The nature, extent and causes of land degradation in South Africa: legacy of the past, lessons for the future?     

M. E. Meadows  & M. T. Hoffman 《Area》2002,34(4):428-437

The aim of this paper is to reassess the land degradation and desertification problem in South Africa. The country has a wide range of interrelated environmental and development challenges existing in a socio–political context recently subject to substantial change. The paper outlines the fundamental environmental constraints and opportunities that underlie degradation phenomena and illustrates the nature, extent and geographical distribution of the major forms of soil and vegetation degradation in the country. The principal causes of degradation are identified and some important land use and land tenure questions that need to be addressed in the near future are posited.  相似文献   

New constraints on the late Cenozoic incision history of the New River, Virginia     

Dylan J. Ward  James A. Spotila  Gregory S. Hancock  John M. Galbraith   《Geomorphology》2005,72(1-4):54-72

The New River crosses three physiogeologic provinces of the ancient, tectonically quiescent Appalachian orogen and is ideally situated to record variability in fluvial erosion rates over the late Cenozoic. Active erosion features on resistant bedrock that floors the river at prominent knickpoints demonstrate that the river is currently incising toward base level. However, thick sequences of alluvial fill and fluvial terraces cut into this fill record an incision history for the river that includes several periods of stalled downcutting and aggradation. We used cosmogenic ¹⁰Be exposure dating, aided by mapping and sedimentological examination of terrace deposits, to constrain the timing of events in this history. ¹⁰Be concentration depth profiles were used to help account for variables such as cosmogenic inheritance and terrace bioturbation. Fill-cut and strath terraces at elevations 10, 20, and 50 m above the modern river yield model cosmogenic exposure ages of 130, 600, and 600–950 ka, respectively, but uncertainties on these ages are not well constrained. These results provide the first direct constraint on the history of alluvial aggradation and incision events recorded by New River terrace deposits. The exposure ages yield a long-term average incision rate of 43 m/my, which is comparable to rates measured elsewhere in the Appalachians. During specific intervals over the last 1 Ma, however, the New River's incision rate reached 100 m/my. Modern erosion rates on bedrock at a prominent knickpoint are between 28 and 87 m/my, in good agreement with rates calculated between terrace abandonment events and significantly faster than 2 m/my rates of surface erosion from ancient terrace remnants. Fluctuations between aggradation and rapid incision operate on timescales of 10⁴− 10⁵ year, similar to those of late Cenozoic climate variations, though uncertainties in model ages preclude direct correlation of these fluctuations to specific climate change events. These second-order fluctuations appear within a longer-term signal of dominant aggradation (until 2 Ma) followed by dominant incision. A similar signal is observed on other Appalachian rivers and may be the result of sediment supply fluctuations driven by the increased frequency of climate changes in the late Cenozoic.  相似文献   

The initial development of solar flares     

J. F. Vesecky  A. J. Meadows 《Solar physics》1969,6(1):80-85

The extent to which the early phases of solar-flare development can be accounted for by a simple high-temperature chromospheric explosion model is investigated without involving a particular energy source. A model is developed in which it is shown that a point explosion in the lower chromosphere can be treated as a virtually instantaneous release of energy throughout a volume of radius R 100 km, which subsequently expands as a classical hydrodynamic blast wave in which R~ t ( < 2/3). This model is in substantial agreement with areal growth-rate observations of disk flares. An explanation for the fact that limb-flare observations can imply > 2/3 is suggested by considering the effects of the large atmospheric density gradient in the lower chromosphere on an upward travelling shock wave.  相似文献   

Deaggregation of multi-hazard damages,losses, risks,and connectivity: an application to the joint seismic-tsunami hazard at Seaside,Oregon     

Sanderson  Dylan  Kameshwar  Sabarethinam  Rosenheim  Nathanael  Cox  Daniel 《Natural Hazards》2021,109(2):1821-1847

This paper presents a methodology to deaggregate the results of a multi-hazard damage analysis by extending the traditional multi-hazard damage analysis to consider both population characteristics and independent hazards. The methodology is applied to the joint seismic-tsunami hazard at Seaside, Oregon, considering four infrastructure systems: (1) buildings, (2) transportation network, (3) electric power network and (4) water supply network. Damages to all infrastructure systems are evaluated, and the networked infrastructures are used to inform parcel connectivity to critical facilities. US Census data and a probabilistic housing unit allocation method are implemented to assign detailed household demographic characteristics at the parcel level. Six dimensions of deaggregation are introduced: (1) spatial, (2) hazard type, (3) hazard intensity, (4) infrastructure system, (5) infrastructure component, and (6) housing unit characteristics. The damages, economic losses and risks, and connectivity to critical facilities are deaggregated across these six dimensions. The results show that deaggregated economic loss and risk plots can allow community resilience planners the ability to isolate high-risk events, as well as provide insights into the underlying driving forces. Geospatial representation of the results allows for the identification of both vulnerable buildings and areas within a community and is highlighted by the spatial pattern of parcel disconnection from critical facilities. The incorporation of population characteristics provides an understanding of how hazards disproportionately impact population subgroups and can aide in equitable resilience planning.

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Probabilistic flood risk analysis considering morphological dynamics and dike failure     

J. Oliver  X. S. Qin  O. Larsen  M. Meadows  M. Fielding 《Natural Hazards》2018,91(1):287-307

A comprehensive flood risk assessment should aim not only at quantifying uncertainties but also the variability of risk over time. In this study, an efficient modelling framework was proposed to perform probabilistic hazard and risk analysis in dike-protected river systems accounting for morphological variability and uncertainty. The modelling framework combined the use of: (1) continuous synthetic discharge forcing, (2) a stochastic dike breach model dynamically coupled to a stochastic unsteady one-dimensional hydraulic model (MIKE1D) describing river flows, (3) a catalogue of pre-run probabilistic inundation maps (MIKE SHE) and (4) a damage and loss model (CAPRA). The methodology was applied using continuous simulations to a 45-km reach of the Upper Koshi River, Nepal, to investigate the changes in breach and flood hazards and subsequent risks after 2 and 5 years of probable river bed aggradation. The study results indicated an increase in annual average loss of 4% per year driven by changes in loss distribution in the most frequent loss return periods (20–500 years). The use of continuous simulations and dike breach model also provided a more robust estimation of risk metrics as compared to traditional binary treatment of flood defence and/or the direct association of flow with loss return periods. The results were helpful to illustrate the potential impacts of dynamic river morphology, dike failure and continuous simulation and their significance when devising flood risk study methodologies.  相似文献   

Surface Estimation for Multiple Misaligned Point Sets     

Wiens  Ashton  Kleiber  William  Barnhart  Katherine R.  Sain  Dylan 《Mathematical Geosciences》2020,52(4):527-542

Mathematical Geosciences - Two common tasks when processing point cloud data sets are surface estimation and point cloud registration. In this paper, a statistical approach is developed to solve...  相似文献   

Bridging the Gap Between Research and Practice          下载免费PDF全文

Dylan J. Irvine 《Ground water》2018,56(1):1-1

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Heat: An Overlooked Tool in the Practicing Hydrogeologist's Toolbox     

Barret L. Kurylyk  Dylan J. Irvine 《Ground water》2019,57(4):517-524

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Characterizing the changing environment of cropland in the Songnen Plain,Northeast China,from 1990 to 2015     

Zhang  Yuan  Zang  Shuying  Sun  Li  Yan  Binghe  Yang  Tianpeng  Yan  Wenjia  Meadows  Michael E.  Wang  Cuizhen  Qi  Jiaguo 《地理学报(英文版)》2019,29(5):658-674

Journal of Geographical Sciences - Quantitative characterization of environmental characteristics of cropland (ECC) plays an important role in maintaining sustainable development of agricultural...  相似文献   

Effects of ozone depletion and increased ultraviolet-B radiation on northern vegetation   总被引：2，自引：0，他引：2  

Lars Olof Björn  Terry V. Callaghan  Carola Gehrke  Dylan Gwynn-Jones  John A. Lee  Ulf Johanson  Mats Sonesson  Nicholas D. Buck 《Polar research》1999,18(2):331-337

The stratospheric ozone layer has been depleted at high and mid-latitudes as a consequence of man's pollution of the atmosphere, and this results in increasing ultraviolet-B radiation at ground level. We investigate the effects of further radiation increases on plants and ecosystems by irradiating natural sub-Arctic and Arctic vegetation with artificial UV-B radiation in field experiments extending over several years. Our experimental sites are located at Abisko, in northern Sweden (68°N), and Adventdalen, on the island of Spitsbergen (78°N). Additional UV-B induced interspecific differences in plant response in terms of reduced (or, in one case, increased) growth, changed morphology and changed pigment content. In some cases effects seem to be accumulated from one year to another. Plant litter decomposition is retarded. We are also studying how UV-B enhancement may affect the interaction between species. In some experiments we combine UV-B enhancement with changes in other factors: carbon dioxide concentration, water availability, and temperature. In some cases the effect of radiation enhancement is modified, or even reversed, by such changes. Over a four year period we did not find any significant radiation induced change in species composition, but based on the effects on individual plant species, such changes can be expected to take place over a longer time.  相似文献