The application of terrestrial laser scanner and SfM photogrammetry in measuring erosion and deposition processes in two opposite slopes in a humid Badlands area (Central Spanish Pyrenees)

Erosion and deposition processes in badland areas are usually estimated using traditional observations of topographic changes, measured by erosion pins or profile metres (invasive techniques). In recent times, remote-sensing techniques (non-invasive) have been routinely applied in geomorphology studies, especially in erosion studies. These techniques provide the opportunity to build high-resolution topographic models at centimetre accuracy. By comparing different 3-D point clouds of the same area, obtained at different time intervals, the variations in the terrain and temporal dynamics can be analysed. The aim of this study is to assess and compare the functioning of terrestrial laser scanner (TLS, RIEGL LPM-321) and structure-from-motion photogrammetry (SfM) techniques (Camera FUJIFILM, Finepix x100 and software PhotoScan by AgiSoft) to evaluate erosion and deposition processes in two opposite slopes in a humid badlands area in the central Spanish Pyrenees. Results showed that TLS data sets and SfM photogrammetry techniques provide new opportunities in geomorphological erosion studies. The data we recorded over 1 year demonstrated that north-facing slopes experienced more intense and faster changing geomorphological dynamics than south-facing slopes as well as the highest erosion rates. Different seasonal processes were observed, with the highest topographic differences observed during winter periods and the high-intensity rainfalls in summer. While TLS provided the highest accuracy models, SfM photogrammetry was still a faster methodology in the field and precise at short distances. Both techniques present advantages and disadvantages, and do not require direct contact with the soil and thus prevent the usual surface disturbance of traditional and invasive methods

Análisis de la variabilidad espacio-temporal de las precipitaciones en el sector Español de la cuenca del Duero (1961-2005)

En este trabajo se estudia la variabilidad espacio-temporal y la tendencia de las precipitaciones (1961-2005, n=45) en el sector español de la cuenca del Duero mediante el análisis de series homogéneas de datos mensuales y anuales correspondientes a un total de 214 estaciones. Los resultados obtenidos muestran una acusada variabilidad estacional, interanual y espacial de las precipitaciones, lo que impide la observación de tendencias estadísticamente significativas, tanto en las series mensuales como anuales. Sólo en el mes de febrero se detectó una tendencia negativa significativa en gran parte del territorio de la cuenca. Con algunos matices, los resultados del análisis confirman la ausencia de tendencias claras observadas en Europa meridional durante la segunda mitad del siglo XX y primeros años del siglo XXI. This work focuses on the spatial and temporal variability of precipitation in the Spanish sector of the Duero basin, for the period 1961-2005 (n=45), and the analysis of temporal trends. Results highlight a marked variability on the seasonal, inter-annual and spatial basis, which usually mask the existence of trends at the monthly and annual scale. Thus, only February shows a negative and significant trend across most of the territory, while annual precipitation has remained rather stationary at the long-term. These results confirm, with few exceptions, the absence of significant trends of precipitation in Southern Europe during the second half of the 20th century

Evaluating observed versus predicted forest biomass: R-squared, index of agreement or maximal information coefficient?

The accurate prediction of forest above-ground biomass is nowadays key to implementing climate change mitigation policies, such as reducing emissions from deforestation and forest degradation. In this context, the coefficient of determination ($${R^2}$$) is widely used as a means of evaluating the proportion of variance in the dependent variable explained by a model. However, the validity of $${R^2}$$ for comparing observed versus predicted values has been challenged in the presence of bias, for instance in remote sensing predictions of forest biomass. We tested suitable alternatives, e.g. the index of agreement ($$d$$) and the maximal information coefficient ($$MIC$$). Our results show that $$d$$ renders systematically higher values than $${R^2}$$, and may easily lead to regarding as reliable models which included an unrealistic amount of predictors. Results seemed better for $$MIC$$, although $$MIC$$ favoured local clustering of predictions, whether or not they corresponded to the observations. Moreover, $${R^2}$$ was more sensitive to the use of cross-validation than $$d$$ or $$MIC$$, and more robust against overfitted models. Therefore, we discourage the use of statistical measures alternative to $${R^2}$$ for evaluating model predictions versus observed values, at least in the context of assessing the reliability of modelled biomass predictions using remote sensing. For those who consider $$d$$ to be conceptually superior to $${R^2}$$, we suggest using its square $${d^2}$$, in order to be more analogous to $${R^2}$$ and hence facilitate comparison across studies

Thinning of the Monte Perdido Glacier in the Spanish Pyrenees since 1981

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

Climate, irrigation, and land cover change explain streamflow trends in countries bordering the northeast Atlantic

Attribution of trends in streamflow is complex, but essential, in identifying optimal management options for water resources. Disagreement remains on the relative role of climate change and human factors, including water abstractions and land cover change, in driving change in annual streamflow. We construct a very dense network of gauging stations (n = 1,874) from Ireland, the United Kingdom, France, Spain, and Portugal for the period of 1961–2012 to detect and then attribute changes in annual streamflow. Using regression‐based techniques, we show that climate (precipitation and atmospheric evaporative demand) explains many of the observed trends in northwest Europe, while for southwest Europe human disturbances better explain both temporal and spatial trends. For the latter, large increases in irrigated areas, agricultural intensification, and natural revegetation of marginal lands are inferred to be the dominant drivers of decreases in streamflow

Evaluación de acolchados para el control de la flora arvense en un cultivo de tomate: dos años de resultados

En el presente proyecto se estudian alternativas al uso de acolchado plástico con polietileno, el cual es un residuo de difícil gestión tanto en producción hortícola ecológica como en convencional. Durante los años 2006 y 2007 se han llevado a cabo diez ensayos de campo en tomate de industria regado por goteo en cinco distintos lugares de España. Se han ensayado diferentes materiales biodegradables: dos plásticos biodegradables (Mater-Bi y Biofilm), un plástico oxobiodegradable (Enviroplast), dos papeles (papel negro Mimcord y marrón Saikraft), un acolchado de paja de cebada y dos testigos (sin desherbar y con control manual de las malas hierbas). Todas las películas fueron colocadas con máquina acolchadora, y los papeles requirieron un ajuste especial para evitar roturas. En todas las localidades y en ambos años el control de la flora arvense fue bueno o muy bueno para todos los acolchados, menos para la paja. Respecto al rendimiento de tomate, éste fue muy similar para todos los acolchados en ambos años, aunque ligeramente inferior que para el polietileno. En algunas localidades fue difícil mantener la paja en el suelo debido a su dispersión con el viento, mientras que en otras se mantuvo durante todo el ciclo. A pesar del peor control de la flora arvense, la paja dio buenos rendimientos en algunas localidades. El plástico oxobiodegradable mostró un comportamiento muy irregular entre localidades en cuanto a su degradación y cabe destacar la ausencia de degradación de la parte enterrada en todos los casos. Los plásticos biodegradables se degradaron de forma correcta cuando el cultivo ya cubría parte del suelo. El papel Mimcord fue más elástico permitiendo una más fácil colocación en el suelo pero es sensiblemente más caro que el marrón. En 2007 el rendimiento fue ligeramente menor para el papel marrón en 2007, posiblemente debido a que se trató de un año más frío. Los diferentes materiales biodegradables y el papel negro han sido los tratamientos más productivos y que mejor han controlado la flora arvense. Se concluye que existen alternativas técnicamente viables para sustituir el acolchado con polietileno en el cultivo de tomate de industria. No obstante, el elevado coste de la mayoría de estos materiales es el principal factor limitante para su adopción.Publishe

Evaluación de acolchados para el control de la flora arvense en un cultivo de tomate

Publishe

A first-principles approach to electrical transport in atomic-scale nanostructures

We present a first-principles numerical implementation of Landauer formalism for electrical transport in nanostructures characterized down to the atomic level. The novelty and interest of our method lies essentially on two facts. First of all, it makes use of the versatile Gaussian98 code, which is widely used within the quantum chemistry community. Secondly, it incorporates the semi-infinite electrodes in a very generic and efficient way by means of Bethe lattices. We name this method the Gaussian Embedded Cluster Method (GECM). In order to make contact with other proposed implementations, we illustrate our technique by calculating the conductance in some well-studied systems such as metallic (Al and Au) nanocontacts and C-atom chains connected to metallic (Al and Au) electrodes. In the case of Al nanocontacts the conductance turns out to be quite dependent on the detailed atomic arrangement. On the contrary, the conductance in Au nanocontacts presents quite universal features. In the case of C chains, where the self-consistency guarantees the local charge transfer and the correct alignment of the molecular and electrode levels, we find that the conductance oscillates with the number of atoms in the chain regardless of the type of electrode. However, for short chains and Al electrodes the even-odd periodicity is reversed at equilibrium bond distances.Comment: 14 pages, two-column format, submitted to PR

The influence of climate and land-cover scenarios on dam management strategies in a highwater pressure catchment in Northeast Spain

Altres ajuts: EU LIFE (LIFE12ENV/ES/000536)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-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 (2021-2050). Results reveal a clear decrease in dam inflow (-34%) since the dam was operational from 1971 to 2013. The simulations obtained with RHESsys show a similar decrease (-31%) from 2021 to 2050. Considering the ecological minimum flow outlined by water authorities and the projected decrease in reservoir's inflows, different water management strategies are needed to mitigate the effects of the expected climate change