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Climate variability conditioned by the effects of climate change justifies the study of past periods in order to identify and characterise episodes of high severity and low frequency. The increase in the irregularity of the precipitation regime in some regions justifies the study of these events for a better assessment of their occurrence in the immediate future. In this regard, the climatic framework of the Maldà Oscillation (1760-1800) offers hydrometeorological anomalies of low frequency and high severity, especially in the dimension of catastrophic floods. One of the episodes that occurred in this period affected the region of the present-day Valencian Community, on the eastern coast of the Iberian Peninsula, between 6 and 8 September 1793.The aim of this work is to reconstruct, in as much detail as possible, the meteorological and hydrological behaviour of an extraordinary rainfall event. At the same time, it also aims to reconstruct the impacts caused on human activity. In order to achieve this objective, data from old instrumental meteorological observation and the result of an extensive collection of information from historical documentary sources are used. Although the meteorological data are scarce, they allow the synoptic characterisation of the episode. The hydrological approach of the episode is only qualitative, but it allows the identification of the affected river basins and the occurrence of river floods and overflows. The social impacts of the episode are significant and occurred due to the exceptional nature of the episode. For example, the overflowing of the top of a hydraulic dam built at the end of the 16th century (Tibi dam, 43 metres above the river course). Despite the presence of hydraulic infrastructures that were able to control the floods, there were numerous catastrophic damages that are represented in a detailed thematic cartography. During 3 days of flooding, 7 river basins belonging to the Júcar and Segura hydrographic demarcations were affected, with 11 towns and villages suffering catastrophic damages. Likewise, the social response to these events is analyzed, basically characterized by the celebration of religious ceremonies.

Under the current climate change situation, the Mediterranean region has been identified as one of the primary hot-spots, expecting not only to become warmer, but also drier during the twenty-first century. Changing conditions also include an increase in the frequency of intense torrential rainfall events, whose occurrence has already caused increasing flash flood events with catastrophic impacts and human casualties. The understanding of the past extreme events is challenging and useful to deal with the current situation.During November 1617 an extreme rain event has been documented by previous studies in a large latitudinal region from southern France to eastern river basins of the Iberian Peninsula (Thorndycraft et al., 2006). Here we present new evidences of the large-scale impact of this extreme event based on a multi-proxy approach. On the one hand, the occurrence of this event is interpreted by means of a flood cave horizon detected in a speleothem from Mallorca (Balearic Islands). On the other hand, historical documents depict this event also in some localities of Pyrenees, enhancing its longitudinal occurrence.Through the integration with previous climate, paleohydrological and qualitative hydrometeorological reconstructions, we try to understand the complex atmospheric mechanisms that caused this event during the Little Ice Age.

Climate variability conditioned by the effects of climate change justifies the study of historical periods in order to identify and characterise episodes of high severity and low frequency. The increase in the irregularity of the rainfall regime in some regions justifies the study of these events for a better assessment of their presence in the immediate future. In this regard, the study of extreme hydrometeorological episodes that happen in unusual seasons of the year for these extreme episodes is of particular interest.One of these unusual episodes was the torrential rainfall and floods of May 1853 in Catalonia (NE Iberian Peninsula). The whole month of May 1853 is a unique hydrometeorological anomaly, being the second most rainy month of May in the whole instrumental series of precipitation of the city of Barcelona (period 1786-2022).This work reconstructs this episode of heavy rainfall and floods using a multidisciplinary approach. Old instrumental meteorological data are used to obtain the daily pluviometric behaviour in Barcelona. Surface atmospheric pressure data from different points of Western Europe allow its synoptic description.Historical information allows the identification of the different river overflow points and the floods caused by this episode. These points are represented cartographically together with the documented impacts on infrastructures. For this episode, there are 38 cases with historical information on impacts caused by floods or overflows. These occurred in eight different river basins which are included in the hydrographic demarcations of the Ebro River and the Catalan Coastal Basins. In order to appreciate the magnitude of the event, a limnimark (or floodmark) located in Tres Ponts Canyon on the Segre River is used. This record enables us to assimilate the episode with the most severe episode measured on the Segre River, one of the main tributaries of the Ebro River, in November 1982, with 1900 m3/s. This confirms the magnitude of the event of 1853, which is one of the most severe episodes of the lower Ebro basin for the last 500 years.

The current climate change scenario increases the concern for water resource management and for the increase in the frequency of droughts in the Mediterranean region. This work proposes the analysis of the instrumental precipitation series of the city of Barcelona (1786-2022), which extends from the end of the Little Ice Age to the current climatic period. This series, due to its temporal length, constitutes a continuous scenario of pluviometric information that allows the identification and analysis of the periods in which the most severe droughts occur.This work is organized following two main objectives. The first objective consists on the analysis of the values of this precipitation series using different statistical techniques, including drought indices. The second objective is the evaluation of the severity of the most significant drought events that appear in the instrumental precipitation series of Barcelona.To achieve these objectives, the methodologies used in this work consist on the application of some statistical techniques on the instrumental precipitation series, such as the detection of its breaking points. At the same time, this work proposes the application of different drought indices as the SPI index and the SPEI index on the entire instrumental precipitation series of Barcelona (1786-2022). The use of these methodologies allows the comparison between the different droughts included in the instrumental series. These also allow distinguishing the most relevant droughts according to their severity. Two significant examples of the most severe droughts are the ones of the first third of 19th century (1812-1825) and the droughts of the 21st century (1998-2008). We also want to determine the relevance of the current drought (2021-2022) in contrast to the overall instrumental series of precipitation of Barcelona.Additionally to these methodologies and results, for the most significant droughts detected in the precipitation series, it is also proposed to use monthly barometric indices to characterise the general atmospheric circulation of those periods. It would have the aim to contrast the results on the instrumental precipitation series with the synoptic conditions that produce these droughts. This comparison also would help to determine if these conditions have changed over time, especially considering recent decades in the context of current climate change.

The current climate change scenario is increasing concerns about the frequency of droughts in the Mediterranean region and the management of water resources. For this reason, it is interesting to study the most severe droughts of the recent past in order to better characterise the current phenomenon and future adaptive strategies.One of these episodes of great magnitude and significant impact on economic and social activity were the droughts that occurred in the first third of the 19th century in the Mediterranean basins of the Iberian Peninsula. This relatively brief period, placed at the end of the Little Ice Age, contains up to four episodes of drought that affected the Spanish Mediterranean Basins. Their occurrence can be linked to known climatic forcing factors. On the one hand, the effects of the Dalton Solar Minimum (1790-1830). On the other hand, the effects of three different volcanic eruptions produced in the intertropical latitudes with a VEI equal or greater than 5: the Unknown eruption of 1809, the Tambora eruption of 1815 and the Galunggung eruption of 1822.The climatic characterisation of the drought in this period is proposed with the use of historical proxy-data based on rogation ceremonies to monitor situations of rainfall deficit at high temporal resolution (daily/monthly). For drought assessment, a drought information classification system is proposed based on an index that takes into account the basic characteristics of each episode (duration, extent and severity). This classification will be tested to determine the behaviour of the droughts that affected the Spanish Mediterranean Basin during the period of the Dalton Solar Minimum.The results obtained from the application of these methodologies and materials allow the identification of severe droughts that affected the Spanish Mediterranean Basin during this period. Some of these years with severe droughts are 1807, 1812, 1817-1818, the most severe drought in the overall of the series, and 1822-1825. The description and cartographic representation of the historical data about these droughts allows us to assess their severity due to the extraordinary persistence of the rainfall deficits and their capacity to affect simultaneously distant regions.Finally, in order to compare the results obtained from the historical data recorded in Barcelona about rainfall deficits, we use the instrumental meteorological series of Barcelona. This data series begun in 1780 recording data on temperature and pressure and begun recording precipitation in 1786. The information from those records allows the comparison with the historical data.

El estudio de las interacciones entre condiciones climáticas adversas y procesos socio-económicos en época histórica permite detectar y analizar, desde un punto de vista interdisciplinar, la presencia de conflictos, problemas y la toma de decisiones de administraciones y grupos sociales. El proceso de derribo del perímetro defensivo de Barcelona a partir de 1854 es un caso de estudio que permite ver como los episodios de lluvias torrenciales de la parte final de la Pequeña Edad del Hielo reactivan un sistema fluvial altomedieval en una trama urbana posterior que no contemplaba este riesgo.Ante la evidencia de una situación de frecuentes impactos en la actividad urbana, se puede describir la percepción y las reacciones de las administraciones competentes, las medidas que adoptan y sus efectos, desde una simple gestión de la emergencia hasta la construcción de un sistema de drenaje completo que sustituye el efecto protector de las murallas medievales.

Current climate modelling frameworks present significant uncertainties when it comes to quantifying flood quantiles in the context of climate change, calling for new information and strategies in hazard assessments. Here, state-of-the-art methods on hydraulic and statistical modelling are applied to historical and contemporaneous flood records to evaluate flood hazards beyond natural climate cycles. A comprehensive flood record of the Duero River in Zamora (Spain) was compiled from documentary sources, early water-level readings and continuous gauge records spanning the last 500 years. Documentary evidence of flood events includes minute books (municipal and ecclesiastic), narrative descriptions, epigraphic marks, newspapers and technical reports. We identified 69 flood events over the period 1250 to 1871, of which 15 were classified as catastrophic floods, 16 as extraordinary floods and 38 as ordinary floods. Subsequently, a two-dimensional hydraulic model was implemented to relate flood stages (flood marks and inundated areas) to discharges. The historical flood records show the largest floods over the last 500 years occurred in 1860 (3450 m3 s−1), 1597 (3200 m3 s−1) and 1739 (2700 m3 s−1). Moreover, at least 24 floods exceeded the perception threshold of 1900 m3 s−1 during the period (1500–1871). Annual maximum flood records were completed with gauged water-level readings (pre-instrumental dataset, PRE: 1872–1919) and systematic gauge records (systematic dataset, SYS: 1920–2018). The flood frequency analyses were based on (1) the expected moments algorithm (EMA) and (2) the maximum likelihood estimator (MLE) method, using five datasets with different temporal frameworks (historic dataset, HISTO: 1511–2018; PRE–SYS: 1872–2018; full systematic record, ALLSYS: 1920–2018; SYS1: 1920–1969; and SYS2: 1970–2018). The most consistent results were obtained using the HISTO dataset, even for high quantiles (0.001 % annual exceedance probability, AEP). PRE–SYS was robust for the 1 % AEP flood with increasing uncertainty in the 0.2 % AEP or 500-year flood, and ALLSYS results were uncertain in the 1 % and 0.2 % AEP floods. Since the 1970s, the frequency of extraordinary floods (>1900 m3 s−1) declined, although floods on the range of the historical perception threshold occurred in 2001 (2075 m3 s−1) and 2013 (1654 m3 s−1). Even if the future remains uncertain, this bottom-up approach addresses flood hazards under climate variability, providing real and certain flood discharges. Our results can provide a guide on low-regret adaptation decisions and improve public perception of extreme flooding., This research has been supported by the Ministerio de Ciencia, Innovación y Universidades (grant no. EPHIMED, CGL2017-86839-C3-1-R) and the Fundación Biodiversidad (grant no. PRCV00446). The CSIC Open Access Publication Support Initiative has provided financial support for the publication fee through its Unit of Information Resources for Research (URICI).

The uncertainties raised by climate change in the Mediterranean region justify a detailed study on rainfall regime over a long time scale. This study is not just about reconstructing and characterizing climate variability, but also identifying the hydrometeorological episodes of greater severity and low frequency. These phenomena, such as floods and droughts, affect the availability of water resources, generate casualties and have significant impacts on human activity. In this context of global warming, knowledge of past extreme hydrometeorological events has gained importance over time. Moreover, the ability to classify these past extreme events in order to compare them with current ones strengthens research capabilities. For this reason, this paper proposes a multivariable classification system for flood episodes, both historical and recent. The classification considers the physical conditions of a flood, its damage to structures and its social impacts. The proposed methodology has been applied to the AMICME flood database for the Spanish Mediterranean catchment areas from CE 1035 to 2022. This paper shows the application of this methodology for six flood episodes from different centuries and locations. It has been possible to display all the indexed information for the different flood cases of every episode through cartographic summary representations. Results prove the adaptability of the classification system to different hydrographical and historical contexts., Present work was funded by Prediflood Project, Ministerio de Economía y Competitividad, Spanish Government (Number CGL2012–35071), 2013–2015; and Mediflood Project. Ministerio de Economía y Competitividad, Spanish Government, Number CGL2016–75996–R, 2016–2019.

espanolEl presente trabajo de climatologia historica pretende aportar los resultados obtenidos para Espana en fuentes documentales y bibliograficas para el siglo XIV. La crisis bajomedieval muestra una vertiente climatica a pesar de una disponibilidad precaria de informacion por el contexto historico en la Peninsula Iberica y la falta de instituciones administrativas con capacidad de generar grandes series documentales. Los resultados ofrecen una vision preliminar de los comportamientos de la variabilidad climatica propia de la Pequena Edad del Hielo. Unas primeras oscilaciones de fuerte frecuencia de inundaciones y sequias entre 1310 y 1330 desencadenan fuertes crisis productivas e incluso sanitarias. Entre 1371 y 1380 se produce una oscilacion de gran magnitud con episodios hidrometeoros extremos muy frecuentes. Sin duda, el siglo XIV con la presencia de estas oscilaciones abre un periodo de fuerte irregularidad hidrometeorologica que se prolonga hasta mediados de siglo XIX. English: Present project on historical climatology aims to provide the results obtained for Spain in documentary and bibliographic sources for the 14th Century. The late medieval crisis shows a climatic dimension despite the precarious availability of information due to the historical context in the Iberian Peninsula and the lack of administrative institutions with capa city to generate large documentary series. The results offer a preliminary vision of climatic variability patterns of the Little Ice Age. A first alteration of high frequency of floods and droughts between 1310 and 1330 triggered strong productive and even health crises. Between 1371 and 1380 there is other oscillation of great magnitude with very frequent extreme hydrometeorological events. Undoubtedly, 14th century, with the presence of these oscillations, opened a period of strong hydrometeorological irregularity that lasted until the mid-19th century.

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.

From 1755 to 1801 in Spain, many articles and reports were written about common bunt, a seed-borne plague that was difficult to control at the time. The objective of the study is to better understand this plague and the relationship between historical rainfall indexes and years of higher reported outbreaks. We compared documentary sources on extreme rain events and annual series of wheat prices in four locations (Murcia, Seville, Toledo, and Zamora) with data from articles about the bunt plague. Increased severity of common bunt in wheat coincided with a concentration of such events, during a period of severe climatic irregularity known as the Maldà Anomaly. However, the cause-and-effect relationship for proxies of historical weather, price volatility and bunt plague was only significant in Seville. A complementary factor that explains the abundance of literature was access to agricultural articles and books from France, where the common bunt also existed. The first experiments to understand the plague and how to control it were performed there. These events are framed in the Spanish Enlightenment and early physiocratic ideas advocating the importance of agriculture in maintaining the wealth of a country. Durante 1755-1801 existen bastantes artículos e informes sobre el tizón del trigo en España, una plaga trasmitida por semilla y de difícil control en esa época. El objetivo de este trabajo es conocer la importancia de esta plaga en esta época, incluida su relación con indicadores históricos de lluvia y los años descritos con mayores ataques. Para ello, se relacionaron registros documentales de lluvias extremas y series anuales de precios de trigo en cuatro localidades (Murcia, Sevilla, Toledo y Zamora) con datos de las descripciones de epifitias de tizón de los artículos. La mayor severidad del tizón del trigo coincidió con una concentración de episodios de lluvia excesiva, en un periodo de fuerte irregularidad climática conocido como anomalía Maldà, aunque la relación causa-efecto entre indicadores de tiempo atmosférico histórico, precio del grano y la plaga solo fue significativa en Sevilla. Otro factor complementario que explica la abundancia de estos artículos sobre el tizón fue una conexión con artículos y libros de agricultura procedentes de Francia, donde también existía el tizón, y donde se realizaron los primeros experimentos para entender la plaga y su control. Todas estas circunstancias se engloban dentro del periodo de la Ilustración española y en el inicio de las ideas fisiocráticas que propugnaban la importancia de la agricultura para mantener la riqueza de un país.

British pre-industrial economic growth has traditionally been analysed from the Malthusian point of view and other more optimistic approaches, but in many cases, ignoring environmental factors. This article explores the inclusion of the climate in this general debate, focusing on one of the colder periods of the last 500 years, known as the Maunder Minimum. The provisional results suggest that climate change and the resulting adaptations may have influenced the start of the English Agricultural Revolution, the Energy Transition and the European Divergence. However, from an econometric point of view these results are not fully conclusive, making it necessary to continue working with better primary sources and other alternative methodologies.

El estudio analiza la severidad de la megasequía del período 1626-1635 y sus consecuencias en la economía y la población del valle medio del Ebro, a partir de fuentes proxy documentales y dendroclimáticas y los registros históricos del coste de los cereales y la evolución demográfica. En el valle del Ebro, y en particular en su sector central, los años comprendidos entre 1626 y 1635 fueron especialmente adversos, con lluvias irregulares y muy escasas, y elevados valores térmicos no repetidos en decenios, que responden en buena medida a los extremismos de la Pequeña Edad del Hielo. No se trató de un único mal año, ni de una dificultad puntual, sino de déficits acumulados que causaron la pérdida progresiva del rendimiento de los cultivos, carestía de alimentos y malnutrición de la población. Las consecuencias más directas fueron el incremento del precio de los cereales y el aumento extraordinario de la mortalidad, que alcanzaron su peor momento en 1631.

Buntgen et al. (2015; hereinafter B15) present the result of new research which question the results of Wetter et al. 2014, (hereinafter W14) and Wetter et al. (2013, hereinafter W13)regarding European climate in 1540. B15 conclude from tree-ring evidence that the results based on documentary data of W14 probably overstated the intensity and duration of the 1540 drought event. W14 termed it Megadrought because of its extreme duration and spatial extent compared to other drought events in central Europe, although they note that the term is generally used for decadal rather than for single-year droughts (Seneviratne et al. 2012). We take the opportunity to recall the following issues. Firstly, when dealing with drought the complexity of this phenomenon should be kept in mind. Meteorological drought defined as a large negative precipitation anomaly during a certain period can trigger agricultural, hydrological, groundwater and socioeconomic droughts. Lloyd-Hughes (2013] and references cited herein) concluded that any workable objective definition of drought does not exist. To quantify droughts, various indices based on precipitation, temperature and evapotranspiration are used such as the Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), Z-index and PDSI. Their calculation depends on different periods (seasons, combination of months) and so different indices may classify the same drought episode differently (e.g. Brazdil et al.2014).

Globally, natural hazards present a serious and critical threat to life, as a result of both endogenous and exogenous processes. Natural hazards (geological, geomorphological, hydrological and meteorological) quickly present a risk to individuals, communities and societies when they are threatened with disruption or losses, with the impact being a function of their ability to cope and respond. Historical research is a key tool in determining the appropriate strategies for the identification of risk scenarios. Many parts of the world suffer from a dearth of instrumental information and data, as such qualitative accounts and records provide a crucial source of information in understanding the risks presented. The significance of long records is particularly pertinent when considering extremes, and such knowledge is crucial in better understanding the risks presented and in undertaking targeted mitigation strategies to reduce the socio-economic consequences and physical impact on private properties, strategic buildings, infrastructures and cultural heritage. This Special Issue aims to stress the importance of historical information and data as a strategic tool in framing planning decisions. Objective one is to demonstrate the significance of historical information in better understanding the risks presented by natural hazards (geological, geomorphological, hydrological and meteorological). Objective two is to stimulate a discussion between the international scientific community, technicians, policymakers and urban planners about the use of historical data and land use, planning and zonation. In this Special Issue, original research articles and reviews are welcome. Research areas may include (but are not limited to) the following themes: 1) Use of historical information in hazard and risk analysis; 2) Use of historical sources to assess and mitigate natural hazard risks to cultural heritage; 3) Land use planning and geo-risk assessment using historical data; 4) Analysis of the spatial-temporal distribution of extreme events; 5) Methodologies for data collection and management from documentary sources; 6) Geomorphological hazard and risk studies by historical sources; 7) Historical climatology and reconstruction of extreme weather events; 8) The analysis of natural hazards in data-poor regions.

El siglo XVII conoció en España varios periodos de crisis agrarias que provocaron escasez de productos de primera necesidad y un aumento del precio de los cereales. Las fluctuaciones de los precios del trigo, cebada y centeno están relativamente bien documentadas en muchas zonas del país; sin embargo, el conocimiento de la influencia que sobre estas variaciones pudieron tener factores climáticos y ambientales es aún muy limitado. En este trabajo se presentan los registros históricos del coste de los cereales de cuatro ciudades de diferentes entornos geográficos del nordeste de la península ibérica durante el periodo 1630-1660 y se comparan con los índices de sequía reconstruidos a partir de fuentes proxy documentales y dendroclimáticas. Se observa que las variaciones de los precios coinciden con anomalías regionales en la sequía de primavera-verano. Las correlaciones directas entre ambos son bajas, apenas superan r=0,435; sin embargo, si el análisis se centra en los valores extremos, la influencia del clima aumenta: los precios son altos durante los periodos más secos y descienden durante los periodos considerados normales o húmedos; aunque con respuestas espacialmente variables. Esta correspondencia es mayor en los años anteriores y posteriores a la Guerra dels Segadors, lo cual indica que el intercambio de bienes y la coherencia de los datos estaban controlados tanto por factores sociopolíticos como ambientales, siendo estos últimos más influyentes en tiempos de paz. The 17th century knew in Spain several periods of agricultural crisis producing shortages in staple foods and a rising in grain prices. The fluctuations of the prices of wheat, barley and rye are relatively well documented in several areas of the country, however, the knowledge about the influence of climatic and environmental factors on these variations is still limited. In this work, we present the historical records of grain prices of four cities of different geographical areas in northeastern Iberian Peninsula during period 1630-1660, and they are compared with drought indices, reconstructed from documentary and dendroclimatic proxies. We observed that prices variations coincide with regional anomalies in spring-summer drought. Direct correlations between them are low (0.435), however, if analysis is focused on extreme values, the climatic influence is higher: prices are high during dry periods and lower during wet periods. This correspondence is higher in previous and following years to the Guerra dels Segadors, showing that the exchange of goods and the coherence of data were controlled by sociopolitical and environmental factors, being the latter more influential in peacetime. Este estudio se ha realizado en el marco del proyecto de investigación CGL2011-28255, financiado por el Ministerio de Economía y Competitividad del Gobierno de España, y el programa de Grupos de Investigación Consolidados «Clima, Agua y Cambio Global» del Gobierno de Aragón y Fondos FEDER.

The study of historical floods is a growing research trend that has generated numerous methodologies that aim to convert the qualitative historical documentation into quantitative information. This codification process aims to make comparable in time and space the manner in which past societies adapted to floods, and so extract the positive or negative points that can help reduce vulnerability and increase the resilience of current societies. However, the diversity of cultural and historical contexts, as well as the spatial-temporal heterogeneity of documentary sources, makes it difficult to extrapolate quantitative methods in historical climatology. This situation means that interpretative analyses of texts are still necessary as a complement to quantitative studies. In this paper, we make a hermeneutic analysis of the three most catastrophic floods that have occurred in the city of Murcia (south-eastern Spain) in the last 400 years. We complete this analysis with a historical cartographic reconstruction of a quantitative nature. Among the main conclusions, we highlight the fact that the society of Murcia had strategies to overcome catastrophes that included the whole of society and an integrated emergency management. However, the state of poverty of privation prior to a flood is a determining factor in explaining the resilience of a social system. A large increase in exposure of flood-prone areas over the past two centuries is noteworthy but unsurprising. However, it is surprising that the percentage of urban area exposed to flooding is now smaller than in the past. Therefore, if we consider hazard avoidance as a form of management, we can say that pre-industrial Murcian society was less efficient in using the mechanisms available to adapt to flooding. El estudio de inundaciones históricas es una corriente investigadora al alza que ha generado numerosas metodologías que persiguen transformar la información cualitativa contenida en la documentación histórica, en información cuantitativa. Este proceso de codificación persigue hacer comparable en el tiempo y en el espacio la forma en que las sociedades se adaptaban a las inundaciones en el pasado, con el fin de extraer los puntos positivos o negativos que pueden ayudar a reducir la vulnerabilidad y aumentar la resiliencia de las sociedades actuales. Sin embargo, la diversidad de los contextos culturales e históricos, así como la heterogeneidad espaciotemporal del material documental, dificulta la capacidad de extrapolación de los métodos cuantitativos en climatología histórica. Esta situación, repercute en que sigan siendo necesarios los análisis hermenéuticos de textos, como complemento a los estudios de carácter cuantitativo. En este trabajo realizamos un análisis hermenéutico de las tres inundaciones más catastróficas ocurridas en la ciudad de Murcia (Sureste de España) en los últimos 400 años. Completamos este análisis con una reconstrucción cartográfica histórica de carácter cuantitativo. Entre las principales conclusiones destaca el hecho de que la sociedad murciana tenía estrategias de superación de catástrofes que involucraban al conjunto de la sociedad y que preconizaban una gestión integral de las emergencias. No obstante, el estado de penuria previo a una inundación es un factor determinante para explicar la capacidad de resiliencia del sistema social. En cuanto a la forma de exponerse al peligro, es destacable el gran aumento de la exposición a zonas inundables producido en los últimos dos siglos. Esto no es algo sorprendente, pero si lo es el hecho de que en el pasado el porcentaje de superficie urbana expuesta sobre el total fuera superior, comparando con la situación actual. Por lo tanto, si consideramos la evasión del peligro, como una forma de gestión, podemos afirmar que la sociedad murciana preindustrial usaba de forma menos eficiente los mecanismos de los que disponía para adaptarse a las inundaciones.

To analyze the river floods dynamics, it is common to fix the observations of the flow at a characteristic checkpoint of the basin, showing its evolution over time: the hydrograph. A less common way of studying this hydrological phenomenon is the analysis of the unit peak discharge of the flood (i.e., the peak flow divided by the contributory area of the basin) along different checkpoints of the drainage axis.If this second methodology is chosen for the analysis of the river flooding, the circulation of flows through the river network generally shows that as the contributory area of the basin increases the unit peak discharge decreases. This is due to the reduction in the amount of precipitation and the slope of the riverbed with the increase of the basin area as it moves away from the headwaters. However, this simple scheme can have very different behavior depending on factors such as the spatial and temporal distribution of precipitation, the presence of snow, the soil moisture, the geological substrate, land uses, or human activities.This study compares the hydrological data of several historical and recent floods in NE basins of the Iberian Peninsula from the perspective of observing the unit peak flows depending on the size of the drained basin (i.e., the spatial evolution of the specific maximum discharge). These basins are small in size (usually below 500 km2) and drain regions such as the central Pyrenees (Garonne, Noguera Pallaresa), the Ebro Depression (rivers Ribera Salada, Sió, Ondara, Corb) and the Catalan Coastal System (Francolí), that is, they belong to very diverse geographical environments.The results allow to compare the magnitude of the unit peak flows in the headwaters and the decreasing of this variable when moving downstream. The unit peak discharges of the tributaries of the Ebro Depression, near the Catalan Coastal System are much higher when comparing with the flow of the Pyrenean rivers. For many floods of the Ebro basin of medium magnitude, the unit peak flow is reduced by the runoff infiltration in the flood plains favored by agricultural activities. In the Pyrenean rivers the spatial decrease of the unit peak discharge is gentle than in those of the Ebro Depression. The results show different patterns of flow generation and propagation that have implications for managing the dangerousness of flood risk, especially in very small basins (< 10 km2), where peak flows can be unexpectedly large and devastating.

Combining historical climatology and environmental history, this article examines the diverse range of strategies deployed by the city government of Barcelona to confront the recurrent drought episodes experienced between 1626 and 1650. First, our reconstruction of drought episodes for the period 1525–1821, based on pro pluvia rogations as documentary proxy data, identifies the years 1625–1635 and 1640–1650 as the most significative drought events of the period 1521–1825 (highest Drought Frequency Weighted Index of the series). Throughout the article, we focus on human responses to drought and discuss how water scarcity was perceived and confronted by Barcelona city authorities. We present the ambitious water supply projects launched by the city government, together with the construction of windmills as an alternative to watermills in order to mill grain, as attempts to cope with diminishing water flows. The context was aggravated by political instability, related first to the tensions between the centralising efforts of the Spanish King Philip IV and later to the impact of the Thirty Years’ War in the border region between the French and Spanish Crowns (1635–1659). Finally, we interpret the efforts of the city government to codify and appropriate knowledge about urban water supply as an attempt to systematise historical information on infrastructure to improve institutional capacities to cope with water scarcity in the future. These efforts materialised in the elaboration of the Llibre de les Fonts de la Ciutat de Barcelona (“Book of Fountains of the City of Barcelona”), a manual compiling the knowledge of Barcelona’s water supply from source to tap, written by the Barcelona water city officer in 1650, after three decades of experience in his post.

Climate change implies changes in the frequency and magnitude of flood events. The influence of climate variability on flooding was evaluated by an analysis of sedimentary (palaeofloods) and documentary archives. A 500-year palaeoflood record at Montlle&oacute, River (657 km2 in catchment area), eastern Spain, revealed up to 31 palaeofloods with a range of discharges of 20&ndash, 950 m3 s&minus, 1, and with at least five floods exceeding 740&ndash, 1. This information contrasts with the available gauged flood registers (since year 1971) with an annual maximum daily discharge of 129 m3 s&minus, 1. Our palaeoflood dataset indicates flood cluster episodes at (1) 1570&ndash, 1620, (2) 1775&ndash, 1795, (3) 1850&ndash, 1890, and (4) 1920&ndash, 1969. Flood rich periods 1 and 3 corresponded to cooler than usual (about 0.3 &deg, C and 0.2 &deg, C) climate oscillations, whereas 2 and 4 were characterised by higher inter-annual climatic variability (floods and droughts). This high inter-annual rainfall variability increased over the last 150 years, leading to a reduction of annual maximum flow. Flood quantiles (&gt, 50 years) calculated from palaeoflood+gauged data showed 30%&ndash, 40% higher peak discharges than those using only instrumental records, whereas when increasing the catchment area (1500 km2) the discharge estimation variance decreased to ~15%. The results reflect the higher sensitivity of small catchments to changes on flood magnitude and frequency due to climate variability whereas a larger catchment buffers the response due to the limited extent of convective storms. Our findings show that extended flood records provide robust knowledge about hazardous flooding that can assist in the prioritization of low-regret actions for flood-risk adaptation to climate change.

In the 1500s-1510s an unusually high number of significant droughts in Central and Western, and partly in Southern Europe; the years 1502-1504, 1506-1507, 1513-1514 and 1516-1518 were dry particularly in Central and Western Europe. Droughts, interspersed with wet years marked even by significant floods and other weather-related extremes, and frequent hard winters were mainly responsible for the reduced or poor crop and hay harvests in multiple years. These circumstances, in combination with other socio-economic factors, contributed to the increased social tension of the period, manifesting itself in major peasant uprisings, and might have acted as a catalyst in the timing and rapid spread of the Reformation.The first part of the presentation is concentrated on the reconstruction and spatial-temporal analysis of the droughts (and hard winters) using documentary evidence – in comparison with the tree-ring based hydroclimate reconstruction (OWDA: Cook et al. 2015) and the multiproxy-based reconstruction of Central European precipitation (Pauling et al. 2006).The most significant groups of socio-economic consequences are analysed in the second part of the presentation, with special emphasis on discussing the possible cumulative effects of the anomalous weather conditions during the period on the ongoing transformation of the late-medieval society and economy and the Reformation itself.

On the 22nd and 23rd of October 2019 a severe rainfall produced floods in the basins of the Catalan Coastal Range-Ebro Depression border (Francolí, Set, Femosa rivers) that affected various towns such as L'Espluga de Francolí, Montblanc, l'Albi, Vinaixa, among others, causing 6 deaths and material damages that exceeded 100 million euros. According to historical records, this rainfall episode would exceed the maximum rainfall estimates expected for 500 years in this region and the maximum heights reached by the water are comparable to, or exceed, those of the remembered Santa Tecla flash flood on September 1874, which would have a recurrence of more than 250 years.This rain was caused by a S-SE warm and wet Mediterranean air mass over the Catalan Coastal System (Prades and Llena Ranges). The area of maximum rainfall was located at the headwaters of the rivers Set, Francolí and Montsant rivers, with rain depths above 200 mm. The hourly distribution at El Vilosell and Prades rain gauges shows 50 mm from 6 to 14 UTC and maximum intensity of 10 to 15 mm h-1, followed by a second pulse of 180-220 mm from 16 to 01 UTC and maximum intensity of 65 mm h-1 (maximum 3.1 mm min-1). Soil moisture content was low at the time of the rain after a dry summer. Early precipitation saturated the topsoil, therefore the soil surface was very wet at the beginning of the second rainfall event and it generated a hortonian overland flow. The highest rainfall intensity occurred around 19 UTC and the peak flow response was immediate, around an hour later, depending on the location.Despite the similarity of rainfall and initial soil moisture conditions, the hydrological response in the two analyzed basins was markedly different. The flows generated in the Set River basin at l'Albagès reservoir produced a peak flow of 245 m3 s-1 (1.5·m3·s-1·km-2) and a very low flood runoff ratio of only 8%. In the basin of the Francolí River, at L'Espluga de Francolí, the peak flow was 1,300 m3 s-1 (13 m3·s-1·km-2) and the runoff ratio was of the order of 70%. The Set river basin is basically agricultural with terraced slopes that retained much of the precipitation, only released after the flood as baseflow. The Francolí river basin has steeper slopes and channels and is dominated by an extensive tree cover but very poorer soils that caused little water retention, giving rise to a major hydrological response, an order of magnitude larger than that of the Set River.

There are concerns that recent climate change is altering the frequency and magnitude of river floods in an unprecedented way. Historical studies have identified flood-rich periods in the past half millennium in various regions of Europe. However, because of the low temporal resolution of existing datasets and the relatively low number of series, it has remained unclear whether Europe is currently in a flood-rich period from a long-term perspective. Here we analyse how recent decades compare with the flood history of Europe, using a new database composed of more than 100 high-resolution (sub-annual) historical flood series based on documentary evidence covering all major regions of Europe. We show that the past three decades were among the most flood-rich periods in Europe in the past 500 years, and that this period differs from other flood-rich periods in terms of its extent, air temperatures and flood seasonality. We identified nine flood-rich periods and associated regions. Among the periods richest in floods are 1560–1580 (western and central Europe), 1760–1800 (most of Europe), 1840–1870 (western and southern Europe) and 1990–2016 (western and central Europe). In most parts of Europe, previous flood-rich periods occurred during cooler-than-usual phases, but the current flood-rich period has been much warmer. Flood seasonality is also more pronounced in the recent period. For example, during previous flood and interflood periods, 41 per cent and 42 per cent of central European floods occurred in summer, respectively, compared with 55 per cent of floods in the recent period. The exceptional nature of the present-day flood-rich period calls for process-based tools for flood-risk assessment that capture the physical mechanisms involved, and management strategies that can incorporate the recent changes in risk., This work was supported by the ERC Advanced Grant ‘FloodChange’ project (no. 291152), the Horizon 2020 ETN ‘System Risk’ project (no. 676027), the DFG project FOR 2416, the FWF projects I 3174 and W1219-N22, the Spanish Agency of Science and FEDER/UE projects CGL2016-75475/R, CGL2017-86839-C3-1-R, CGL2016-75996-R and CTM2017-83655-C2-2-R, the ICREA Academia programme, and project CZ.02.1.01/0.0/0.0/16_019/0000797, Ministry of Education, Youth and Sports of the Czech Republic.

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.

The Spanish Mediterranean river basin provides a good background for studying floods from documentary and bibliographical sources within the specialty of historical climatology. This study region's long history of human occupation and climatic conditions together determine a high risk of flooding. As a result, there exists an enormous amount of documentary heritage containing flood information. However, the heterogeneity of documentary sources and different approaches to classifying floods through historical documents can generate some biases and uncertainties about the quantity and quality of the available data. For this reason, this paper proposes a methodology for reconstructing historical floods based on cross-referencing documentary sources. This approach, together with additional archival work, has allowed us to increase the number of flood series for the Spanish Mediterranean coast by 17% and has generated a surprising increase of 233% in the number of flood cases detected. The data obtained have allowed us to analyze the variability of floods and their relationship with climatic and social factors from the fourteenth century to the present. Different climatic oscillations related to the Little Ice Age are detected between the 14th and 19th centuries. Additionally, we detected a strong influence of the defense infrastructures and urban growth, which explain the recent flood trends. However, the difficulty in analyzing the influence of social factors on long-term flood behavior invites us to reflect on the need for further work for emphasizing these issues. This work has been partially supported by the Spanish Ministry of Economy and Innovation (CGL2016-75996-R). SG-G acknowledges the support of the Spanish Ministry of Science, Innovation and Universities through “Juan de la Cierva-Incorporación” grant (IJCI-2016-29016). AA acknowledges the support of the Spanish Ministry of Economy and Innovation (HAR2017-82810-P). MB acknowledges the support of the Research Group of Generalitat de Catalunya “Paleogeoecologia, Riscs Naturals i Gestió Ambiental (PaleoRisk)” (2017SGR1106).

Documentary evidence can provide high-resolution data pertaining to past droughts. This may include a wide range of sources, among them: narratives (annals, chronicles, memoirs); diaries kept by persons specifically interested in the weather; accountancy and economic-administrative archives; legal-administrative records; religious observances; letters; songs; newspapers and magazines; paintings and pictographic evidence; chronograms; epigraphic evidence; early instrumental meteorological observations; society and professional reports; and weather compilations. Most of these are generally available for many European countries. Such a variety of documentary information is sufficient to distinguish between the basic types of drought (meteorological, agricultural, hydrological and socio-economic) and reconstruct hydroclimatic conditions in the form of series of precipitation totals, drought frequencies and drought indices. This paper presents a European overview of existing documentary-based drought studies for the Mediterranean, western, central and eastern areas of Europe. Examples of outstanding European droughts are drawn from events of 1361, 1616 and 1718–1719 CE. The descriptions of European droughts and of human responses to them, pay particular attention to impacts on society, to perceptions of drought and to spiritual and ritual responses, as well as to the institutional/legal-administrative decisions and changes droughts have brought about. Perspectives for future research into historical droughts in Europe are also presented.

River flooding is among the most destructive of natural hazards globally, causing widespread loss of life, damage to infrastructure and economic deprivation. Societies are currently under increasing threat from such floods, predominantly from increasing exposure of people and assets in flood¿prone areas, but also as a result of changes in flood magnitude, frequency, and timing. Accurate flood hazard and risk assessment are therefore crucial for the sustainable development of societies worldwide. With a paucity of hydrological measurements, evidence from the field offers the only insight into truly extreme events and their variability in space and time. Historical, botanical, and geological archives have increasingly been recognized as valuable sources of extreme flood event information. These different archives are here reviewed with a particular focus on the recording mechanisms of flood information, the historical development of the methodological approaches and the type of information that those archives can provide. These studies provide a wealthy dataset of hundreds of historical and palaeoflood series, whose analysis reveals a noticeable dominance of records in Europe. After describing the diversity of flood information provided by this dataset, we identify how these records have improved and could further improve flood hazard assessments and, thereby, flood management and mitigation plans., This publication is a contribution to the Past Global Changes (PAGES) Floods Working Group. PAGES is supported by the US National Science Foundation and the Swiss Academy of Sciences.

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.

Rapid advection of extremely warm and dry air is studied during two events in the Mediterranean basin. On 27 August 2010 a rapid advection of extremely warm and dry air affected the northeast Iberian Peninsula during few hours. At the Barcelona city center, the temperature reached 39.3 °C, which is the maximum temperature value recorded during 230 yr of daily data series. On 23 March 2008 a similar synoptic situation was the cause of a rapid increase of temperature and drop of relative humidity recorded for few hours in Heraklion (Crete). During the morning on that day the recorded temperature reaches 34 °C for several hours in the north coastline of this island. According to the World Meteorological Organization none of these events can be classified as a heat wave, which requires at least two days of abnormally high temperatures; or as a heat burst as defined by the American Meteorological Society, where abnormal temperatures take place over a few minutes. For this reason, we suggest naming this type of event flash heat. By using data from automatic weather stations in the Barcelona and Heraklion area and WRF mesoscale numerical simulations, these events are analyzed. Additionally, the primary risks and possible impacts on several fields are presented.

In the northeast of the Iberian Peninsula, drought recurrence, intensity, persistence and spatial variability have been mainly studied by using instrumental data covering the past ca. 60 years. Fewer studies have reconstructed drought occurrence and variability for the preinstrumental period using documentary evidence and natural proxies. In this study, we compiled a unique dataset of rogation ceremonies, religious acts to ask god for rain, from 13 cities in the northeast of Spain and investigated the annual drought variability from 1650 to 1899 AD. We converted the qualitative information into three regionally different coherent areas (Mediterranean, Ebro Valley and Mountain) with quantitative, annually resolved (December to August) drought indices according to the type of religious act. We found common periods with prolonged droughts (during the mid and late 18th century) and extreme drought years (1775, 1798, 1753, 1691 and 1817) associated with more blocking situations. A superposed epoch analysis (SEA) was performed to test the regional hydroclimatic responses after major tropical volcanic eruptions. The SEA shows a significant decrease in drought events one year after the volcanic events, which might be explained by the decrease in evapotranspiration due to decreases in surface temperatures and, consequently, the higher water availability that increases soil moisture. In addition, we discovered a common and significant drought response two years after the Tambora volcanic eruption in the three regional drought indices. Documented information on rogations thus contains important independent information to reconstruct extreme drought events for specific seasons in areas and periods for which instrumental information and other proxies are scarce.

The eruption of Mount Tambora (Indonesia) in April 1815 is the largest documented volcanic eruption in history. It is associated with a large global cooling during the following year, felt particularly in parts of Europe and North America, where the year 1816 became known as the "year without a summer". This paper describes an effort made to collect surface meteorological observations from the early instrumental period, with a focus on the years of and immediately following the eruption (1815–1817). Although the collection aimed in particular at pressure observations, correspondent temperature observations were also recovered. Some of the series had already been described in the literature, but a large part of the data, recently digitised from original weather diaries and contemporary magazines and newspapers, is presented here for the first time. The collection puts together more than 50 sub-daily series from land observatories in Europe and North America and from ships in the tropics. The pressure observations have been corrected for temperature and gravity and reduced to mean sea level. Moreover, an additional statistical correction was applied to take into account common error sources in mercury barometers. To assess the reliability of the corrected data set, the variance in the pressure observations is compared with modern climatologies, and single observations are used for synoptic analyses of three case studies in Europe. All raw observations will be made available to the scientific community in the International Surface Pressure Databank.

A multidisciplinary methodology for historical floods reconstruction was applied to 1874 Santa Tecla floods occurred in Catalonia (NE Iberian Peninsula), using both historical information and meteorological data from 20th Century Reanalysis. The results confirmed the exceptionality of the event: the highest modeled specific peak flow was around 14.6 m3 s-1 km-2 in a 100 km2 catchment and all the modeled total rainfall values were above 110 mm in about six hours, with maximum intensities around 60 mm min-1. The peak-flows peak flows' return periods were about 260 years and the rainfalls periods were between 250 and 500 years. The meteorological cause of the rainstorms was the flash triggering effect, initiated by the withdrawal of a mass of hot air at mid-levels. A sensitivity analysis on the various sources of error shows that peak flow errors from hydraulic modeling ranged from 5% to 44%, and rainfall errors from hydrological modeling were about 36%. The authors were financed by Spanish MINECO projects CGL2012-35071 and CGL2012-37416-C04-03, and by the INTERREG EU project FLUXPYR EFA 34/08. One of the authors has a pre-doctoral grant from the University of Lleida.

This paper presents a new methodological approach in the analysis of the influence of the North Atlantic circulation on the flood magnitude of the Tagus River, the largest Atlantic draining river of the Iberian Peninsula. This methodology is based on Correspondence Analysis viewed as a qualitative regression tool. A daily scale database (sea level atmospheric pressure, river discharge, rainfall) was used for this study. The selected streamflow station, Vila Velha de Rodão (Portugal, near the Spanish border), holds the longest continuous daily river discharge register of the Iberian Peninsula (over 160 years, since 1852). The annual maximum flood magnitudes were classified into seven categories according to their specific recurrence intervals (T). The qualitative regression approach was used to relate annual peak flood occurrence with the North Atlantic Oscillation (NAO) index mode (positive or negative) registered, during the preceding 40 days (divided in 8 successive 5-day periods). Large floods (categories 1–2 of T > 50 years and category 3, T 25–50 years) were found to be associated with a very high frequency of the negative NAO mode during the initial 20–25 days (within a total 40 days period length) before de flood peak. The lack of significant association of these flood categories with a predominant NAO mode during the immediately preceding 15 days, prior to the flood, suggest a time lag of 15 days before the peak. Minor flooding (category 7, T < 2 years) show a high degree of association with the presence of a positive NAO mode during the previous 20–25 days. The analysis of flood response under natural and dam-regulated regimes (before and after the construction of dams ca 1960) revealed no changes in the behaviour of major floods (responding to a period of 25 days with a dominant negative NAO index mode). Moderate flooding of category 4 (T: 10–25 years), that during the pre-dam construction period were linked to the existence of an initial 5–15 days of negative NAO mode, were not documented during the post-dam period, probably due to flood peak discharge attenuation by reservoirs. The clear climatic control (rainfall accumulation and number of persisting NAO negative mode days) in the onset of flood category 3 (T: 25–50 years) was also statistically blurred during the post-dam period, due to the effective role of dam operation in flood management during wet winters. This dam management effect does not seem to mask the meteorologically related largest flood magnitude events (T > 50 years), indicating that catastrophic events will likely occur under the NAO negative daily and seasonal patterns defined in this work. The robustness of the model was assessed by the phenomenological analysis of misclassified Flood/NAO events. Results also indicate that flood management practises may benefit from improved climate scenarios and forecasting of the NAO index.