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排序方式: 共有105条查询结果,搜索用时 39 毫秒
61.
Ren Verburg Elke Stehfest Geert Woltjer Bas Eickhout 《Global Environmental Change》2009,19(4):434-446
This study explores the effects of agricultural trade liberalisation and concomitant changes in agricultural areas and livestock production on greenhouse gas emissions using the coupled LEITAP–IMAGE modelling system. The results indicate that liberalisation leads to an increase in total greenhouse gas emissions by about 6% compared to the reference scenario value in 2015. The increase in CO2 emissions are caused by vegetation clearance due to a rapid expansion of agricultural area; mainly in South America and Southeast Asia. Increased methane emissions in the case of full liberalisation are caused by less intensive cattle farming in regions such as South America and Southeast Asia. This pattern is observed up to 2050. Total global production of milk, dairy and beef do not change with full liberalisation, but production shifts were observed from North America and Europe to South America and Southeast Asia. Results are less pronounced in variants where trade liberalisation is only implemented partially. Remarkably, our study shows in the trade barrier removal scenario larger numbers of dairy cows in Australia and New Zealand (ANZ) then with full liberalisation scenario or a variant in which only milk quota are abolished. This illustrates that different types of liberalisation need to be analysed regionally and per commodity before general conclusions on the impact of trade liberalisation can be drawn. Our study contributes new information on greenhouse gas emissions to a vast number of trade liberalisation studies that focus on economic impacts. The combined economic-environmental impacts need to be assessed in detail before general conclusions on trade liberalisation can be given. 相似文献
62.
Antonio Rius Oleguer Nogués-Correig Serni Ribó Estel Cardellach Santi Oliveras Enric Valencia Hyuk Park José Miguel Tarongí Adriano Camps Hans van der Marel Roel van Bree Bas Altena Manuel Martín-Neira 《GPS Solutions》2012,16(2):231-241
The Global Navigation Satellite System Reflectometry (GNSS-R) concept was conceived as a means to densify radar altimeter measurements of the sea surface. Until now, the GNSS-R concept relied on open access to GNSS transmitted codes. Recently, it has been proposed that the ranging capability of the technique for ocean altimetric applications can be improved by using all the signals transmitted in the bandwidth allocated to GNSS, which includes open access as well as encrypted signals. The main objective of this study is to provide experimental proof of this enhancement through a 2-day experiment on the Zeeland Bridge (The Netherlands). In the experiment, we used a custom built GNSS-R system, composed of high gain GPS antennas, calibration subsystem, and an FPGA-based signal processor which implemented the new concepts, an X-band radar altimeter and a local geodetic network. The results obtained indicate that the new approach produces a significant improvement in GNSS-R altimetric performance. 相似文献
63.
Robert Marchant Hermann Behling Juan‐Carlos Berrio Antoine Cleef Joost Duivenvoorden Henry Hooghiemstra Peter Kuhry Bert Melief Elisabeth Schreve‐Brinkman Bas Van Geel Thomas Van der Hammen Guido Van Reenen Michael Wille 《第四纪科学杂志》2002,17(2):113-129
Colombian biomes are reconstructed at 45 sites from the modern period extending to the Last Glacial Maximum (LGM). The basis for our reconstruction is pollen data assigned to plant functional types and biomes at six 3000‐yr intervals. A reconstruction of modern biomes is used to check the treatment of the modern pollen data set against a map of potential vegetation. This allows the biomes reconstructed at past periods to be assessed relative to the modern situation. This process also provides a check on the a priori assignment of pollen taxa to plant functional types and biomes. For the majority of the sites, the pollen data accurately reflect the potential vegetation, even though much of the original vegetation has been transformed by agricultural practices. At 18 000 14C yr BP, a generally cool and dry environment is reflected in biome, assignments of cold mixed forests, cool evergreen forests and cool grassland–shrub; the latter extending to lower altitudes than presently recorded. This signal is strongly recorded at 15 000 and 12 000 14C yr BP, the vegetation at these times also reflecting a relatively cool and dry environment. At 9000 14C yr BP there is a shift to biomes thought to result from slightly cooler environmental conditions. This trend is reversed by 6000 14C yr BP; most sites, within a range of different environmental settings, recording a shift to more xeric biome types. There is an expansion of steppe and cool mixed‐forest biomes, replacing tropical dry forest and cool grassland–shrub biomes, respectively. These changes in biome assignments from the modern situation can be interpreted as a biotic response to mid‐Holocene climatic aridity. At 3000 14C yr BP the shift is mainly to biomes characteristic of slightly more mesic environmental conditions. There are a number of sites that do not change biome assignment relative to the modern reconstruction, although the affinities that these sites have to a specific biome do change. These ‘anomalies’ are interpreted on a site‐by‐site basis. Spatially constant, but differential response of the vegetation to climatic shifts are related to changes in moisture sources and the importance of edaphic controls on the vegetation. The Late Quaternary reconstruction of large‐scale vegetation dynamics in Colombia allows an understanding of the environmental controls on these to be developed. In particular, shifts in the character of the main climatic systems that influence Colombian vegetation are described. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
64.
Category 5 tropical cyclone Pam hit Vanuatu in March 2015, affecting thousands of people. Three months after the event, this study compared the responses from both external aid agencies and the disaster-affected communities to identify convergences, duplications and gaps. The research relies on 13 interviews with aid agencies and eight focus group discussions with participatory activities at local community level. While aid agencies actively responded during and after Pam, local people too responded to the event with strategies based on livelihoods diversification, food security techniques, traditional knowledge and cooperation intra- and inter-communities. The study emphasizes the need for an integrative approach where disaster responses from the top-down integrate that from the bottom-up. Aid agencies should build on the livelihood mechanisms developed at local level so responses and recovery can be more effective, socioculturally acceptable and may lead to sustainable outcomes of disaster risk reduction including climate change adaptation. 相似文献
65.
Crystallographic preferred orientations (CPOs) in deformed rocks are commonly interpreted as resulting from crystal plastic deformation mechanisms, where deformation is achieved by the movement of dislocations. In this paper we investigate the possibility of CPO-development by dissolution–precipitation creep or pressure solution. A numerical model is presented, which simulates the development of a grain aggregate that deforms by reaction-controlled dissolution–precipitation creep. Grains are simulated as rectangular boxes that change their shape by growth, or dissolution of their surfaces, depending on the normal stresses acting on the individual surfaces. Grains can also rotate due to an applied vorticity (for non-coaxial deformation) and if they have a non-equidimensional shape. For each strain increment, stress that is applied to the grains is the same for all grains, while individual grains deform and rotate by different amounts. A variety of CPOs develop at moderate strains, depending on the reaction rates of the different crystal-surfaces and type of deformation (uni-axial shortening, plane strain pure shear and simple shear). The modelling results confirm that dissolution–precipitation creep may play a role in CPO-development in rocks. 相似文献
66.
Gebeyehu Taye Jean Poesen Bas Van Wesemael Matthias Vanmaercke Daniel Teka Jozef Deckers 《自然地理学》2013,34(3):236-259
April lightning production in Richmond County, Georgia, from 1995 to 2003 is considered with regard to the associated risk to golfers and spectators at the Master's Golf Tournament and courses throughout the county. An examination of the April lightning climatology of Georgia, focusing on Richmond County, reveals a minimum in lightning activity during the time of the tournament (the first full week of April). A discriminant analysis of Richmond County lightning production utilizes several meteorological variables in order to discern between three categories of April lightning days: little or no lightning activity, minimal lightning activity, and high lightning activity. The analysis distinguishes relatively well between the categories with only 13.5% of the events misclassified. A composite regional analysis of the three lightning categories illustrates the environmental differences between these events. Although the little or no lightning and high lightning categories are somewhat similar environmentally, the intensity of features separates these events and allows for interpretation. The statistical and synoptic analyses together emphasize the importance of low-level instability and frontal proximity and intensity in enhancing lightning production in thunderstorms during April in and surrounding Richmond County. A multitude of meteorological conditions can lead to thunderstorm development. Localized studies of these environments, especially during times of major outdoor sporting events, are needed to help mitigate the risk associated with lightning. 相似文献
67.
Rocio L. Fernandez Stuart McLelland Daniel R. Parsons Bas Bodewes 《地球表面变化过程与地形》2021,46(11):2315-2329
With riverine flooding set to be more frequent in many parts of the world as a result of climate change, the interactions between fluvial morphodynamics and riparian vegetation may depend in part on the sequence of flood events. This paper describes a laboratory study of the geomorphic adjustment of a braided river to sequences of floods across five different strengths of braidplain vegetation. By using alfalfa as a proxy for braidplain vegetation, the differing plant life stages were used to represent the varying strengths of biogeomorphic feedbacks across the floods. Boundary conditions were constrained by sets of experimental runs with both equilibrium sediment loads and deficit loads. Changes in bed topography were monitored and assessed using a detailed digital elevation model, digital imagery and continuous monitoring of the transported sediment. Results demonstrate that in absence of plant colonization, vegetation placed the rivers in a non-equilibrium condition, in which riparian vegetation encouraged the development of new channels, increased the system channel width and enhanced topographic irregularity, these effects being more noticeable during the low-flow periods. The morphodynamics was found to be less sensitive to variations in flood discharges as the vegetation influence (strength) increased from minimum to maximum, until vegetation began to die back and the impacts of flood sequences became yet again evident. Although the overall sediment transport rate was reduced under full-grown vegetation conditions, the presence of the mature plants across the braid bars resulted in the greatest channel scour depths. Results are considered in light of expected changes in flood frequency with climate and likely morphodynamic responses of river systems as a result. 相似文献
68.
Aurore Voldoire Bas Eickhout Michiel Schaeffer Jean-François Royer Fabrice Chauvin 《Climate Dynamics》2007,29(2-3):177-193
To include land-use dynamics in a general circulation model (GCM), the physical system has to be linked to a system that represents
socio-economy. This issue is addressed by coupling an integrated assessment model, IMAGE2.2, to an ocean–atmosphere GCM, CNRM-CM3.
In the new system, IMAGE2.2 provides CNRM-CM3 with all the external forcings that are scenario dependent: greenhouse gas (GHGs)
concentrations, sulfate aerosols charge and land cover. Conversely, the GCM gives IMAGE changes in mean temperature and precipitation.
With this new system, we have run an adapted scenario of the IPCC SRES scenario family. We have chosen a single scenario with
maximum land-use changes (SRES A2), to illustrate some important feedback issues. Even in this two-way coupled model set-up,
land use in this scenario is mainly driven by demographic and agricultural practices, which overpowers a potential influence
of climate feedbacks on land-use patterns. This suggests that for scenarios in which socio-economically driven land-use change
is very large, land-use changes can be incorporated in GCM simulations as a one-way driving force, without taking into account
climate feedbacks. The dynamics of natural vegetation is more closely linked to climate but the time-scale of changes is of
the order of a century. Thus, the coupling between natural vegetation and climate could generate important feedbacks but these
effects are relevant mainly for multi-centennial simulations. 相似文献
69.
The N Pakistan carbonatites of Loe Shilman, Silai Patti and those within the Ambela complex were formerly considered as comprising one alkaline igneous province associated with a Peshawar rift valley. New data show that these alkaline rocks occur in two distinct periods, Carboniferous and Tertiary, and are not related to any Tertiary rift faulting. K-Ar dates determined on biotites from the Loe Shilman and Silai Patti carbonatites reveal that the carbonatites were emplaced at 31±2 Ma, and along thrust planes, not rift faults. Subsequent movement of the thrusts reset the argon contents in some biotites to indicate a deformation age of 24±2 Ma for the carbonatites at both localities.The Koga carbonatite in the Ambela complex occurs as a plug associated with nepheline syenites and ijolites, and Rb-Sr isotope determinations on the silicate rocks give dates of approximately 297–315 Ma.The study implies that there were thrust movements associated with the Indian — Asian plate collision more than 31 Ma ago, which is much earlier than the 20 Ma date previously advocated for the initiation of thrusting.
Zusammenfassung Die nordpakistanischen Karbonatite Loe Shilman, Silai Patti und jene aus dem Ambela-Komplex wurden bisher zusammen mit einer Alkaligesteins-Provinz betrachtet, deren Bildung mit dem Peshawar Riff zusammenhÄngt. Neue Daten zeigen auf, da\ die Alkaligesteine von Shilman und Silai Patti dem Karbon zuzuordnen sind und jene aus dem Ambela-Komplex dem TertiÄr. Beide Gesteinserien gehören keiner tertiÄren Riff-Faltung an. K-Ar Altersdaten, bestimmt an Biotiten aus den Karbonatiten von Loe Shilman und Silai Patti, ergeben ein Alter von 31±2 Ma für die Platznahme der Karbonatite entlang einer überschiebungszone. Nachfolgende Bewegungen in der überschiebungsbahn verÄnderten den Argongehalt in einigen Biotiten, so da\ sich ein Deformationsalter von 24±2 Ma ergibt. Die Koga Karbonatite aus dem Ambela Komplex kommen dagegen als Propfen vor. Sie sind assoziiert mit Nephelinsyeniten und Ijoliten. Rb-Sr Bestimmungen an diesen Silikatgesteinen ergeben ein Alter zwischen 297–315 Ma.Diese Untersuchung zeigt, da\ die Indisch-Asiatische Plattenkollision vor 31±2 Ma Jahren stattfand, da sie mit der überschiebungsbewegung assoziiert werden kann. Bisher wurde für diese Kollision ein Alter von 20 Ma angenommen.
Résumé Les carbonatites du Pakistan septentrional, situées à Loe Shilman, Silai Patti et dans le complexe d'Ambela, ont été regardées jusqu'ici comme appartenant à une seule province magmatique alcaline associée au fossé de Peshawar. Des données nouvelles démontrent que ces roches alcalines appartiennent à deux périodes différentes, le Carbonifère et le Tertiaire, et qu'elles ne sont associées à aucun fossé tertiaire. Des datations K-Ar, effectuées sur les biotites des carbonatites de Loe Shilman et de Silai Patti, montrent que ces roches se sont mises en place il y a 31±2 Ma et ce, le long de failles de charriage et non de failles radiales. Des mouvements plus récents le long de ces charriages ont modifié la teneur en argon de certaines biotites, qui fournissent pour cette déformation un âge des 24±2 Ma dans les carbonatites des deux localités.La carbonatite de Koga dans le complexe d'Ambela est un culot associé à des syénites à néphéline et à des ijolites sur lesquelles les déterminations Rb-Sr donnent des aes approximatifs de 297 à 315 Ma.Cette étude montre que des mouvements de charriage, associés à la collision des plaques indienne et asiatique, ont eu lieu avant 31±2 Ma, c'est-à-dire beaucoup plus tÔt que les 20 Ma admis jusqu'ici.
Loe Shilman, Silai Patti Ambela , , Peshawar. , Shilman Silai Patti , Ambela — . . Loe Shilman Silai Patti, K/, 31±2 . , 24 ± 2 . Koga Ambela «». - ; , Rb/Sr, 297–315 . , 31 ± 2 , . . , . , 20 .相似文献
70.
Bas Katsoulis 《Pure and Applied Geophysics》1977,115(3):583-591
Summary In this study, values of the Ångström turbidity coefficient () determined from Solar radiation observations at the National Observatory of Athens over the period 1955–1972 are analysed. Mean daily turbidity lies between 0.020–0.100. Turbidity is higher in summer than in winter. The main factor determining the turbidity is the air mass type. The scavenging by rainfall probably has a considerable effect in determining this distribution. There is some evidence of a trend of increasing turbidity during the period. 相似文献