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Subsidence is a highly destructive natural hazard, which can be caused by both natural and anthropogenic causes. Its impacts include a decrease in storage capacity of aquifer systems, the creation of cracks and fissures, damages to buildings and infrastructures, and an increase of the susceptibility to flooding. In this study, Persistent Scattered Interferometry (PSI) has been used to process Synthetic Aperture Radar (SAR) images, for the detection and analysis of ground deformation and subsidence processes in the island of Mallorca. The study database is composed of 120 images captured by the Sentinel 1A and 1B satellites (between May 2016 and December 2019), from which we derived a map of accumulated displacement rates occurred during a 3 years and a half period. The results show important subsidence processes of up to 3 cm per year in large areas of the sedimentary basin of Palma, and of lesser magnitude (between 1 and 2 cm per year) in locations of the Inca basin and in small basins in the Tramuntana Range. A significant relationship has been observed between the thickness of the Quaternary sediment and the observed subsidence rates. The results highlight the high degree of geomorphological dynamism at very short time scales that characterizes Mallorca, and the vulnerability of certain urban areas, such as the city of Palma (400000 inhabitants), and agricultural areas, such as the Central Depression, facing the risk of subsidence and associated damages.

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., Ministerio de Educación, Cultura y Deporte, Grant/Award Number: FPU16/00902; Ministry of Economy and Competitiveness, Grant/Award Numbers: CGL2017‐82216‐R, CGL2014‐52599‐P; Ministry of Education, Culture and Sports, Grant/Award Numbers: FPU15, FPU16 .

An extraordinary convective rainfall event, unforeseen by most numerical weather prediction models, generated a devastating flash flood (305 m3 s−1) in the town of Sant Llorenç des Cardassar, Mallorca, on 9 October 2018. Four people died inside this village, while casualties were up to 13 over the entire affected area. This extreme event has been reconstructed by implementing an integrated flash flood modelling approach in the Ses Planes catchment up to Sant Llorenç (23.4 km2), based on three components: (i) generation of radar-derived precipitation estimates, (ii) modelling of accurate discharge hydrographs yielded by the catchment (using FEST and KLEM models), and (iii) hydraulic simulation of the event and mapping of affected areas (using HEC-RAS). Radar-derived rainfall estimates show very high agreement with rain gauge data (R2=0.98). Modelled flooding extent is in close agreement with the observed extension by the Copernicus Emergency Management Service, based on Sentinel-1 imagery, and both far exceed the extension for a 500-year return period flood. Hydraulic simulation revealed that water reached a depth of 3 m at some points, and modelled water depths highly correlate (R2=0.91) with in situ after-event measurements. The 9 October flash flood eroded and transported woody and abundant sediment debris, changing channel geomorphology. Water velocity greatly increased at bridge locations crossing the river channel, especially at those closer to the Sant Llorenç town centre. This study highlights how the very low predictability of this type of extreme convective rainfall events and the very short hydrological response times typical of small Mediterranean catchments continue to challenge the implementation of early warning systems, which effectively reduce people's exposure to flash flood risk in the region.

The spatial characteristics and patterns of snow accumulation and ablation inform the amount of water stored and subsequently available for runoff and the timing of snowmelt. This paper characterizes the snow accumulation phase to investigate the spatiotemporal snow water equivalent (SWE) distribution by fitting a function to the trajectory plot of the standard deviation versus mean SWE across a domain. Data were used from 90 snow stations for a 34-year period across the Southern Rocky Mountains in the western United States. The stations were divided into sub-sets based on elevation, latitude, and the mean annual maximum SWE. The best function was a linear fit, excluding the first 35 mm of SWE. There was less variability with SWE data compared to snow depth data. The trajectory of the accumulation phase was consistent for most years, with limited correlation to the amount of accumulation. These trajectories are more similar for the northern portion of the domain and for below average snow years. This work could inform where to locate new stations, or be applied to other earth system variables.

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., This study was supported by the projects: “Bosque, nieve y recursos hídricos en el Pirineo ante el cambio global” funded by Fundación Iberdrola, CGL2014-52599-P (IBERNIEVE) and CGL2017-82216-R (HIDROIBERNIEVE) funded by the Spanish Ministry of Economy and Competitiveness. ASV was supported by a pre-doctoral University Professor Training grant [FPU16/00902] funded by the Spanish Ministry of Education, Culture and Sports. EAG was supported by a pre-doctoral FPI grant [BES-2015-071466] funded by the Spanish Ministry of Economy and Competitiveness. JJC, AG and MC acknowledge funding by project RTI2018-096884-B-C31 (Spanish Ministry of Economy and Competitiveness).

In 2015, a new automatic weather station (AWS) was installed in a high elevation site in Gredos mountains (Central System, Spain). Since then, a surprisingly high number of heavy precipitation events have been recorded (55 days with precipitation over 50 mm, and a maximum daily precipitation of 446.9 mm), making this site a hotspot in Spain in terms of annual precipitation (2177 mm year) and extreme precipitation events. The neighboring stations available in the region with longer data series, including the closest ones, already informed of wet conditions in the area, but not comparable with such anomaly behavior detected in the new station (51% higher). In this study, we present the temporal variability of detected heavy precipitation events in this mountain area, and its narrow relation with atmospheric patterns over the Iberian Peninsula. Results revealed that 65% of the events occurred during advections from West, Southwest, South and cyclonic situations. A regression analysis showed that the precipitation anomaly is mostly explained by the location windward to the Atlantic wet air masses and the elevation. However, the variance explained by the models is rather low (average R for all events > 50 mm is 0.21). The regression models underestimate on average a 60% intensity of rainfall events. Oppositely, the high-resolution weather forecast model AROME at 0.025° was able to point out the extraordinary character of precipitation at this site, and the underestimation of observed precipitation in the AWS was about 26%. This result strongly suggests the usefulness of weather models to improve the knowledge of climatic extremes over large areas, and to improve the design of currently available observational networks., This study was funded by the Spanish Ministry of Economy and Competitiveness projects CGL2011- 27536/HID (HIDRONIEVE), CGL2014-52599-P (IBERNIEVE) and CGL2017-82216-R (HIDROIBERNIEVE). C. A-M. was supported by the Ramon y Cajal Fellowship (RYC-2017–22830).

An extraordinary convective rainfall event –unforeseen by most numerical weather prediction models– led to a devastating flash flood in the town of Sant Llorenç des Cardassar, eastern Mallorca, on 9th October 2018. Four people died inside the village, while the total death toll was of 13 and economic damages amounted to 91 M€. The observed flooded extension inside the town by the Copernicus Emergency Management Service –based on Sentinel-1 imagery– far exceeded the extension for a 500-year return period flood. This extreme event has been reconstructed by implementing an integrated flood modelling approach over the semi-arid and small-sized Ses Planes basin up to Sant Llorenç (23.4 km²). This procedure is based on three components: (i) generation of high spatial and temporal resolution radar-derived precipitation estimates; (ii) modelling of the hydrologic response based on post-flood peak discharge estimates; and (iii) hydraulic simulation and mapping of the affected areas based on high water marks. Radar-derived rainfall estimates and the simulated flooding extent and water depths highly correlate with observations. The hydraulic simulation has revealed that water reached a depth of 3 m at some points inside Sant Llorenç and that water velocity greatly increased at bridges’ locations close to the town centre. Even if the catastrophic flash flood was not a debris flow, the flood bore eroded enough material to change channel geomorphology. This study also highlights how the concurrence of the very low predictability of this type of extreme convective rainfall events and the very short hydrological response times typical of small Mediterranean catchments still challenges the implementation of early warning systems, which effectively reduce people’s exposure to flash flood risk in the region.

The Mediterranean basin has been characterized by intense human presence and landscape transformation for centuries. Recent land-use changes point to a general expansion of shrub and forest cover in low-productive mountain areas, especially in the countries on the northern side of the Mediterranean, as a consequence of farmland and grazing abandonment. However, strong urbanization and agriculture intensification are occurring in valleys and coastal areas, particularly on the southern and eastern rims of the basin that are affected by rapid population growth. Extensive revegetation on formerly cultivated land can reduce notably runoff generation and deep water percolation, with important consequences for freshwater supplies. The expansion of irrigated land and urban areas, often accompanied by tourism development, greatly increases water consumption, which may also lead to decline in river discharges and aquifer overexploitation. Projected future decline in the availability of freshwater resources and increased water demand, exacerbated by the present context of changes in climate conditions, make it urgent to establish sustainable land and water management strategies. These require deep understanding of the impact of land-use changes on water resources. Any significant advance in understanding the water cycle requires field observations and measurements accompanied by hydrological modeling approaches that simulate hydrological changes under different land-use and climate scenarios.

Rain-on-snow (ROS) events can trigger severe floods in mountain regions. There is high uncertainty about how the frequency of ROS events (ROS) and associated floods will change as climate warms. Previous research has found considerable spatial variability in ROS responses to climate change. Detailed global assessments have not been conducted. Here, atmospheric reanalysis data was used to drive a physically based snow hydrology model to simulate the snowpack and the streamflow response to climate warming of a 5.25 km2 virtual basin (VB) applied to different high mountain climates around the world. Results confirm that the sensitivity of ROS to climate warming is highly variable among sites, and also with different elevations, aspects and slopes in each basin. The hydrological model predicts a decrease in the frequency of ROS with warming in 30 out 40 of the VBs analyzed; the rest have increasing ROS. The dominant phase of precipitation, duration of snow cover and average temperature of each basin are the main factors that explain this variation in the sensitivity of ROS to climate warming. Within each basin, the largest decreases in ROS were predicted to be at lower elevations and on slopes with sunward aspects. Although the overall frequency of ROS drops, the hydrological importance of ROS is not expected to decline. Peak streamflows due to ROS are predicted to increase due to more rapid melting from enhanced energy inputs, and warmer snowpacks during future ROS.

Groundwater is one of the largest and most important sources of fresh water on many regions under Mediterranean climate conditions, which are exposed to large precipitation variability that includes frequent meteorological drought episodes, and present high evapotranspiration rates and water demand during the dry season. The dependence on groundwater increases in those areas with predominant permeable lithologies, contributing to aquifer recharge and the abundance of ephemeral streams. The increasing pressure of tourism on water resources in many Mediterranean coastal areas, and uncertainty related to future precipitation and water availability, make it urgent to understand the spatio-temporal response of groundwater bodies to precipitation variability, if sustainable use of the resource is to be achieved. We present an assessment of the response of aquifers to precipitation variability based on correlations between the Standardized Precipitation Index (SPI) at various time scales and the Standardized Groundwater Index (SGI) across a Mediterranean island. We detected three main responses of aquifers to accumulated precipitation anomalies: (i) at short time scales of the SPI ( 24 months). The differing responses were mainly explained by differences in lithology and the percentage of highly permeable rock strata in the aquifer recharge areas. We also identified differences in the months and seasons when aquifer storages are more dependent on precipitation; these were related to climate seasonality and the degree of aquifer exploitation or underground water extraction. The recharge of some aquifers, especially in mountainous areas, is related to precipitation variability within a limited spatial extent, whereas for aquifers located in the plains, precipitation variability influence much larger areas; the topography and geological structure of the island explain these differences. Results indicate large spatial variability in the response of aquifers to precipitation in a very small area, highlighting the importance of having high spatial resolution hydro-climatic databases available to enable full understanding of the effects of climate variability on scarce water resources.

This study demonstrated the usefulness of very long-range terrestrial laser scanning (TLS) for analysis of the spatial distribution of a snowpack, to distances up to 3000 m, one of the longest measurement range reported to date. Snow depth data were collected using a terrestrial laser scanner during 11 periods of snow accumulation and melting, over three snow seasons on a Pyrenean hillslope characterized by a large elevational gradient, steep slopes, and avalanche occurrence. The maximum and mean absolute snow depth error found was 0.5-0.6 and 0.2-0.3 m respectively, which may result problematic for areas with a shallow snowpack, but it is sufficiently accurate to determine snow distribution patterns in areas characterized by a thick snowpack. The results indicated that in most cases there was temporal consistency in the spatial distribution of the snowpack, even in different years. The spatial patterns were particularly similar amongst the surveys conducted during the period dominated by snow accumulation (generally until end of April), or amongst those conducted during the period dominated by melting processes (generally after mid of April or early May). Simple linear correlation analyses for the 11 survey dates, and the application of Random Forests analysis to two days representative of snow accumulation and melting periods indicated the importance of topography to the snow distribution. The results also highlight that elevation and the Topographic Position index (TPI) were the main variables explaining the snow distribution, especially during periods dominated by melting. The intra- and inter-annual spatial consistency of the snowpack distribution suggests that the geomorphological processes linked to presence/absence of snow cover act in a similar way in the long term, and that these spatial patterns can be easily identified through several years of adequate monitoring.

In this study temporal trends of 14 climate and snow parameters related to ski conditions were analyzed for 11 ski stations located in the central Pyrenees (Spain and Andorra). We also investigated whether there was a temporal association for the analyzed parameters, such that the occurrence in a particular year of good (or bad) climate or snow conditions as represented by one parameter was similarly reflected by the other parameters. The lack of reliable climate and snow measurements was overcome by the use of simulated climate data retrieved from a high resolution hindcast simulation available for the period 1960–2006. These data were also used as inputs for an energy and mass snow energy model to obtain snow series. The results showed trends in ski reliability parameters for the 1960–2006 period. The number of days having a snowpack deeper than 30 cm and 100 cm showed declines at low and mid altitudes. The start of the ski season appears progressively delayed for all stations, and the ski season shortened. The frequency of rainy days increased at 3 stations and decreased at 8, while the frequency of days having heavy snowfall increased at 8 stations and declined at 3. Days having potential for snowmaking declined at all stations. The number of days having a wind-chill

We analyze the temporal and spatial patterns of rain-on-snow (ROS) events during the last 4 decades in Switzerland and project the future occurrence of ROS events based on atmospheric warming under the A1B greenhouse gas emissions scenario. The results indicate that ROS events occur mainly during winter months at low elevations, and during summer months at high elevations. The solid/liquid precipitation ratio and the duration of the snowpack explain the spatio-temporal characteristics of ROS events. Observations indicate a trend towards a slight reduction in ROS events during the study period (1972−2012) due to decreasing rainfall, and a reduction in snowpack duration due to warming temperatures. However, increased warming may increase the frequency of ROS events in future decades, especially at high elevations (>2000 m) where the snowpack will still be present during most of the year, but liquid precipitation will become more frequent.

Climate warming is responsible for observed reduction in snowpack depth and an earlier and faster melt-out in many mountains of the Northern Hemisphere. Such changes in mountain hydroclimate could negatively affect productivity and tree growth in high-elevation forests, but few studies have investigated how and where recent warming trends and changes in snow cover influence forest growth. A network comprising 36 high-elevation Pinus uncinata forests was sampled in the NE Iberian Peninsula, mainly across the Spanish Pyrenees, using dendrochronology to relate tree radial growth to a detailed air temperature and snow depth data. Radial growth was negatively influenced by a longer winter snow season and a higher late-spring snowpack depth. Notably, the effect of snow on tree growth was found regardless the widely reported positive effect of growing-season air temperatures on P. uncinata growth. No positive influence of moisture from spring snowmelt on annual growth of P. uncinata was detected in sampled forests. Tall trees showed a lower growth responsiveness to snow than small trees. Decreasing trends in winter and spring snow depths were detected at most Pyrenean forests, suggesting that the growth of high-elevation P. uncinata forests can beneficiate for a shallower and of shorter duration snowpack associated with warmer conditions. However, water-limited sites located on steep slopes or on rocky substrates, with poor soil-water holding capacity, could experience drought stress because of early depleted snow-related soil moisture., This study was funded by the Spanish Ministry of Economy and Competitiveness [grant numbers CGL2014-52599-P (IBERNIEVE), CGL2017-82216-R (HIDROIBERNIEVE)]. A. Sanmiguel-Vallelado is supported by a University Professor Training grant [grant number FPU16/00902] funded by the Spanish Ministry of Education, Culture and Sport.

A set of 17 air temperature and relative humidity sensors were used to analyze the temporal variability of surface air temperature (Tair), wet bulb temperature (Twb), and daily snowmaking hours (SM, number of hours per day with Twb < − 2 °C), lapse rates, and the occurrence of thermal inversions at the Formigal ski resort (Spanish Pyrenees) from December to March during three consecutive ski seasons (2012–2013, 2013–2014, and 2014–2015). The Tair and Twb lapse rates showed strong hourly and daily variability, with both exhibiting almost identical temporal fluctuations. The Twb exhibited average lapse rates that were slightly steeper (− 5.2 °C/km) than those observed for Tair (− 4.9 °C/km). The less steep lapse rates and most thermal inversions were observed in December. Days having less (more) steep Tair and Twb lapse rates were observed under low (high) wind speeds and high (low) relative humidity and air pressure. The temporal dynamics of the SM lapse rates was more complex, as this involved consideration of the average Tair in the ski resort, in addition to the driving factors of the spatio-temporal variability of Twb. Thus, on a number of cold (warm) days, snowmaking was feasible at all elevations at the ski resort, independently of the slopes of the lapse rates. The SM exhibited an average daily lapse rate of 8.2 h/km, with a progressive trend of increase from December to March. Weather types over the Iberian Peninsula tightly control the driving factors of the Tair, Twb, and SM lapse rates (wind speed, relative humidity, and Tair), so the slopes of the lapse rates and the frequency of inversions in relation to elevation for the three variables are very dependent on the occurrence of specific weather types. The less steep lapse rates occurred associated with advections from the southeast, although low lapse rates also occurred during advections from the east and south, and under anticyclonic conditions. The steepest Tair and Twb lapse rates were observed during north and northwest advections, while the steepest rates for SM were observed during days of cyclonic circulation and advections from the northeast. © 2018, Springer-Verlag GmbH Austria, part of Springer Nature., This study was funded by the research project CGL2014-52599-P >Estudio del manto de nieve en la montaña española y su respuesta a la variabilidad y cambio climatico> (Ministry of Economy and Development, MINECO).

The Balearic Islands are a major Mediterranean tourist destination that features one of the greatest swimming pool densities within Europe. In this paper, standard meteorological data were combined with a diachronic swimming pool inventory to estimate water evaporation from swimming pools over the Balearic archipelago. Evaporation was estimated using an empirical equation designed for open-water surfaces. Results revealed a 32% increase in swimming pools&rsquo, water use by 2015. Evaporation from swimming pools added 9.6 L of water to touristic consumption per guest night and person, and represented 4.9% of the total urban water consumption. In 2015, almost 5 hm3 (5 billion L) were lost from pools across the Balearic Islands. In several densely urbanized areas, evaporative water loss from pools exceeded four million litres per square kilometre and year. The water needed to refill the total of 62,599 swimming pools and to counteract evaporative water loss is equivalent to 1.2 pools per year. Swimming pools have rapidly proliferated across the islands. We have expounded on this development in view of much-needed responsible water management across the islands.

This paper evaluates the response of streamflow in a Mediterranean medium-scaled basin under land-use and climate change scenarios and its plausible implication on the management of Boadella&ndash, Darnius reservoir (NE Spain). Land cover and climate change scenarios supposed over the next several decades were used to simulate reservoir inflow using the Regional Hydro-Ecologic Simulation System (RHESsys) and to analyze the future impacts on water management (2021&ndash, 2050). Results reveal a clear decrease in dam inflow (&minus, 34%) since the dam was operational from 1971 to 2013. The simulations obtained with RHESsys show a similar decrease (&minus, 31%) from 2021 to 2050. Considering the ecological minimum flow outlined by water authorities and the projected decrease in reservoir&rsquo, s inflows, different water management strategies are needed to mitigate the effects of the expected climate change.

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.

This work was supported by the projects “Creacion de una base de datos climatica de calidad para el estudio del cambio climatico de las montanas del Peru-COOPB20042” and ‘Test multisectorial y actividades demostrativas sobre el potencial desarrollo de sistemas de monitorizacion de sequias en tiempo real en la region del oeste de Sudamerica-I-COOP H2O 2013CD0006’, both funded by the CSIC (Spanish Research Council). We thank the Ecuador National Institute for Meteorology and Hydrology (Instituto Nacional de Meteorologia e Hidrologia, INAMHI) and the International Research Center on EL Nino (Centro Internacional para la Investigacion del Fenomeno de El Nino, CIIFEN) for providing and pre-processing the climate data used in this work. ASL was supported by the postdoctoral fellowship JCI-2012-12508.

Climate warming will reduce the duration of mountain snowpacks and spring runoff, impacting the timing, volume, reliability, and sources of water supplies to mountain headwaters of rivers that support a large proportion of humanity. It is often assumed that snow hydrology will change in proportion to climate warming, but this oversimplifies the complex non-linear physical processes that drive precipitation phases and snowmelt. In this study, snow hydrology predictions made using a physical process snow hydrology model for 44 mountains areas worldwide enabled analysis of how snow and hydrological regimes will respond and interact under climate warming. The results show a generalized decoupling of mountain river hydrology from headwater snowpack regimes. Consequently, most river hydrological regimes shifted from reflecting the seasonal snowmelt freshet to responding rapidly to winter and spring precipitation. Similar to that already observed in particular regions, this study confirms that the worldwide decline in snow accumulation and snow cover duration with climate warming is substantial and spatially variable, yet highly predictable from air temperature and humidity data. Hydrological regimes showed less sensitivity, and less variability in their sensitivity to warming than did snowpack regimes. The sensitivity of the snowpack to warming provides crucial information for estimating shifts in the timing and contribution of snowmelt to runoff. However, no link was found between the magnitude of changes in the snowpack and changes in annual runoff.

Glaciers in the inner tropics are rapidly retreating due to atmospheric warming. In Colombia, this retreat is accelerated by volcanic activity, and most glaciers are in their last stages of existence. There is general concern about the hydrological implications of receding glaciers, as they constitute important freshwater reservoirs and, after an initial increase in melting flows due to glacier retreat, a decrease in water resources is expected in the long term as glaciers become smaller. In this paper, we perform a comprehensive study of the evolution of a small Colombian glacier, Conejeras (Parque Nacional Natural de los Nevados) that has been monitored since 2006, with a special focus on the hydrological response of the glacierized catchment. The glacier shows great sensitivity to changes in temperature and especially to the evolution of the El Niño–Southern Oscillation (ENSO) phenomenon, with great loss of mass and area during El Niño warm events. Since 2006, it has suffered a 37 % reduction, from 22.45 ha in 2006 to 12 ha in 2017, with an especially abrupt reduction since 2014. During the period of hydrological monitoring (June 2013 to December 2017), streamflow at the outlet of the catchment experienced a noticeable cycle of increasing flows up to mid-2016 and decreasing flows afterwards. The same cycle was observed for other hydrological indicators, including the slope of the rising flow limb and the monthly variability of flows. We observed an evident change in the daily hydrograph, from a predominance of days with a purely melt-driven hydrograph up to mid-2016, to an increase in the frequency of days with flows less influenced by melt after 2016. Such a hydrological cycle is not directly related to fluctuations of temperature or precipitation; therefore, it is reasonable to consider that it is the response of the glacierized catchment to retreat of the glacier. Results confirm the necessity for small-scale studies at a high temporal resolution, in order to understand the hydrological response of glacier-covered catchments to glacier retreat and imminent glacier extinction.

Land use and climate change play a significant role in hydrological processes. This study assesses the impact of land use and climate change in a snow and glacier dominated high altitude watershed, located in the southwestern part of Switzerland. Climate projections until the middle of the 21st century were analyzed using a Regional Climate Model from the IPCC A1B scenario. Land use maps were created using Idrisi TAIGA land change modeler, based on historical changes over two time periods and transformed for future forecasting. Logistic regression was used to generate these maps containing the probability of change between two different land use categories. Subsequently, the allocation of the land use was based on a multi-objective land distribution. The semi-distributed hydrological model called the Soil and Water Assessment Tool (SWAT) was used for simulating streamflow. The analysis was done to assess the impact of streamflow in three time periods where 1981–2010 is considered as the observed period and the two other time periods from 2011 to 2025 and 2026–2050 are considered as the scenario periods. Flow Duration Curves (FDC) were generated to assess the impact of low and high streamflow periods. Our study shows a decrease in the summer peak flow and an early start of the melt driven peak flow. The major change observed in this study is the rising period of the hydrograph, i.e. in May and June an early shift is observed in the discharge. Independent analysis from land use change and climate change shows that the peak flow reduction occurs as a result of land use change, but the peak flow together with the timing of peak flow occurrence is also influenced by climatic change. The combined effect suggests a reduction of peak flow and early melt driven streamflow in the future. Information obtained from this study can be useful for water managers, especially for the hydropower based energy production sector in the Rhone watershed.

This work was supported by the projects ‘Creacion de una base de datos climatica de calidad para el estudio del cambio climatico de las montanas del Peru-COOPB20042’ and ‘Test multisectorial y actividades demostrativas sobre el potencial desarrollo de sistemas de monitorizacion de sequias en tiempo real en la region del oeste de Sudamerica- I-COOP H2O 2013CD0006’, both funded by the CSIC (Spanish Research Council). C. A-M was supported by the JCI-2011-10263 grant. A. S-L was supported as a postdoctoral fellow (2011 BP-B 00078 and JCI-2012-12508). Both funded by the Spanish Ministry of Economy.

This paper evaluates the response of stream flow and other components of the water balance to changes in climate and land use ina Pyrenean watershed. It further provides a measure of uncertainty in water resources forecasts by comparing the performance of two hydrological models: the Soil and Water Assessment Tool (SWAT) and Regional Hydro-ecological Simulation System(RHESSys). Regional climate model outputs for the 2021–2050 time frame and hypothetical (but plausible)land-use scenarios considering re-vegetation and wild fire processes were used as inputs to the models. Results indicate an overall decrease in river flows (up to 30%, depending on the combination of scenarios) when the scenarios are considered, except for the post-fire vegetation scenario, in which stream flows are simulated to increase (between 2% and 10%). However, the magnitude of these projections varies between the two models used, as SWAT tends to produce larger hydrological changes under climate change scenarios and RHESSys shows more sensitivity to changes in land cover. The final prediction will therefore depend largely on the combination of the land-use and climate scenarios and on the model used.

Unmitigated anthropogenic climate change is set to exacerbate current stresses on water resources management and creates the need to develop strategies to face climate change impacts on water resources, especially in the long term. Insufficient information on possible impacts on water availability limits the organization and promotion of efforts to adapt and improve the resilience and efficiency of water systems. To document the potential impacts of climate change in the region of Mendoza, Argentina, we perform a hydrological modeling of the Mendoza River watershed using a SWAT model and project climate change scenarios to observe hydrological changes. The results show the impact of higher temperature on glaciers as river flow increases due to glacier melting; at the same time, runoff decreases as precipitation is reduced. Furthermore, the runoff timing is shifted and an earlier melting becomes more important in more pronounced climate change scenarios. Scenarios show a reduction in water availability that ranges between 1 and 10%. An additional scenario under stronger climate change conditions without glaciers data shows a reduction of the river flow by up to 11.8%. This scenario would correspond to a future situation in which glaciers have completely melted. These situations would imply a reduction in the water availability and the possibility of future unsatisfied water uses, in particular for irrigation, which received most of the available water in Mendoza, on which agricultural activities and regional economy depends.

14 Pags., 4 Figs., We evaluated the response of the Earth land biomes to drought by correlating a drought index with three global indicators of vegetation activity and growth: vegetation indices from satellite imagery, tree-ring growth series, and Aboveground Net Primary Production (ANPP) records. Arid and humid biomes are both affected by drought, and we suggest that the persistence of the water deficit (i.e., the drought time-scale) could be playing a key role in determining the sensitivity of land biomes to drought. We found that arid biomes respond to drought at short time-scales; that is, there is a rapid vegetation reaction as soon as water deficits below normal conditions occur. This may be due to the fact that plant species of arid regions have mechanisms allowing them to rapidly adapt to changing water availability. Humid biomes also respond to drought at short time-scales, but in this case the physiological mechanisms likely differ from those operating in arid biomes, as plants usually have a poor adaptability to water shortage. On the contrary, semiarid and subhumid biomes respond to drought at long time-scales, probably because plants are able to withstand water deficits, but they lack the rapid response of arid biomes to drought. These results are consistent among three vegetation parameters analyzed and across different land biomes, showing that the response of vegetation to drought depends on characteristic drought time-scales for each biome. Understanding the dominant time-scales at which drought most influences vegetation might help assessing the resistance and resilience of vegetation and improving our knowledge of vegetation vulnerability to climate change., This work was supported by projects financed by the Spanish Commission of Science and Technology (CGL2011-27574-CO2-02, CGL2011-27536 and CGL2011-26654) and the Aragón Government. C.G. and R.T. were supported by Project MEDIATIC (PTDC/AAC-CLI/103361/2008) funded by the Portuguese Foundation for Science and Technology (FCT). J.J.C. thanks the support of ARAID and A.S-L. was supported by a postdoctoral fellowship from the Generalitat de Catalunya (2009 BP-A 00035).

The mountain cryosphere is recognized to have important impacts on a range of environmental processes. This paper reviews current knowledge on snow, glacier, and permafrost processes, as well as their past, current and future evolution in mountain regions in mainland Europe. We provide a comprehensive assessment of the current state of cryosphere research in Europe and point to the different domains requiring further research to improve our understanding of climate–cryosphere interactions, cryosphere controls on physical and biological mountain systems, as well as related impacts. We highlight advances in the modeling of the cryosphere, and identify inherent uncertainties in our capability of projecting changes in the context of a warming global climate.

The Pyrenees constitute one of the greatest sources of freshwater in the Spanish territory, but, like many other mountain systems in the world, they are subject to environmental changes that ultimately affect the availability of water resources in areas downstream. In this study, we offer an assessment of hydrological changes in the Pyrenees, from a warming climate perspective, including climate and snow cover trends, changes in the timing of river flows, and future changes under climate change scenarios. Overall, we found that increasing temperatures are responsible for a lesser accumulation of snow over time, although with spatial differences. As a consequence, the occurrence of spring flows (that largely depend on snowmelt) on the studied rivers, has shifted earlier by approximately one month (from mid-June to mid-May). Future projections, which are made by coupling regional climate models outputs and hydrological modelling, indicate that observed decrease in snow accumulation and shifts in streamflow timing will exacerbate in a warmer short-term future (2050). The amount of water yields will not change significantly, only will suffer a slight decrease due to increased evapotranspiration. Observed and projected hydrological changes must be considered by water managers and environmental technicians if a sustainable management of the water resource and the mountain territory is to be done.

48 Pags.- 1 Tabl.- 18 Figs. The definitive version is available at: http://link.springer.com/journal/382, In this study, we analyzed the influence of El Niño–Southern Oscillation (ENSO) on the spatio-temporal variability of droughts in Ecuador for a 48-year period (1965–2012). Droughts were quantified from 22 high-quality and homogenized time series of precipitation and air temperature by means of the Standardized Precipitation Evapotranspiration Index. In addition, the propagation of two different ENSO indices (El Niño 3.4 and El Niño 1 + 2 indices) and other atmospheric circulation processes (e.g., vertical velocity) on different time-scales of drought severity were investigated. The results showed a very complex influence of ENSO on drought behavior across Ecuador, with two regional patterns in the evolution of droughts: (1) the Andean chain with no changes in drought severity, and (2) the Western plains with less severe and frequent droughts. We also detected that drought variability in the Andes mountains is explained by the El Niño 3.4 index [sea surface temperature (SST) anomalies in the central Pacific], whereas the Western plains are much more driven by El Niño 1 + 2 index (SST anomalies in the eastern Pacific). Moreover, it was also observed that El Niño and La Niña phases enhance droughts in the Andes and Western plains regions, respectively. The results of this work could be crucial for predicting and monitoring drought variability and intensity in Ecuador., This work was supported by the EPhysLab (UVIGO-CSIC Associated Unit) and the research projects I-COOP H2O 2013CD0006: “Test multisectorial y actividades demostrativa sobre el potencial desarrollo de sistemas de monitorización de sequías en tiempo real en la región del oeste de Sudamérica” financed by the Spanish National Research Council, CGL2011-27574-CO2-02, CGL2014-52135-C03-01 and Red de variabilidad y cambio climático RECLIM (CGL2014-517221-REDT), financed by the Spanish Commission of Science and Technology and FEDER, and “LIFE12 ENV/ES/000536-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. Cesar Azorin-Molina was supported by the JCI-2011-10263 Grant. Arturo Sanchez-Lorenzo was supported by the JCI-2012-12508 Grant. Miquel Tomas-Burguera was supported by a doctoral grant by the Ministry of Economy and Competitiveness and Natalia Martin-Hernandez was supported by a doctoral grant by the Aragón Regional Government. E. Aguilar was funded by the Grant CCI-009-ATN/OC-12439-RG-2012 from the Banco Iberoamericano de Desarrollo.

16 páginas.- Ilustraciones.- 3 apéndices al final del documento.- © Higher Education Press and Springer-Verlag Berlin Heidelberg 2017., The purpose of this study was to characterize mountain river regimes in the Spanish Pyrenees and to assess the importance of snow accumulation and snowmelt on the timing of river flows. Daily streamflow data from 9 gauging stations in the Pyrenees were used to characterize river regimes. These data were analyzed by hydrological indices, with a focus on periods when snow accumulation and snowmelt occurred. These results were combined with data on Snow Water Equivalent (SWE) (from measurements of depth and density of snow in the main river basins and also simulated by a process-based hydrological model), snowmelting (simulated by a process-based hydrological model), precipitation (from observations), and temperature (from observations). Longitude and elevation gradients in the Pyrenees explain the transition of river regimes from those that mostly had low nival signals (in the west and at low elevations) to those that mostly had high nival signals (low winter runoff and late spring peakflow, in the east and at high elevations). Although trend analyses indicated no statistically significant changes, there was a trend of decreased nival signal over time in most of the analyzed rivers. Our results also demonstrated that snow processes cannot explain all of the interannual variability of river regimes, because the temporal distribution of liquid precipitation and temperature play key roles in hydrography., This study was funded by the research project CGL2014-52599-P, "Estudio del manto de nieve en la montana espanola y su respuesta a la variabilidad y cambio climatico" from the Spanish Ministry of Economy and Competitiveness. The authors thank the ERHIN program for providing the snow data used in this study.

In this study, the spatio-temporal variability and trends of droughts across Bolivia between 1955 and 2012 were investigated using two climate drought indices: the Standardized Precipitation Index (SPI), which is based on precipitation data, and the Standardized Precipitation Evapotranspiration Index (SPEI), which is based on the difference between the precipitation and the reference evapotranspiration (ETo). We found that the average drought conditions across the country showed a temporal behaviour mainly characterized by decadal variations. The spatial pattern of drought evolution showed marked differences between the Amazonian region and the Bolivian Altiplano. Both regions showed different drought periods, a lower frequency of drought variability in the Amazon region and trends towards drier conditions in the Altiplano, mainly due to a higher atmospheric water demand as a consequence of increased ETo. We also showed that inclusion of ETo, obtained from maximum and minimum temperature records, increased the spatial heterogeneity of the drought evolution in relation to the evolution observed when only precipitation droughts were considered. The SPEI, the calculation of which includes precipitation and ETo, indicated intensification in drought severity in the last years analysed relative to the pattern found when precipitation droughts alone were considered, and also indicated an increase in the magnitude and duration of drought events. The potential for increasing drought conditions under various climate change scenarios is discussed.

This study was supported by the research projects Hidrologia nival en el Pirineo Central Espanol: Variabilidad espacial, importancia hidrologica y respuesta a la variabilidad y cambio climatico (CGL2011-27536/HID, Hidronieve) and CGL2011-27753-C02-01, financed by the Spanish Commission of Science and Technology and FEDER; CTTP1/12 ‘Creacion de un modelo de alta resolucion espacial para cuantificar la esquiabilidad y la afluencia turistica en el Pirineo bajo distintos escenarios de cambio climatico’, financed by the Comunidad de Trabajo de los Pirineos; and 844/2013 ‘El glaciar de Monte Perdido: Monitorizacion y estudio de su dinamica actual y procesos criosfericos asociados como indicadores de procesos de cambio global’, financed by MAGRAMA, National Parks. SRFs and GASs time were funded by the NASA Terrestrial Hydrology Program entitled ‘Improved Characterization of Snow Depth in Complex Terrain Using Satellite Lidar Altimetry’ (Grant # NNX11AQ66G led by PI Dr. M.F. Jasinski).

We analyzed 19 annual Landsat Thematic Mapper images from 1984 to 2011 to determine changes of the glaciated surface and snow line elevation in six mountain areas of the Cordillera Huaytapallana range in Peru. In contrast to other Peruvian mountains, glacier retreat in these mountains has been poorly documented, even though this is a heavily glaciated area. These glaciers are the main source of water for the surrounding lowlands, and melting of these glaciers has triggered several outburst floods. During the 28-year study period, there was a 55% decrease in the surface covered by glaciers and the snowline moved upward in different regions by 93 to 157. m. Moreover, several new lakes formed in the recently deglaciated areas. There was an increase in precipitation during the wet season (October-April) over the 28-year study period. The significant increase in maximum temperatures may be related to the significant glacier retreat in the study area. There were significant differences in the wet season temperatures during El Niño (warmer) and La Niña (colder) years. Although La Niña years were generally more humid than El Niño years, these differences were not statistically significant. Thus, glaciers tended to retreat at a high rate during El Niño years, but tended to be stable or increase during La Niña years, although there were some notable deviations from this general pattern. Climate simulations for 2021 to 2050, based on the most optimistic assumptions of greenhouse gas concentrations, forecast a continuation of climate warming at the same rate as documented here. Such changes in temperature might lead to a critical situation for the glaciers of the Cordillera Huaytapallana, and may significantly impact the water resources, ecology, and natural hazards of the surrounding areas. © 2013 Elsevier B.V., This work was supported by funding from the Spanish Research Council (research project I-COOP0089: “Glacier retreat in the Cordillera Blanca and Cordillera Huaytapallana in Peru: Evidences and Impacts on local population”)

[1] In this study, we assess the role of altitude in determining the relative performance of temperature and precipitation as predictors of snowpack variability in Switzerland. The results indicate a linear relationship between altitude and the correlation of temperature (precipitation) with snowpack depth and duration. We identify a threshold altitude of approximately 1400 m a.s.l. ( 200 m, depending on the snow index considered), below which temperature is the main explanatory variable and above which precipitation is a better predictor of snowpack variability. The results also highlight that as climate warms, the altitude at which temperature is the main constraint on snow accumulation increases. This has important implications for the future viability of snowdependent economic sectors in Switzerland, where projections indicate a continuous warming during the course of the 21st century. Citation: Moran-Tejeda, E., J. I. Lopez-Moreno, and M. Beniston (2013), The changing roles of temperature and precipitation on snowpack variability in Switzerland as a function of altitude, Geophys. Res. Lett., 40, doi:10.1002/grl.50463.

We thank the Agencia Estatal de Meteorologia for providing the temperature data used in this study. This work was supported by the research projects CGL2011-27574-CO2-02 and CGL2011-27536, financed by the Spanish Commission of Science and Technology and FEDER; and ACQWA (FP7-ENV-2007-1-212250), financed by the VII Framework Programme of the European Commission; Efecto de los escenarios de cambio climatico sobre la hidrologia superficial y la gestion de embalses del PirineoAragones, financed by Obra Social La Caixa and the Aragon Government and Influencia del cambioclimatico en el turismo de nieve CTTP01/10, financed by the Comunidad de Trabajo de los Pirineos.