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The temporal concentration of snowfalls has direct implications on the management of water resources as well as on the economic activity of mountain areas, conditioning, for example, the seasonal performance of ski resorts. This work uses the daily concentration index (CI) for analysing the frequency concentration of snowfalls in the Iberian Peninsula Mountain ranges. First, we provide a spatiotemporal analysis of the CI patterns and trends for the 1980–2014 period. Subsequently, we determine the atmospheric circulation patterns that control the CI variability. In addition, we determine the geographical and low‐frequency climate modes that control the CI for this mid‐latitude area. In addition, we have estimated the partial dependence relationship between the CI and several geographical factors by fitting a multiple linear regression. The results from these analyses show that elevation as well as the distance from the Atlantic are the main geographical pattern that controls the CI in the Iberian Peninsula Mountain ranges. These geographical factors also reflect the role of the main atmospheric circulation patterns in the Iberian Peninsula in controlling the spatial dynamics of the CI. The Cantabrian, Iberian, and northern slopes of the Pyrenees show the lowest CI due to their exposition to northern and Atlantic circulation weather types. On the contrary, the highest CI values are found in the southern and eastern slopes of the Pyrenees, eastern slopes of Sierra Nevada, and southern slopes of the Central system. Trend analysis shows a slight increase of CI in the Central system and in the western Sierra Nevada. However, eastern Sierra Nevada, Cantabrian, Central, and Iberian show a downward CI trend. CI is principally driven by the East‐Atlantic/Western Russia pattern and the North Atlantic Oscillation (NAO) in the Cantabrian, Iberian, and northern slopes of the Central range. The CI values in the Pyrenees show a different relationship with the Western Mediterranean Oscillation (WeMO) depending on whether it is the southern or the northern slope. In addition, the positive phase of the NAO oscillation controls the higher values of CI for the whole Pyrenees, especially in the mid‐south part. Finally, in Sierra Nevada the CI dynamics are controlled mostly by the WeMO. [ABSTRACT FROM AUTHOR]

Climate warming is changing the magnitude, timing, and spatial patterns of mountain snowpacks. A warmer atmosphere may also induce precipitation phase shifts, resulting in a decreased snowfall fraction (Sf). The combination of Sf and snowpack directly influences the frequency and intensity of rain-on-snow (ROS) events, a common cause of flash-flood events in snow-dominated regions. In this work, we investigate ROS patterns and their sensitivity to temperature and precipitation changes in the Pyrenees by modeling ROS through a physically based snow model. This model is forced with reanalysis climate data for elevations of 1500, 1800, and 2400 m perturbed using a range of temperature and precipitation values consistent with 21st century climate projections. ROS patterns are characterized by their frequency, rainfall quantity, and snow ablation. The highest ROS frequency for the historical climate period (1980–2019) is found in the 2400 m zones of the southwest Pyrenees (17 d yr -1). The maximum ROS rainfall amount is detected in 1800 m areas of the southeast (45 mm d -1 , autumn), whereas the highest ROS ablation is found in the 2400 m zones of the northwest (- 10 cm d -1 , summer). When air temperature increases from 1 to 4 ∘ C compared to the historical climate period, ROS rainfall amount and frequency increase at a constant rate during winter and early spring for all elevation zones. For the rest of the seasons, non-linear responses of ROS frequency and ablation to warming are found. Overall, ROS frequency decreases in the shoulders of the season across eastern low-elevation zones due to snow cover depletion. However, ROS increases in cold, high-elevation zones where long-lasting snow cover exists until late spring. Similarly, warming induces greater ROS ablation (+ 10 % ∘ C -1) during the coldest months of the season, 2400 m elevations, and northern sectors, where the deepest snow depths are found. In contrast, small differences in ROS ablation are found for warm and marginal snowpacks. These results highlight the different ROS responses to warming across the mountain range, suggest similar ROS sensitivities in near-mid-latitude zones, and will help anticipate future ROS impacts in hydrological, environmental, and socioeconomic mountain systems. [ABSTRACT FROM AUTHOR]

The Aneto glacier, although it may be considered a very small glacier (<0.5 km 2), is the largest glacier in the Pyrenees. Its surface and thickness loss have been continuous in recent decades, and there have been signs of accelerated melting in recent years. In this study, thickness and surface losses of the Aneto glacier from 1981 to 2022 are investigated using historical aerial imagery, airborne lidar point clouds and unoccupied aerial vehicle (UAV) imagery. A ground-penetrating radar (GPR) survey conducted in 2020, combined with data from photogrammetric analyses, allowed us to reconstruct the current ice thickness and also the existing ice distribution in 1981 and 2011. Over the last 41 years, the total glacierised area has decreased by 64.7 %, and the ice thickness has decreased, on average, by 30.5 m. The mean remaining ice thickness in autumn 2022 was 11.9 m, as against the mean thickness of 32.9, 19.2 and 15.0 m reconstructed for 1981 and 2011 and observed in 2020, respectively. The results demonstrate the critical situation of the glacier, with an imminent segmentation into two smaller ice bodies and no evidence of an accumulation zone. We also found that the occurrence of an extremely hot and dry year, as observed in the 2021–2022 season, leads to a drastic degradation of the glacier, posing a high risk to the persistence of the Aneto glacier, a situation that could extend to the rest of the Pyrenean glaciers in a relatively short time. [ABSTRACT FROM AUTHOR]

Climate warming is changing the magnitude, timing, and spatial patterns of mountain snowpacks. A warmer atmosphere may also lead to precipitation phase shifts, with decreased snowfall fraction (Sf). The combination of Sf and snowpack decreases directly affects the frequency and intensity of rain-on-snow (ROS) events, a common cause of flash-flood events in snow dominated regions. In this work we examine the ROS patterns and sensitivity to temperature and precipitation change (delta-change) in the Pyrenees using a physical-based snow model forced with reanalysis climate data perturbed following 21st century climate projections for this mountain range. ROS patterns are characteritzed by their frequency, rainfall quantity and snow ablation. The highest ROS fr for the baseline climate period (1980–2019) are found in South-West high-elevations sectors of the Pyrenees (17 days/year). Maximum ROS rain is detected in South-East mid-elevations areas (45 mm/day, autumn), whereas the highest ROS ablation is found in North-West high-elevations zones (−10 cm/day, summer). When air temperature is increased from 1 ºC to 4 ºC, ROS rain and frequency increase at a constant rate during winter and early spring for all elevation zones. For the rest of the seasons, non-linear responses of the ROS frequency and ablation to warming are found. Overall, ROS frequency decreases in the shoulders of the season across eastern low-elevated zones due to snow cover depletion. However, ROS increases in cold, high-elevated zones where long-lasting snow cover exists until late spring. Similarly, warming triggers fast ROS ablation (+10 % per ºC) during the coldest months of the season, high-elevations, and northern sectors where the deepest snow depths are found. On the contrary, slow, and non-changes in ROS ablation are expected for warm and marginal snowpacks. These results highlight the different ROS responses to warming across the mountain range, suggest similar ROS sensitivities in near mid-latitude zones, and will help anticipate future ROS impacts in hydrological, environmental, and socioeconomic mountain systems. [ABSTRACT FROM AUTHOR]

The Mediterranean Basin has experienced one of the highest warming rates on earth during the last few decades, and climate projections predict water scarcity in the future. Mid-latitude Mediterranean mountain areas, such as the Pyrenees, play a key role in the hydrological resources for the highly populated lowland areas. However, there are still large uncertainties about the impact of climate change on snowpack in the high mountain ranges of this region. Here, we perform a snow sensitivity to temperature and precipitation change analysis of the Pyrenean snowpack (1980–2019 period) using five key snow–climatological indicators. We analyzed snow sensitivity to temperature and precipitation during four different compound weather conditions (cold–dry (CD), cold–wet (CW), warm–dry (WD), and warm–wet (WW)) at low elevations (1500 m), mid elevations (1800 m), and high elevations (2400 m) in the Pyrenees. In particular, we forced a physically based energy and mass balance snow model (FSM2), with validation by ground-truth data, and applied this model to the entire range, with forcing of perturbed reanalysis climate data for the period 1980 to 2019 as the baseline. The FSM2 model results successfully reproduced the observed snow depth (HS) values (R2>0.8), with relative root mean square error and mean absolute error values less than 10 % of the observed HS values. Overall, the snow sensitivity to temperature and precipitation change decreased with elevation and increased towards the eastern Pyrenees. When the temperature increased progressively at 1 ∘ C intervals, the largest seasonal HS decreases from the baseline were at +1 ∘ C. A 10 % increase in precipitation counterbalanced the temperature increases (≤1 ∘ C) at high elevations during the coldest months because temperature was far from the isothermal 0 ∘ C conditions. The maximal seasonal HS and peak HS max reductions were during WW seasons, and the minimal reductions were during CD seasons. During WW (CD) seasons, the seasonal HS decline per degree Celsius was 37 % (28 %) at low elevations, 34 % (30 %) at mid elevations, and 27 % (22 %) at high elevations. Further, the peak HS date was on average anticipated for 2, 3, and 8 d at low, mid, and high elevation, respectively. Results suggest snow sensitivity to temperature and precipitation change will be similar at other mid-latitude mountain areas, where snowpack reductions will have major consequences for the nearby ecological and socioeconomic systems. [ABSTRACT FROM AUTHOR]

Accurate knowledge of the seasonal snow distribution is vital in several domains including ecology, water resources management, and tourism. Current spaceborne sensors provide a useful but incomplete description of the snowpack. Many studies suggest that the assimilation of remotely sensed products in physically based snowpack models is a promising path forward to estimate the spatial distribution of snow water equivalent (SWE). However, to date there is no standalone, open-source, community-driven project dedicated to snow data assimilation, which makes it difficult to compare existing algorithms and fragments development efforts. Here we introduce a new data assimilation toolbox, the Multiple Snow Data Assimilation System (MuSA), to help fill this gap. MuSA was developed to fuse remotely sensed information that is available at different timescales with the energy and mass balance Flexible Snow Model (FSM2). MuSA was designed to be user-friendly and scalable. It enables assimilation of different state variables such as the snow depth, SWE, snow surface temperature, binary or fractional snow-covered area, and snow albedo and could be easily upgraded to assimilate other variables such as liquid water content or snow density in the future. MuSA allows the joint assimilation of an arbitrary number of these variables, through the generation of an ensemble of FSM2 simulations. The characteristics of the ensemble (i.e., the number of particles and their prior covariance) may be controlled by the user, and it is generated by perturbing the meteorological forcing of FSM2. The observational variables may be assimilated using different algorithms including particle filters and smoothers as well as ensemble Kalman filters and smoothers along with their iterative variants. We demonstrate the wide capabilities of MuSA through two snow data assimilation experiments. First, 5 m resolution snow depth maps derived from drone surveys are assimilated in a distributed fashion in the Izas catchment (central Pyrenees). Furthermore, we conducted a joint-assimilation experiment, fusing MODIS land surface temperature and fractional snow-covered area with FSM2 in a single-cell experiment. In light of these experiments, we discuss the pros and cons of the assimilation algorithms, including their computational cost. [ABSTRACT FROM AUTHOR]

The Mediterranean basin has experienced one of the highest warming rates on Earth over the last decades and climate projections anticipate water-scarcity future scenarios. Mid-latitude Mediterranean mountain areas such as the Pyrenees play a key role in the hydrological resources for intensely populated lowland areas. However, there are still large uncertainties about the impact of climate change on the snowpack in high mountain ranges of the Mediterranean region. Here, we provide a climate sensitivity analysis of the Pyrenean snowpack through five key snow climate indicators. Snow sensitivity is analyzed during compound temperature and precipitation extreme seasons, namely Cold-Dry (CD), Cold-Wet (CW), Warm-Dry (WD) and Warm-Wet (WW) seasons, for low (1500 m), mid (1800 m) and high (2400 m) elevation sectors of the Pyrenees. To this end, a physically-based energy and mass balance snow model (FSM2) is validated by ground-truth data, and subsequently applied to the entire range, forcing perturbed reanalysis climate data for the 1980–2019 baseline scenario. The results have shown that FSM2 successfully reproduces the observed snow depth (HS) values, reaching R2 > 0.8, and relative RMSE and MAE lower than 10 % of the observed HS. Overall, climate sensitivity decreases with elevation and increases towards the eastern Pyrenees. When temperature is progressively warmed at 1 ºC intervals, the largest seasonal HS decreases from baseline climate are found at +1 ºC, reaching values of -47 %, -48 % and -25 % for low, mid and high elevations, respectively. Only an upward trend of precipitation (+10 %) could counterbalance temperature increases (<= 1 ºC) at high elevations during the coldest months of the season, since temperature is far from the isothermal 0 ºC conditions. The maximum (minimum) seasonal HS and peak HS max reductions are observed on WW (CD) seasons. During the latter seasons, the seasonal HS is expected to be reduced by -37 % (- 28 %), -34 % (- 30 %), -27 % (-22 %) per ºC, at low, mid and high elevation areas, respectively. For snow ablation climate indicators, the largest decreases are observed during WD seasons, when the peak HS date is anticipated 10 days and snow duration (ablation) decreases (increases) 12 % per ºC. The results suggest similar climate sensitivities in mid-latitude mountain areas; where significant snowpack reductions are anticipated, with relevant consequences in the ecological and socioeconomic systems. [ABSTRACT FROM AUTHOR]

Permafrost is a relevant component of the Pyrenean high mountains, triggering a wide range of geomorphological cryogenic processes. Although in the past decades there has been an increase in frozen ground studies in the Pyrenees, there are no specific studies about rock wall permafrost, its presence, distribution, thermal regime, or historical evolution. This work combines measured rock surface temperatures (RSTs, from August 2013 to April 2016) along an elevation profile (four sites) on the north facing the rock wall of the Vignemale peak (3,298 m a.s.l., 42°46′16″N/0°08′33″W) and temperature modeling (CryoGRID2) to determine the presence of permafrost and to analyze its evolution since the mid‐20th century. Simulations are run with various RST forcings and bedrock properties to account for forcing data uncertainty and varying degrees of rock fracturing. Results reveal that warm permafrost may have existed down to 2,600 m a.s.l. until the early 1980s and that warm permafrost is currently found at ~2,800 m a.s.l. and up to 3,000 m a.s.l. Cold (<−2°C) permafrost may exist above 3,100–3,200 m a.s.l. Systematic investigations on rock wall permafrost must be conducted to refine those results in the Pyrenees. The elevation shift in warm permafrost suggests an imminent disappearance of permafrost in the Vignemale peak. [ABSTRACT FROM AUTHOR]

In a warmer climate, significant variations in the snow regime are expected. Thus, it is crucial to better understand present‐day snow cover regime, its duration and thickness, in order to anticipate future changes. This work presents the first characterization of snow patterns in the Catalan Pyrenees based on 11 snow stations located in high elevation areas (>2,000 m). Here, we examine spatio‐temporal evolution of the daily snow depth and new snow height (HN) since the earliest 2000s to 2020. In addition, we analyse the different synoptic patterns that cause HN events in the study area as well as the low frequency climate modes on the different stages of the snow season. Our results show evidence that the measured snow amount differs considerably between the western and the eastern Catalan Pyrenees independently of the considered elevation. While the eastern part has an average seasonal cumulative HN of 278 cm, the western sector gets almost twice (433 cm). Nonetheless, the onset of the snow melting does not show substantial differences, being primarily ruled by the elevation in both areas. The longest snow records (Núria, 1971 m) point to an increase of HN from 1985 to 2020, a trend which is also observed in most stations from 2000 to 2020. Nevertheless, some stations of the N western fringe record negative trends associated with the low frequency variability of the Western Mediterranean Oscillation (WeMO). Results also indicate that the NW Atlantic low‐pressure systems are the circulation weather types that provide more abundant HN in the majority of snow stations. The Atlantic advections are more frequent in autumn and winter, while the Mediterranean advections provide more intense and recurrent HN in spring. The atmospheric circulation is basically ruled by the East Atlantic/West Russia and the WeMO teleconnection patterns. [ABSTRACT FROM AUTHOR]

Recent developments in unmanned aerial vehicles (UAV) and structure from motion (SfM) algorithms have shown reliable results for retrieving snow depth distribution. However, their ability to obtain accurate results usually relies on deploying and measuring the exact position of ground control points (GCP) for georeferencing the information. Commercial UAVs can now provide real time kinematic (RTK) positioning of the images with centimetric accuracy. Nonetheless, their operational applicability for observing snow distribution in highly heterogeneous mountain areas has not been evaluated. This study presents a complete assessment of the reliability of snow depth observations from a fixed‐wing UAV working in RTK mode with an RGB camera. During the 2018–2019 season, seven field campaigns (13 UAV flights) were undertaken covering 0.48 km2 in complex alpine terrain in the Pyrenees. The UAV observations obtained under different light conditions and flight block configurations (altitude and image overlaps) in the same day were evaluated with terrestrial laser scanner acquisitions. Two SfM processing options of the UAV images were also compared. When the study area received direct solar light, the results were comparable to previous studies that had used GCPs, with an average root mean squared error of 0.19 m and an average absolute snow volume discrepancy lower than 4%. However, when large areas were under shadow from the terrain, or solar light was affected by clouds, the estimated error tripled. The quality of the snow depth maps was little affected by the snow covered area and the flight mission configurations. Key Points: Under good lighting conditions results were comparable to previous studies that had used ground control points, with an average root mean squared error of 0.19 mWhen large areas were under shadow from the terrain, or solar light was affected by clouds, the estimated error increased noticeablyUnmanned aerial vehicles with real time kinematic positioning allow a fast acquisition of snow distribution over large areas dramatically reducing the exposure to nature hazards [ABSTRACT FROM AUTHOR]

Mountain glaciers have generally experienced an accelerated retreat over the last 3 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 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 southern European 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 (NE Spain), Monte Perdido Glacier (MPG), carried out by different radiochronological techniques and a comparison with geochemical proxies from neighbouring palaeoclimate records. The chronological model evidences that the glacier persisted during the Roman period and the Medieval Climate Anomaly. The apparent absence of ice in the past ∼ 600 years suggests that any ice accumulated during the Little Ice Age has since ablated. This interpretation is supported by measured concentrations of anthropogenic metals, including Zn, Se, Cd, Hg and Pb, which have concentrations well below those typical of industrial-age ice measured at other glaciers in Europe. This study strengthens the general understanding that warming of the past few decades has been exceptional for the past 2 millennia. [ABSTRACT FROM AUTHOR]

Snowpacks and forests have complex interactions throughout the large range of altitudes where they co‐occur. However, there are no reliable data on the spatial and temporal interactions of forests with snowpacks, such as those that occur in nearby areas that have different environmental conditions and those that occur during different snow seasons. This study monitored the interactions of forests with snowpacks in four forest stands in a single valley of the central Spanish Pyrenees during three consecutive snow seasons (2015/2016, 2016/2017 and 2017/2018). Daily snow depth data from time‐lapse cameras were compared with snow data from field surveys that were performed every 10–15 days. These data thus provided information on the spatial and temporal changes of snow–water equivalent (SWE). The results indicated that forest had the same general effects on snowpack in each forest stand and during each snow season. On average, forest cover reduced the duration of snowpack by 17 days, reduced the cumulative SWE of the snowpack by about 60% and increased the spatial heterogeneity of snowpack by 190%. Overall, forest cover reduced SWE total accumulation by 40% and the rate of SWE accumulation by 25%. The forest‐mediated reduction of the accumulation rate, in combination with the occasional forest‐mediated enhancement of melting rate, explained the reduced duration of snowpacks beneath forest canopies. However, the magnitude and timing of certain forest effects on snowpack had significant spatial and temporal variations. This variability must be considered when selecting the location of an experimental site in a mountainous area, because the study site should be representative of surrounding areas. The same considerations apply when selecting a time period for study. [ABSTRACT FROM AUTHOR]

Seasonally frozen ground, mountain permafrost and cryogenic geomorphological processes are important components of the Pyrenean high mountains. This work presents the results of a study on the distribution of frozen ground in a marginal and paraglacial environment of temperate mountains. An inventory was made of landforms and indicators of frozen ground, and frozen ground was mapped accordingly. During 2014 and 2016 ground temperatures and thermal regimes were monitored, basal temperatures of snow-cover (BTS) were measured and a thermal map was drawn. Differential thermal behaviours were detected among different elevations and slope orientations. Periglacial processes are the most widespread, in which frost weathering and nivation, together with gelifluction and cryoturbation, are the most efficient processes; the latter two are generally linked to the presence of frozen ground. The fall in air and ground temperatures with altitude, slope orientations, and snowpack thickness and evolution determine ground thermal regimes. In the study area, three types of thermal regimes were established: climate-controlled, snowcover-controlled, and frozen ground-controlled. Seasonally frozen ground occurs across a broad range of elevation between 2650 and 3075 m asl, whereas possible permafrost only occurs above 2750 m asl. [ABSTRACT FROM AUTHOR]

The presence of a seasonal snowpack determines the hydrology, geomorphology and ecology of wide parts of the Iberian Peninsula, with strong implications for the economy, transport and risk management. Thus, reliable information on snow is necessary from a scientific and operational point of view. This is the case of the Iberian Peninsula where, lack of observation has impeded proper analysis of snowpack duration, magnitude and interannual variability. In this study, we present the first snow climatology of the entire Iberian Peninsula. The scarcity of in situ observations has been overcome, using a newly developed remote sensing snow database from MODIS satellite sensors for the period 2000–2014 and a physically based snow model (Factorial Snow Model—FSM), driven by a regional atmospheric model (Weather Research and Forecast model—WRF) over the Iberian Peninsula for the period 1980–2014. The snowpack of the main mountain areas (Pyrenees, Cantabrian, Central, Iberian range and Sierra Nevada) are described, estimated from the generated databases. The information has been processed using a k‐means cluster algorithm, looking for similarities in snow indices at different elevation bands. Results show four different types of snowpack in terms of depth, duration and interannual variability, lying over different elevation bands in the different ranges, proving the variability of the snowpack over Iberia. Analyses reveal areas characterized by ephemeral snowpacks, while in some sectors snowpack lasts, on average, 198 days per year with 3.02 m of peak snow depth. The coefficient of variation of interannual peak snow depth oscillated between 35.2 and 162.4%. All the analysed indices show that at common elevations the Cantabrian range and the Pyrenees host the deepest and longest lasting snowpacks, followed by the Central and Iberian ranges. The Sierra Nevada exhibits the shortest, shallowest snowpack and more year‐to‐year variability. [ABSTRACT FROM AUTHOR]

The periglacial belt is located in the highest parts of temperate mountains. The balance between mean air and ground temperatures and the presence of water determine the effectiveness of periglacial processes related to permafrost, the active layer or seasonally frozen ground (SFG). This study combines thermal and geomorphological data obtained in four Pyrenean massifs (Infierno‐Argualas, Posets, Maladeta and Monte Perdido) to improve knowledge on the occurrence and distribution of frozen ground. The methodology used is based on the study of landforms as frozen ground indicators, mapping processes, ground temperature analysis, basal temperature of snow, thermal mapping and geomatic surveys on rock glaciers and protalus lobes. In the Pyrenean high mountain areas the lower limit of frozen ground is at ~2,650m a.s.l., possible permafrost appears above 2,650m a.s.l. on north‐ and south‐facing slopes, and probable permafrost is dominant above 2,900m a.s.l. Unfrozen ground with cold‐associated geomorphological processes reach 2,900m a.s.l. and unfrozen and frozen ground distribution points to a patchy pattern throughout the periglacial belt. The most widespread frozen grounds are SFG. The thermal data, mean annual ground temperature, cold season temperatures, bottom temperature snow measurements, freeze/thaw cycles and distribution of landforms permit the establishment of a periglacial land system divided into three main belts: infraperiglacial, middle periglacial and supraperiglacial. The large number of processes and landforms that are involved and their altitudinal and spatial organization make up a complex environment that determines the geoecological dynamics of high mountain areas. [ABSTRACT FROM AUTHOR]

Mid-latitude mountain snowpacks are highly vulnerable to climate warming. Past and future hydroclimate changes require a thorougout knowledge of snow ablation physical processes and the associate climate drivers. In this work we provide the first spatio-temporal characteritzation of the energy available for snow ablation (Q m) in the Pyrenees for the period 1959–2020, during the main ablation season (March to June) for low (1200 m), mid (1800 m) and high (2400 m) elevations. We analyze the role of the the main Circulation Weather Types (CTs) in the Q m components for the entire mountain range. Finally, we train and tune a machine learning algorithm, the Random Forest, with atmospheric data (Surface Level Pressure and 500 hPa Geopotential Height) as an independent variable and Q m as the dependent one, in order to determine how much of the observed changes in Q m can be related with atmospheric circulation variability. The largest contribution of Q m is Net Radiation (Rn), increasing with elevation. Q m has shown a statistically significant increase since the 1980s. The comparison between the period 1959–1980 and the 2000–2020 revealed that positive Q m fluxes have been anticipated 22 and 12 days at mid and high elevations, respectively, showing evidence of an advance in the timing of the ablation season and faster snow ablation in high-elevation areas of the Pyrenees. The Q m is principally driven by Rn during the prevailing antyciclonic situations, characterized by the extension of high-pressure systems, low-barometric gradients and the SE advection of hot and dry air masses. The positive frequency of these anticyclonic CTs explains the majority (75%) of the Qm variability, the upward Qm trends and the earlier snow ablation onset since the 1980s. • The energy available for ablate snow (Q m) is increasing in the Pyrenees (1959–2020). • The energy available for ablate snow is mainly ruled by net radiation. • The upward trend has been accentuated at high elevation areas. • The positive Q m trends are explained by the increase of anticyclonic weather types. [ABSTRACT FROM AUTHOR]

Winter tourism is the main source of income and the driving force of local development in many mountain areas. However, in recent years, the industry has been identified as being extremely vulnerable to future climate change. Although the Pyrenees has the largest ski area in Europe after the Alps, there are few detailed climate change vulnerability assessments on the ski resorts based in this region. This paper analyzes the vulnerability of the Pyrenean ski resorts to projected changes in the snowpack under various future climate scenarios. In addition, the study analyzes the sustainability of the snowmaking systems to offset the climate variability of natural snow cover. On average, the study predicts a shorter ski-season length, especially in low-altitude ski resorts in a moderate climate change scenario and for all ski resorts in a more intensive climate change scenario. However, a significant regional variability has been identified for the projected impacts at very short geographical distances within the studied area. Moreover, this paper shows that snowmaking cannot completely solve the problem for all ski resorts in the Pyrenees, as the measure can only act as a robust adaptation strategy in the region provided climate change is limited to +2 °C snowmaking. [ABSTRACT FROM AUTHOR]

Deglaciation processes in the upper Gállego Valley, central–southern Pyrenees, were studied using geomorphological mapping and 36 Cl 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 17 ka. A range of ages (16 to 11 ka) was found among three tributary valleys within the general trend of deglaciation. The retreat rate to cirque was estimated to be relatively rapid (approximately 5 km 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study we analysed the spatial distribution of the long-term average and interannual variability of the number of snow days ( NSD) and the number of precipitation days ( NPD) in winter ( DJFM) in the Spanish Pyrenees, using data from 38 meteorological stations for the period 1981-2010. The interannual variability of the NSD and the NPD in winter was related to the frequency of weather types over the Iberian Peninsula. Data from six stations were also used to analyse a longer time period (1961-2013) to confirm the consistency of the results obtained during the main study period (1981-2010). The results indicated that the NPD is only influenced by the distance to sea whereas the NSD is determined by elevation and distance to the sea. A high frequency of west (W), northwest ( NW) and cyclonic (C) weather systems led to a high NPD in winter across the entire study area, whereas the frequency of north (N) weather types was only correlated with the NPD at the most westerly stations. For the NSD there was a gradient from the Western Pyrenees to eastern areas, mainly explained by the frequency of N weather types in the former area, and high frequencies of NW and W weather types associated with the latter. For most stations there was no significant trend found in the NPD or the NSD for the 1981-2010 period. However, a slight decrease was found for stations strongly correlated with NW weather types, and a slight increase was found for stations strongly correlated with the C weather type, which was related to a decreasing (increasing) frequency of NW (C) weather types during the same period. Analysis of the 1961-2013 and 1971-2000 time slices using a smaller subset of stations revealed a similar relationship between weather types and the NSD. This indicates that the 1981-2010 period is sufficiently representative to describe the relationship of the NSD and the NPD to weather type frequency. However, the study period chosen can markedly influence the trends observed, as the results showed a statistically significant decrease in the NSD for the 1971-2000 period, but no significant trends for the 1961-2013 and 1980-2010 periods. [ABSTRACT FROM AUTHOR]

The intensity and frequency of heavy snowfall events in the Pyrenees were simulated using data from the HIRHAM regional climate model for a control period (1960-1990) and two greenhouse emission scenarios (SRES B2 and A2) for the end of the twenty-first century (2070-2100). Comparisons between future and control simulations enabled a quantification of the expected change in the intensity and frequency of these events at elevations of 1,000, 1,500, 2,000 and 2,500 m a.s.l. The projected changes in heavy snowfall depended largely on the elevation and the greenhouse gas emission scenario considered. At 1,000 m a.s.l., a marked decrease in the frequency and intensity of heavy snowfall events was projected with the B2 and A2 scenarios. At 1,500 m a.s.l., a decrease in the frequency and intensity is only expected under the higher greenhouse gas emission scenario (A2). Above 2,000 m a.s.l., no change or heavier snowfalls are expected under both emission scenarios. Large spatial variability in the impacts of climate change on heavy snowfall events was found across the study area. [ABSTRACT FROM AUTHOR]

Large areas in the Spanish Pyrenees are covered by snow between December and April, especially above 1650 m a.s.l., the location of the cold season 0°C isotherm. However, a significant negative trend in Pyrenean snow pack was detected during the second half of the 20th century. This paper analyses the interannual evolution of snow accumulation in these mountains in relation to the variability of atmospheric circulation. The study considers two spatial scales, from weather types over the Iberian Peninsula to hemispheric atmospheric patterns. The results show strong relationships between the annual occurrence of several weather types and spring snow accumulation. Changes in the frequency of several weather types are explained by the evolution of large scale hemispheric circulation patterns, especially the North Atlantic Oscillation (NAO). Thus, the positive trend observed in the NAO index leads to a decrease in the occurrence of types that favour snow accumulation and an increase in unfavourable conditions for snow pack during the second half of the 20th century. [ABSTRACT FROM AUTHOR]

This paper analyses the spatial and temporal variability of winter droughts in a semi-arid geographic gradient in Northeast Spain, from the Pyrenees in the north to the Mediterranean coastland in the south. Droughts that occurred between 1952 and 1999 were analysed by means of the Standardised Precipitation Index (SPI). The influence of the weather-type frequency and of the general North Atlantic atmospheric circulation patterns was analysed. The results indicate that winter droughts show an important spatial variability in the study area, differentiating three well-defined patterns. These correspond to the Pyrenees, the centre of the Ebro Valley, and the Mediterranean coastland. General negative trends in winter SPI have been found, which are indicative of the increase in winter drought conditions in the study area. Nevertheless, important spatial differences have also been recorded. Dominant north-south gradients in the influence of weather types are shown. Moreover, the negative trends in winter-SPI values agree with the negative trend in the frequency of the weather types prone to cause precipitation, such as the C, SW and W weather types and the increase in the frequency of A weather types. Nevertheless, in the Mediterranean coastland, the positive trend in SPI values agrees with the increase in the frequency of weather types of the east (E, SE), which are prone to cause precipitation in this area. Interannual variations in the frequency of the different weather types have been highly determined by different general atmospheric circulation patterns, mainly the North Atlantic Oscillation (NAO). Nevertheless, the correlation between the time series of weather-type frequency and the winter SPI is higher than that found between the SPI and the NAO. Thus, although the interannual NAO variability explains a high percentage of the interannual differences in the frequency of different weather types, it is not sufficient to explain the spatial and temporal variability of droughts, which respond better to atmospheric variability at more detailed (synoptic) spatial scales. Copyright © 2006 Royal Meteorological Society. [ABSTRACT FROM AUTHOR]

Until the middle of the 20th century, Pyrenean rivers were characterized by braided channels, unstable sedimentary structures and an almost complete lack of plant cover in the alluvial plain, due to the high sediment yield in hillslopes and the occurrence of frequent and intense flooding. This was probably related to strong demographic pressures, including the cultivation of steep slopes, frequent fires, deforestation and overgrazing. Depopulation and farmland abandonment resulted in plant recolonization in formerly cultivated areas, causing a decrease in runoff and sediment yield. As a consequence, most Pyrenean rivers tend to reduce the width of the alluvial plain and to replace the braided pattern with an incised, somewhat meandering pattern, involving the construction of new terrace levels and the stabilization of fluvial bars. [ABSTRACT FROM AUTHOR]

Assesses the effect of climate oscillation and land-use changes on streamflow in the Central Spanish Pyrenees. Main variables that control water yield in a basin; Key factors which govern fluvial discharge; Trend in discharge in the Pyrenean rivers.

• Pyrenean glaciers have a negligible contribution to water resources in the región. • Discussed paper oversimplified understanding of the climatic andhydrological conditions of the study area • Discussed paper has limited to provide a meaningful contribution to water scarcity problems on the Pyrenees region [ABSTRACT FROM AUTHOR]

The aim of this work is to understand aerosol transfers to the snowpack in the Spanish Pyrenees (Southern Europe) by determining their episodic mass-loading and composition, and to retrieve their regional impacts regarding optical properties and modification of snow melting. Regular aerosol monitoring has been performed during three consecutive years. Complementarily, short campaigns have been carried out to collect dust-rich snow samples. Atmospheric samples have been chemically characterized in terms of elemental composition and, in some cases, regarding their mineralogy. Snow albedo has been determined in different seasons along the campaign, and temporal variations of snow-depth from different observatories have been related to concentration of impurities in the snow surface. Our results noticed that aerosol flux in the Central Pyrenees during cold seasons (from November to May, up to 12–13 g m−2 of insoluble particles overall accumulated) is much higher than the observed during the warm period (from June to October, typically around 2.1–3.3 g m−2). Such high values observed during cold seasons were driven by the impact of severe African dust episodes. In absence of such extreme episodes, aerosol loadings in cold and warm season appeared comparable. Our study reveals that mineral dust particles from North Africa are a major driver of the aerosol loading in the snowpack in the southern side of the Central Pyrenees. Field data revealed that the heterogeneous spatial distribution of impurities on the snow surface led to differences close to 0.2 on the measured snow albedo within very short distances. Such impacts have clear implications for modelling distributed energy balance of snow and predicting snow melting from mountain headwaters. [ABSTRACT FROM AUTHOR]

Air temperature changes as a function of elevation were analyzed in a valley of the Spanish Pyrenees. We analyzed insolation, topography and meteorological conditions in order to understand how complex topoclimatic environments develop. Clustering techniques were used to define vertical patterns of air temperature covering more than 1000 m of vertical elevation change. Ten locations from the bottom of the valley to the summits were monitored from September 2016 to June 2019. The results show that (i) night-time lapse rates were between −4 and −2 °C km−1, while in the daytime they were from −6 to −4 °C km−1, due to temperature inversions and topography. Daily maximum temperature lapse rates were steeper from March to July, and daily minimum temperatures were weaker from June to August, and in December. (ii) Different insolation exposure within and between the two analyzed slopes strongly influenced diurnal air temperatures, creating deviations from the general lapse rates. (iii) Usually, two cluster patterns were found (i.e., weak and steep), which were associated with stable and unstable weather conditions, respectively, in addition to high-low atmospheric pressure and low-high relative humidity. The results will have direct applications in disciplines that depend on air temperature estimations (e.g., snow studies, water resources and sky tourism, among others). [ABSTRACT FROM AUTHOR]

The North Atlantic Oscillation (NAO) is considered to be the main atmospheric factor explaining the winter climate and snow evolution over much of the Northern Hemisphere. However, the absence of long-term snow data in mountain regions has prevented full assessment of the impact of the NAO at the regional scales, where data are limited. In this study, we assessed the relationship between the NAO of the winter months (DJFM-NAO) and the snowpack of the Iberian Peninsula. We simulated temperature, precipitation, and snow data for the period 1979–2014 by dynamic downscaling of ERA-Interim reanalysis data, and correlated this with the DJFM-NAO for the five main mountain ranges of the Iberian Peninsula (Cantabrian Range, Central Range, Iberian Range, the Pyrenees, and the Sierra Nevada). The results confirmed that negative DJFM-NAO values generally occur during wet and mild conditions over most of the Iberian Peninsula. Due to the direction of the wet air masses, the NAO has a large influence on snow duration and the annual peak snow water equivalent (peak SWE) in most of the mountain ranges in the study, mostly on the slopes south of the main axis of the ranges. In contrast, the impact of NAO variability is limited on north-facing slopes. Negative (positive) DJFM-NAO values were associated with longer (shorter) duration and higher (lower) peak SWEs in all mountains analyzed in the study. We found marked variability in correlations of the DJFM-NAO with snow indices within each mountain range, even when only the south-facing slopes were considered. The correlations were stronger for higher elevations in the mountain ranges, but geographical longitude also explained the intra-range variability in the majority of the studied mountains. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pllan d'Están paleolake sequence shows Pyrenean climate evolution for last 47 ka. • A subglacial-proglacial lake started at 47 ka BP with the Ésera glacier retreat. • The glaciated landscape changed at 13.8 ka (Allerød), later than northern sites. • A peat bog environment developed in the Holocene surrounded by a mixed forest. Last deglaciation was a complex period in southern European mountains with several glacier advances associated to rapid climate changes which differ in terms of timing and intensity. The 46.7 ka BP lacustrine sequence of Pllan d'Están paleolake (1840 m a.s.l.) located in the Central Southern Pyrenees (northern Spain) provides new information about that deglaciation period for the first time in the Ésera valley. We present a multiproxy analysis including sedimentological, geochemical and biological (pollen and diatoms) indicators that, together with a chronological frame constrained by 14C and OSL dates, enabled the longest reconstruction of the glacier evolution, climate and environmental change made in the Pyrenees to date. This lacustrine sedimentary sequence (4.9 m) is composed of banded to finely laminated silts with few intercalations of massive sections where carbonatic, siliciclastic and organic facies appear from the bottom to the top, characterizing environmental changes from a subglacial/proglacial lake to the current peatbog. A cold and glacier dominated period from 46.7 to 15.9 ka BP was interrupted by a warmer period spanning from 38.2 to 34.8 ka BP. The vegetation succession determined by the palynological analyses is similar to other Pyrenean valleys but dates the onset of mesophytes expansion at 13.8 ka BP during the Allerød, pointing to a difference with other European sequences where temperate forest development took place earlier, associated to the Bølling period. The colder conditions of the Younger Dryas (13–11.7 ka BP) have been detected from cold tolerant diatom taxa that preceded a peatbog development during the Holocene (11.7 ka BP – present-day). These results, together with previously studied Pyrenean sequences, allow characterizing past environmental changes during last deglaciation phases in southern Europe. [ABSTRACT FROM AUTHOR]

• Peak SWE dominates the interannual variability of the snow duration. • The melt rates dominates the duration of the snowpack in the lower elevations. • The importance of the melt rates due to warmer conditions will increase. The duration of the seasonal snowpack determines numerous aspects of the water cycle, ecology and the economy in cold and mountainous regions, and is a balance between the magnitude of accumulated snow and the rate of melt. The contribution of each component has not been well quantified under contrasting topography and climatological conditions although this may provide useful insights into how snow cover duration could respond to climate change. Here, we examined the contribution of the annual peak snow water equivalent (SWE) and the seasonal melt rate to define the duration of the snowpack over temperate mountains, using snow data for mountain areas with different climatological characteristics across the Iberian Peninsula. We used a daily snowpack database for the period 1980–2014 over Iberia to derive the seasonal peak SWE, melt rate and season snow cover duration. The influence of peak SWE and melt rates on seasonal snow cover duration was estimated using a stepwise linear model approach. The stepwise linear models showed high R-adjusted values (average R-adjusted = 0.7), without any clear dependence on the elevation or geographical location. In general, the peak SWE influenced the snow cover duration over all of the mountain areas analysed to a greater extent than the melt rates (89.1%, 89.2%, 81.6% 93.2% and 95.5% in the areas for the Cantabrian, Central, Iberian, Pyrenees and Sierra Nevada mountain ranges, respectively). At these colder sites, the melt season occurs mostly in the spring and tends to occur very fast. In contrast, the areas where the melt rates dominated snow cover duration were located systematically at lower elevations, due to the high interannual variability in the occurrence of annual peak SWE (in winter or early spring), yielding highly variable melt rates. However, in colder sites the melt season occurs mostly in spring and it is very fast in most of the years. The results highlight the control that the seasonal precipitation patterns, in combination with temperature, exert on the seasonal snow cover duration by influencing the peak SWE and suggest a future increased importance of melt rates as temperatures increase. Despite the high climatological variability of the Iberian mountain ranges, the results showed a consistent behaviour along the different mountain ranges, indicating that the methods and results may be transferrable to other temperate mountain areas of the world. [ABSTRACT FROM AUTHOR]

• The presence of forest cover affects the snowpack response to climate perturbations. • Forest effects on snow accumulation processes are enhanced with warming. • Forest effects on snow melting processes are diminished with warming. • Forest-driven reduction in snow duration is significantly enhanced with warming. • Spatial variability in the forest−snow interactions in response to climate forcing. Mountain forests affect spatial and temporal variability of snow processes through snow interception and by modifying the energy balance of snowpack. The high sensitivity of snow cover to seasonal temperatures in mid–latitude mountains is well known and is of particular interest with regard to a future warmer climate. The snowpack in the Pyrenees is expected to be the most impacted by climate change in the Mediterranean mountains, where future climate trends project rising temperatures and decreasing precipitation. This study analyzes how changes in temperature and precipitation can affect current forest–snow interactions in four forests, located near each other but under contrasting topographic settings, in the Spanish Pyrenees. This understanding will allow us to anticipate the future hydrological responses of Pyrenean forested mountain basins. The research was accomplished by performing a sensitivity analysis using simulations from the Cold Regions Hydrological Model (CRHM) and by comparing forest canopy sites (F) vs. openings (O). The CRHM platform focuses on the incorporation of physically based descriptions of snow–dominated regions hydrological processes. It was found that forest cover induced different snowpack sensibility to climatic change conditions in the studied forests. Delayed onset of snow accumulation (F: 13 days·°C−1; O: 5 days·°C−1) and reduced snowpack duration (F: 28 %·°C−1; O: 23 %·°C−1) under warmer temperatures were more intense in areas beneath the forest canopy compared to openings. A lower annual peak of snow water equivalent (SWE) (F: 81 mm·°C−1; O: 129 mm·°C−1), earlier melt-out date (F: 8 days·°C−1; O: 10 days·°C−1) and slower melting rates (F: 0.4 mm·day−1·°C−1; O: 0.5 mm·day−1·°C−1) with increasing temperatures were more intense in forest openings. The forest–driven reduction in snowpack duration (40%) was significantly enhanced with warming (10% per °C). Lower precipitation (20% precipitation reduction) could increase the response of this forest effect to warming (32%), while higher precipitation (20% precipitation increment) could reduce it (−26%). There was relevant topographic variability in the forest−snow interactions in response to climate change among the study stands, despite their proximity. [ABSTRACT FROM AUTHOR]

Abstract: The hydrological and geomorphic effects of land use/land cover changes, particularly those associated with vegetation regrowth after farmland abandonment were investigated in the Central Spanish Pyrenees. The main focus was to assess the interactions among slope, catchment, basin, and fluvial channel processes over a range of spatial scales. In recent centuries most Mediterranean mountain areas have been subjected to significant human pressure through deforestation, cultivation of steep slopes, fires, and overgrazing. Depopulation commencing at the beginning of the 20th century, and particularly since the 1960s, has resulted in farmland abandonment and a reduction in livestock numbers, and this has led to an expansion of shrubs and forests. Studies in the Central Spanish Pyrenees, based on experimental plots and catchments, in large basins and fluvial channels, have confirmed that these land use changes have had hydrological and geomorphic consequences regardless of the spatial scale considered, and that processes occurring at any particular scale can be explained by such processes acting on other scales. Studies using experimental plots have demonstrated that during the period of greatest human pressure (mainly the 18th and 19th centuries), cultivation of steep slopes caused high runoff rates and extreme soil loss. Large parts of the small catchments behaved as runoff and sediment source areas, whereas the fluvial channels of large basins showed signs of high torrentiality (braided morphology, bare sedimentary bars, instability, and prevalence of bedload transport). Depopulation has concentrated most human pressure on the valley bottoms and specific locations such as resorts, whereas the remainder of the area has been affected by an almost generalized abandonment. Subsequent plant recolonization has resulted in a reduction of overland flow and declining soil erosion. At a catchment scale this has caused a reduction in sediment sources, and channel incision in the secondary streams. At the regional scale, the most important consequences include a reduction in the frequency of floods, reduced sediment yields, increasing stabilization of fluvial channels (colonization of sedimentary bars by riparian vegetation and a reduction in the braiding index), and stabilization of alluvial fans. These results demonstrate the complexity and multiscalar nature of the interactions among land use and runoff generation, soil erosion, sediment transport, and fluvial channel dynamics, and highlight the need to adopt a multiscale approach in other mountain areas of the world. [Copyright &y& Elsevier]

• The seasonal growth of Pinus uncinata forests was affected by snow dynamics. • Snow dynamics exerted strong influence on soil temperature. • Soil temperature has a key role in Pinus uncinata wood formation. Snow dynamics are key to understanding tree growth in mountain forests and future response to climate change. However, precise monitoring of microclimate conditions and variables related to tree growth and functioning are lacking. To advance on those issues, snow cover and microclimate conditions, tree phenology, xylogenesis, intra-annual radial growth and the concentration of sapwood and needle non-structural carbohydrates were intensively monitored in four Pinus uncinata forests along an altitudinal gradient over three years in a Pyrenean valley (NE Spain). Snow dynamics exerted strong influence on soil temperature and moisture, particularly before and during the early growing season. Soil temperature was the most relevant microclimate variable during the overall xylogenesis, mainly influencing the production of mature tracheids. Large snow accumulation resulted in later snow depletion and a consequent delay in soil warming onset. Low soil temperatures in the spring, related to prolonged snow persistence, retarded cambial reactivation and led to lower growth rate. Despite strong spatial variability among plots, wood production was determined by snow dynamics in three out of the four studied plots. This study highlights the major role played by early and late growing season soil temperatures on radial growth of mountain conifers. The results of this study suggest that a future shallower and more transitory snowpack in the studied forests, together with warmer soil and air temperatures, may increase radial growth and productivity of similar mid-latitude, young mountain forests. [ABSTRACT FROM AUTHOR]

• Transhumance is the main deforestation factor in the subalpine belt. • The Middle Ages is the period when deforestation progressed the most. • Deforestation of the subalpine belt induced strong erosion processes. • Transhumance has reorganized the altitudinal distribution of forests. • Scientists from various fields provide a holistic view on mountain deforestation. 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. [ABSTRACT FROM AUTHOR]