The importance of population,climate change and CO2 plant physiological forcing in determining future global water stress     

Andrew Wiltshire  Jemma Gornall  Ben Booth  Emily Dennis  Pete Falloon  Gillian Kay  Doug McNeall  Carol McSweeney  Richard Betts 《Global Environmental Change》2013,23(5):1083-1097

Future levels of water stress depend on changes in several key factors including population, climate-change driven water availability, and a carbon dioxide physiological-forcing effect on evaporation and run-off. In this study we use an ensemble of the HadCM3 climate model forced with a range of future emissions scenarios combined with a simple water scarcity index to assess the contribution of each of these factors to the projected population living in water stress over the 21st century.Population change only scenarios increase the number of people living in water stress such that at peak global population 65% of people experience some level of water stress. Globally, the climate model ensemble projects an increase in water availability which partially offsets some of the impacts of population growth. The result is 1 billion fewer people living in water stress by the 2080s under the high end emissions scenarios than if population increased in the absence of climate change.This study highlights the important role plant-physiological forcing has on future water resources. The effect of rising CO₂ is to increase available water and to reduce the number of people living in high water stress by around 200 million compared to climate only projections. This effect is of a similar order of magnitude to climate change.  相似文献   

Last glacial–interglacial sea-ice cover in the SW Atlantic and its potential role in global deglaciation     

Claire S. Allen  Jennifer Pike  Carol J. Pudsey 《Quaternary Science Reviews》2011,30(19-20):2446-2458

Sea-ice growth and decay in Antarctica is one of the biggest seasonal changes on Earth, expanding ice cover from 4 × 10⁶ km² to a maximum of 19 × 10⁶ km² during the austral winter. Analyses of six marine sediment cores from the Scotia Sea, SW Atlantic, yield records of sea-ice migration across the basin since the Lateglacial. The cores span nearly ten degrees of latitude from the modern seasonal sea-ice zone to the modern Polar Front. Surface sediments in the cores comprise predominantly diatomaceous oozes and muddy diatom oozes that reflect Holocene conditions. The cores exhibit similar down-core stratigraphies with decreasing diatom concentrations and increasing magnetic susceptibility from modern through to the Last Glacial Maximum (LGM). Sediments in all cores contain sea-ice diatoms that preserve a signal of changing sea-ice cover and permit reconstruction of past sea-ice dynamics. The sea-ice records presented here are the first to document the position of both the summer and winter sea-ice cover at the Last Glacial Maximum (LGM) in the Scotia Sea. Comparison of the LGM and Holocene sea-ice conditions shows that the average winter sea-ice extent was at least 5° further north at the LGM. Average summer sea-ice extent was south of the most southerly core site at the LGM, and suggests that sea-ice expanded from approximately ～61°S to ～52°S each season. Our data also suggest that the average summer sea-ice position at the LGM was not the maximum extent of summer sea-ice during the last glacial. Instead, the sediments contain evidence of a pre-LGM maximum extent of summer sea-ice between ～30 ka and 22 ka that extended to ～59°S, close to the modern average winter sea-ice limit. Based on our reconstruction we propose that the timing of the maximum extent of summer sea-ice and subsequent retreat by 22 ka, could be insolation controlled and that the strong links between sea-ice and bottom water formation provide a potential mechanism by which Southern Hemisphere regional sea-ice dynamics at the LGM could have a global impact and promote deglaciation.  相似文献   

Coupled HM analysis using zero‐thickness interface elements with double nodes. Part I: Theoretical model     

J. M. Segura  I. Carol 《国际地质力学数值与分析法杂志》2008,32(18):2083-2101

In recent years, the authors have proposed a new double‐node zero‐thickness interface element for diffusion analysis via the finite element method (FEM) (Int. J. Numer. Anal. Meth. Geomech. 2004; 28 (9): 947–962). In the present paper, that formulation is combined with an existing mechanical formulation in order to obtain a fully coupled hydro‐mechanical (or HM) model applicable to fractured/fracturing geomaterials. Each element (continuum or interface) is formulated in terms of the displacements (u) and the fluid pressure (p) at the nodes. After assembly, a particular expression of the traditional ‘u–p’ system of coupled equations is obtained, which is highly non‐linear due to the strong dependence between the permeability and the aperture of discontinuities. The formulation is valid for both pre‐existing and developing discontinuities by using the appropriate constitutive model that relates effective stresses to relative displacements in the interface. The system of coupled equations is solved following two different numerical approaches: staggered and fully coupled. In the latter, the Newton–Raphson method is used, and it is shown that the Jacobian matrix becomes non‐symmetric due to the dependence of the discontinuity permeability on the aperture. In the part II companion paper (Int. J. Numer. Anal. Meth. Geomech. 2008; DOI: 10.1002/nag.730 ), the formulation proposed is verified and illustrated with some application examples. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Wide-angle deep crustal reflections in the northern Appalachians     

James H. Luetgert  Carol E. Maim  Simon L. Klemperer 《Geophysical Journal International》1987,89(1):183-188

Summary. Seismic refraction data collected in the northern Appalachians provide an unusual opportunity to use wide-angle reflections to examine the lower crust and upper mantle. The PmP phase, clearly identified on several hundred records, has been used to construct an isopach map of the crust which shows a stepwise regional thickening of the crust beneath the axis of the Appalachians. The data have been examined to times of up to 40 s two-way travel time to investigate the possibility of coherent upper-mantle reflections such as those recently observed by BIRPS on near-vertical data northwest of Britain. Although substantial coherent energy appears after the PmP phase, synthetic seismogram modelling shows that all of these arrivals are explicable by S-phases, converted phases and multiples from within the crust. We conclude that in this region of the northern Appalachians we have not detected any significant regionally extensive reflecting horizons within the upper mantle.  相似文献   

A second-order global solution of the ideal resonance problem     

Boris Garfinkel  Carol A. Williams 《Celestial Mechanics and Dynamical Astronomy》1974,9(1):105-125

The Ideal Resonance Problem, as formulated in 1966 (Paper I), is defined by the Hamiltonian Following the procedure adopted in the construction of a first-orderglobal solution (Papers II, III, and V), we derive a second-order solution from the von Zeipel-Bohlin recursive algorithm of Paper II. The singularities inherent in the Bohlin expansion in powers of μ have been suppressed by means of theregularizing function of Paper III, and the singularities in the coefficients atAB″=0 have been removed by thenormalization technique of Paper V. As a check, it is shown that the global solution includes asymptotically theclassical solution, expanded in powers ofμ ², and carrying thecritical divisor B′.  相似文献   

Temporal and spatial variations in suspended matter in continental shelf and slope waters off the north-eastern United States     

Michael H. Bothner  Carol M. Parmenter  John D. Milliman 《Estuarine, Coastal and Shelf Science》1981,13(2):213-IN2

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Factors influencing nitrate within a low-gradient agricultural stream   总被引：1，自引：1，他引：0  

Eric W. Peterson  Carol Benning 《Environmental Earth Sciences》2013,68(5):1233-1245

In low-gradient agricultural streams, the proportion of land use devoted to agriculture, the sinuosity of the stream and the time of year influence the concentration of nitrate in the stream waters. Land use influences the source of nitrate and also the morphology of the stream. Greater agricultural land use weakly correlated (r = 0.67) to higher nitrate concentrations. Streams in agricultural areas have been straightened, which decreases the sinuosity. As a stream meanders and becomes more sinuous, the potential for lateral hyporheic flow increases, which can enhance a stream system’s ability to remove nitrate. Logically, higher sinuous streams should remove more nitrate and likely sulfate as there is a greater potential for lateral hyporheic flows. To test this hypothesis, nitrate and sulfate were monitored. Mass fluxes of nitrate along six stream segments with varying sinuosity values were calculated and statistically analyzed to assess if differences in mass fluxes along the segments existed. Along the segments, there are statistically significant differences in the mass fluxes of nitrate [F(5,174) = 4.777; p = 0.001]. Stream segments with higher sinuosity index values exhibited a loss or lower gain in nitrate and sulfate than lower sinuosity index segments. The data suggest that stream segments with high sinuosity indices provide greater stream distance and increased hyporheic interaction within the streambed. Additionally, the more sinuous segments provide for an increase in lateral hyporheic flow beneath meander lobes. These additional hyporheic flows lead to enhanced denitrification in low-gradient agricultural streams. Seasonal differences were also noted. August through October experienced the lower nitrate concentrations as compared to June and July which exhibited the highest nitrate concentrations.  相似文献   

Physical Geography: crossing from the past to the future     

Carol P. Harden 《自然地理学》2013,34(1)

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Three-dimensional digital imaging of environmental data: selection of gridding parameters     

Carol A. EDDY  B. Looney 《International journal of geographical information science》2013,27(2):165-172

Abstract. Three-dimensional imaging is a powerful technique for the visualization and interpretation of environmental data. The success of the process is linked to careful, technically-justifiable selection of variable parameters during the gridding and imaging process. The impacts of various approaches to gridding and possible setting of parameters on the final image and volume calculations were examined by generating alternative images for a very well characterized contaminated site in layered coastal plain sediments. To image properly scattered data collected at close intervals in wells from layered geological media, a higher grid density in the z direction is required along with a weighting factor to emphasize the influence of data in the x and y directions. For steeply-varying contaminant concentration data, the best results were obtained by gridding the log of the property value; an anti-log transformation is carried out to restore property values to the correct value before the visualization file is prepared. The techniques and recommendations made in this article were designed for modelling contaminant values with very steep gradients dispersed in a strongly anisotropic media. These recommendations may not apply directly to other sites but the process of selecting parameters should be similar.  相似文献   

Olivine or impact melt: Nature of the “Orange” material on Vesta from Dawn     

Lucille Le Corre  Vishnu Reddy  Nico Schmedemann  Kris J. Becker  David P. O’Brien  Naoyuki Yamashita  Patrick N. Peplowski  Thomas H. Prettyman  Jian-Yang Li  Edward A. Cloutis  Brett W. Denevi  Thomas Kneissl  Eric Palmer  Robert W. Gaskell  Andreas Nathues  Michael J. Gaffey  David W. Mittlefehldt  William B. Garry  Holger Sierks  Christopher T. Russell  Carol A. Raymond  Maria C. De Sanctis  Eleonora Ammanito 《Icarus》2013

NASA’s Dawn mission observed a great variety of colored terrains on asteroid (4) Vesta during its survey with the Framing Camera (FC). Here we present a detailed study of the orange material on Vesta, which was first observed in color ratio images obtained by the FC and presents a red spectral slope. The orange material deposits can be classified into three types: (a) diffuse ejecta deposited by recent medium-size impact craters (such as Oppia), (b) lobate patches with well-defined edges (nicknamed “pumpkin patches”), and (c) ejecta rays from fresh-looking impact craters. The location of the orange diffuse ejecta from Oppia corresponds to the olivine spot nicknamed “Leslie feature” first identified by Gaffey (Gaffey, M.J. [1997]. Icarus 127, 130–157) from ground-based spectral observations. The distribution of the orange material in the FC mosaic is concentrated on the equatorial region and almost exclusively outside the Rheasilvia basin. Our in-depth analysis of the composition of this material uses complementary observations from FC, the visible and infrared spectrometer (VIR), and the Gamma Ray and Neutron Detector (GRaND). Several possible options for the composition of the orange material are investigated including, cumulate eucrite layer exposed during impact, metal delivered by impactor, olivine–orthopyroxene mixture and impact melt. Based on our analysis, the orange material on Vesta is unlikely to be metal or olivine (originally proposed by Gaffey (Gaffey, M.J. [1997]. Icarus 127, 130–157)). Analysis of the elemental composition of Oppia ejecta blanket with GRaND suggests that its orange material has ∼25% cumulate eucrite component in a howarditic mixture, whereas two other craters with orange material in their ejecta, Octavia and Arruntia, show no sign of cumulate eucrites. Morphology and topography of the orange material in Oppia and Octavia ejecta and orange patches suggests an impact melt origin. A majority of the orange patches appear to be related to the formation of the Rheasilvia basin. Combining the interpretations from the topography, geomorphology, color and spectral parameters, and elemental abundances, the most probable analog for the orange material on Vesta is impact melt.  相似文献