Search

Following the Holocene Thermal Maximum, dated between 11 and 6 ka, the Neoglacial period was one of the progressive, fluctuating cooling that peaked during the Little Ice Age (LIA). The almost total absence of glacial tills prior to the LIA in the Pyrenees forces recourse to a high variety of proxies, including lacustrine sediments, palynological records, dendroclimatology, ice cores from glaciers and caves, speleothems, historical documentation and glacial records. This has enabled us to identify several colder periods during the mid- and late-Holocene: (i) the first phase of the Neoglacial period occurred at some time around 6 ka; (ii) a glacial pulse immediately before 3.4 ka; (iii) a glacial re-advance during the Dark Ages, i.e., immediately before the Medieval Climate Anomaly, between the fourth and ninth centuries; and (iv) the Little Ice Age, which started at the beginning of the fourteenth century and finished in the mid-nineteenth century. During the LIA, there was remarkable climate variability, with two, and probably three, glacial pulses, mainly between 1620 and 1715 and in the first half of the nineteenth century. Of all of the Holocene cold periods, most of the European paleoclimatic records coincide on the occurrence of the LIA. For the remaining Holocene cold periods, European records show high variability and uncertainty, particularly for the onset of the Neoglacial, although the phases of glacial pulses in the Pyrenees broadly coincide with those identified in the Alps and northern Europe.

The action of the Quaternary glaciers in the Central-Western Pyrenees is responsible for the various kinds of the relief features found there, including the well-configured cirques, large U-shaped valleys, overexcavation basins, detailed shapes, and moraine accumulations of very different ages. With almost continuous divides exceeding 2500 m and very complex basins that integrate numerous tributary valleys, the main Pyrenean glaciers reached over 30 km in length and 400 m in thickness, descending to altitudes of c. 800 m. The largest glaciers were those in the Gallego and Esera valleys. Their size is attributed to the large extents of their headwaters and the altitudes of their highest peaks. The long tradition of studies on Pyrenean glacial processes allows us to trace a fairly complete sequence of events, especially during the Last Glacial Cycle. Thus, a considerable amount of data confirm that the maximum ice extent did not occur during the global Last Glacial Maximum (20 ka or MIS-2) but at 60 ka, that is, during MIS-4. There is indirect evidence of a glacial advance between 22 and 19 ka as well as successive advances and retreats in the Oldest Dryas and Younger Dryas during deglaciation. Moreover, small reactivations likely took place during the Holocene from 6 ka, especially during the Little Ice Age. It is also interesting to note that scattered moraine remains, erratic blocks, and fluvioglacial terraces corresponding to previous glacial cycles have been found in some valleys.

The European Mediterranean highlands have undergone a sharp economic decline from the mid-20th century, causing heavy environmental impacts and loss of ecosystem services. These mountain areas have limited opportunities to integrate into in the current financial system, which demands high productivity from workers and a very competitive product. Extensive livestock farming is one of the few activities able to survive in this context, as it needs little labour and can make use of poor grazing resources. In the north-west Iberian Range, northern Spain, the Leza valley (La Rioja) is showing a growing interest in developing extensive livestock farming. To this end, the regional Government is implementing a pasture regeneration plan for clearing shrubland. Since 1986, almost 30% of the shrubs have been cleared, mainly abandoned fields recolonized by Genista scorpius on lime substrate, and Cistus laurifolius on siliceous substrate. This has increased the available pasture, as the average production in G. scorpius areas has risen from 4566 Mj ha -1 yr -1 (δ ± 1271) to 10,167.3 Mj ha -1 yr -1 (δ ± 2850.3), and on C. laurifolius areas from 2435 Mj ha -1 yr -1 (δ ± 492) to 7628.6 Mj ha -1 yr -1 (δ ± 1428.2). The livestock numbers show an upward trend, going from 1833.9 LU in 1972 to 7207.8 LU in 2017, with a simultaneous increase in the size of farms (27.6 LU in 1972 and 115.2 LU in 2017). In addition, new livestock farms established by people from outside the study area (41.7% in 2017). Finally, there is a discussion on the environmental benefits provided by extensive livestock farming.

espanolEl Antropoceno puede considerarse como el origen de la configuracion paisajistica actual, y en relacion a la vegetacion, como el periodo en el que la intervencion humana es el agente principal de los cambios que se producen de forma clara, intensa y permanente en el tiempo. En este trabajo se recopilan y comparan datos de secuencias palinologicas y de microcarbones, ocupaciones de yacimientos arqueologicos y dataciones de paleoincendios localizados en el Pirineo Central, ademas de informacion documental, exponiendo una reflexion sobre las supuestas evidencias que promulgan una deforestacion temprana y el uso del fuego de origen antropico como senal inequivoca de intervencion humana y surgimiento de los paisajes culturales desde hace milenios. En realidad, lo que se constata es una alta diversidad temporal y espacial entre todos los indicios, y solo a partir de la Baja Edad Media (ultimos 700 anos, 1300 AD), los indicadores y valores de los mismos ofrecen autentico consenso sobre el inicio de cambios consistentes y duraderos que marcarian el inicio del Antropoceno. EnglishThe Anthropocene is related to the origin of current landscape configuration, and in terms of vegetation, with the consideration of human action as main forcing of clear, intense and permanent changes through time. In this paper we compile and compare data from palynological sequences, microcharcoal records, archaeological sites and radiocarbon dates from palaeofires located in the Central Pyrenees besides historical documents, and we argue that some evidences related to early deforestation processes and use of human fire are not so clear than some authors point. Conversely, indicators of unequivocal human use and the origin of cultural landscapes are located only a few centuries and not a few millennia ago. In fact, high temporal and spatial variability is recorded until the Middle Ages (last 700 years, 1300 AD), when a series of consistent and permanent changes suggest the onset of the Anthropocene.

Mountain glaciers have generally experienced an accelerated retreat over the last three decades as a rapid response to current global warming. However, the response to previous warm periods in the Holocene is not well-described for glaciers of the of southern Europe mountain ranges, such as the Pyrenees. The situation during the Medieval Climate Anomaly (900–1300 CE) is particularly relevant since it is not certain whether the glaciers just experienced significant ice loss or whether they actually disappeared. We present here the first chronological study of a glacier located in the Central Pyrenees (N Spain), the Monte Perdido Glacier (MPG), carried out by different radiochronological techniques and their comparison with geochemical proxies with neighboring paleoclimate records. The result of the chronological model proves that the glacier endured during the Roman Period and the Medieval Climate Anomaly. The lack of ice from last 600 years indicates that the ice formed during the Little Ice Age has melted away. The analyses of the content of several metals of anthropogenic origin, such as Zn, Se, Cd, Hg, Pb, appear in low amounts in MPG ice, which further supports our age model in which the record from the industrial period is lost. This study confirms the exceptional warming of the last decades in the context of last two millennia. We demonstrate that we are facing an unprecedented retreat of the Pyrenean glaciers which survival is compromised beyond a few decades.

3 Pags. The definitive version is available at: https://www.sciencedirect.com/science/journal/03014797, The authors want to acknowledge funding by the projects Capitalización, observación, transferencia y apropiación de estrategias de adaptación al cambio climático en los Pirineos en un contexto de cooperación transfronteriza. ADAPYR: OPCC3 and EFA210/16-PIRAGUA, both co-founded by the European Regional Development Fund (ERDF) through the Interreg V Spain-France-Andorre Programme (POCTEFA 2014–2020) of the European Union; INNOMED, co-funded by the Agencia Estatal de Investigación of Spain in the framework of the ERA-NET WaterWorks2015 cofunded Call (project INNOMED); Cross-sectoral impact assessment of droughts in complex European basins-CROSSDRO funded by ERANET-AXIS Joint Call for Transnational Collaborative Research and “El papel de la nieve en la hidrología de la península ibérica y su respuesta a procesos de cambio global- CGL 2017-82216-R” funded by the Spanish Ministry of Economy.

46 Pags.- 4 Figs. The definitive version is available at: https://www.sciencedirect.com/science/journal/03418162, A key problem in explaining the mountain landscapes of the Mediterranean region is the relationship between the development of transhumance (seasonal movement of livestock over long distances) and deforestation of the subalpine and upper montane belts at 1350–2200 m above sea level (m a.s.l.). We examined this relationship in the Central Southern Pyrenees using information from multiple proxies—archaeology, pollen analysis, lacustrine sedimentation patterns, historical documents, and geomorphology. Although there is evidence of forest clearing since the Neolithic, and we can infer the presence of shepherds and livestock in mountain areas based on archaeological sites and pollen analysis in some lacustrine records, there is no strong evidence for transhumance between the Ebro Depression and the Pyrenees during the Prehistory. Instead, we found evidence of transterminance (seasonal movement of livestock over short distances) during this time. Growth of human populations and the establishment of large-scale markets favored longer livestock movements during the Roman period, although we only have indirect information on this for other areas of the Iberian Peninsula and the Mediterranean region. A few documents indicate the occurrence of transhumance during the Early Middle Ages, whereas all other proxies indicate a general expansion of livestock and transhumance during the 12th and 13th centuries. This coincides with the Christian conquest of the Central Ebro Depression by the Aragon Kingdom, the organization of large wool markets in Western Europe, and the exemptions conferred by the kings of Aragon to herders in the city of Saragossa. This led to rapid deforestation, in that forests were rapidly logged or burned to expand the summer grasslands. During this period, written documents indicate many conflicts between people in the villages and valleys for control of summer grasslands, pollen analyses show a rapid decline of arboreal pollen, and geomorphology studies indicate greatly increased sedimentation rates following deforestation, suggesting intense erosion. Transhumance has declined since the end of the 18th century, and particularly throughout the 20th century, and this has led to tree re-colonization of less accessible and marginal areas. The hydrological and geomorphological consequences of these recent events are important topics for future studies., This research was supported by the ESPAS Project (CGL2015-65569-R) and the Gaps and Sites Project (HAR2017-85023-P), both funded by the MINECO-FEDER, and by the Research Group from the Aragon Government (H14_17R). R. Domingo is a Ramón y Cajal Research Fellow (RyC2013-12613, MINECO). P. Diarte-Blasco is an Atracción de Talento-CAM Research Fellow (2018-T1/HUM-10636).

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.

Geotourism is a useful way to educate societies in the field of geomorphology and related natural hazards. Geosites, including geomorphosites, represent the basis for the development of this type of tourism. This study describes 12 representative gully regions within nine European countries. The characteristics of 42 permanent gullies, gully systems, and badland landscapes are presented. Based on scientific values of the sites, educational lessons to be learned were identified that are mainly related to (i) gullies as a geological window, (ii) present-day geomorphological processes and (iii) stages of historical gully erosion reflecting past human¿environment interactions. To evaluate possible education activities, a geotouristic assessment of the studied gullies and badlands was made, based on scientific, educational, functional and touristic indicators. This assessment demonstrates a large difference between the selected gully and badland sites, particularly with regard to functional and tourist values. The geotouristic potential of gullies (badlands) is the highest in Italy and Spain and the lowest in Romania and Latvia. In some countries, permanent gullies are not regarded as geotouristic attractions at all,while in others, they constitute a significant element of their tourism development strategy. In our opinion, all activities must be part of a broader strategy for the development of geotourism in gully and badland regions, for example, gullies may be included as geosites within existing or planned geoparks., The research in Slovakia was supported by the Slovak Research and Development Agency under the contract no. APVV0625-11. Estela Nadal-Romero was the recipient of a Ramón y Cajal postdoctoral contract (Spanish Ministry of Economy and Competitiveness). Geomorphic reclamation initiatives on gullies degraded by mining, in Central Spain, are supported by the Ecological Restoration Network 502 REMEDINAL-3 of the Madrid Community (S2013/MAE-2719).

The only glaciers existing today in the Iberian Peninsula are small features located in the Pyrenees, though their number and extension has undergone significant changes over the Late Quaternary. The wide range of glacial landforms and deposits distributed across different Iberian ranges suggests the occurrence of several past periods with larger glacial systems. The objective of this research is to summarize the current knowledge on the spatial and temporal patterns of glacial activity in the Iberian mountains during the Late Quaternary. To this purpose, the chronological framework was divided in six periods: glaciations prior to the Last Glacial Cycle (Middle Pleistocene), Last Glacial Cycle (Late Pleistocene), Termination-1, Holocene, Little Ice Age (LIA) and present-day. The data were geographically divided considering the mountain systems where glacial evidence exists: Pyrenees, Cantabrian Range, NW ranges, Central Range, Iberian Range and Sierra Nevada. During Quaternary cold stages, ice accumulated in the head valleys of these mountain ranges and glaciers flowed down-valleys. In all cases, glaciers remained confined within the mountain systems and did not reach the surrounding lowlands. Depending on the combination of temperatures and moisture conditions, more or less ice was stored. In some ranges, there is evidence of Middle Pleistocene glaciations, one potentially correlating with marine isotope stage (MIS) 12 and another correlating with MIS 6 with glaciation dated to ca. 130-170 ka. However, most of the glacial records correspond to the Last Glacial Cycle and subsequent Termination. The maximum glacial expansion of this last Pleistocene glaciation stage occurred well before the global Last Glacial Maximum (LGM) between 30 and 60 ka in the Cantabrian Mountains and Pyrenees, at ca. 30 ka in Sierra Nevada and NW ranges, and (almost) synchronously to the LGM in the Central Range and Iberian Range. A massive glacial retreat occurred in all ranges at 19-20 ka, but the long-term deglaciation process was interrupted by cold intervals, such as the Oldest and Younger Dryas, which favoured glacial expansion in the highest mountains. Temperature increase recorded during the Holocene conditioned the melting of glaciers, which only reappeared in the highest massifs during the coldest periods, such as the LIA. However, post-LIA warming led to glacier disappearance in the Cantabrian Mountains, Sierra Nevada and most massifs of the Pyrenees, together with an accelerated shrinkage of the small glaciers still existing in this range at elevations near 3000 m.

11 Pags.- 8 Figs.- 9 Tabls., As with other mountain areas in Europe, the subalpine belt of the Central Spanish Pyrenees (approximately 1600–2200 m a.s.l.) has undergone constant deforestation since the Neolithic era and particularly during the Late Middle Ages, in favour of livestock management and grazing in summer. This furthered the rise of transhumance between the lowlands and the highlands. The abrupt change in land cover triggered a variety of geomorphic processes and landforms that partially contributed to land degradation and an increase in erosion and sediment yield: shallow landslides, solifluction lobes, soil creeping, terracettes, parallel deep incisions (henceforth: gullies) and stone-banked lobes. The main factors explaining the location of the various landforms are elevation, gradient, aspect, plant cover, soil characteristics, and the topographic index. The statistical analysis clearly separates two types of landforms: (i) shallow landslides, solifluction lobes, and areas of soil creeping, located at relatively low elevations, deep soils and fairly gentle gradients; and (ii) terracettes, gullies and stone-banked lobes, which are generally found at high elevations, on thin soils, north-facing slopes and steep gradients. The declining livestock pressure from the beginning of the 19th century, and particularly from the mid-20th century, explains the progressive re-colonization of the subalpine belt by forest and the reduction in shallow landslides over the last few decades. Most likely, this forest recovery will continue in the near future, with the hydrological, geomorphological and biogeographical consequences still being far from understood., This research was supported by the MANMOUNT (PID2019-105983RB-100) project, funded by the Spanish Ministry of Science and FEDER and by the Research Group from the Aragón Government E02_17E.

The Sierra Nevada of Santa Marta (12°N) hosts a unique glaciated environment (6.5 km2) only 40 km distant from the Caribbean Sea. However, the remoteness of the glaciers and restricted access to the region has so far prevented onsite field work research from being undertaken. We worked with several very high resolution airborne and satellite images to delimit the extension of the glaciers during the maximum extension of the Little Ice Age (ca. 1850), when glaciers covered 81.6 km2, and the ice cover in four subsequent phases (1954, 1995, 2010 and 2016). Polar plots and Random Forest models enabled characterization of the spatial distribution of ice cover in the region, and how the impact of topographic and geographical variables changed over time. Results show that elevation was the most important variable in explaining the existence of glaciers during the LIA. Since then, the ice cover has gradually been receding to areas shielded from solar radiation, even though the solar angle at this latitude is very high. Thus, results clearly confirm that topography is increasing its importance to explain the glacier distribution over the study area, and the particular characteristics of where each ice body is found will gain importance. Nonetheless, the probability of ice being present as predicted by Random Forests in 2017 suggests that most of the ice cover located outside the most elevated areas of the Sierra is very likely to disappear in coming years.

Farmland abandonment and the decline of livestock activity in the Mediterranean mountains have resulted in dramatic landscape changes, including the generalized expansion of shrublands and forests, and the homogenization of the old cultural landscapes. This process has a variety of consequences from ecological, geomorphological and hydrological points of view, as well as from the perspectives of land management and public awareness. An intense debate currently surrounds the discussion and evaluation of rewilding (the process of passively allowing woody encroachment, as well as the reintroduction of large mammals) as an opportunity for enhancing biodiversity and restoring original landscapes after centuries of human activity versus ecological restoration (activities leading to the recovery of degraded ecosystems, including clearing and light human activity). There is no clear consensus regarding the best way to improve the ecological relationships and functioning within an ecosystem. Biodiversity and sustainability can be seen under different levels of human pressure and landscape transformation; total farmland abandonment is not always the best alternative, particularly when local inhabitants aim to sustain themselves using local resources. Many geographers and ecologists consider that extensive stockbreeding in a partially open landscape is a rational way to (i) improve landscape organization, (ii) increase flows and turnover within the ecosystems, (iii) increase the diversity of plants and animals that benefit from a relatively light human presence, and (iv) reduce wildfire risk. However, it has proven challenging for land managers and stockbreeders to clear the best old abandoned fields and “construct” a sustainable, balanced landscape that combines forests, shrublands and open lands. Private landowner involvement and support from the general public is crucial for both funding and the long-term maintenance of benefits. The best old fields should be cleared in the context of high-resolution knowledge of the topography, grassland characteristics, grassland cycles and livestock management. Such efforts are likely to be an excellent opportunity to introduce compatibility between light human activity and increases in biodiversity and sustainability for many marginal mountains, where land abandonment and general forest/shrub recovery are the inevitable tendencies. This paper examines some of the contrasting positions of the scientific community regarding the rewilding or ecological restoration of mountain landscapes, and briefly highlights some experiences in which intentional clearing of old abandoned fields has benefited stockbreeding, biodiversity, runoff generation and wildfire risks. Notably, we describe a sub-Mediterranean valley of the Iberian Range, Northern Spain, as an example. In the long term, we find that the intentional clearing of the best old fields allows the slow organization of a final landscape that will be more useful for local inhabitants, thereby helping to reverse human depopulation in these regions., This research was supported by the ESPAS (CGL2015-66569) and MANMOUNT (PID2019-105983RB-100) projects, both funded by the Spanish Ministry of Science and FEDER and by the Research Group from the Aragón Government E02_17E.

El Dryas Reciente (Younger Dryas) (GS-1, entre 12,9 y 11,7 ka BP) se caracterizó por un marcado descenso de la temperatura a escala global. La consecuencia fue un re avance de los glaciares que afectó también a las cordilleras más importantes de la Península Ibérica. Este trabajo revisa la información disponible sobre la localización, evolución y extensión de tales glaciares. La actividad geomorfológica durante el Dryas Reciente en la Península Ibérica se ha identificado mediante depósitos morrénicos, umbrales rocosos pulidos por el hielo, y glaciares rocosos, datados en la mayor parte de los casos mediante métodos cosmogénicos. Los mejores ejemplos de morrenas del Dryas Reciente se localizan en los Pirineos, donde se desarrollaron cortas lenguas glaciares de hasta 4 km de longitud en los macizos más elevados y numerosos glaciares de circo. También hay evidencias de pequeños glaciares de circo y glaciares rocosos en la Cordillera Cantábrica y en el Sistema Central (sierras de Gredos y Guadarrama), como indican umbrales rocosos y depósitos morrénicos en el frente de circos glaciares. En cambio, en Sierra Nevada, en el extremo meridional de la Península Ibérica, las únicas evidencias del Younger Dryas son glaciares rocosos que se desarrollaron durante el Dryas Antiguo y estuvieron funcionales durante todo el Dryas reciente

García M.B. et al.- 12 páginas.- Ilustraciones.- Artículo publicado en Open Access bajo los términos de Creative Commons attribution Non Comercial License 3.0. [EN] The Ordesa and Monte Perdido National Park and the Pyrenean Institute of Ecology (CSIC) recently joined the Spanish LTER network. As part of our strategy to understand recent changes in this protected area, we are carrying out a number of projects to evaluate changes at different spatio-temporal scales, using a variety of methods and approaches. We highlight here some of the most consolidated ones: long-term reconstructions from sedimentary lake records and cave speleothemes, the dynamics of one of the few active Iberian glaciers, the physico-chemical components of alpine streams, springs and lakes, the fingerprint of climatic change from ancient trees, changes in the composition and structure of biodiversity of alpine communities, natural and man-made grasslands at different altitudes, and the treeline, and population dynamics of endangered species or habitat indicators. The ecological monitoring shows that changes in both climate and land use, are having a strong influence in the physiognomy and structure of some of the most iconic and abundant habitats in the National Park. However, we found an important spatial variability in some processes, and also that others do not fit the established paradigms. The integration of partial results obtained from different methodologies and approaches diminishes the importance of each perception separately, helps to evaluate current changes in a long-term framework (geological scale), and will serve to validate the forecasts when modeling future environmental scenarios. [ES] Los espacios protegidos, por el hecho de albergar una gran geo-biodiversidad y asegurar una baja intervención humana, constituyen lugares muy adecuados para el seguimiento de organismos y procesos a escala ecológica, así como para la obtención de series temporales largas a escala geológica. En el marco de la red LTER-España, el Parque Nacional de Ordesa y Monte Perdido (PNOMP) y el Instituto Pirenaico de Ecología-CSIC están impulsando estudios para la detección de cambios a distintas escalas mediante variados métodos y aproximaciones. Destacamos aquí los más consolidados, entre los que se encuentran los análisis de registros de sedimentos en lagos, espeleotemas en cuevas, la dinámica de uno de los pocos glaciares activos de la Península ibérica, el análisis físico-químico de aguas corrientes e ibones de alta montaña, el registro del cambio climático actual en árboles longevos, la afección que éste ejerce sobre masas actuales de pinos en el límite superior del bosque y de abetales en zonas húmedas, la matorralización de algunos pastos y los procesos mecanicistas que subyacen, la reorganización de la diversidad florística en pastos tras el abandono paulatino o drástico de la ganadería, la biodiversidad de las comunidades alpinas y la dinámica poblacional de especies amenazadas o indicadoras de hábitats o de motores de cambio global. Los seguimientos ecológicos actuales muestran que tanto el cambio climático como el de usos del suelo están teniendo una considerable trascendencia en la fisionomía y la estructura de algunos de los ambientes más icónicos y frecuentes del parque (deterioro del glaciar, termofilización de la flora en cumbres alpinas, densificación del bosque en su límite superior, pérdida de productividad en algunos pastos supraforestales, etc.). También sugieren una importante variabilidad espacial en los procesos (por ej. en el PNOMP conviven pastos matorralizados y pastos muy estables), y evidencian que los cambios observados no siempre siguen los paradigmas establecidos (por ej., las especies amenazadas mantienen dinámicas poblacionales estables). La integración de resultados parciales proporcionados por cada aproximación relativiza la importancia de las percepciones que cada estudio destaca por separado, y permite medir los cambios actuales en el marco de referencia de los cambios a escala geológica.Predecir la resistencia y resiliencia de los ecosistemas o las poblaciones de seres vivos para enfrentarse a los futuros cambios ambientales es complicado, no sólo por la falta de conocimientos disponibles sino también porque las respuestas que observamos no siempre son tan rápidas o lineales como se espera. La modelización constituye una herramienta cada vez más utilizada, pero requiere de evidencias reales para validar sus pronósticos, por lo que la observación de los procesos que actúan en el PNOMP ha de incluir un esfuerzo continuado de monitorización multiescalar y multidisciplinar de los distintos componentes de la geo, hidro-, crio- y biosfera, sin olvidar el componente humano. Entender la complejidad supone conectar las interacciones que existen entre todos los sistemas y ponderar sus efectos según las escalas de trabajo. Los resultados presentados proceden de proyectos subvencionados por el Organismo Autónomo de Parques Nacionales: 125/2010 (C.L. Alados), 387/2011 (J.J. Camarero), 430/211 (M.B. García), 258/2011 (A. Moreno), 533S/2012 (P. Mata y M.I. Rieradeval), 623/2012 (M.I. Rieradeval), 083/2009 (B. Valero), 844/2013 (J.I. López-Moreno).

We review the evolution of glaciers in the Iberian Mountains during the Younger Dryas (12.9–11.7 ka, following the chronology of Greenland Stadial 1 – GS1) and compare with available environmental and climate data to investigate glacier dynamics during cold stadial episodes. The best examples of Younger Dryas moraines are found in the Central Pyrenees, involving short ice tongues up to 4 km in length in the highest massifs (above 3000 m a.s.l.) of the southern versant. Small cirque glaciers and rock glaciers formed during the YD occurred in other Pyrenean massifs, in the Cantabrian Range and in the Gredos and Guadarrama sierras (Central Range), as indicated by several rocky, polished thresholds that were ice-free at the beginning of the Holocene. Although some former rock glaciers were re-activated during the Younger Dryas, glacial activity was limited in the southernmost part of the Iberian Peninsula (Sierra Nevada). Most Iberian records show vegetation changes during the YD characterized by a forest decline and an expansion of shrubs (mainly Juniperus) and steppe herbs, although the vegetation response was not homogeneous because of variable resilience among ecosystems. Available records also document a variable lake response in terms of hydrology and productivity, with a decrease in sedimentation rates and organic productivity in most high altitude lakes and increases in salinity and relatively lower lake levels at lower altitudes. The impact of the Younger Dryas on the coastal environment was almost negligible, but it was responsible for a brief cessation in sea level rise. High-resolution analyses of new speleothem records have documented a double structure for the YD with an earlier drier phase followed by a relatively more humid period. The review of geomorphological evidence demonstrates a strong latitudinal control of glacial activity during the YD, with more intense development in the northern than in the southern regions. The increase in humidity during the second phase of the YD in southern latitudes could have been a decisive factor for glacier advance in the northern Iberian mountains.

Producción Científica, This paper analyzes the evolution of the Monte Perdido Glacier, the third largest glacier in the Pyrenees, from 1981 to the present. We assessed the evolution of the glacier's surface area by analysis of aerial photographs from 1981, 1999, and 2006, and changes in ice volume by geodetic methods with digital elevation models (DEMs) generated from topographic maps (1981 and 1999), airborne lidar (2010) and terrestrial laser scanning (TLS, 2011, 2012, 2013, and 2014) data. We interpreted the changes in the glacier based on climate data from nearby meteorological stations. The results indicate that the degradation of this glacier accelerated after 1999. The rate of ice surface loss was almost three times greater during 1999–2006 than during earlier periods. Moreover, the rate of glacier thinning was 1.85 times faster during 1999–2010 (rate of surface elevation change = −8.98 ± 1.80 m, glacier-wide mass balance = −0.73 ± 0.14 m w.e. yr−1) than during 1981–1999 (rate of surface elevation change = −8.35 ± 2.12 m, glacier-wide mass balance = −0.42 ± 0.10 m w.e. yr−1). From 2011 to 2014, ice thinning continued at a slower rate (rate of surface elevation change = −1.93 ± 0.4 m yr−1, glacier-wide mass balance = −0.58 ± 0.36 m w.e. yr−1). This deceleration in ice thinning compared to the previous 17 years can be attributed, at least in part, to two consecutive anomalously wet winters and cool summers (2012–2013 and 2013–2014), counteracted to some degree by the intense thinning that occurred during the dry and warm 2011–2012 period. However, local climatic changes observed during the study period do not seem sufficient to explain the acceleration of ice thinning of this glacier, because precipitation and air temperature did not exhibit statistically significant trends during the study period. Rather, the accelerated degradation of this glacier in recent years can be explained by a strong disequilibrium between the glacier and the current climate, and likely by other factors affecting the energy balance (e.g., increased albedo in spring) and feedback mechanisms (e.g., heat emitted from recently exposed bedrock and debris covered areas)., Ministerio de Economía, Industria y Competitividad - IBERNIEVE (project CGL2014-52599-P), Ministerio de Agricultura y Pesca, Alimentación y Medio Ambiente (project 844/2013)

Using a database of all the catalogued dolmens and stone circles in six Pyrenean valleys, we investigated the distribution of these megalithic monuments on the basis of elevation, gradient, aspect, terrain ruggedness, and terrain position, and identified factors potentially explaining the distribution of the monuments. A map of the areas having the highest probabilities of occurrence of megalithic monuments was developed, and showed that megalithic monuments are located in relatively accessible areas having gentle gradients and low terrain ruggedness close to the fluvial network, with wide U-shaped glacial valleys being the preferred locations. The altitudinal distribution showed one concentration of dolmens and stone circles at relatively low elevation (1250–1400 m a.s.l.) in the mid montane belt, and another at high elevation, at approximately the level of the timberline (1750–1900 m a.s.l.) adjacent to the alpine belt. Today, both areas are pastures that have historically sustained livestock, the traditional economic basis of Pyrenean valleys. The map showing the probability of occurrence of megalithic monuments in the study area suggests that a number of potentially favorable areas were largely inaccessible or too far from the main livestock routes, and remained forested until the Middle Ages. These findings and a variety of archaeological studies contribute to propose that the first shepherds: (i) understood the altitudinal organization of mountain areas; (ii) used the best accessible flat areas in the mid montane belt in late spring and early summer; and (iii) used the upper subalpine/alpine belt in summer.

31 Pags.- 4 Tabls- 6 Figs. The definitive version is available at: https://link.springer.com/journal/10113, The montane and subalpine belts in European mountains were affected by intense land use/land cover changes during the twentieth century. In the case of the subalpine belt, most European mountains were affected by complex deforestation processes from Neolithic times, leading to the expansion of summer grasslands to support grazing by transhumant sheep and goats flocks. This resulted in an altitudinal reduction of the tree line and the occurrence of severe soil erosion and shallow landsliding. The intense livestock pressure over centuries explains why the landscape remained without major change until the middle of the twentieth century. Since then, depopulation, land abandonment, and the disappearance of the transhumant system have resulted in a marked decline in livestock numbers and subsequent encroachment of shrubs and trees in the subalpine belt. The Urbión Mountains (Iberian Range, northern Spain) provides one of the clearest examples in the Iberian Peninsula, where there was intense deforestation since the Neolithic period to enlarge the area of subalpine summer grasslands. The recent reversal of this situation in the last decades led to (i) a marked trend to dense forest, which resulted in an average 200 m altitudinal advance, and (ii) the spatial contraction of shrublands, which have been replaced by dense forest in the highest areas. Changes will continue in the future, possibly enhanced by global warming., Support for this research was provided by the projects ESPAS (CGL2015-65569-R) and INDICA (CGL2011-27753-C02- 01 and -02), funded by the Spanish Ministry of Economy and Competitiveness.

This chapter reviews the most significant aspects of erosion in badlands, one of the most impressive erosion landforms on Earth. Badlands occur in arid, semiarid and humid areas, are characterized by intense erosion processes and generally have extremely high sediment yields. They lead to sedimentation in pediments, high sediment load in fluvial channels and sediment silting in reservoirs. The present study examines the factors that most affect erosion in badlands: lithology, seasonal contrasts in climate, rainfall intensity, and low plant cover, weathering and erosion processes, spatial and temporal variability of erosion processes and the complex spatial and temporal connections at the catchment scale. Two sections examine critical future issues: the relationship between conservation and reclamation in badlands and the future evolution of badland erosion in the context of global change. In many cases, badland initiation and development occurred due to interactions between climate changes and human activities, particularly the use of fire and cultivation on steep slopes of soft bedrock material. The largest badlands should be preserved as geomorphological monuments because of their importance to education, research and tourism.

Combined geomorphic features, stratigraphic characteristics and sedimentologic interpretation, coupled with optically stimulated luminescence (OSL) dates, of a glacio-fluvio-lacustrine sequence (Linas de Broto, northern Spain) provide new information to understand the palaeoenvironmental significance of dynamics of glacier systems in the south-central Pyrenees during the Last Glacial Cycle (≈130 ka to 14 ka). The Linas de Broto depositional system consisted of a proglacial lake fed primarily by meltwater streams emanating from the small Sorrosal glacier and dammed by a lateral moraine of the Ara trunk glacier. The resulting glacio-fluvio-lacustrine sequence, around 55 m thick, is divided into five lithological units consisting of braided fluvial (gravel deposits), lake margin (gravel and sand deltaic deposits) and distal lake (silt and clay laminites) facies associations. Evolution of the depositional environment reflects three phases of progradation of a high-energy braided fluvial system separated by two phases of rapid expansion of the lake. Fluvial progradation occurred during short periods of ice melting. Lake expansion concurred with ice-dam growth of the trunk glacier. The first lake expansion occurred over a time range between 55 ± 9 ka and 49 ± 11 ka, and is consistent with the age of the Viu lateral moraine (49 ± 8 ka), which marks the maximum areal extent of the Ara glacier during the Last Glacial Cycle. These dates confirm that the maximum areal extent of the glacier occurred during Marine Isotope Stages 4 and 3 in the south-central Pyrenees, thus before the Last Glacial Maximum. The evolution of the Linas de Broto depositional system during this maximum glacier extent was modulated by climate oscillations in the northern Iberian Peninsula, probably related to latitudinal shifts of the atmospheric circulation in the southern North-Atlantic Ocean, and variations in summer insolation intensity.

La Geomorfología es una ciencia muy compleja desarrollada entre la Geografía y la Geología, con el objetivo de estudiar y explicar las formas de relieve a diferentes escalas espaciales y temporales. Este trabajo revisa aquellos aspectos que confirman la necesidad de ser global en Geomorfología. Las formas de relieve son el resultado de la actividad de procesos geomórficos sobre una estructura geológica durante un periodo de tiempo muy variable. Cada forma de relieve es consecuencia de una interacción compleja entre sustrato rocoso, disposición estructural, clima, actividad biológica, procesos geomórficos y tiempo. El papel de los geomorfólogos es desentrañar esa complejidad a partir del relieve actual, en el que los restos de formas de relieve y depósitos de diferente origen dan lugar a un palimpsesto en el que la mayor parte de la información ha desaparecido. La interpretación del relieve y su dinámica necesita análisis detallados y el empleo creciente de técnicas ligadas a ordenadores (teledetección y SIG), y especialmente una perspectiva global para interpretar el relieve y su dinámica. La colaboración con ecólogos ha contribuido a ampliar la función de los geomorfólogos en los estudios ambientales.

Fernández-Fernández, José M. et. al.- 18 páginas.- Ilustraciones.- © 2017 Elsevier Ltd. All rights reserved., In this study, fossil debris-covered glaciers are investigated and dated in the Sierra de la Demanda, northern Spain. They are located in glacial valleys of approximately 1 km in length, where several moraines represent distinct phases of the deglaciation period. Several boulders in the moraines and fossil debris-covered glaciers were selected for analysis of Be-10 surface exposure dating. A minimum age of 17.8 +/- 2.2 ka was obtained for the outermost moraine in the San Lorenzo cirque, and was attributed to the global Last Glacial Maximum (LGM) or earlier glacial stages, based on deglaciation dates determined in other mountain areas of northern Spain. The youngest moraines were dated to approximately 16.7 +/- 1.4 ka, and hence correspond to the GS-2a stadial (Oldest Dryas). Given that the debris-covered glaciers fossilize intermediate moraines, it was deduced that they developed between the LGM and the Oldest Dryas, coinciding with a period of extensive deglaciation. During this deglaciation phase, the cirque headwalls likely discharged large quantities of boulders and blocks that covered the residual ice masses. The resulting debris-covered glaciers evolved slowly because the debris mantle preserved the ice core from rapid ablation, and consequently they remained active until the end of the Late Glacial or the beginning of the Holocene (for the San Lorenzo cirque) and the Holocene Thermal Maximum (for the Mencilla cirque). The north-facing part of the Mencilla cirque ensured longer preservation of the ice core. (C) 2017 Elsevier Ltd. All rights reserved., Support for this research was provided by the projects ESPAS (CGL2015-65569-R) (MINECO/FEDER), MOUNTAIN WARMING (CGL2015-65813-R) (Spanish Ministry of Economy and Competitiveness). The study was assisted by the High Mountain Physical Geography research group (Complutense University of Madrid) and the research group on Geomorphology and Global Change, which is supported by the Aragon Government and the European Social Fund. The 10Be measurements were performed at the ASTER AMS national facility (CEREGE, Aix en Provence, France), which is supported by the INSU, CNRS and the ANR through the "Projets thematiques d'excellence" program for the "Equipements d'excellence" ASTER-CEREGE action and IRD. Jose M. Fernandez-Fernandez received a grant from the FPU programme (FPU14/0650) (Spanish Ministry of Education, Culture and Sport).

In this study, we document deglaciation in a sector of the southern–central Pyrenees (the Panticosa massif and the upper Gallego and Ossau valleys) using cosmic-ray exposure (CRE) dating methods, which were applied to samples from high altitude polished rock steps and rock glacier boulders. The obtained CRE dates show a coherent spatial distribution and confirm results previously obtained in this study area, thus demonstrating the reliability and robustness of the method. The results of analyses based on two distinct isotopes (10Be and 36Cl) are consistent, although the error is higher for results based on the 36Cl isotope. The study provides evidence for ice extent in the High Gallego Valley during the Oldest Dryas, with glacial advance until the bottom of the valleys, although the main glacier tongues remained disconnected from each other. During this period, the extent of glacier advance was directly related to the elevation of the associated summits. The Younger Dryas glaciers were constrained to cirques or very short ice tongues, and dating of the polished rock steps indicates that the ice masses were present until the first millennium of the Holocene. The Brazato rock glacier developed at the beginning of the Holocene and remained active until the Holocene Thermal Optimum, because of the protective effect of large masses of blocks and boulders.

Producción Científica The dynamics of the torrential upper reach of the Ijuez River, Central Spanish Pyrenees, was analyzed in relation to the spatial organization of grain size. The reach is located in the Eocene flysch, which usually acts as a high sediment production area, particularly during periods of intense human activity. The Ijuez Valley was cultivated and densely populated until the middle of the 20th century, resulting in general deforestation and the development of debris flows, shallow landslides, sheet wash erosion and deep gullies. As a consequence, the alluvial plain became characterized by the presence of large quantities of coarse sediment. The spatial organization of sediment showed a progressive downstream decline in the cobble and boulder size, especially in the channel, whereas the remainder of the alluvial plain showed large variability. No trend in the occurrence of the largest boulders was evident throughout the reach, confirming the importance of debris and hyperconcentrated flows in sediment transport. The torrential reach did not have a negative exponential longitudinal profile, in contrast to that usually observed for mountain rivers. This was attributed to the large quantity of heterometric sediment derived from the hillslopes, which resulted in no marked decline in sediment size and consequent change in the longitudinal profile. A recent trend of scouring was detected, reflecting the reduction in sediment supply following farmland abandonment and reforestation, which have reduced connectivity between the hillslopes and the channel. Se estudia un tramo torrencial en la cabecera del río Ijuez, Pirineo central español, con el fin de analizar su dinámica en relación con la distribución espacial de los sedimentos. Este tramo se instala en el flysch eoceno, que habitualmente se comporta como altamente productor de sedimento, especialmente en condiciones de intensa actividad humana. El valle del río Ijuez fue cultivado y densamente poblado hasta mediados del siglo XX, causando la eliminación de la mayoría de los bosques y dando lugar a flujos de derrubios (debris flows), deslizamientos superficiales, erosión difusa y formación de barrancos muy activos. La consecuencia fue el desarrollo de una llanura aluvial caracterizada por el escombrado de grandes volúmenes de sedimento grueso. La organización espacial de los sedimentos muestra un progresivo descenso en el tamaño de los cantos, especialmente en el cauce actual, y mucho menos en el resto de la llanura aluvial, donde la variabilidad es muy grande. Los grandes bloques no presentan ninguna tendencia a lo largo del curso, reflejando la importancia de los flujos de derrubios e hiperconcentrados en el transporte de sedimento. El tramo torrencial estudiado no muestra un perfil longitudinal exponencial negativo, al contrario de lo que es habitual en los ríos de montaña. Este fenómeno se atribuye a la gran cantidad de sedimentos heterométricos que llegan masivamente desde las laderas, que impiden un marcado descenso en el tamaño del sedimento y el consiguiente ajuste del perfil longitudinal. Se ha detectado una tendencia reciente hacia la incisión del río en sus propios sedimentos, reflejando la reducción en el aporte de estos últimos debido al abandono de tierras y la reforestación, limitando la conectividad entre laderas y cauce. Ministerio de Economía y Competitividad - Proyectos (CGL2011-27753-CO2-01 y 02) y (CGL2011-27574-CO2-CO1)

38 páginas, 2 tablas, 11 figuras, [EN] Debris flows occurred three weeks after a wildfire in August 1986 in the Najerilla River valley in the Iberian Range, northern Spain. The flows were triggered by a brief, intense rainstorm (approximately 25 mm h− 1 over 15 min) in a small area with steep slopes covered by a thick colluvium of quartzite clasts. This storm resulted in the development of several unconfined hillslope debris flows and the formation of an alluvial fan at the mouth of the Pítare stream, which partially blocked the Najerilla River. We analysed the conditions that led to the development of the debris flows, and estimated the rainfall threshold for the debris flows to occur as well as the total volume of mobilised sediment. Four factors contributed to the debris flows: (i) the occurrence of a rainstorm three weeks after a wildfire, which had removed the plant cover from the soil; (ii) the steep slopes in the area (> 30°), which were the most affected by debris flows; (iii) the presence of quartzite scarps on the hillslopes, which favoured the development of a ‘firehose effect’ involving channelised surface runoff; and (iv) the low plasticity index values of the fine material of the colluvium (indices of 7 to 8), which enabled rapid liquefaction. Estimates of rainfall intensity derived from the estimated peak flow in the Pítare stream suggests that around 80 mm of rainfall fell in approximately 15 min, although this is clearly an overestimated value given the high proportion of sediment load transported during the peak flow. Various equations estimated a rainfall-threshold of approximately 25 mm h− 1 considering a concentration time of 15 min. The total sediment transported by the debris flows was 10,500 m3 (15,750 Mg, 6800 Mg km− 2), and the Pítare stream alone transported a minimum of 4000 m3 (6000 Mg, 2500 Mg km− 2). These results suggest that the rainfall threshold for initiating debris flows decreases following a wildfire, such that an ordinary rainstorm is able to trigger a severe erosion and sediment transport event. Given the absence of fresh landslide scars on the hillslopes, the origin of the fire-related debris flows in the Najerilla River valley appears to have been directly linked to increased rates of overland flow having a greater effect than infiltration for triggering debris flows., Support for this research was provided by the projects PROBASE (CGL2006-11619/HID) and INDICA (CGL2011-27753-C02-01 and CGL2011-27753-C02-02), which was funded by the Spanish Ministry of Education and Science, and ACQWA (FP7-ENV-2007-1-212250), which was financed by the European Commission. Noemí Lana-Renault was the recipient of a research contract (Programme “Juan de la Cierva”, Human Resources Mobility, funded by the Spanish Ministry of Economy and Competitivity). The authors gratefully acknowledge Dr. Susan Canon, Dr. Francisco Gutiérrez-Santolalla and an anonymous reviewer for their comments and suggestions, which significantly helped to improve this paper.

In this paper we synthesize the research in glacial geomorphology and geochronology in northern Spain, with special attention to the evidence of local glacier maximum extent earlier than the global LGM of MIS 2 (18-21. ka BP). More accurate models of glacier evolution have been defined based on limnogeological, geochronological and geomorphological data. In the Pyrenees, OSL (Optically Stimulated Luminescence), surface exposure and radiocarbon dating techniques have identified end moraines and fluvial terraces corresponding to MIS 6 (about 170. ka) and even to MIS 8 (about 260. ka), and also established the timing of the last local glacial maxima as prior to global LGM (MIS 4, ca. 50-70. ka). During the global LGM a smaller re-advance occurred but glaciers reached different extents in the Central and the Eastern Pyrenees. In NW Iberia, radiocarbon and OSL techniques point to local glacial maximum prior to ca 26. ka-38. ka and probably synchronous with 45. ka. Although some bias might have been introduced by the dating procedures, this review demonstrates that in both regions the local maximum extent occurred prior to the global LGM. The asynchronies between the glacial maxima chronologies in the different mountain ranges of northern Spain suggest that local climate factors exert a strong control on mountain glacier dynamics. © 2012 Elsevier B.V., This research has been funded through the projects LIMNOCAL (CGL2006-13327-C04-01) and GRACCIE (CONSOLIDER Program, CSD2007-00067) provided by the Spanish Inter-Ministry Commission of Science and Technology (CICYT). Additional funding was provided by the Spanish National Parks Agency (OAPN) through the Project 53/2006 and the Fundación Patrimonio Natural de Castilla y León (Sanabria project); and by the Project PC 10‐14 (Geoarchaeology and Global Change in Asturias) provided by FICYT-RIOGLASS. The authors thank Dr. Cendrero, Dr. Woodward and another anonymous reviewer for their comments and suggestions that contributed to improve the original manuscript. L. Rodríguez-Rodríguez has developed her research under a Severo Ochoa Programme fellowship (FICYT- Asturias).

The authors indentify the source-areas of sediments in a braided river. Studying the slope dynamics and the gravel-size along the channel, they conclude that the mass movements and the active headwaters of ravines are the most important areas o.f sediment production. In this sense, some tributaries into the Sierra de la Demanda and the basin border conglomerates behave as responsible sectors of the origin and increase of braiding.

33 páginas, 9 figuras.- Versión pre-print, [EN] The Aragón Valley glacier (Central Western Pyrenees) has been studied since the late nineteenth century and has become one of the best areas in the Pyrenees to study the occurrence of Pleistocene glaciations and the relationships between moraines and fluvial terraces. New morphological studies and absolute ages for moraines and fluvial terraces in the Aragón Valley allow a correlation with other Pyrenean glaciers and provide solid chronologies about the asynchroneity between global last glacial maximum (LGM) and the maximum ice extent (MIE). Six frontal arcs and three lateral morainic ridges were identified in the Villanúa basin terminal glacial complex. The main moraines (M1 and M2) correspond to two glacial stages (oxygen isotopic stages MIS 6 and MIS 4), dated at 171±22ka and 68±7ka, respectively. From a topographical point of view, moraine M1 appears to be linked to the 60m fluvioglacial terrace, dated in a tributary of the Aragón River at 263±21ka. The difference in age between M1 moraine and the 60m fluvioglacial terrace suggests that the latter belongs to an earlier glacial stage (MIS 8). Moraine M2 was clearly linked to the fluvioglacial 20m terrace. Other minor internal moraines were related to the 7-8m terrace. The dates obtained for the last glacial cycle (20-18ka) are similar to other chronologies for Mediterranean mountains, and confirm the occurrence of an early MIE in the Central Pyrenees that does not coincide with the global LGM. © 2012 Swedish Society for Anthropology and Geography., Support for this research was provided by the projects CALIBRE-LIMNOCAL (CGL2006-13327-C04-01) and GRACCIE-CONSOLIDER (CSD2007-00067), financed by the Spanish Inter-Ministry Commission of Science and Technology; and PIRINEOS ABRUPT (PM073/2007), financed by the Diputación General de Aragón. Additional funding was provided by the Spanish National Parks Agency through the project “Evolución climática y ambiental del Parque Nacional Picos de Europa desde el ultimo máximo glaciar” (ref. 53/2006), provided by the Spanish Ministry of Environment. The authors gratefully acknowledge Dr P.D. Hughes and an anonymous reviewer for their comments and suggestions, which significantly improve this paper.

12 Pags.- 6 Figs.- 1 Tabl. © 2016 CSIC This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) Spain 3.0., [ES] Este trabajo es una síntesis de la evolución paisajística, funcional y geomorfológica del piso subalpino de la Sierra de Urbión, proporcionando una perspectiva geoecológica de las interacciones entre actividades humanas, organización del espacio, dinámica geomorfológica y transformaciones recientes en los usos del suelo. Los cambios paisajísticos del piso subalpino en la Sierra de Urbión se iniciaron al menos en el Neolítico tardío con incendios que procuraban eliminar el bosque para permitir la expansión de los pastos de aprovechamiento estival y así favorecer una incipiente trashumancia de ganado lanar. Los incendios se prolongaron a lo largo del Calcolítico y las edades del Bronce y del Hierro, culminando durante la Edad Media. Es probable que en este último periodo los incendios fueran menos necesarios dados los cambios producidos anteriormente. La deforestación del piso subalpino sería responsable de la ocurrencia de numerosos deslizamientos, que han desmantelado el suelo en gran parte de la Sierra por encima de 1500 m s.n.m. La crisis del sistema trashumante a partir de comienzos del siglo xix ha reducido la presión ganadera sobre los pastos de verano y, especialmente en la segunda mitad del siglo xx, ha contribuido a la expansión de matorrales y bosques, mientras los pastos subalpinos se han reducido notablemente. El descenso de la presión ganadera indica que la expansión del bosque va a continuar en el futuro, en un contexto de calentamiento global y menor duración del manto de nieve en el piso subalpino., [EN] This paper is a synthesis of the landscape, geomorphic and functional evolution of the subalpine belt in the Urbión Sierra, providing a geoecological perspective of the interactions between human activity, spatial organization, geomorphological dynamics and recent land use changes. Landscape changes in the subalpine belt started at least during the Late Neolithic, with forest fires that tried to waste the forest to enable the expansion of summer grasslands favouring an incipient sheep transhumance. Fires occurred also through the Chalcolithic and the Bronze and Iron Ages, and culminated during the Middle Ages. Deforestation of the subalpine belt would be responsible for the triggering of a number of shallow landslides and soil erosion in steep slopes above 1500 m a.s.l. The crisis of the transhumance since the beginning of the 19th century reduced the livestock pressure, particularly in the second half of the 20th century, and has contributed to shrub and forest expansion, whereas the area occupied by summer grasslands has been remarkably reduced. The decreasing livestock pressure suggests that forest expansion will continue in the next future, in a favourable context of global warming and declining presence of snowpack in the subalpine belt., La elaboración de este trabajo ha contado con el apoyo del proyecto ESPAS, CGL2015-65569-R (MINECO-FEDER).

26 Pags.- 6 Figs.- 2 Tabls. The definitive version is available at: http://link.springer.com/journal/11629, The conversion of subalpine forests into grasslands for pastoral use is a well-known phenomenon, although for most mountain areas the timing of deforestation has not been determined. The presence of charcoal fragments in soil profiles affected by shallow landsliding enabled us to date the occurrence of fires and the periods of conversion of subalpine forest into grasslands in the Urbión Mountains, Iberian Range, Spain. We found that the treeline in the highest parts of the northwestern massifs of the Iberian Range (the Urbión, Demanda, Neila, and Cebollera massifs) is currently between 1500 and 1600 m a.s.l., probably because of pastoral use of the subalpine belt, whereas in the past it would have reached almost the highest divides (at approximately 2100–2200 m a.s.l.). The radiocarbon dates obtained indicate that the transformation of the subalpine belt occurred during the Late Neolithic, Chalcolithic, Bronze Age, Iron Age, and Middle Ages. Forest clearing was probably moderate during fires prior to the Middle Ages, as the small size of the sheep herds and the local character of the markets only required small clearings, and therefore more limited fires. Thus, it is likely that the forest recovered burnt areas in a few decades; this suggests the management of the forest and grasslands following a slash-and-burn system. During the Middle and Modern Ages deforestation and grassland expansion affected most of the subalpine belt and coincided with the increasing prevalence of transhumance, as occurred in other mountains in the Iberian Peninsula (particularly the Pyrenees). Although the occurrence of shallow landslides following deforestation between the Neolithic and the Roman Period cannot be ruled out, the most extensive shallow landsliding processes would have occurred from the Middle Ages until recent times., Support for this research was provided by the projects INDICA (CGL2011- 27753-C02-01 and -02) and DINAMO2 (CGL2012-33063), funded by the Spanish Ministry of Economy and Competitiveness.

29 Pag., 1 Tabl., 11 Fig. The definitive version is available at: http://www.sciencedirect.com/science/journal/0169555X, This study investigated the characteristics, triggering factors, and spatial distribution of shallow landslides in relation to historical deforestation in the sub-alpine belt of the Pyrenees, particularly in the flysch sector. Shallow landslides in this area occur on straight and concave slopes, mainly covered by mesophyte grasslands, and contribute substantially to soil erosion and landscape deterioration. The investigated landslides were variable in shape and size, although common features included delimitation by a scar or semi-circular crown (averaging 32 m long × 10.15 m wide) and a tongue with a lobe at the foot of the scar area. The sliding surface coincided with the zone of contact of the C soil horizon with the bedrock, although in 13% of the cases the sliding surface occurred within the soil. The frontal lobes frequently trigger new landslides because of water accumulation and instability, resulting in a succession of interconnected landslides that can attain 100–200 m in length. Slope gradient appeared to be the most important factor correlated with shallow landslides. Thus, with slopes > 30° the soil was unstable and tended to slide even in dry conditions, whereas with slopes < 15° the soil was stable even under saturated conditions; shallow landslides were consequently concentrated on slopes between 15° and 30°. Rapid deforestation of the sub-alpine belt during the Middle and Modern Ages caused a sudden increase in hillslope instability. The studied landslides occurred only on deforested, grassland-covered hillslopes, and not in adjacent forested areas. Therefore, deforestation is considered to be a major factor contributing to shallow landslides, because of changes in soil hydrology and reduced soil strength as a consequence of decreased root cohesion, mainly coinciding with snowmelt and large rainstorms., Support for this research was provided by the projects PROBASE (CGL2006-11619/HID, Consolider), financed by the Spanish Commission of Science and Technology, ACQWA (FP7-ENV-2007-1), by the European Commission, and PI032/08 financed by the Aragón Regional Government. The authors also acknowledge support from the Program of Research Groups of the Aragón Regional Government, and from RESEL (The Spanish Ministry of Environment).

12 páginas, 9 figuras., In this study the climatic and hydrological trends across 88 sub-basins of the Ebro River basin were analyzed for the period 1950–2006. A new database of climate information and river flows for the entire basin facilitated a spatially distributed assessment of climate-runoff relationships. It constitutes the first assessment of water yield evolution across the whole Ebro basin, a very representative example of large Mediterranean rivers. The results revealed a marked decrease in river discharges in most of the sub-basins. Moreover, a number of changes in the seasonality of the river regime was found, resulting from dam regulation and a decrease in snowpack in the headwaters. Significant and positive trends in temperature were observed across most of the basin, whereas most of the precipitation series showed negative coefficients, although the decrease in magnitude was low. The time evolution of the residuals from empirical models that relate climate and runoff in each sub-basin provided evidence that climate alone does not explain the observed decrease in river discharge. Thus, changes in water yield are associated with an increase in evapotranspiration rates in natural vegetation, growth of which has expanded as a consequence of land abandonment in areas where agricultural activities and livestock pressure have decreased. In the lowlands of the basin the decrease in water yield has been exacerbated by increased water consumption for domestic, industrial and agricultural uses. Climate projections for the end of the 21st century suggest a reduced capacity for runoff generation because of increasing temperature and less precipitation. Thus, the maintenance of water supply under conditions of increasing demand presents a challenging issue requiring appropriate coordination amongst politicians and managers., This work has been supported by the research projects CGL2006-11619/HID, CGL2008-01189/BTE, and CGL2008-05112-C02-01/CLI financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7-ENV-2008-1-226487), ACQWA (FP7-ENV-2007-1- 212250) financed by the VII Framework Programme of the European Commission, “Las sequías climáticas en la cuenca del Ebro y su respuesta hidrológica” and “La nieve en el Pirineo Aragonés y su respuesta a la variabilidad climática” financed by “Obra Social La Caixa” and the Aragón Government.

Support for this research was provided by the projects: “Processes and sediment balances at different spatial scales in Mediterranean environments: Effects of climate fluctuations and land use changes” (PROBASE, CGL2006- 11619/HID CONSOLIDER), and “Spatiotemporal behaviour and models of the sediment transfer on different land uses” (CETSUS, CGL2007-66644-C04- 01/HID), both funded by the Spanish Ministry of Education and Science, “Development and validation of coupled hydrological and hydraulic models in catchments at different spatial scales” (PI032/08) funded by the DGA, and ACQWA, supported by the EU-FP7 (www.acqwa.ch) under Contract Nr 212250. Monitoring of the catchment was supported by an agreement between the CSIC and the Spanish Ministry of Environment (RESEL). The first author benefited from a research contract (I+D+I 2008-2011 National Program), funded by the Spanish Ministry of Education and Science., 18 páginas, 6 figuras, 3 tablas y 1 fotografía, [EN] A small catchment affected by agricultural practices in the past, then progressively abandoned and naturally re-vegetated was monitored in the central Spanish Pyrenees. The results obtained over a 9-year period revealed the complexity of its hydrological and geomorphological behaviour. Several runoff generation processes can occur at the same time and in different parts of the catchment, depending on the water reserves conditions and rainfall characteristics. Sediment response is mainly controlled by the spatial and temporal dynamics of water and sediment contributing areas within the catchment. The sediment output illustrates the complexity of the geomorphic response of mountain environments modified by past farmland activities., [ES] Se presenta una síntesis de la investigación realizada en una pequeña cuenca experimental afectada por una intensa actividad agraria en el pasado y sujeta a un proceso de revegetación natural en la actualidad en el Pirineo Central. Los principales resultados obtenidos demuestran su complejo comportamiento hidrogeomorfológico. El análisis de la información hidrológica sugiere que diferentes procesos dominantes de generación de escorrentía pueden ocurrir de manera simultánea en diferentes áreas de la cuenca, en función del estado de humedad de la misma y de las características de la precipitación. La respuesta sedimentológica está principalmente controlada por la dinámica espacio-temporal de las áreas fuente de escorrentía y de sedimento. La exportación de sedimento ilustra la complejidad de la respuesta geomorfológica en los ambientes de montaña afectados por actividades agrarias en el pasado.

41 Pag., 14 Fig. The definitive version is available at: http://www.sciencedirect.com/science/journal/00221694, The influence of climate variation on the availability of water resources was analyzed in the headwaters of the Tagus River basin using two drought indices, the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI). This basin is highly regulated and strategic, and contains two hyperannual reservoirs that are the origin of the water supply system for Mediterranean areas of southeast Spain. The indices confirmed that drought conditions have prevailed in the headwaters of the Tagus River since the 1970s. The responses in river discharge and reservoir storage were slightly higher when based on the SPEI rather than the SPI, which indicates that although precipitation had a major role in explaining temporal variability in the analyzed parameters, the influence of temperature was not negligible. Moreover, the greatest response in hydrological variables was evident over longer timescales of the climatic drought indices. Although the effect of climate variability on water resources was substantial during the analyzed period, we also showed a major change in hydrological–climatic relationships in regulated systems including reservoir storage and outflow. These were closely related to changes in external demand following commencement of the water transfer system to the Júcar and Segura basins after the 1980s. The marked reduction in water availability in the basin, which is related to more frequent droughts, contrasts with the amount of water transferred, which shows a clear upward trend associated with increasing water demand in the Mediterranean basin., This work has been supported by the research projects CGL2006-11619/HID, CGL2008-01189/BTE, and CGL2008-1083/CLI financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7-ENV-2008-1-226487) and ACQWA (FP7-ENV-2007-1- 212250) financed by the VII Framework Programme of the European Commission, STRIVER (Strategy and methodology for Improved IWRM—An integrated interdisciplinary assessment in four twinning river basins), financed by the VI Framework Programme of the European Commission. “Las sequías climáticas en la cuenca del Ebro y su respuesta hidrológica” Financed by “Obra Social La Caixa” and the Aragón Government and “Programa de grupos de investigación consolidados” financed by the Aragón Government.

Two study areas were selected in the Cantabrian Range, in northern Spain, in order to analyse the morphometric characteristics of Pleistocene glacial cirques in a relatively mar- ginal glacial environment. The Western Massif of Picos de Europa (WMPE) (highest altitude at 2,596 m) is characterised by Alpine-like relief and a geological landscape mainly dominated by calcareous outcrops. The sierras of Southwest Asturias (SSWA) (highest altitude at 2,002 m) is a typical Palaeozoic landscape of Appalachian-like relief and is dominated by old erosion surfaces. A statistical analysis found few relationships between environmental factors (altitude, aspect and lithology) and cirque morphometry in the WMPE. Glacial cirque development in this area is therefore likely to be more influenced by structural processes (such as differential erosion and fractures) and karstic erosion. In contrast, a clear increase in cirque size is observed with increasing altitude in the SSWA. In both study areas, cirques are predominantly distrib- uted in areas with N and NE aspects, but particularly so in the SSWA which is of lower alti- tude than the WMPE. In the SSWA but not the WMPE, the horizontal dimensions of the cirques tend to increase more rapidly than the vertical dimensions, supporting the allometric model of glacial cirque development in this area.

This paper analyzes the evolution of the Monte Perdido Glacier, the third largest glacier of the Pyrenees, from 1981 to the present. We assessed the evolution of the glacier's surface area by use of aerial photographs from 1981, 1999, and 2006, and changes in ice volume by geodetic methods with digital elevation models (DEMs) generated from topographic maps (1981 and 1999), airborne LIDAR (2010) and terrestrial laser scanning (TLS, 2011, 2012, 2013, and 2014). We interpreted the changes in the glacier based on climate data from a nearby meteorological station. The results indicate an accelerated degradation of this glacier after 2000, with a rate of ice surface loss that was almost three-times greater from 2000 to 2006 than for earlier periods, and a doubling of the rate of ice volume loss from 1999 to 2010 (the ice depth decreased 8.98 ± 1.8 m, −0.72 ± 0.14 m w.e. yr−1) compared to 1981 to 1999 (the ice depth decreased 8.35 ± 2.12 m, −0.39 ± 0.1 m w.e. yr−1). This loss of glacial ice has continued from 2011 to 2014 (the ice depth decreased 2.1 ± 0.4 m, −0.64 ± 0.36 m w.e. yr−1). Local climatic changes during the study period cannot explain the acceleration in wastage rate of this glacier, because local precipitation and snow accumulation increased slightly, and local air temperature during the ablation period did not significantly increase. The accelerated degradation of this glacier in recent years can be explained by the lack of equilibrium between the glacier and the current climatic conditions. In particular, the average air temperature increased by at least 0.9 °C in this region since the end of the Little Ice Age (LIA) in the mid-1800s. Thus, this glacier shrinks dramatically during years with low accumulation or high air temperatures during the ablation season, but cannot recover during years with high accumulation or low air temperatures during the ablation season. The most recent TLS data support this interpretation. These data indicated that two consecutive markedly anomalous wet winters and cool summers (2012–13 and 2013–14) led to near zero mass balance conditions, with significant losses of ice in some areas. These anomalous periods could not counteract the dramatic shrinkage that occurred during the dry and warm period of 2011–2012.

Deglaciation processes in the upper Gállego Valley, central-southern Pyrenees, were studied using geomorphological mapping and 36Cl cosmogenic dating of moraine and rock glacier boulders, as well as polished bedrock. Although the precise position of the Gállego Glacier during the global last glacial maximum is not known, there is evidence that ice tongues retreated to the headwaters, which caused subdivision of the main glacier into a number of individual glaciers prior to 17ka. A range of ages (16 to 11ka) was found among three tributary valleys within the general trend of deglaciation. The retreat rate to cirque was estimated to be relatively rapid (approximately 5km per ka). The mapped glacial sedimentology and geomorphology appears to support the occurrence of multiple minor advances and retreats, or periods of stasis during the late deglaciation. Geomorphological and geological differences among the tributary valleys, and error estimates associated with the results obtained, prevented unambiguous correlations of the advances with the late Pleistocene cold periods. During the latter advances, small glaciers and rock glaciers developed close to the cirque headwalls, and co-occurred under the same climatic conditions. No evidence for Holocene re-advance was found for any of the three tributary valleys. © 2015 University of Washington., This study was performed with the support of the projects CGL2006-11619/HID, CGL2011-27753-C02-01 and CGL2012-35858, funded by the Spanish Ministry of Economy and Competitiveness. The research group on Geomorphology and Global Change was financed by the Aragón Government and the European Social Found (ESF-FSE) (E68). The authors acknowledge Dr David Fink, Dr Magali Delmas and an anonymous reviewer for their valuable comments on the manuscript. We also particularly thank Dr Irene Schimmelpfennig, whose collaboration was essential to the study.

13 páginas, 7 figuras, 7 tablas.-- El documento en word es la versión post-print del artículo., This paper analyses the factors which influence the presence or absence of tributary-junction fans in the Iberian Range, northern Spain. Two valleys were selected, both characterised by wide variations in lithology, altitude, land use and plant cover. Two groups of factors were studied: those related to the internal characteristics of the drainage basins, which particularly control sediment generation; and those related to the characteristics of the depositional area which control accommodation space and main river power. Among the internal factors, the development of alluvial fans was related to: (i) the capacity of the basin to yield large volumes of sediment, (ii) the occurrence of intense human pressure until recent times, a good indicator of sediment yield, and (iii) the capacity of the basin to quickly increase discharge during rainstorms (discharge density and torrentiality). It is suggested that the areas that were intensively cultivated in the past, and have therefore been affected by intense erosion, have played a decisive role on the development of alluvial fans. This would imply that many of these alluvial fans have a relatively recent origin, perhaps related to the beginning of a widespread deforestation. The basins without alluvial fans are characterised by relatively steep hillslope gradients (that is, slopes that never were subjected to historical cultivation), low drainage densities and dense forest and shrub cover, mostly coinciding with high altitude basins composed of quartzite and shale bedrocks. Regarding the external factors, the shape, size and longitudinal gradient of the main river to which the fans are tributary are the most relevant conditioning factors determining the development of alluvial fans., Support for this research was provided by the following projects: PIRIHEROS (REN2003-08678/ HID) and CANOA (CGL2004-04919-C02-01), both funded by CICYT, the Spanish Ministry of Education and Science.

The spatial distribution of 961 debris flows in the Upper Aragon and Gallego valleys (Central Spanish Pyrenees) was analyzed. Most were located in the Flysch Sector (with a colluvium mantle derived from strongly tectonically modified materials), between 1000 and 1400 m above sea level, on 25–35° gradients with sunny exposure. These gradients were either hillslopes covered by frequently burned scrubland, abandoned fields, or reforested land, confirming the influence of land use and disturbed landscapes on the occurrence of debris flows.

9 Pags., 6 Figs. The Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the of the work, journal citation and DOI., We use high quality climate data from ground meteorological stations in the Iberian Peninsula (IP) and robust drought indices to confirm that drought severity has increased in the past five decades, as a consequence of greater atmospheric evaporative demand resulting from temperature rise. Increased drought severity is independent of the model used to quantify the reference evapotranspiration. We have also focused on drought impacts to drought-sensitive systems, such as river discharge, by analyzing streamflow data for 287 rivers in the IP, and found that hydrological drought frequency and severity have also increased in the past five decades in natural, regulated and highly regulated basins. Recent positive trend in the atmospheric water demand has had a direct influence on the temporal evolution of streamflows, clearly identified during the warm season, in which higher evapotranspiration rates are recorded. This pattern of increase in evaporative demand and greater drought severity is probably applicable to other semiarid regions of the world, including other Mediterranean areas, the Sahel, southern Australia and South Africa, and can be expected to increasingly compromise water supplies and cause political, social and economic tensions among regions in the near future., This work has been supported by research projects CGL2011-27574-CO2-02, CGL2011-27536 and CGL2011–24185 financed by the Spanish Commission of Science and Technology and FEDER, 'Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (LIFE MEDACC)' financed by the LIFE programme of the European Commission, CTTP1/12, financed by the Comunidad de Trabajo de los Pirineos, and QSECA (PTDC/AAG-GLO/4155/2012) funded by the Portuguese Foundation for Science and Technology (FCT). ASL was supported by a postdoctoral fellowship from the Catalan Government (2011 BP-B 00078) and CAM was supported by a Juan de la Cierva fellowship by the Spanish Government.

The Ordesa and Monte Perdido National Park was created in 1918 and enlarged in 1982 to highlight and protect spectacular high mountain relief dominated by limestone. Alpine tectonics resulted in the piling-up of south-verging thrust sheets leading to the thick sedimentary successions exposed in impressive vertical cliffs. The presence of massive limestones has favoured the development of deep canyons and karst landforms, including karren, dolines, and caves with large shafts. Quaternary glaciations contributed to increase the geomorphic diversity, forming cirques and stunning U-shaped valleys. Small glaciers from the Little Ice Age still remain on the north-facing slopes of the Monte Perdido. Periglacial processes in the most elevated areas of the National Park, as well as erosion in thick soils developed on marly limestone have produced unique geomorphological features.

The Marboré Cirque, which is located in the southern Central Pyrenees on the north face of the Monte Perdido Peak (42°40′0″N; 0.5°0″W; 3355 m), contains a wide variety of Holocene glacial and periglacial deposits, and those from the ‘Little Ice Age’ (‘LIA’) are particularly well developed. Based on geomorphological mapping, cosmogenic exposure dating and previous studies of lacustrine sediment cores, the different deposits were dated and a sequence of geomorphological and paleoenvironmental events was established as follows: (1) The Marboré Cirque was at least partially deglaciated before 12.7 kyr BP. (2) Some ice masses are likely to have persisted in the Early Holocene, although their moraines were destroyed by the advance of glaciers during the Mid Holocene and ‘LIA’. (3) A glacial expansion occurred during the Mid Holocene (5.1 ± 0.1 kyr), represented by a large push moraine that enclosed a unique ice mass at the foot of the Monte Perdido Massif. (4) A melting phase occurred at approximately 3.4 ± 0.2 and 2.5 ± 0.1 kyr (Bronze/Iron Ages) after one of the most important glacial advances of the Neoglacial period. (5) Another glacial expansion occurred during the Dark Age Cold Period (1.4–1.2 kyr), followed by a melting period during the Medieval Climate Anomaly. (6) The ‘LIA’ represented a clear stage of glacial expansion within the Marboré Cirque. Two different pulses of glaciation were detected, separated by a short retraction. The first pulse occurred most likely during the late 17th century or early 18th century (Maunder Minimum), whereas the second occurred between 1790 and ad 1830 (Dalton Minimum). A strong deglaciation process has affected the Marboré Cirque glaciers since the middle of the 19th century. (7) A large rock avalanche occurred during the Mid Holocene, leaving a chaotic deposit that was previously considered to be a Late Glacial moraine. © The Author(s) 2014., This work was supported by HORDA (ref: 83/2009), funded by the Organismo Autónomo de Parques Nacionales, and by INDICA (CGL2011-27753-C02-01 and -02) and CGL2012-35858, funded by the Spanish Ministry of Economy and Competitiveness. Financial support for the Research Group on Geomorphology and Global Change was provided by the Aragón Government and the European Social Fund (ESF-FSE).

Three alluvial fans in the Ribera de Biescas, upper Gallego Valley, and central Spanish Pyrenees, have been studied in order to explain the most recent changes and to identify the spatial organization of the sediment. In the alluvial fans surveyed, the proximal area is dominated by debris flows, which pass downslope into transitional and fluvial deposits. The relative importance of each type of sediment is closely related to the size and gradient of the alluvial fan, as well as to the gradient in the final stretch of the stream. In general, the size of the sediment decreases from the proximal to the distal area, while the roundness increases. Nevertheless, there are noticeable irregularities in the trend both in longitudinal and transverse transects, due mainly to the sedimentary dynamics of the debris flows, as they advance towards the inner part of each alluvial fan during the most intense peak flows. A sudden shrinkage of the most active area and incision along the fan channels has been assessed and related to land-use changes in the catchments.

27 páginas, 8 figuras, 3 tablas.- Versión pre-print. - The definitive version is available at: http://onlinelibrary.wiley.com/doi/10.1002/ldr.2221/abstract, [EN] An exceptional rainfall and hydrological event occurred on 19–21 October 2012 in the central western Pyrenees and was particularly significant in the Upper Aragón River basin and its tributaries, mainly the Irati River. Analysis of historical records showed that, considered separately, the event of 19 and 20 October ranked between the second and fifth highest most extreme daily precipitation events. For the two days combined (with a total between 200 and 260 mm), the precipitation event was the most extreme 2-day event among all observation stations but one. The consequent flood destroyed part of an urban area, and a long stretch of a national road triggered landslides, enlarged the alluvial plain and caused generalised soil erosion in cultivated fields cropped with winter cereals. Badlands in the marls of the Inner Depression yielded high volumes of sediment. The floods in the tributaries were relatively moderate (return periods of 14–42 years), whereas in the Upper Aragón River, the flood corresponded to a return period of approximately 400–500 years and to 142 years at the end of the Yesa reservoir, although difficulties in estimating the discharge increased the uncertainty of these values. The Yesa and Itoiz reservoirs considerably reduced the intensity of the flood in the middle and lower Aragón River and confirmed the importance of the water level in the reservoirs when such rainfall events occur. The water storage in the Yesa reservoir increased from 16% to 53% as a consequence of the event. More integrated studies are necessary to decrease the risks associated with flood hazards. This is particularly the case in mountain areas, where the steep slopes and longitudinal gradients of the rivers shorten the concentration time of floods and increase the energy that erodes channels and riverbanks. Copyright © 2013 John Wiley & Sons, Ltd, Support for this research was provided by the projects INDICA (CGL2011-27753-C02-01 and 02), DISPROSPEC (CGL2011-24185) and HIDROCAES (CGL2011-27574- C02-01), funded by the Spanish Ministry of Economy and Innovation; ACQWA (FP7-ENV-2007-1-212250), financed by the European Commission, and an agreement between the CSIC and the Spanish Ministry of Environment (RESEL). The research group on Geomorphology and Global Change was financed by the Aragón Government and the European Social Fund (ESF-FSE). E. Nadal-Romero and N. LanaRenault benefited from a research contract (Spanish Ministry of Economy and Innovation, Programme Juan de la Cierva). The authors acknowledge the free availability of the hydrological information from the Ebro River Authority and the help provided by the team of the Centro de Proceso de Cuenca del Sistema Automático de Información Hidrológica de la Confederación Hidrográfica del Ebro. The cartographic help from Paz Errea and Sergio Valdivielso was also acknowledged.

Purpose: Sediment delivery from headwater catchments to reservoirs is a serious threat to reservoir sustainability, and is a critical issue in Mediterranean environments where water resources are scarce. In this study we assessed the consequences of two landscape management scenarios (natural vegetation recovery and scrub clearance) on soil erosion and sediment yield. The results were analyzed in relation to predicted and measured rates of soil erosion and sediment yield, with the aim of promoting better management practices. Materials and methods: The study area was the Arnás River catchment (284 ha), which is located in the central Spanish Pyrenees; the area includes abandoned and poorly managed fields. The combination of the RUSLE and SEDD models of soil erosion and sediment delivery was evaluated in terms of its ability to predict annual rates of sediment yield, using field measurement data for seven water years at the gauging station. The consequences of natural plant succession in other areas of the Spanish Pyrenees, and scrub clearance practices implemented by certain regional governments to increase grazing meadow areas and reduce the incidence of wildfires, were spatially analyzed using GIS. The main sediment source areas were identified and their specific and total sediment yield rates were calculated. Results and discussion: The predicted soil loss under existing conditions was 2.6 Mg ha–1 yr–1, with 5% of the surface area affected by rates greater than 2 tons. The measured sediment yield (SY) range was 69–534 Mg yr–1. The maximum SY detected was associated with an extraordinary debris flow. The predicted rates were strongly correlated to measured rates (Nash–Sutcliffe coefficient = 0.72). The main sources of were alluvial deposits (Specific Sediment Yield = 51 Mg ha–1 yr–1), bare soil (SSY = 12), unpaved trails (SSY = 11), lots (SSY = 4) and pastures (SSY = 1). Under a scenario of vegetation recovery, decreases of 3, 17 and 16% in soil loss, and sediment delivery and yield (respectively) are predicted, whereas increases of 15, 5 and 2% are predicted following scrub clearance practices. Conclusions: Coupling the RUSLE and SEDD models enabled estimation of annual values of soil erosion and delivery in monitored and unmonitored catchments of small and medium size, making this approach a useful tool for risk analysis. Management practices that combine fire-risk control, by the implementation of scrub clearance practices, with the effects of plant succession on the sediment production are suggested as the best management strategy., Acknowledgements: This research was financially supported by the projects: “Soil erosion and carbon dynamic in Mediterranean agroecosystems: radioisotopic modelling at different spatial and temporal scales” (MEDEROCAR, CGL2008-00831/BTE), and “Processes and sediment balances at different spatial scales in Mediterranean environments: Effects of climate fluctuations and land use changes” (PROBASE, CGL2006-11619/HID), both funded by the Spanish Ministry of Science and Innovation. Monitoring of the catchment was supported by an agreement between the CSIC and the Spanish Ministry of Environment (RESEL).

64 Pag., 8 Tabl., 10 Fig., Soil erosion and sediment delivery to streams are important environmental problems and major concerns in sustainable development. In recent years several tools have been proposed for assessing the delivery of sediment from hillslopes to stream networks, but there are still few examples of their application to large basins, and studies include a discussion of calibration and validation issues. In this study a spatially distributed soil erosion and sediment delivery model (WATEM/SEDEM) was applied to the watershed of the Barasona Reservoir (1504 km2, Central Spanish Pyrenees), which is drained by the Ésera and Isábena Rivers. Model calibration and validation was based on the depositional history of the Barasona Reservoir and suspended sediment records over 3 years (May 2005–May 2008) at the outlet of the Isábena River. Despite interannual differences in precipitation and runoff, it was possible to establish an optimum value (7–23) for the ktc parameter. This enabled estimation of the long-term average annual sediment yield to the reservoir, as well as the relative contribution of each river. Large spatial variability in hillslope sediment delivery was found, and the major sediment sources were in the lower part of the watershed (agricultural fields) and in the badlands developed on Eocene marls in the middle part of the watershed (Pyrenean Inner Ranges). The relative importance of sediment source areas was assessed in relation to land use, and the relationship between the sediment delivery ratio and the catchment area was studied as a function of the geomorphological units. For the moment WATEM/SEDEM remains mainly as a researcher’s tool, until either the problem of the scarcity of soil erosion data or the need for calibration of the transport parameters will be solved., This research was financially supported by the projects CGL2006-11619/HID and CGL2008-00831/BTE, funded by CICYT, Spanish Ministry of Education and Science. The contribution of the first author was possible through a scholarship granted by The National Council for Science and Technology of Mexico (CONACYT).

[1] This study examines the effects of a large dam on hydrological droughts in the transboundary Tagus River, central Spain and Portugal. The magnitude and duration of droughts are analyzed by comparing a monthly drought index calculated for the flow series upstream and downstream of the Alcantara reservoir. The dam was built in 1969, and the reservoir is the second largest in Europe (3,162 hm3). Water management in the area is complex because of large seasonal and interannual variability in the flow regime, which is characteristic of Mediterranean environments. This paper demonstrates that, as a result of exploitation of the Alcantara reservoir, (1) during periods of water scarcity, the releases in winter and spring are reduced dramatically and the magnitude and duration of summer low flow show a slight increase and (2) the nature of droughts along the Tagus river basin downstream of the dam has shown severe changes since construction of the dam. In fact, during the predam period (1943–1969), droughts were longer and more intense in the Spanish part of the basin than that in the Portuguese part. Since the construction of the Alcantara dam, however, the Portuguese part of the basin has experienced more severe droughts than did the upstream part in terms of both magnitude and duration.