Publication list

Navas A., Machín J., Beguería S., López-Vicente M., Gaspar. L. (in press). Soil properties and physiographic factors controlling the natural vegetation re-growth in a disturbed catchment of the Central Spanish Pyrenees. Agroforestry Systems. [abstract]

Since the Middle Age, a large mountainous region across the southern portion of the Central Pyrenees in Spain has undergone changes in land use. Those anthropogenic impacts affected soil quality, which threatens the sustainability of agroecosystems in the region. In this study, a soil survey was performed to identify the soil types and the physico-chemical properties of the soil that are relevant to the maintenance of soil function for the recovery of vegetation in a mountain catchment that is representative of the region. In the Arnás River catchment, the highest CEC, nutrients, water retention, water availability, and infiltration rates, and the lowest pH and carbonates occurred in Lithic Hapludolls and Calcic Haploxerolls on forest slopes that had a northerly aspect. Lithic Ustochrepts and Lithic Xerorthents on sunny aspect slopes, which were covered by shrubs, were of lesser quality than were the deeper and better-developed soils on the northeast-facing forest slopes, which indicated different patterns of soil degradation and re-growth of natural vegetation in recent years. The results provide insights into the main soil factors that affect the re-establishment of natural vegetation. Recommendations are given for designing effective strategies for soil conservation where lands are abandoned in areas that are similar to these mountain environments.

Pueyo Y., Beguería S. (in press). Modelling the rate of secondary succession after farmland abandonment in a Mediterranean mountain area: the role of abiotic factors. Landscape and Urban Planning, DOI: 10.1016/j.landurbplan.2007.04.008. [abstract] [pdf]

Secondary succession after farmland abandonment has become a common process in north Mediterranean countries, specially in mountain areas. In this paper a methodology is tested which combines Markov chains and logistic multivariate regression to model secondary succession after farmland abandonment in environments where abiotic constraints play a major role, like mountain areas. In such landscapes a decay in the succession rate with time is usually found, as the best locations are progressively occupied. This is frequently addressed using non-stationary Markov chains. The combination of logistic multivariate regression with Markov chains, however, allows for spatially distributed transitions probabilities based on abiotic factors and therefore it is able to reproduce the preferential colonization of the most favourable locations. As a result, the decay in the succession rate can be successfully modelled. The model is tested in the Ijuez valley in the Spanish Pyrenees, which undergone generalised land abandoned during the 50s, but the method is applicable to any area where vegetation dynamics are constrained by environmental factors.

López-Moreno J.I., Beguería S., Vicente-Serrano S.M., García-Ruiz J.M. (2007). The influence of the NAO on water resources in Central Iberia: precipitation, streamflow anomalies and reservoir management strategies. Water Resources Research 43, W09411, doi:10.1029/2007WR005864. [abstract] [pdf]

This paper analyses the influence of the extreme phases of the winter North Atlantic Oscillation (NAO) on water resources in the Spanish region of the Tagus River basin. By analysing a winter NAO index based on station sea level pressure, the years between 1957 and 2003 were classified as normal, positive, and negative NAO years. A statistical test was then applied to monthly data series for precipitation, river discharge, reservoir storage, and reservoir release to analyse the variations in these variables. For all four variables, significant differences were found between positive and negative NAO years, the former resulting in reduced water availability (negative anomalies), and the latter in increased water availability (positive anomalies). The influence of extreme NAO winters was found to act with different time lags on different variables: the effect of extreme NAO winters on precipitation was found to be quite immediate (and significant for December to March), but this effect was observed later in the year and lasted longer for river discharge, reservoir storage, and water release. Positive and negative NAO years were also found to have different effects on these variables, in that the effects of positive years were more sustained and those of negative years were more rapid and less prolonged. In spite of the high variability of the availability of water resources, the strategies for management of the reservoir system of the basin were found in most cases to provide a regular supply that meets water demands. However, our results also indicate that these water management practises are not adequate for the expected scenarios of climate change and increasing water demand.

Bathurst J.C., Moretti G., El-Hames A., Beguería S., García-Ruiz J.M. (2007). Modelling the impact of forest loss on shallow landslide sediment yield, Ijuez river catchment, Spanish Pyrenees. Hydrology and Earth System Sciences, 11(1):569—583. [abstract]

The SHETRAN model for simulating the sediment yield arising from shallow landslides at the scale of a river catchment was applied to the 45—km2 Ijuez catchment in the central Spanish Pyrenees, to investigate the effect of loss of forest cover on landslide and debris flow incidence and on catchment sediment yield. The application demonstrated how such a model, with large parameter evaluation requirements, can be used even when directly measured data are not available: rainfall and discharge time series were generated by reference to other local records and data providing the basis for a soil map were obtained by a short field campaign. Uncertainty bounds for the outputs were determined as a function of the uncertainty in the values of key model parameters. For a four-year period and for the existing forested state of the catchment, a good ability to simulate the observed long term spatial distribution of debris flows (represented by a 45—year inventory) and to determine catchment sediment yield within the range of regional observations was demonstrated. The lower uncertainty bound on simulated landslide occurrence approximated the observed annual rate of landsliding and suggests that landslides provide a relatively minor proportion of the total sediment yield, at least in drier years. A scenario simulation in which the forest cover was replaced by grassland indicated an increase in landsliding but a decrease in the number of landslides which evolve into debris flows and, at least for drier years, a reduction in sediment delivery to the channel network.

Lana-Renault N., Regüés D., Martí-Bono C., Beguería S., Nadal E., Serrano P., García-Ruiz J.M. (2007). Temporal variability in the relationships between precipitation, discharge and suspended sediment concentration in a Mediterranean mountain catchment. Nordic Hydrology, 38(2):139—150. [abstract] [pdf]

Relationships between discharge and suspended sediment are very complex in most Mediterranean catchments. In the case of the Arnás catchment (Central Spanish Pyrenees), with a long history of human activity, the main factors that explain the variability of suspended sediment concentration (SCC) during floods are the peak flow, the intensity of precipitation and the antecedent base flow. A cluster analysis distinguishes four types of floods according to different characteristics of precipitation, discharge, suspended sediment transport and antecedent moisture conditions. G1 and G2 floods occur under dry conditions (that prevail most of the year), with moderate rainfall and low precipitation intensity; the discharge and suspended sediment response is very fast but limited in intensity. This suggests that the origin of water and sediment is restricted to areas located very close to the channel. G3 floods also occur under dry conditions, although during intense rainfall events; then the response in both discharge and suspended sediment is very high, showing an enlargement of the contributing areas and the splash effect due to the intensity of precipitation. Under very wet conditions (G4 floods) relatively moderate precipitation produces a very high response in discharge, but suspended sediment concentration records moderate values due to the effect of dilution when the entire catchment is contributing.

López-Moreno J.I., Beguería S., García-Ruiz J.M. (2006). Trends on high flows in the Central Spanish Pyrenees: response to climatic factors or to land-use change?, Hydrological Sciences Journal, publ. scheduled for December 2006, vol. 51(6): 1039—1050 [abstract] [pdf]

This paper analyses the evolution of high flows in the Central Spanish Pyrenees during the period 1955—1995. The method applied makes it possible to assess whether the contribution of the largest daily discharge and rainfall events to the total annual runoff and precipitation remains stationary or shows any temporal trend. The results show a general negative trend in flood intensity in the last decades, together with an increase in the importance of low flows in the total annual contribution. However, a change in the frequency distribution of precipitation events has not been detected. The different behaviour shown by runoff and precipitation could only be explained as being due to the increase in plant cover that is a consequence of the farmland abandonment and reforestation that occurred during the 20th century.

Beguería S. (2006). Identifying erosion areas at basin scale using remote sensing data and GIS. International Journal of Remote Sensing, 20: 4585—4598. [abstract] [pdf]

The inventory and monitoring of eroded areas at basin (Mm2) scale can be a very useful tool for environmental planning that can help to reduce land degradation and sediment yield to streams. The combined use of remotely sensed data and auxiliary geocoded information has been widely used for mapping different environmental features, including surface erosion. Here an example is presented in the Yesa reservoir catchment in the Spanish Pyrenees. Different combinations of radiometric data (a sequence of images from different seasons of the year) and other geocoded information, including topographical (altitude and slope) and geological maps, were analysed using multinomial logistic regression to predict previously identified erosive features. One of the main goals was discriminating between resistant, little erodible rock outcrops and highly erodible rock outcrops, in which the most part of the erosive morphologies were found. The different classification models were compared in terms of classification error statistics. The addition of auxiliary information enhanced the discrimination of the eroded areas, but also led to some sampling problems, apart from the higher cost of obtaining the new information. A final map of eroded areas was obtained by using multitemporal remotely sensed data and the geological map.

Beguería S., López-Moreno J.I., Gómez-Villar A., Rubio V., Lana-Renault N., García-Ruiz J.M. (2006). Fluvial adjustments to soil erosion and plant cover changes in the Central Spanish Pyrenees. Geografiska Annaler series A - Physical Geography, 88A(3): 177—186. [abstract] [pdf]

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.

Lasanta T., Beguería S., García-Ruiz J.M. (2006). Geomorphic and hydrological effects of traditional shifting agriculture in a Mediterranean mountain, Central Spanish Pyrenees. Mountain Research and Development, 26(2): 146—152. [abstract] [pdf]

Shifting agriculture occupied large areas of middle latitude mountains during periods of strong demographic pressure. On average, this practice accounted for about 22.8% of the total cultivated area in the Central Spanish Pyrenees at the beginning of the 20th century. The use of experimental plots between 1992 and 2003 demonstrated that shifting agriculture increased overland flow, suspended sediment and solute concentration. Total soil loss was about 14 times higher under shifting agriculture than under dense shrub cover, and almost 3 times higher than permanent sloping fields. Erosion rates ranged between 0.1 and 1.4 t yr-1. The abandonment of shifting practices resulted in rapid plant recolonization and a decrease in runoff and soil erosion. Nevertheless, severe geomorphic processes are still active several decades after abandonment, explaining landscape degradation and the triggering of shallow landslides.

Beguería S., Vicente-Serrano S.M. (2006). Mapping the hazard of extreme rainfall by peaks-over-threshold extreme value analysis and spatial regression techniques. Journal of Applied Meteorology and Climatology, 45(1): 108—124. [abstract] [pdf]

This paper analyses fifty-year time series of daily precipitation in a region of the middle Ebro valley (northern Spain) in order to predict extreme dry-spell risk. A comparison of observed and estimated maximum dry spells (50-year return period) showed that the Generalised Pareto (GP) distribution combined with partial duration series (PDS) gives better results than the Gumbel distribution fitted to annual maximum series (AMS) Indeed, the classical Gumbel approach underestimated the empirical duration of dry spells. The PDS/GP approach was successfully applied in the study of extreme hydro-climatic variable values. The results reported here could be applied in estimating climatic drought risks in other geographical areas.

Beguería S. (2006). Changes in land cover and shallow landslide activity: A case study in the Spanish Pyrenees. Geomorphology, 74(1—4): 196—206. [abstract] [pdf]

The Pyrenees, like many other mountain areas in Europe, have experienced depopulation and land abandonment during the 20th Century. This has encouraged vegetation recovery in formerly occupied areas, including reforestation to promote woodland. The objective of this study is to analyse the effects of these changes on shallow landsliding, a process responsible for erosion and land degradation in many mountain areas. A sequence of aerial images reveals a slight decrease in the landslide occurrence rate in the last half of the 20th Century and a parallel increase in the landslide extinction rate, i.e. the rate at which evidence of landslide activity is removed by vegetation colonisation. A logistic regression routine was used to assess the influence of land use and vegetation recovery in the occurrence of shallow landslides. The result shows that the former arable fields on the valley slopes still facilitate landsliding, even after land abandonment and revegetation by shrubs or trees. A shift in the topographic location of landslides was also detected, pointing to an increased importance of water redistribution in the slopes after prolonged rainfall periods.

Beguería S. (2006). Validation and evaluation of predicitive models in hazard assessment and risk management. Natural Hazards, 37(3): 315—329. [abstract] [pdf]

The paper deals with the validation and evaluation of mathematical models in natural hazard analysis, with a special focus on establishing their predictive power. Although most of the tools and statistics available are common to general classification models, some peculiarites arise in the case of hazard assessment. This is due to the fact that the target for validation, the propensity to develop a dangerous characteristic, is not really known and must be estimated from a (usually) very small sample. This implies that the two types of errors (false positives and false negatives) should be given different meanings. Related to this, a very frequent situation is the presence of prevalence (different proportion of positive and negative cases) in the sample. It is shown that sample prevalence can have a dramatic effect in some very common validation statistics, like the confusion matrix and model efficiency. Here some statistics based on the confusion matrix are presented and discussed, and the use of threshold-independent approaches (especially the ROC plot) is shown. The ROC plot is also proposed as a convenient tool for decision-taking in a risk management context. A general scheme for hazard predictive modeling is finally proposed.

Beguería S. (2005). Uncertainties in partial duration series modelling of extremes related to the choice of the threshold value. Journal of Hydrology, 303(1—4): 215—230. [abstract] [pdf]

Partial duration series modelling is a robust tool with which to model hydrologic extremes, but because of several technical problems it remains underused. The most important obstacle is the choice of the threshold value, a matter that is currently under investigation by several authors. The truncation value affects the basic assumptions of the model, including arrival times and exceedance magnitudes. This paper considers changes in parameter and quantile estimates as a function of the threshold value (sampling variability) Simulated and real data were used to test the consistency of the model, and a new modelling procedure based on increasing threshold censoring is proposed to overcome these problems. Poisson arrivals and Generalized Pareto exceedances were assumed, and the suitability of this model at different threshold values has been also addressed.

López-Moreno J.I., Beguería S., García-Ruiz J.M. (2004). The management of a large Mediterranean reservoir: Storage regimes of the Yesa Reservoir, upper Aragón river basin, Central Spanish Pyrenees. Environmental Management, 34(4): 508—515. [abstract] [pdf]

Historical and present day changes in land use and plant cover explain the complex interactions assessed in the Central Spanish Pyrenees between geomorphic processes in hillslopes and channels. More intense erosion periods caused an enlargement of sediment source areas and an increase of sediment supply toward the rivers, characterized by braided channels. A sharp difference existed between the human-induced eroded areas and the rest of the territory, which shows moderate erosion rates. Farmland abandonment in the last few decades has reduced the sediment sources, thus decreasing both sediment delivery and streamflow, as a consequence of plant colonization of the old fields. Fluvial channels also show a decreasing torrential activity over the 20th century.

García-Ruiz J.M., Arnáez J., Beguería S., Seeger M., Martí-Bono C., White S. (2005). Runoff generation in an intensively disturbed, abandoned farmland catchment, Central Spanish Pyrenees. Catena, 59(1): 79—92. [abstract] [pdf]

This paper studies the hydrological response to rainstorm events of a small experimental catchment in the Central Spanish Pyrenees. The Arnás catchment was cultivated until 40 years ago, and then abandoned and affected by plant recolonisation, especially shrubs. A rainfall of a few mm is enough to produce a sudden increase in discharge, due most probably to the steep gradients and the small size of the catchment and the extensive areas with low vegetation density and thin soils. The intensity of the response shows a very high variability, depending on the intensity of precipitation and soil humidity conditions before the flood. This paper identifies two types of floods according to the relationships between precipitation and discharge, and confirms that antecedent soil moisture explains much of the response. The shape of the hydrograph, very similar to the hyetograph, suggests that the Arnás catchment is dominated by overland flow processes. However, more intense rainstorms do not generate higher peak flows, thus demonstrating the existence of different runoff generating areas.

Seeger M., Errea M.P., Beguería S., Arnáez J., Martí C., García-Ruiz J.M. (2004). Catchment soil moisture and rainfall characteristics as determinant factors for discharge/suspended sediment hysteretic loops in a small headwater catchment in the Spanish pyrenees. Journal of Hydrology, 288(3—4): 299—311. [abstract] [pdf]

The concentration of suspended sediment and discharge generated during flood events are not normally homogenous, and the curve representing sediment concentration vs. discharge through time is often a hysteretic loop. Three types of hysteretic loops were found at Arnás, a Mediterranean headwater catchment in the Central Spanish Pyrenees: clockwise (the most frequent) counter-clockwise and eightshaped. They are associated with different levels of humidity and rainfall and therefore indicators of different processes of runoff and sediment transport. Clockwise loops are generated under “normal” stormflow conditions, when the catchment is very moist and runoff generation and sediment supply is limited to areas next to the channel (i.e., sediments are removed, transported and depleted rapidly) Counter-clockwise curves occur under very high moisture and high antecedent rainfall conditions. In this case, flood propagation occurs as a kinematic wave. Sediment sources are incorporated all over the catchment. In both cases, saturation excess overland flow generates the superficial runoff. The eight-shaped loop (partial clockwise followed by counterclockwise) occurs with low water content. Here, the runoff generation process is supposed to be infiltration excess overland flow, which causes a rapid extension of the contributing areas both near the channel and over the whole catchment.

Beguería S., López-Moreno J.I., Lorente A., Seeger M., García-Ruiz J.M. (2003). Assessing the Effect of Climate Oscillations and Land-use Changes on Streamflow in the Central Spanish Pyrenees'. Ambio, 32(4): 283—286. [abstract] [pdf]

Plans to increase the amount of irrigated land in Mediterranean countries should consider how changes in climate and land-use affect water resources. In this study, both precipitation and temperature were used to analyze regional trends in discharge in the basins of the Central Spanish Pyrenees since the mid-20th century. Annual variations in the relationship between precipitation and discharge suggested that discharge was relatively lower in the second half of the study period, coinciding with major changes in land use. On a monthly scale, precipitation increased significantly in October, April, and July, and decreased in March, and temperature increased in January and February and decreased in April. Nevertheless, discharge has decreased significantly in most months in the past 50 years. Land-use and plant-cover changes are the only nonclimatic factor that can explain the loss of around 30% of the average annual discharge.

Vicente-Serrano S., Beguería-Portugués S. (2003). Estimating extreme dry-spell risk in the Middle Ebro valley (Northeastern Spain). a comparative analysis of partial duration series with a General Pareto distribution and annual maxima series with a Gumbel distribution. International Journal of Climatology, 23(9): 1103—1118. [abstract] [pdf]

This paper analyses fifty-year time series of daily precipitation in a region of the middle Ebro valley (northern Spain) in order to predict extreme dry-spell risk. A comparison of observed and estimated maximum dry spells (50-year return period) showed that the Generalised Pareto (GP) distribution combined with partial duration series (PDS) gives better results than the Gumbel distribution fitted to annual maximum series (AMS) Indeed, the classical Gumbel approach underestimated the empirical duration of dry spells. The PDS/GP approach was successfully applied in the study of extreme hydro-climatic variable values. The results reported here could be applied in estimating climatic drought risks in other geographical areas.

López-Moreno J.I., Beguería S., García-Ruiz J.M. (2002). Influence of the Yesa reservoir on floods of the Aragón River, Central Spanish Pyrenees. Hydrology and Earth System Sciences, 6(4): 753—762. [abstract]

The Yesa reservoir, the largest Pyrenean reservoir, was constructed in 1959 to supply water to new irrigated areas in the Ebro Depression, NE Spain. It is filled from October to May-June and then releases large quantities of water in the summer via the Bardenas Canal. The results confirm that the frequency of floods downstream of the dam decreased. The reduction mainly depends on two factors: i) the water storage level, and ii) the season of the year. Floods are very well controlled when the reservoir level is lower than 50%. Between 50 and 70%, only the highest floods are controlled. Finally, the reservoir retains mainly autumn and spring floods; most winter floods are released downstream to ensure the safety of the dam.

Lorente A., Beguería S., Bathurst J.C. y García-Ruiz J.M. (2003). Debris flow characteristics and relationships in the Central Spanish Pyrenees. Natural Hazards and Earth System Sciences, 3(6): 683—691. [abstract] [pdf]

Unconfined debris flows (i.e., not in incised channels) are one of the most active geomorphic processes in mountainous areas. Since they can threaten settlements and infrastructure, statistical and physically based procedures have been developed to assess the potential for landslide erosion. In this study, information on debris flow characteristics was obtained in the field to define the debris flow runout distance and to establish relationships between debris flow parameters. Such relationships are needed for building models which allow us to improve the spatial prediction of debris flow hazards. In general, unconfined debris flows triggered in the Flysch Sector of the Central Spanish Pyrenees are of the same order of magnitude as others reported in the literature. The deposition of sediment started at 17.8º, and the runout distance represented 60% of the difference in height between the head of the landslide and the point at which deposition started. The runout distance was relatively well correlated with the volume of sediment.

García-Ruiz J.M., Martí-Bono C., Lorente A., Beguería S. (2002). Geomorphological consequences of frequent and infrequent pluviometric and hydrological events in a Mediterranean mountain area. Mitigation and adaptation strategies for global change, 7(3): 303—320. [abstract] [pdf]

Intense rainfall events are a major trigger for flooding and landslides throughout regions with a Mediterranean climate. They create problems for settlements and infrastructures built across their paths. Changes in landuse have also been important in increasing or decreasing the intensity of the flood problem and the mobility of land surface materials, especially changes in the intensity of grazing on mountain pastures or historical deforestation and recent reforestation. This paper focuses on the rainfall thresholds that distinguish common events from rare, hazardous events. During the last few years, rainstorms of different intensities have occurred in the Central Spanish Pyrenees, including one of exceptional character. Large, historical debris flows have been studied, as well as the actual sediment transport in small experimental catchments. This study shows that during the most frequent events suspended sediment transport is the common geomorphic process. River bedload is mobilized in river channels several times per year, while small rock avalanches and channelized debris flows have a return period of at least 5 years. Hillslope debris flows are triggered by rainfall events with a 25—30 year return period. Reactivation of large, deep mass movements is linked to rainfalls of around 100 year return period (between 130 and 160 mm in 24 hours) Catastrophic geomorphic processes occur when precipitation exceeds a 100 year return period, as was the case of the Biescas campsite disaster. Geomorphic processes triggered by intense rainfall events have caused major damages and human disasters but the hazards have been reduced by the introduction of several control measures, including reforestation, the construction of check-dams, canalization of river segments and improved flood forecasting.

Lorente A., García-Ruiz J.M., Beguería S., Arnáez J. (2002). Factors explaining the spatial distribution of hillslope debris flows. A case study in the flysch sector of the Central Spanish Pyrenees. Mountain Research and Development, 22(1): 32—39. [abstract]

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

García-Ruiz J.M., Valero-Garcés B., González-Sampériz P., Lorente A., Martí-Bono C., Beguería S., Edwards L. (2001). Stratified scree in the Central Spanish Pyrenees: Palaeoenvironmental implications. Permafrost and Periglacial Processes, 12(3): 233—242. [abstract]

Sedimentological, geomorphological and palynological study of three stratified screes from two environments in the central Spanish Pyrenees allows reconstruction of climate and vegetational change since the last glacial maximum. In both localities (at 700 and 1000 m a.s.l.) the deposits show a similar stratigraphy: (i) a basal stratified scree, in one case fossilized by speleothems; (ii) a palaeosol, with abundant charcoal and evidence of human activity; and (iii) a massive coarse scree. The stratified scree developed during the glacial maximum and late glacial. A humid period during the early Holocene was characterized by speleothem formation and carbonate cementation in some screes. Forest fires around 3300 BP were widespread in the Pyrenees and were probably related to human impact. Recent scree reactivation due to an increase in clast supply is limited to cold stages during the late Holocene.

García-Ruiz J.M., Arnáez J., White S.M., Lorente A., Beguería S. (2000). Uncertainty assessment in the prediction of extreme rainfall events: an example from the Central Spanish Pyrenees. Hydrological Processes, 14(5): 887—898. [abstract]

Extreme rainfall events occur frequently in the central Pyrenees, but they are responsible for mass movements and short, very intense erosion periods, accompanied at times by loss of human life and high costs of infrastructure. This paper tries to assess the existence of patterns in the spatial distribution of maximum precipitation. The calculation of return periods of the most intense rainfall demonstrates that in the Pyrenees it exhibits an erratic spatial and temporal distribution and can be extremely localized. In the case of precipitation between 150 and 200 mm in 24 h, some influence from the surrounding relief has been found, but this is not the case for precipitation exceeding 200 mm, characterized by the absence of patterns governing their spatial distribution. Geomorphological approaches are, therefore, the only way for assessing the areas more subject to hydromorphological risks

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Vicente-Serrano S., Beguería S., Lasanta T. (In press). Diversidad espacial de la actividad vegetal en el pirineo central español: análisis de los procesos de sucesión mediante imágenes landsat (1984—2001). Pirineos.

López Moreno J.I., Beguería S., García Ruiz J.M. (2003). Efecto de los embalses en el control de avenidas en el Pirineo Central Español. Geographicalia, 44: 57—74.

López Moreno J.I., Beguería S., Valero Garcés B., García Ruiz J.M. (2002). Intensidad de las avenidas y aterramiento de embalses en el Pirineo Central Español. Ería, 61: 159—167.

López Moreno J.I., Beguería S., García Ruiz J.M. (2002). El régimen del río Ésera, Pirineo aragonés, y su tendencia reciente. Boletín glaciológico aragonés, 3: 131—162.

López Moreno J.I., Beguería S., García Ruiz J.M. (2002). Floods downstream the Yesa Reservoir. Cuadernos de investigación geográfica, 28: 101—108

González-Sampériz P., Valero- Garcés B., Marti C., García-Ruiz J.M., Lorente A., Beguería S. (2001). Holocene environmental change in the Upper Gállego valley (western Spanish Pyrenees). climate, environment and human impact. Terra Nostra, 2001(2): 37—41.

Valero-Garcés B.L., Marti C., García-Ruiz J.M., González-Sampériz P., Lorente A., Beguería S. , Navas A., Machin J., Delgado-Huertas A., Stevenson T., Davis B. (2001). Lateglacial and Early Holocene paleohydrological and environmental change along a humid-arid transect from the Central Pyrenees to the Ebro valley (Spain) Terra Nostra, 2001/3: 211—218.

López I., Beguería S., García Ruiz J.M. (2000). El régimen del embalse de Yesa (cuenca alta del río Aragón, Pirineo Central) y su adaptación a la variabilidad del régimen fluvial. Cuadernos de Investigación Geográfica, 26: 131—145.

García Ruiz J.M., Martí Bono C., Arnáez Vadillo J., Beguería Portugués S., Lorente Grima A., Seeger M. (2000). Las cuencas experimentales de Arnás y San Salvador en el Pirineo Central Español: escorrentía y transporte de sedimento. Cuadernos de Investigación Geográfica, 26: 23—40.

Lorente A., Martí C., Beguería S., Arnáez J., García Ruiz J.M. (2000). La exportación de sedimento en suspensión en una cuenca de campos abandonados, Pirineo central. Revista Cuaternario y Geomorfología, 14(1—2): 21—34.

García Ruiz J.M., Beguería S., Lorente A. (2000). Eventos hidrológicos de baja frecuencia en el Pirineo central español y sus efectos geomorfológicos. Serie Geográfica, 9: 163—176.

Beguería S., Lorente A. (1999). Distribución espacial del riesgo de precipitaciones extremas en el Pirineo aragonés occidental. Geographicalia, 37: 17—36.

Arnáez J., Martí C., Beguería S., Lorente A., Errea M. P., García Ruiz, J. M. (1999). Factores en la generación de crecidas en una cuenca de campos abandonados, Pirineo central español. Cuadernos de investigación geográfica, 7: 7—24.

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Beguería S. (2005). Erosión y fuentes de sedimento en la cuenca del embalse de Yesa (Pirineo Occidental). Ensayo de una metodología basada en teledetección y análisis SIG, Instituto Pirenaico de Ecología, Zaragoza, 148 p., CD-ROM, ISBN 84—921842—6—4.

Beguería S. (2003). Identificación y caracterización de las fuentes de sedimento en áreas de montaña: Erosión y transferencia de sedimento en la cuenca alta del río Aragón, Tesis Doctoral, Universidad de Zaragoza, Zaragoza, 439 p. y 8 mapas, ISBN 84—96214—10-9.

García-Ruiz J.M., Beguería S., López-Moreno J.I., Lorente A., Seeger M. (2001). Los recursos hídricos superficiales del Pirineo aragonés y su evolución reciente, Geoforma ediciones, Logroño, 192 p., ISBN 84—87779—31—X.

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Beguería S., López-Moreno J.I., Lana-Renault N., Nadal-Romero E., Serrano-Muela P., Latron J., Regüés-Muñoz D., Lasanta T., Martí-Bono C., García-Ruiz J.M. (2006). Global Change and Water Resources in the Mediterranean Mountains: Threats and Opportunities, in E. Kulke, H. Monheim, P. Wittmann (eds.), GrenzWerte. Tagungsbericht und wissenschaftliche Abhandlungen. 55 Deutscher Geographentag - Trier 2005, Deutsche Gesellschaft für Geographie, Berlin-Leipzig-Trier, ISBN 3—9808754—2—3, p. 641—650. [abstract] [pdf]

The Department of Geoenvironmental Processes and Global Change (DGPGC) at the Pyrenean Institute of Ecology – CSIC (Spanish Council for Scientific Research) has been doing research on Environmental Hydrology at various spatial and temporal scales since 1990. Hydrological consequences of land cover change in mountain headwaters have proved to be complex and scale dependent. At plot scale, abandonment of traditional cultivation practices in the valley slopes had the consequence of decreasing runoff production and soil erosion and sediment yield, which were more pronounced as the revegetation process progressed. At catchment scale the differences are smaller, because part of the water that infiltrates into the soils in the vegetated areas reappears later in lower parts of the catchment. An important effect of revegetation at catchment scale is the attenuation of the catchment's response to any precipitation event (except the most extreme ones), resulting in less torrential behaviour. A decrease in total water yield has also been observed in the long term evolution (1945—1995) of discharge series in the Central Pyrenees basins, during a period in which no significant decrease of precipitation has been recorded. We attribute this trend to the process of revegetation after farmland abandonment. Changes have been found also on the monthly discharge regimen, as well as on the frequency of high flows, which decreased during the studied period. All this changes have increased the stress on water resources management, as shown by changes in reservoir management practices. We question whether we will be able to satisfy water demands in the near future, considering expected changes in climate and land cover, and we show the importance of increasing research effort on water resources in global change scenarios.

Seeger M., Errea M.P., Lana-Renault N., Beguería S., Arnáez J., Martí C., Regüés D., García-Ruiz J.M. (2005). Charakteristika des Sedimenttransports in einem Kleineinzugsgebiet der Aragonesischen Pyrenäen. In Schmidt, K.H., Becht, M., Brunotte, E., Eitel, B., Schrott, L. (eds.) Geomorphology in Environmental Application (Mountain Geomorphology, Mass Movements, Fluvial Geomorphology). Zeitschrift für Geomorphologie supl., 138: 211—228. [abstract] [pdf]

Characteristics of sediment transport in a small catchment in the Spanish Pyrenees. The transport of suspended sediment during a stormflow event is very variable. The resulting hysteretic loop of the relationship of the discharge and suspended sediment concentration is used in the present paper to classificate rainfall-runoff-events and identify by canonical discriminant analysis the factors determining the different event types. The analysis of 19 events in a headwater catchment of the Central Pyrenees leads to the identification of 3 types of floods. A majoritary with clockwise shaped hysteretic loop, a second one with anti-clockwise shaped hysteretic loop and a third group with eight shaped hysteretic loop. The most important factor for generating different types of events is the soil moisture in the catchment. On a secondary level, total rainfall amount and precipitation of the 3 days before are important. So, the different flood types are generated with different contributing areas or by different processes. Clockwise shaped events have limited sources of suspended sediment near the channel with limited supply. Anti clockwise shaped events lead sediments from all over the catchment to the ravine. Eight-shaped events are produced under dry conditions, when rainfall intensity exceeds infiltration capacity, so sediments sources may be localised all over the catchment, but their conection to the fluvial network is stoped rapidly with decreasing precipitation.

García-Ruiz J.M., Lasanta T., Valero B., Martí C., Beguería S., López-Moreno J.I. (2004). Soil erosion and runoff generation related to land use changes in mountain areas, en U. Huber, H.K.M. Bugmann y M.A. Reasoner (eds.) Global change and mountain regions. An overview of current knowledge. Springer, Dordrecht (Países Bajos) 321—330.

García-Ruiz J.M., Lana-Renault N., Beguería S., Valero-Garcés B., Arnáez J., López-Moreno J.I., Regüés D., Martí C. (2004). Temporal and spatial interactions of slope and catchment processes in the Central Spanish Pyrenees. In Valentin Golosov, Vladimir Belyaev, Des E. Walling (eds.) Sediment Transfer Through The Fluvial System. IAHS Publications, 288: 21—28. [abstract] [pdf]

Historical and present day changes in land uses and plant cover explain the complex interactions assessed in the Central Spanish Pyrenees between geomorphic processes in hillslopes and channels. More intense erosion periods caused an enlargement of sediment sources areas and an increase of sediment supply toward the rivers, characterized by braided channels. A sharp difference existed between the human-induced eroded areas and the rest of the territory, which shows moderate erosion rates. Farmland abandonment in the last few decades has reduced the sediment sources, thus decreasing both sediment delivery and streamflow, as a consequence of plant colonization of the old fields. Fluvial channels also show a decreasing torrential activity.

Ollero A., Sánchez M., Marín J.M., Fernández D., Ballarín D., Mora D., Montorio R., Beguería S., Zúñiga M. (2004). Caracterización hidromorfológica del río Gállego, en J.L. Peña, L.A. Longares y M. Sánchez (eds.) Geografía Física de Aragón. Aspectos generales y temáticos, Universidad de Zaragoza e Institución Fernando el Católico, Zaragoza, pp. 117—129.

López-Moreno J.I., Beguería S., García-Ruiz, J. M. (2004). Laminación y estacionalidad de avenidas en los embalses pirenaicos. Riesgos naturales y antrópicos en geomorfología, en G.Benito y A. Díez Herrero (eds.) Actas de la VII reunión nacional de Geomorfología, Madrid, Sociedad Española de Geomorfología, pp. 70-78.

López-Moreno J.I., Beguería S., García-Ruiz J.M. (2004). Tendencias espacio-temporales en la intensidad de avenidas en el Pirineo Central, en G.Benito y A. Díez Herrero (eds.) Actas de la VII reunión nacional de Geomorfología, Madrid, Sociedad Española de Geomorfología, pp. 79—87.

García-Ruiz J.M., Lasanta T., Valero B., Martí C., Beguería S., López-Moreno J.I. (2004). Soil erosion and runoff generation related to land use changes in mountain areas, en U. Huber (ed.) Global Change and Mountain Regions, Suiza.

Seeger M., Beguería S. (2003). La respuesta hidrológica en dos cuencas experimentales con diferentes usos del suelo en el Pirineo Aragonés - Das hydrologische Verhalten zweier kleiner Einzugsgebiete mit unterschiedlicher Nutzungsgeschichte und intensität in den Aragonesischen Pyrenäen, en I. Marlzoff, J. de la Riva y M. Seeger (eds.) Landnutzungswandel und Landdegradation in Spanien - El cambio en el uso del suelo y la degradación del territorio en España, Zaragoza, Johann Wolfgang Goethe Universität - Frankfurt am Main y Universidad de Zaragoza, pp. 203—221.

Beguería S., López Moreno J.I., Lorente A., Seeger M., García Ruiz J.M. (2002). Cambios en las relaciones entre factores climáticos y recursos hídricos en el Pirineo central español, en L.A. Longares Aladrén y J.L. Peña Monné (eds.) Aportaciones geográficas en memoria del profesor L. Miguel Yetano Ruiz, Zaragoza, Universidad de Zaragoza, pp. 47—54.

Beguería S. (2002). Revisión de métodos paramétricos para la estimación de la probabilidad de ocurrencia de eventos extremos en Climatología e Hidrología: El uso de series de excedencias y su comparación con las series de máximos anuales, en J.M. Cuadrat, S.M. Vicente y M.A. Saz (eds.) La información climática como herramienta de gestión ambiental, Zaragoza, Universidad de Zaragoza, 2002, pp. 83—92. [pdf]

Vicente S.M., Beguería S. (2002). Estimación del riesgo de ocurrencia de sequías extremas a partir de series de excedencias y distribución General Pareto: aplicación al valle medio del río Ebro, en J.M. Cuadrat, S.M. Vicente y M.A. Saz (eds.) La información climática como herramienta de gestión ambiental, Zaragoza, Universidad de Zaragoza, 2002, pp. 137—144.

Lorente A., Beguería S. (2002). Variation saisonniere de l'intensité des précipitations maximales dans les Pyreneées Centrales: Analyse spatiale et cartographique, en C. Kergomard (ed.) Publications de la Association Internationale de Climatologie, Vol. 14, Aix-en-Provence, 327—334.

Arnáez J., Beguería S., Martí C., Lorente A., García-Ruiz J.M. (2002). Avenidas y transporte de sedimento en cuencas con diferente cubierta vegetal. Estudio experimental en el Pirineo Central Español, en A. Pérez-González, J. Vegas y M.J. Machado (eds.) Aportaciones a la Geomorfología de España en el Inicio del Tercer Milenio, Madrid, Instituto Geológico y Minero de España - Sociedad Española de Geomorfología, pp. 227—234.

García-Ruiz J.M., Lorente A., González P., Valero B., Martí-Bono C., Beguería S. (2002). El mega-slump de Biescas-Arguisal, Pirineo Central, y su posible contexto temporal, en A. Pérez-González, J. Vegas y M.J. Machado (eds.) Aportaciones a la Geomorfología de España en el Inicio del Tercer Milenio, Madrid, Instituto Geológico y Minero de España - Sociedad Española de Geomorfología, pp. 507—516.

Lorente A., Beguería S., Arnáez J., García-Ruiz J.M. (2002). Distribución de coladas de piedras de ladera (hillslope debris flows) en el Pirineo central español, en A. Pérez-González, J. Vegas y M.J. Machado (eds.) Aportaciones a la Geomorfología de España en el Inicio del Tercer Milenio, Madrid, Instituto Geológico y Minero de España - Sociedad Española de Geomorfología, pp. 517—524.

López-Moreno J.I., Beguería S., García-Ruiz J.M. (2002). Floods downstream the Yesa reservoir, Spanish Pyrenees, en J.M. García-Ruiz, J.A.A. Jones y J. Arnáez (eds.) Environmental change and water sustainability, Zaragoza, Instituto Pirenaico de Ecología, pp. 305—312.

García Ruiz J.M., Martí Bono C., Valero B., González P., Lorente A., Beguería S., Edwards L. (2000). Derrubios de ladera en el Pirineo Central español: significación cronológica y paleoclimática, en J. L. Peña Monné et al. (eds.) Procesos y formas periglaciares en la montaña mediterránea, Instituto de Estudios Turolenses, 63—79, Teruel.

Vicente S., Beguería S., Lasanta T. (2000). El proceso de revegetación en un área de montaña como consecuencia de los cambios de gestión: aplicación de un SIG al valle de Borau (Pirineo Central Español) en I. Aguado y M. Gómez (eds.) Tecnologías Geográficas para el Desarrollo Sostenible, Alcalá de Henares (Madrid) Departamento de Geografía - Universidad de Alcalá, pp. 448—469.

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Beguería S., Lorente A. (2002). Landslide hazard mapping by multivariate statistics: comparison of methods and case study in the Spanish Pyrenees, 20 pp. DAMOCLES project deliverables. [pdf]

Lorente A., Beguería S., García-Ruiz J.M. (2002). Debris flow relationships in the Central Spanish Pyrenees, 14 p. DAMOCLES project deliverables. [pdf]

García-Ruiz J.M., Beguería S., Lorente A, Martí C. (2002). Comparing debris flow relationships in the Alps and the Pyrenees, 10 p. DAMOCLES project deliverables. [pdf]

Beguería S. (2001). Estudio bibliométrico de la producción científica de los jóvenes investigadores en España (A bibliometric analysis of the scientific production of Young Researchers in Spain), 17 pp (in Spanish) Report on the results of a survey about the scientific production of young researchers in Spain. www.precarios.org.

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