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1.
The playa-lakes of the Monegros desert in north-east Spain are saline wetlands in an arid environment, a rare phenomenon in Europe. These extremely valuable habitats are threatened by changes associated with agricultural expansion and incorporation of new irrigated areas. An understanding of the present hydrologic regime will enable changes to be identified, particularly those brought about by flooding and pollution caused by irrigation surplus. This study sets out to show the results of applying a daily water balance in three selected playa-lakes. The balance was in two parts and consisted of: (1) the average balance for all the endorheic basin using the BALAN_11 program, and (2) the water balance in some playa-lakes, applying discharge flows obtained from the previous balance. The resulting volumes of water were converted to water depths and contrasted with reference volumes taken from field and Landsat images. The model was calibrated by applying various hypotheses of function which enabled the results to be adjusted. The proposed balance is an acceptable reproduction of field water measurements during this period, and underlines the consistency of the conceptual model. The methodology used is appropriate for understanding the playa-lakes function and for monitoring them for conservation purposes. 相似文献
2.
José M. García-Ruiz Yasmina Sanjuán Graciela Gil-Romera Penélope González-Sampériz Santiago Beguería José Arnáez Paz Coba-Pérez Amelia Gómez-Villar Javier Álvarez-Martínez Noemí Lana-Renault Estela Pérez-Cardiel Carlos López de Calle 《山地科学学报》2016,13(10):1760-1772
The conversion of subalpine forests into grasslands for pastoral use is a well-knownphenomenon, although for most mountain areas the timing of deforestation has not been determined. The presence of charcoal fragments in soil profiles affected by shallow landsliding enabled us to date the occurrence of fires and the periods of conversion ofsubalpine forest into grasslands in the Urbión Mountains, Iberian Range, Spain. We found that the treeline in the highest parts of the northwestern massifs of the Iberian Range(the Urbión, Demanda, Neila, and Cebollera massifs) is currently between 1500 and 1600 m a.s.l., probably because of pastoral use of the subalpine belt, whereas in the past it would have reached almost the highest divides(at approximately 2100–2200 m a.s.l.). The radiocarbon dates obtained indicate that the transformation of the subalpine belt occurred during the Late Neolithic, Chalcolithic, Bronze Age, Iron Age, and Middle Ages. Forest clearing was probably moderate during fires prior to the Middle Ages, as the small size of the sheep herds and the local character of the markets only required small clearings, and therefore more limited fires. Thus, it is likely that the forest recovered burnt areas in a few decades; this suggests the management of the forest and grasslands following a slash-andburn system. During the Middle and Modern Ages deforestation and grassland expansion affected most of the subalpine belt and coincided with the increasing prevalence of transhumance, as occurred in other mountains in the Iberian Peninsula(particularly the Pyrenees). Although the occurrence of shallow landslides following deforestation between the Neolithic and the Roman Period cannot be ruled out, the most extensive shallow landsliding processes would have occurred from the Middle Ages until recent times. 相似文献
3.
F. A. Nava L. Ávila-Barrientos V. H. Márquez-Ramírez I. Torres F. R. Zúñiga 《Journal of Seismology》2018,22(1):315-324
The Aki-Utsu method of Gutenberg-Richter (G-R) b value estimation is often misapplied so that estimations not using the G-R histogram are often meaningless because they are not based on adequate samples. We propose a method to estimate the likelihood Pr(b?b m , N, M 1, M 2) that an observed b m estimate, based on a sample of N magnitudes within an [M 1????≤?ΔM/2,?M 2?+?ΔM/2) range, where ΔM?=?0.1 is the usual rounding applied to magnitudes, is due to a “true” source b value, b, and use these likelihoods to estimate source b ranges corresponding to various confidence levels. As an example of application of the method, we estimate the b values before and after the occurrence of a 7.4-magnitude earthquake in the Mexican subduction zone, and find a difference of 0.82 between them with 100% confidence that the b values are different. 相似文献
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Vladimir Yu. Semenov Josef Pek Antal Ádám Waldemar Jóźwiak Boris Ladanyvskyy Igor M. Logvinov Pavel Pushkarev Jan Vozar 《Acta Geophysica》2008,56(4):957-981
In the years 2001–2003, we accomplished the experimental phase of the project CEMES by collecting long-period magnetotelluric
data at positions of eleven permanent geomagnetic observatories situated within few hundreds kilometers along the south-west
margin of the East European Craton. Five teams were engaged in estimating independently the magnetotelluric responses by using
different data processing procedures. The conductance distributions at the depths of the upper mantle have been derived individually
beneath each observatory. By averaging the individual cross-sections, we have designed the final model of the geoelectrical
structure of the upper mantle beneath the CEMES region. The results indicate systematic trends in the deep electrical structure
of the two European tectonic plates and give evidence that the electrical structure of the upper mantle differs between the
East European Craton and the Phanerozoic plate of west Europe, with a separating transition zone that generally coincides
with the Trans-European Suture Zone. 相似文献
6.
Lenin Campozano Daniel Mendoza Giovanny Mosquera Kenneth Palacio-Baus Rolando Célleri Patricio Crespo 《水文研究》2020,34(11):2302-2312
The problem of discharge forecasting using precipitation as input is still very active in Hydrology, and has a plethora of approaches to its solution. But, when the objective is to simulate discharge values without considering the phenomenology behind the processes involved, Artificial Neural Networks, ANN give good results. However, the question of how the black box internally solve this problem remains open. In this research, the classical rainfall-runoff problem is approached considering that the total discharge is a sum of components of the hydrological system, which from the ANN perspective is translated to the sum of three signals related to the fast, middle and slow flow. Thus, the present study has two aims (a) to study the time-frequency representation of discharge by an ANN hydrologic model and (b) to study the capabilities of ANN to additively decompose total river discharge. This study adds knowledge to the open problem of the physical interpretability of black-box models, which remains very limited. The results show that total discharge is adequately simulated in the time frequency domain, although less power spectrum is evident during the rainy seasons in the ANN model, due to fast flow underestimation. The wavelet spectrum of discharge represents well the slow, middle and fast flow components of the system with transit times of 256, 12–64 and 2–12 days, respectively. Interestingly, these transit times are remarkably similar to those of the soil water reservoirs of the studied system, a small headwater catchment in the tropical Andes. This result needs further research because it opens the possibility of determining MMT on a fraction of the cost of isotopic based methods. The cross-power spectrum indicates that the error in the simulated discharge is more related to the misrepresentation of the fast and the middle flow components, despite limitations in the recharge period of the slow flow component. With respect to the representation of individual signals of the slow, middle and fast flows components, the three neurons were uncapable to individually represent such flows. However, the combination of pairs of these signals resemble the dynamics and the spectral content of the aforementioned flows signals. These results show some evidence that signal processing techniques may be used to infer information about the hydrological functioning of a basin. 相似文献
7.
Climate change in the European region during the twentieth and twenty-first centuries is analyzed according to Feddema’s method. Precipitation and air temperature data from the twentieth century are taken from the Climatic Research Unit, while data for the twenty-first century are taken from the ENSEMBLES climate change project. The latter were bias-corrected to ensure homogeneity across the twentieth and twenty-first centuries. Climate classes based on monthly and annual values of potential evapotranspiration, precipitation and their ratio, are defined for 30-year averages, from which trend and spatial agreement analysis are calculated. There are separate classes for annual values and for intra-annual variation. The results indicate that the change of annual climate characteristics will be much more intense in the twenty-first than it was in the twentieth century. The dominant process in the projections is warming, mostly via cold to cool (about 45% of grid points) in north Europe and cool to warm (about 8% of grid points) transformations. The second most important process is the drying of moderately moist classes affecting about 10% of the grid points in south Europe. Changes in intra-annual variability classes are more common than changes in the annual ones during the twentieth century. The chance of increase in intra-annual temperature variation from high to extreme is about 5% during the course of the twentieth century, and about 10% in the following century. 相似文献
8.
Emily Fung Pablo Imbach Lenin Corrales Sergio Vilchez Nelson Zamora Freddy Argotty Lee Hannah Zayra Ramos 《Climatic change》2017,141(1):77-92
Climate change and land use conversion are global threats to biodiversity. Protected areas and biological corridors have been historically implemented as biodiversity conservation measures and suggested as tools within planning frameworks to respond to climate change. However, few applications to national protected areas systems considering climate change in tropical countries exist. Our goal is to define new priority areas for biodiversity conservation and biological corridors within an existing protected areas network. We aim at preserving samples of all biodiversity under climate change and facilitate species dispersal to reduce the vulnerability of biodiversity. The analysis was based on a three step strategy: i) protect representative samples of various levels of terrestrial biodiversity across protected area systems given future redistributions under climate change, ii) identify and protect areas with reduced climate velocities where populations could persist for relatively longer periods, and iii) ensure species dispersal between conservation areas through climatic connectivity pathways. The study was integrated into a participatory planning approach for biodiversity conservation in Costa Rica. Results showed that there should be an increase of 11 % and 5 % on new conservation areas and biological corridors respectively. Our approach integrates climate change into the design of a network of protected areas for tropical ecosystems and can be applied to other biodiversity rich areas to reduce the vulnerability of biodiversity to global warming. 相似文献
9.
Lenin Ávila-Barrientos Carlos Valdés-González David A. Novelo-Casanova 《Natural Hazards》2011,59(2):655-664
Acceleration and velocity data of large earthquakes recorded by the Mexican National Broadband Seismological Network were
used to generate isoseismal maps for Mexico. The seismic data consist of 99 events recorded at 27 seismic stations located
in the southern and northern regions of Mexico from 2004 to 2009. The magnitude (Mw) of these events ranged from 4.1 to 7.1.
Peak ground velocity values (PGV) and peak ground accelerations (PGA) were estimated, and velocity-derived peak ground accelerations
(PGAv) were calculated. No important differences between PGAv and PGA values were found; thus, both parameters were used in
the isoseismal determination. The generated synthetic isoseismal maps were compared with those from an existing catalog for
large earthquakes in Mexico. Using empiric relations between PGA and MMI (modified Mercalli intensity) and PGV and MMI, the
obtained simulated intensity maps showed similar behavior to those reported in the catalog. The results indicate that the
PGAv values can be used to determine intensities when acceleration records (PGA) are unavailable. 相似文献
10.
Tamás Bozóki Eszter Ágnes Krasznai-Kun András Csercsa Gábor Várbíró Pál Boda 《Environmental Earth Sciences》2018,77(15):559
Urbanization is a current and increasing threat to biodiversity. The effects of urbanization on the functional and taxonomic composition of macroinvertebrate assemblages were investigated in two seasons along a small urban stream. Species composition was determined by the rate of urbanization; however, response of species richness could not be evidenced. Relative abundance of the sensitive macroinvertebrate groups (EPT%) was negatively related to urbanization. Almost all feeding groups showed a sharp decline in the number of specimens along the increase of urbanization. The study supports the view that urbanization has a negative effect on the biological quality of a stream, yet, this obvious impact can be overridden by different measures such as modification in streambed morphology. The altered conditions and new circumstances in urban environments lead to the creation of novel ecosystems, inhabited by macroinvertebrate communities with species richness approaching that of low impacted sites. However, species composition of these communities could be basically different from that of the natural ones. 相似文献