Análisis fractal de caudales de ríos

[ES] El análisis fractal se está convirtiendo en una herramienta para el estudio de datos experimentales que, en muchos casos, van a estar ligados a fenómenos naturales. El estudio de los caudales de ríos es un claro ejemplo de series temporales que pueden ser interpretadas desde una perspectiva fractal. En este trabajo se ha procedido a la determinación del exponente de Hurst para distintos aforos del río Ebro a lo largo de su curso, utilizando dos procedimientos de cálculo diferentes. Se ha llevado a cabo también un estudio fractal fundamental para verificar la dependencia funcional de las desviaciones acumuladas de caudal en función del intervalo temporal utilizado para la observación. En el caso de la determinación del exponente de Hurst no se han encontrado tendencias definidas en función de la situación de las estaciones de aforo. Por el contrario, el estudio del comportamiento fractal de las desviaciones acumuladas indica una fuerte influencia de las infraestructuras de regulación deMahamud López, M. (2004). Análisis fractal de caudales de ríos. Ingeniería del agua. 11(2):191-199. https://doi.org/10.4995/ia.2004.2527OJS191199112Burgos, T.R. y Pérez, E. (1999). Estimation of the Fractal Dimension of a Rainfall Time Series over a Zone Relevant to the Agriculture in Havana. SOMETCUBA Bulletin, 5(1). Edición on-line.Fadeev, A.Y., Borisova, O.R. y Lisichin, G.V. (1996). Fractality of Porous Silicas: A Comparison of Adsorption and Porosimetry data. Journal of Colloid and Interface Science, 183: 1-5.Feder, J. (1998). Fractals. Plenum Press, Nueva York.Friesen, W.I. y Mikula, R.J. (1987). Fractal Dimensions of Coal Particles. J. Colloid Interface Sci., 120(1): 263-271.Hurst, H.E., Black, R.P. y Simaika, Y.M. (1965). Long Term Storage: An Experimental Study. Constable, Londres.Mahamud, M. (2002). El Análisis Fractal en Ingeniería Ambiental. Ingeniería Química. (En prensa).Mandelbrot, B.B. (1975). Les Objects Fractals: Forme, Hasard et Dimension. Flammarion, París.Mandelbrot, B.B. (1977). The Fractal Geometry of Nature. W.H. Freeman, Nueva York.Miranda, J.G.V. y Andrade, R.F.S. (1999). Rescaled Range Analysis of Pluviometric Records in Notheast Brazil. Theor. Appl. Climatolol. 63, 79-88.North, C.P. y Halliwell, D.I. (1994). Bias in Estimating Fractal Dimension with the Rescaled-Range (R/S) Technique. Mathematical Geology, 26(5), 531-555.Oñate Rubalcaba, J.J. (1997). Fractal Análisis of Climatic Data: Annual Precipitation Records in Spain. Theor. Appl. Climatolol., 56, 83-87.Pfeifer, P. y Avnir, D. (1983). Chemistry in Noninteger Dimensions between Two and Three. I. Fractal Theory of Heterogeneous Surfaces. Journal of Chemical Physics, 79(7), 3558-3565.Rao, A.R. y Bhattacharya, D. (2001). Effect of Short-Term Memory on Hurst Phenomenon. Journal of Hydrologic Engineering, marzo/abril, 125-131.Turcotte, D.L. (1994). Fractal Theory and the Estimation of Extreme Floods. J. Res. Natl. Inst. Stand. Technol., 99, 377-389

Learning from the past to address the future. Environmental challenges of Spanish agriculture in the 21st century: a look from the legacy of Fernando González Bernáldez

Based on the pioneering reflections of González Bernáldez at the end of the 1980s on the environmental consequences of agricultural intensification and abandonment, we review the changes experienced by the Spanish agriculture up to the present in environmental issues, identifying some of the future challenges. First, we review the progressive integration of environmental and territorial aspects in the European Common Agricultural Policy (CAP), as well as Spain's response in terms of adoption and implementation of its main instruments: Conditionality on direct payments and Agri-environmental measures. The CAP reforms have not counteracted the effects of agricultural intensification, to which the severe negative trends observed in the main agri-environmental indicators, analyzed here for the period 1989-2020, can be related. The new governance model introduced by the CAP 2023-2027, focused on results, is expected to contribute decisively to the objectives of the "European Climate Law" and the "Farm to Fork" and "Biodiversity 2030" strategies; however, doubts persist about its transformative potential. Finally, we review the main contributions of Agroecology, Organic Agriculture, Sustainable Intensification and Ecological Intensification, which can help in the transition towards a more sustainable and resilient agriculture. The actions of the CAP aimed at producers must pursue the multifunctional redesign of the agroecosystems, through payments for environmental services that make them sufficiently attractive and profitable as González Bernáldez suggested three decades ag

The impact of ideological positions and personal attributes of candidates in intraparty competition: a study under the swiss open-list PR system

Intraparty preference voting systems offer different incentives for candidates to cultivate a personal vote, but little is known about how the candidates' policy positions affect their elec-toral success in intraparty competition. This article analyses the effect of candidates' ideological positions and personal attributes on their preference vote share in the 2015 and 2019 Swiss Lower House elections. We used candidate survey data combined with official election statistics. Our findings demon-strate that the ideological distance between candidates' posi-tions and their party's median position is of minor importance for their electoral success when compared to their personal attributes. However, ideological distance between candidates and their party's median position reduce their preference vote share

Assessing vulnerability of functional diversity to species loss: a case study in Mediterranean agricultural systems

"This is the peer reviewed version of the following article: Functional Ecology 31.2 (2017): 427-435, which has been published in final form at https://doi.org/10.1111/1365-2435.12709. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions"Increasing land-use intensification is leading to biodiversity losses world-wide, which can reduce the functioning of ecosystems. However, it is increasingly clear that not all species are equally important for ecosystem processes: whereas the loss of a functionally unique species may reduce the capacity of the community to perform some functions, losing a functionally redundant species should have a much smaller impact. Assessing the vulnerability of functional diversity (FD) to species extinctions can help to predict the impacts of land-use intensification. This approach consists in ranking species according to their risk of extinction and then estimating the trajectory followed by FD as species are lost from local communities. However, the most widely used FD indices are not independent of species richness, being much more sensitive to the loss of species in species-poor than in species-rich sites. This may result in misleading interpretations, affecting our ability to rank communities according to the vulnerability of their FD to species loss, by confounding it with the initial level of species richness. Here, we propose comparing the trajectory of FD under the most plausible order of species loss with that followed under random species losses as an effective way to remove the trivial effect of species richness in the assessments of vulnerability to species loss. After decoupling vulnerability from species richness, we used it to analyse the effect of agricultural intensification on the vulnerability of arable plant communities in Mediterranean agricultural fields. Our results show that management strategies aiming to increase the functionality of these systems should focus on intermediately intensified fields, where small reductions in the level of intensification are likely to benefit arable plant diversity, increasing the number of species and FD and decreasing the vulnerability of FD to species losses. Removing the effect of species richness is essential to attain unbiased estimations of the vulnerability of communities to species loss, especially when species-poor communities are considered. Combining vulnerability with information on taxonomic and functional diversity appears as a promising tool to inform decision-making processes, anticipating the effects of local extinction

Agriculture intensification reduces plant taxonomic and functional diversity across European arable systems

Los autores de la UAM pertenecen al Terrestrial Ecology Group (TEG)Agricultural intensification is one of the main drivers of species loss worldwide, but there is still a lack of information about its effect on functional diversity of arable weed communities. Using a large-scale pan European study including 786 fields within 261 farms from eight countries, we analysed differences in the taxonomic and functional diversity of arable weeds assemblages across different levels of agricultural intensification. We estimated weed species frequency in each field, and collected species' traits (vegetative height, SLA and seed mass) from the TRY plant trait database. With this information, we estimated taxonomic (species richness), functional composition (community weighted means) and functional diversity (functional richness, evenness, divergence and redundancy). We used indicators of agricultural management intensity at the individual field scale (e.g. yield, inputs of nitrogen fertilizer and herbicides, frequency of mechanical weed control practices) and at the landscape scale surrounding the field (i.e. number of crop types, mean field size and proportion of arable land cover within a radius of 500 m from the sampling points). The effects of agricultural intensification on species and functional richness at the field scale were stronger than those of intensification at the landscape scale, and we did not observe evidence of interacting effects between the two scales. Overall, assemblages in more intensified areas had fewer species, a higher prevalence of species with ruderal strategies (low stature, high leaf area, light seeds), and lower functional redundancy. Maintaining the diversity of Europe's arable weed communities requires some simple management interventions, for example, reducing the high intensity of field-level agricultural management across Europe, which could be complemented by interventions that increase landscape complexity. A free Plain Language Summary can be found within the Supporting Information of this articl

A complex scenario of glacial survival in Mediterranean and continental refugia of a temperate continental vole species (Microtus arvalis) in Europe

Los autores de la UAM pertenecen al grupo Terrestrial Ecology Group (TEG)"This is the peer reviewed version of the following article: Journal of Zoological Systematics and Evolutionary Research 58.1 (2020): 459-474, which has been published in final form at https://doi.org/10.1111/jzs.12323. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions"The role of glacial refugia in shaping contemporary species distribution is a long-standing question in phylogeography and evolutionary ecology. Recent studies are questioning previous paradigms on glacial refugia and postglacial recolonization pathways in Europe, and more flexible phylogeographic scenarios have been proposed. We used the widespread common vole Microtus arvalis as a model to investigate the origin, locations of glacial refugia, and dispersal pathways, in the group of “Continental” species in Europe. We used a Bayesian spatiotemporal diffusion analysis (relaxed random walk model) of cytochrome b sequences across the species range, including newly collected individuals from 10 Iberian localities and published sequences from 68 localities across 22 European countries. Our data suggest that the species originated in Central Europe, and we revealed the location of multiple refugia (in both southern peninsulas and continental regions) for this continental model species. Our results confirm the monophyly of Iberian voles and the pre-LGM divergence between Iberian and European voles. We found evidence of restricted postglacial dispersal from refugia in Mediterranean peninsulas. We inferred a complex evolutionary and demographic history of M. arvalis in Europe over the last 50,000 years that does not adequately fit previous glacial refugial scenarios. The phylogeography of M. arvalis provides a paradigm of ice-age survival of a temperate continental species in western and eastern Mediterranean peninsulas (sources of endemism) and multiple continental regions (sources of postglacial spread). Our findings also provide support for a major role of large European river systems in shaping geographic boundaries of M. arvalis in Europ

Definition of a temporal distribution index for high temporal resolution precipitation data over Peninsular Spain and the Balearic Islands: the fractal dimension; and its synoptic implications

Precipitation on the Spanish mainland and in the Balearic archipelago exhibits a high degree of spatial and temporal variability, regardless of the temporal resolution of the data considered. The fractal dimension indicates the property of self-similarity, and in the case of this study, wherein it is applied to the temporal behaviour of rainfall at a fine (10-min) resolution from a total of 48 observatories, it provides insights into its more or less convective nature. The methodology of Jenkinson & Collison which automatically classifies synoptic situations at the surface, as well as an adaptation of this methodology at 500 hPa, was applied in order to gain insights into the synoptic implications of extreme values of the fractal dimension. The highest fractal dimension values in the study area were observed in places with precipitation that has a more random behaviour over time with generally high totals. Four different regions in which the atmospheric mechanisms giving rise to precipitation at the surface differ from the corresponding above-ground mechanisms have been identified in the study area based on the fractal dimension. In the north of the Iberian Peninsula, high fractal dimension values are linked to a lower frequency of anticyclonic situations, whereas the opposite occurs in the central region. In the Mediterranean, higher fractal dimension values are associated with a higher frequency of the anticyclonic type and a lower frequency of the advective type from the east. In the south, lower fractal dimension values indicate higher frequency with respect to the anticyclonic type from the east and lower frequency with respect to the cyclonic type