and daily precipitation probability have been obtained for Andorra (Pyrenees). The 20 daily-circulation patterns cover the period 1960–2001 and were generated using new approaches based on the rotated principal component analysis (PCA) and clustering technique. The final maps of Andorra associated with each circulation pattern have been constructed using altitude, latitude, continentality and solar radiation as multiple regression predictors (Ninyerola, Pons and Roure, Int J Climatol 20:1823–1841, 2000). The daily temperature and rainfall series used from Andorran, French and Catalan/Spanish weather stations have been checked for data quality. The results confirm the complexity of the spatial distribution of meteorological phenomena over mountainous areas such as in Andorra, and show the importance of the Mediterranean and Atlantic influence upon the climate of this country of the Pyrenees. On the other hand, different tests have been made showing that the classification results could improve the resulting interpolated climate maps by the use of the circulation-pattern frequencies.

In this work we introduce the rationale behind the ongoing compilation of a parallel measurements database, in the framework of the International Surface Temperatures Initiative (ISTI) and with the support of the World Meteorological Organization. We intend this database to become instrumental for a better understanding of inhomogeneities affecting the evaluation of long-term changes in daily climate data. Long instrumental climate records are usually affected by non-climatic changes, due to, e.g., (i) station relocations, (ii) instrument height changes, (iii) instrumentation changes, (iv) observing environment changes, (v) different sampling intervals or data collection procedures, among others. These so-called inhomogeneities distort the climate signal and can hamper the assessment of long-term trends and variability of climate. Thus to study climatic changes we need to accurately distinguish non-climatic and climatic signals. The most direct way to study the influence of non-climatic changes on the distribution and to understand the reasons for these biases is the analysis of parallel measurements representing the old and new situation (in terms of e.g. instruments, location, different radiation shields, etc.). According to the limited number of available studies and our understanding of the causes of inhomogeneity, we expect that they will have a strong impact on the tails of the distribution of air temperatures and most likely of other climate elements. Our abilities to statistically homogenize daily data will be increased by systematically studying different causes of inhomogeneity replicated through parallel measurements. Current studies of non-climatic changes using parallel data are limited to local and regional case studies. However, the effect of specific transitions depends on the local climate and the most interesting climatic questions are about the systematic large-scale biases produced by transitions that occurred in many regions. Important potentially biasing transitions are the adoption of Stevenson screens, relocations (to airports) efforts to reduce undercatchment of precipitation or the move to automatic weather stations. Thus a large global parallel dataset is highly desirable as it allows for the study of systematic biases in the global record. We are interested in data from all climate variables at all time scales; from annual to sub-daily. High-resolution data is important for understanding the physical causes for the differences between the parallel measurements. For the same reason, we are also interested in other climate variables measured at the same station. For example, in case of parallel air temperature measurements, the influencing factors are expected to be global radiation, wind, humidity and cloud cover; in case of parallel precipitation measurements, wind and wet-bulb temperature are potentially important. Metadata that describe the parallel measurements is as important as the data itself and will be collected as well. For example, the types of the instruments, their siting, height, maintenance, etc. Because they are widely used to study moderate extremes, we will compute the indices of the Expert Team on Climate Change Detection and Indices (ETCCDI). In case the daily data cannot be shared, we would appreciate contributions containing these indices from parallel measurements. For more information: http://tinyurl.com/ISTI-Parallel

Varios estudios anteriores han demostrado que el índice de la Oscilación del Mediterráneo Occidental (WeMOi) tiene una correlación estadísticamente significativa con los totales pluviométricos de la vertiente oriental de la Península Ibérica. En este trabajo se presenta un calendario del WeMOi a partir de los valores medios obtenidos por períodos de diez días, y se relaciona con la ocurrencia de episodios torrenciales en las provincias costeras de Cataluña (Girona, Barcelona y Tarragona). A lo largo de los 64 años del período de estudio 1950-2013, se han detectado 375 días (5,9 por año) con precipitación torrencial (≥100 mm en 24 h) y 36 episodios de torrencialidad extrema (≥200 mm en 24 h) (0,6 por año). Se ha obtenido una buena correspondencia entre los valores intraanuales del WeMOi y la frecuencia de episodios. Los valores más negativos del WeMOi tienen lugar en otoño, concretamente, durante la segunda década de octubre (del 11 al 20 de octubre). En esa década se registra la máxima frecuencia de episodios de 100 y 200 mm en 24 h en el área de estudio. En el análisis también se consideran dos subperíodos de estudio de 32 años (1950-1981 y 1982-2013) para detectar variaciones tanto en el calendario del WeMOi como en la frecuencia de episodios torrenciales. El segundo subperíodo muestra en la mayoría de décadas valores del WeMOi más negativos que el primer subperíodo, especialmente, a finales de otoño y principios de invierno. En correspondencia con ello se observa un aumento de la frecuencia de episodios torrenciales en el segundo subperíodo (222 días) respecto al primero (153 días). Several previous studies have demonstrated that the Western Mediterranean Oscillation index (WeMOi) has a statistically significant correlation with total rainfall amount over eastern Iberia. In the present paper, we present a WeMOi calendar using mean daily values derived from 10-day periods, relating it to the occurrence of heavy rainfall episodes over the coastal provinces of Catalonia (Girona, Barcelona and Tarragona). During the 1950-2013 study period, i.e. 64 years, 375 days (5.9 per year) were found to present heavy rainfall (≥100 mm in 24 h) and 36 days to present extremely heavy rainfall (≥200 mm in 24 h) (0.6 per year). We found a good match between the intra-annual WeMOi values and the occurrence of heavy rainfall. The most negative WeMOi values are observed in autumn, especially during the second decade of October (from 11th to 20th). In this decade, the rainfall episodes of 100 and 200 mm in 24 h over the study area accumulate the highest frequency. The study analysis also considers two subperiods of 32 years (1950-1981 and 1982-2013) in order to detect variations both in the WeMOi calendar and in the frequency of heavy rainfall episodes. In most decades, the second subperiod exhibits lower WeMOi values than the first subperiod, particularly at the end of autumn and the start of winter. Accordingly, we observed an increase in the frequency of heavy rainfall episodes during the second subperiod (222 days) compared with the first subperiod (153 days). Este trabajo ha sido financiado por el proyecto WEMOTOR (CSO2014-55799-C2-1-R, 2015-2017) del Ministerio de Economía y Competitividad, y por el Grup de Climatologia de la Universitat de Barcelona (UB) (2014 SGR 300, Generalitat de Catalunya).

Homogenization methods are developed to reduce the impact of non-climatic factors on climate series. Martinex et al. (2009), (International Journal of Climatology, Doi 10.1002/joc.1884) applied a set of homogenization procedures to available Spanish temperature series. In this report, we address critical issues of that paper concerning a specific property of the standard normal homogeneity test and the application scheme of the homogenization tests. We conclude with some important recommendations on the application of homogenization methodologies. Copyright © 2010 Royal Meteorological Society

The main objective of this study is to estimate the probable maximum precipitation (PMP) in Barcelona for durations ranging from 5 min to 30 h. To this end, rain records from the Jardi gauge of the Fabra Observatory located in Barcelona (1927–1992) and the urban pluviometric network supported by Clavegueram de Barcelona, S.A. (CLABSA, 1994–2007) were analysed. Two different techniques were used and compared: a physical method based on the maximization of actual storms, and the Hershfield' statistical method. The PMP values obtained using the two techniques are very similar. In both cases, the expected increasing behaviour of the PMP with duration was found, with the increase especially notable for the mesoscale durations 2–9 h, and not significant from 12 h on up. This result seems to be related to the scale of the meteorological situations producing high intense rainfall amounts over our territory. Copyright © 2010 Royal Meteorological Society

We identify monthly circulation patterns of variability over the European continent within the first year after eight large tropical volcanic eruptions since the early 19th century. For this purpose, we apply an empirical orthogonal function (EOF) technique to a gridded sea level pressure data set covering the period 1780-1995. The post-eruption months with above-normal variance represented by the leading two EOFs are retained. Afterwards, we mapped their rotated equivalents to simplify physical interpretation of the results. Following the eight tropical eruptions, four months are identified during the first year fulfilling the criterion of exceptional values of variance in EOF1: January, June, July and September. January shows an anomalously dominant zonal pattern responsible for warmer temperatures over continental Europe. The summer months tend to show a more persistent south-westerly or westerly circulation over the continent, indicating a likely reduction in the strength of the Azores high. The results showing modification of the atmospheric circulation following large volcanic eruptions are consistent with previous studies based on instrumental records for more recent periods. This underscores the robustness of the circulation changes as a response to volcanic forcing. The analysis also demonstrates that empirical orthogonal functions provide a useful tool to detect these dynamical features.

En este artículo se describe el proceso y metodología para lacreación de una base de datos térmica del Pirineo para el periodo temporal1950-2010, y se avanzan los primeros resultados del análisis espacial de lastemperaturas y del cálculo de la tendencia de las mismas a escala anual.Para el control de calidad y homogeneización se ha empleado el métodoHOMER que incorpora los últimos métodos y técnicas de gestión de datos,incluyendo la eliminación de valores atípicos, la detección por paresy la selección de punto de ruptura (reforzada por los metadatos). Las seriesfinales proporcionan datos homogeneizados para analizar la evolucióndel clima y el comportamiento climático del conjunto del Pirineo.