Mapping land cover changes in Mexico, 1976–2000 and applications for guiding environmental management policy     

Alejandro Velázquez  Jean‐François Mas  Gerardo Bocco  José Luis Palacio‐Prieto 《Singapore journal of tropical geography》2010,31(2):152-162

Land use conversion typically implicates deforestation and fragmentation of primary land cover types, which invariably translates into impoverishment of both natural and cultural capital. Understanding where conversion is taking place crucially underpins sound environmental policy instruments to prevent these enormous social and economic costs. This paper examines 30 years of semi‐detailed (1:250 000) land cover mapping in Mexico. Pre‐existing analogue databases describing land cover patterns in the 1970s and 1990s were reviewed, corrected, reorganized and transformed into a digital format. Current land cover patterns were depicted by conducting updated reinterpretation on Landsat ETM+ imagery. Digital cartographic overlaying was performed and the results were used to construct a spatially explicit land use/land cover change (LULCC) database with an additional accuracy assessment procedure. The value of the results of this analysis is also seen in the light of their direct applications for identifying critical watershed trends, for guiding the allocation of financial funds for sound land use planning and for assessing the effectiveness of established protected areas. This effort highlights the importance of new and more effective geographical approaches to depict, understand and contribute to informed measures to mitigate ongoing negative trends in land cover and climatic changes.  相似文献   

A depth-averaged 2-D model of flow and sediment transport in coastal waters     

Alejandro Sanchez  Weiming Wu  Tanya M. Beck 《Ocean Dynamics》2016,66(11):1475-1495

  相似文献   

Multifractality in Seismicity Spatial Distributions: Significance and Possible Precursory Applications as Found for Two Cases in Different Tectonic Environments   总被引：1，自引：0，他引：1  

Víctor Hugo Márquez-Rámirez  F. Alejandro Nava Pichardo  Gabriel Reyes-Dávila 《Pure and Applied Geophysics》2012,169(12):2091-2105

We explore fractal properties of two observed seismicity distributions prior to the 2003 M _w 7.4 Colima, Mexico and 1992 M _w 7.3 Landers, USA earthquakes, together with several mathematical fractal distributions and two non-fractal ones, in order to estimate minimum reliable sample sizes, determine whether fractality for observed seismicity is essentially different from random uniform distributions, and explore the possibility of extracting premonitory information from fractal characteristics of seismicity before large earthquakes. Sample sizes above 800 events for whole catalogs appear to be sufficient to maintain ordered multifractality and to yield dimension estimates that vary smoothly and reliably. Fractal estimates appear to be best for whole catalogs that include aftershocks. The fractal characteristics of spatial distributions of seismicity are essentially different from those of the uniform random distribution, which is the null hypothesis of a non-fractal distribution with minimum information. The fractal dimensions and afractality measures of seismicity distributions change with time and show distinctive behaviors associated with foreshocks and main events, although these behaviors are different for each example. Results suggest the possibility of a priori identification of foreshocks to large earthquakes. A combination of fractal dimension and afractality measures over time may be helpful in large earthquake premonitory studies.  相似文献   

Simulation and properties of a non-homogeneous spring-block earthquake model with asperities   总被引：1，自引：0，他引：1  

Alejandro Muñoz-Diosdado  Adolfo H. Rudolf-Navarro  Fernando Angulo-Brown 《Acta Geophysica》2012,60(3):740-757

The spring-block model proposed by Olami, Feder and Christensen (OFC) has several properties that are similar to those observed in real seismicity. In this paper we propose a modification of the original model in order to take into account that in a real fault there are several regions with different properties (non-homogeneity). We define regions in the network that is reminiscent of the real seismic fault, with different sizes and elastic parameter values. We obtain the Gutenberg-Richter law for the synthetic earthquake distributions of magnitude and the stair-shaped plots for the cumulative seismicity. Again, as in the OFC-homogeneous case, we obtain the stability for the cumulative seismicity stair-shaped graphs in the long-term situation; this means that the straight line slopes that are superior bounds of the staircases have a behavior akin to the homogeneous case. We show that with this non-homogeneous OFC model it is possible to include the asperity concept to describe high-stress zones in the fault.  相似文献   

Controls on monthly estuarine residuals: Eulerian circulation and elevation     

Jennifer M. Brown  Rodolfo Bolaños  Alejandro J. Souza 《Ocean Dynamics》2014,64(4):587-609

The Dee Estuary, at the NW English–Welsh border, is a major asset, supporting: one of the largest wildlife habitats in Europe, industrial importance along the Welsh coastline and residential and recreational usage along the English coast. Understanding of the residual elevation is important to determine the total water levels that inundate intertidal banks, especially during storms. Whereas, improved knowledge of the 3D residual circulation is important in determining particle transport pathways to manage water quality and morphological change. Using mooring data obtained in February–March 2008, a 3D modelling system has been previously validated against in situ salinity, velocity, elevation and wave observations, to investigate the barotropic–baroclinic wave interaction within this estuary under full realistic forcing. The system consists of a coupled circulation-wave-turbulence model (POLCOMS-WAM-GOTM). Using this modelling system the contribution of different processes and their interactions to the monthly residuals in both elevation and circulation is now assessed. By studying a tidally dominated estuary under wave influence, it is found that baroclinicity induced by a weak river flow has greater importance in generating a residual circulation than the waves, even at the estuary mouth. Although the monthly residual circulation is dominated by tidal and baroclinic processes, the residual estuarine surface elevation is primarily influenced by the seasonal external forcing to the region, with secondary influence from the local wind conditions. During storm conditions, 3D radiation stress becomes important for both elevation and circulation at the event scale but is found here to have little impact over monthly time scales.  相似文献   

Semi-Periodic Sequences and Extraneous Events in Earthquake Forecasting. II: Application,Forecasts for Japan and Venezuela     

Claudia Beatriz Quinteros Cartaya  Fidencio Alejandro Nava Pichardo  Ewa Glowacka  José Duglas Frez Cárdenas 《Pure and Applied Geophysics》2014,171(7):1367-1383

In order to analyze observed seismicity in central Japan and Venezuela, we applied a new method to identify semi-periodic sequences in the occurrence times of large earthquakes, which allows for the presence of multiple periodic sequences and/or events not belonging to any sequence in the time series. We also explored a scheme for diminishing the effects of a sharp cutoff magnitude threshold in selecting the events to analyze. A main four-event sequence with probability P _c  = 0.991 of not having occurred by chance was identified for earthquakes with M ≥ 8.0 in central Japan. Venezuela is divided, from West to East, into four regions; for each of these, the magnitude ranges and identified sequences are as follows. Region 1: M ≥ 6.0, a six-event sequence with P _c  = 0.923, and a four-event sequence with P _c  = 0.706. Region 2: M ≥ 5.6, a five-event sequence with P _c  = 0.942. Region 3: M ≥ 5.6, a four-event sequence with P _c  = 0.882. Region 4: M ≥ 6.0, a five-event sequence with P _c  = 0.891. Forecasts are made and evaluated for all identified sequences having four or more events and probabilities ≥0.5. The last event of all these sequences was satisfactorily aftcast by previous events. Whether the identified sequences do, in fact, correspond to physical processes resulting in semi-periodic seismicity is, of course, an open question; but the forecasts, properly used, may be useful as a factor in seismic hazard estimation.  相似文献   

Semi-Periodic Sequences and Extraneous Events in Earthquake Forecasting: I. Theory and Method,Parkfield Application     

Fidencio Alejandro Nava Pichardo  Claudia Beatriz Quinteros Cartaya  Ewa Glowacka  José Duglas Frez Cárdenas 《Pure and Applied Geophysics》2014,171(7):1355-1366

We present a new method to identify semi-periodic sequences in the occurrence times of large earthquakes, which allows for the presence of multiple semi-periodic sequences and/or events not belonging to any identifiable sequence in the time series. The method, based on the analytic Fourier transform, yields estimates of the departure from periodicity of an observed sequence, and of the probability that the sequence is not due to chance. These estimates are used to make and to evaluate forecasts of future events belonging to each sequence. Numerous tests with synthetic catalogs show that the method is surprisingly capable of correctly identifying sequences, unidentifiable by eye, in complicated time series. Correct identification of a given sequence depends on the number of events it contains, on the sequence’s departure from periodicity, and, in some cases, on the choice of starting and ending times of the analyzed time window; as well as on the total number of events in the time series. Some particular data combinations may result in spectra where significant periods are obscured by large amplitudes artifacts of the transform, but artifacts can be usually recognized because they lack harmonics; thus, in most of these cases, true semi-periodic sequences may not be identified, but no false identifications will be made. A first example of an application of the method to real seismicity data is the analysis of the Parkfield event series. The analysis correctly aftcasts the September 2004 earthquake. Further applications to real data from Japan and Venezuela are shown in a companion paper.  相似文献   

A simplified storm index method to extrapolate intensity–duration–frequency (IDF) curves for ungauged stations in central Chile          下载免费PDF全文

Roberto Pizarro  Rodrigo Valdés  Alejandro Abarza  Pablo Garcia‐Chevesich 《水文研究》2015,29(5):641-652

Most of meteorological stations in Chile register rainfall amounts once every 24 h. The creation of intensity–duration–frequency (IDF) curves requires continuous recorded data, and this insufficiency of proper instrumentation has resulted in a lack of IDF curves nationwide. The objective of this study is to further develop and evaluate the feasibility of a new method to estimate IDF curves in ungauged stations under Mediterranean climates of central Chile. A technique used to address this problem is the use of a storm index (S_I), also known as the ‘K’ method, which allows the construction of IDF curves from stations with discontinuous data, by extrapolating data from stations with continuous records, as long as daily rainfall intensities for both stations differ by less than 2 mm h^?1. To test the applicability of this method, S_I values were calculated for 40 meteorological stations located throughout Central Chile (latitudes 30°S to 40°S). The extrapolated IDF curves were then compared with observed data, and the goodness of fit was determined. The results indicate that the storm index method can adequately estimate hourly IDF curve values for stations lacking of continuous rainfall data. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Past to future extreme events in Liverpool Bay: model projections from 1960–2100     

Jennifer?M.?BrownEmail author  Judith?Wolf  Alejandro?J.?Souza 《Climatic change》2012,111(2):365-391

Knowledge of the likely future wind, wave and surge climate in Liverpool Bay is of importance for coastal flood defence management. We examine a 140-year time series (1960–2100) of wind and wave model projections at the WaveNet buoy location in Liverpool Bay and also of surge model projection at two ports in Liverpool Bay, namely Liverpool and Heysham. To this end we use model projections from the UK Climate Projections 09 (UKCP09) programme. We use a medium emissions scenario ensemble from the HadCM3 climate model sensitivity tests. A continental shelf model (CS3) with ~12 km resolution was used to separately simulate the waves and the surge. The models are forced by hourly wind and pressure data from the Met Office (Hadley Centre) regional climate model (RCM). Swell wave boundary conditions are generated over the full Atlantic using global climate model (GCM) winds. Analysis of significant changes in the statistics over time shows that there is little change in extreme wave and surge conditions in Liverpool Bay. Although there is a slight increase in the severity of the most extreme events, the frequency of extreme wind and wave events is slightly reduced, while the frequency of extreme surge events slightly increases over the 140-year period. From the model projections, we find that the trends in the local wind are directly reflected in the wave field within Liverpool Bay. The trends in the skew surge projections deviate slightly from those in the wind patterns.  相似文献   

Hydrodynamic modelling of mesoscale eddies in the Black Sea     

Cecilia E. Enriquez  Georgy I. Shapiro  Alejandro J. Souza  Andrei G. Zatsepin 《Ocean Dynamics》2005,55(5-6):476-489

A three dimensional structure of mesoscale circulation in the Black Sea is simulated using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System. A number of sensitivity tests reveal the response of the model to changes in the horizontal resolution, time steps, and diffusion coefficients. Three numerical grids are examined with x-fine (3.2 km), fine (6.7 km) and coarse (25 km) resolution. It is found that the coarse grid significantly overestimates the energy of the currents and is not adequate even for the study of basin-scale circulation. The x-fine grid, on the other hand, does not give significant advantages compared to the fine grid, and the latter is used for the bulk of simulations. The most adequate parameters are chosen from the sensitivity study and used to model both the basin-scale circulation and day-to-day variability of mesoscale currents for the months of May and June of 2000. The model is forced with actual wind data every 6 h and monthly climatic data for evaporation, precipitation, heat fluxes and river run-off. The results of the fine grid model are compared favourably against the satellite imagery. The model adequately reproduces the general circulation and many mesoscale features including cyclonic and anticyclonic eddies, jets and filaments in different parts of the Black Sea. The model gives a realistic geographical distribution and parameters of mesoscale currents, such as size, shape and evolution of the eddies.  相似文献