Showing papers in "Progress in Physical Geography in 1997"
TL;DR: In this article, general circulation models (GCMs) suggest that rising concentrations of greenhouse gases may have significant consequences for the global climate, but the extent to which local (local) GCMs are able to cope with these changes is not clear.
Abstract: General circulation models (GCMs) suggest that rising concentrations of greenhouse gases may have significant consequences for the global climate. What is less clear is the extent to which local (s...
1,396 citations
TL;DR: In this paper, a review of recent approaches to the monitoring and modelling of deforestation and dryland degradation in tropical regions is presented, highlighting the requirement to tailor the investigation method to the specific research question of interest.
Abstract: Transformations in terrestrial ecosystems are increasingly regarded as an important element of global change. Quantitative data on where, when and why land-cover changes take place globally are still incomplete. This article reviews recent approaches to the monitoring and modelling of deforestation and dryland degradation in tropical regions. The review highlights the requirement to tailor the investigation method to the specific research question of interest. Different techniques to monitor land-cover changes at regional scales are analysed. The following modelling scenarios are discussed and illustrated by specific studies: projection of future land-cover changes with descriptive models, explanation of land-cover changes with empirical models, projection of future spatial patterns of changes with spatial statistical models, test of scenarios on future changes in land-cover with dynamic ecosystem models, and design of policy interventions with economic models. The article stresses the needs for a better integration of social science knowledge in land-cover change models and for a comprehensive theory of land-use changes.
589 citations
TL;DR: In this paper, the authors proposed that soil erosion by water is one of the most important land degradation processes in Mediterranean environments and that this process is strongly linked to problems of flooding and channel management.
Abstract: Soil erosion by water is one of the most important land degradation processes in Mediterranean environments. This process is strongly linked to problems of flooding and channel management. This art...
365 citations
TL;DR: Quasi-periodicities in annual rainfall totals over southern Africa have been identified; in particular, an approximately 18-year cycle may be related to interdecadal variability in sea surface temp as discussed by the authors.
Abstract: Quasi-periodicities in annual rainfall totals over southern Africa have been identified; in particular, an approximately 18-year cycle may be related to interdecadal variability in sea-surface temp...
273 citations
TL;DR: In this paper, the authors reviewed previous investigations into gully and badland research and discussed processes and definitions in the context of existing research in southeast Spain, including overland flow, hillslope processes, pipe initiation and enlargement, mass failures and the magnitude and frequency distribution of storm events.
Abstract: This article reviews previous investigations into gully and badland research and discusses processes and definitions in the context of existing research in southeast Spain. The theory of badland development is summarized and definitions are proposed which draw on previous work and continuing studies. The processes influencing gully and channel head morphology are then discussed including overland flow, hillslope processes, pipe initiation and enlargement, mass failures and the magnitude and frequency distribution of storm events. Finally, modelling of badland landscapes is discussed. The article highlights that much detailed research has been carried out on badlands, but long-term rates of gully development are not well understood. There are also gaps in our understanding of pipe network formation and collapse. In the short term theoretical modelling may provide the way forward and a direction for more holistic investigations.
173 citations
TL;DR: It is proposed that the term 'transitional area' is used to describe all types of vegetation boundary when working at the local/community scale and the range of research methods available to describe and analyse variations in patterns of floristics and associated environmental variables across transitional areas is critically reviewed.
Abstract: The increasing relevance and importance of the subject of landscape ecology to bio geography are introduced. Research into landscape and plant community boundaries, never theless, remains comparatively neglected. In particular, the nature of those boundaries in terms of the patterns of floristic change and related ecosystem properties constitutes a potentially signifi cant new area of research for biogeographers. The term 'ecotone' has traditionally been used to describe boundaries between plant communities and ecosystems at a range of scales. Various definitions are presented and the often confusing terminology surrounding the word 'ecotone' is reviewed. Boundary types range from sharp, clearly defined boundaries (ecotones) between more highly modified plant communities and anthropogenically created land-use types at one extreme, to more gradual and diffuse boundaries (ecoclines) between natural and semi-natural plant communities at the other. It is proposed that the term 'transitional area' is used to d...
164 citations
TL;DR: The current state of regional climate and climate change modelling using GCMs is reviewed for southern Africa, and several approaches to regional climate change prediction which have been applied t... as mentioned in this paper.
Abstract: The current state of regional climate and climate change modelling using GCMs is reviewed for southern Africa, and several approaches to regional climate change prediction which have been applied t...
96 citations
TL;DR: In this paper, the establishment of a winter rainfall regime in the southwestern part of the subcontinent probably dates from around 2.6 myr, which ushered in the cyclical fluctuations of the Pleistocene.
Abstract: Since the end of the Cretaceous, Africa's latitudinal drift has been relatively small and has not significantly modified the general pattern of stepwise cooling and aridification that has characterized the Cainozoic era. Tectonic uplift has, in contrast, strongly influenced regional climates in east and southern Africa, especially during the late Neogene, and has accentuated the east-west moisture gradient which has prevailed, with minor interruptions, since the Oligocene. In common with most other midlatitude regions, southern African environments responded dramatically to the global episode of cooling and drying between 2.8 and 2.6 myr which ushered in the cyclical fluctuations of the Pleistocene. The establishment of a winter rainfall regime in the southwestern part of the subcontinent probably dates from around 2.6 myr. In the north east, new proxy data spanning the last 200 000 years indicate that summer rainfall varied in relation to receipts of solar insolation at precessional frequencies. Superimp...
95 citations
TL;DR: Most of the literature on pronival (protalus) ramparts deals with supposed fossil examples with very few studies devoted to active features and/or observed processes as discussed by the authors, which has led...
Abstract: Most of the literature on pronival (protalus) ramparts deals with supposed fossil examples with very few studies devoted to active features and/or observed processes. Not surprisingly, this has led...
88 citations
TL;DR: South Africa is already hydrologically vulnerable and this is likely to be exacerbated by both nonpermanent ENSO-related as well as more permanently greenhouse-gas forced climate changes as discussed by the authors.
Abstract: South Africa is already hydrologically vulnerable and this is likely to be exacerbated by both nonpermanent ENSO-related as well as more permanently greenhouse-gas forced climate changes. Climate c...
57 citations
TL;DR: The Younger Dryas refers to the final phase of cold, glacial conditions preceding the abrupt climatic warming at the beginning of the Holocene as mentioned in this paper, and has been linked with a large-scale shift of the North Atlantic thermohaline circulation (THC) to a near glacial mode with a consequent reduction in northward heat transport.
Abstract: The Younger Dryas refers to the final phase of cold, glacial conditions preceding the abrupt climatic warming at the beginning of the Holocene. The existence of the Younger Dryas in Europe has been known for most of this century, although recent research suggests that the Younger Dryas cooling may have been global. Estimates of the timing of the event have also improved in recent years, showing that both the onset and termination of the Younger Dryas were abrupt, occurring within decades. The Younger Dryas has been linked with a large-scale shift of the North Atlantic thermohaline circulation (THC) to a near glacial mode with a consequent reduction in northward heat transport. This shift in the THC may have been triggered by a discharge of Laurentide ice, combined with meltwater inputs from several locations around the North Atlantic. Further study of the events leading up to the Younger Dryas is necessary for improving theoretical understanding of abrupt climatic change, and for evaluating GCM models whi...
TL;DR: In this article, recent developments concerning the transport of air, aerosols and other airborne material over and out of a region has important consequences for global change, and the authors present a survey of these developments.
Abstract: Atmospheric transport of airborne material over and out of a region has important consequences for global change. In this article, recent developments concerning the transport of air, aerosols and ...
TL;DR: Although there has been a series of progress reports on sea level (Woodroffe, 1993, 1994, Woodroffe and Nash, 1995, Reed, 1996) and articles on coastal topics have appeared in this journal (i.e., Reed, 1993; Sherman and Bauer, 1993b; Forbes and Taylor, 1994; Nordstrom, 1994), there has not been a progress report on coastal geomorphology since that of Viles (1991) as mentioned in this paper.
Abstract: Although there has been a series of progress reports on sea level (Woodroffe, 1993; 1994; Woodroffe and Nash, 1995; Reed, 1996) and articles on coastal topics have appeared in this journal (i.e., Reed, 1993; Sherman and Bauer, 1993b; Forbes and Taylor, 1994; Nordstrom, 1994), there has not been a progress report on coastal geomorphology since that of Viles (1991). The task of summarizing the developments in coastal research since
TL;DR: A number of new texts have appeared, either specifically concerned with savannas (Scholes and Walker, 1993, Young and Solbrig, 1993; Solbrigen et al., 1996a), or with associated types of vegetation (Bullock et al. as discussed by the authors ).
Abstract: Since the last report (Furley, 1994), there has been considerably more attention paid to the biological significance of savannas and their resources, as well as to development impacts on these diverse formations. A number of new texts have appeared, either specifically concerned with savannas (Scholes and Walker, 1993; Young and Solbrig, 1993; Solbrig et al., 1996a), or with associated types of vegetation (Bullock et al., 1995; McClaran and
TL;DR: In this paper, a combination of a simple geometric optics model of bidirectional reflectance and computer graphics is given, where simulations of remotely sensed scenes are produced, and the output of a SVAT scheme can also be used to drive radiative transfer models at different wavebands.
Abstract: This article assesses the potentially powerful combination of remotely sensed data and soil-vegetation-atmosphere transfer (SVAT) schemes. SVATS represent the hydrological processes occurring at the land surface and can be used to estimate, among other processes, the exchange of water and energy between the soil, vegetation and the atmosphere. They require information about the interaction of radiation with the soil and vegetation. Bidirectional reflectance models are now starting to be used to determine the partitioning of radiation. An example of the combination of a simple geometric optics model of bidirectional reflectance and computer graphics is given, where simulations of remotely sensed scenes are produced. The next step is to couple these models to a SVAT scheme. The output of a SVAT scheme can also be used to drive radiative transfer models at different wavebands. This approach is illustrated by the estimation of soil hydraulic properties using a time series of passive microwave emission observa...
TL;DR: In the mid-1960s, there was a tension between historical and process approaches to the study of landforms as discussed by the authors, and it was no surprise that the first reading of Schumm and Lichty produced a sense of both relief and excitement.
Abstract: No student of Advanced Physiography in the Cambridge Geography Department in the mid-1960s could doubt that there was a tension between ’historical’ and ’process’ approaches to the study of landforms. On the one hand there was B.W. Sparks, the student of Wooldridge, with his insistence on the long-term development of relationships between rocks and relief; on the other R.J. Chorley, the student of Strahler, emphasizing the ’timelessness’ of the ’new’ process studies emanating largely from North America. I can still recall the arguments: my supervision partner, an ardently process-orientated character, was regularly rendered apoplectic by Sparks’s lack of enthusiasm for some supposed insights of the ’process’ school which, in his view, had little of relevance to say about the evolution of the landscape. In such a context, it was scarcely surprising that the first reading of Schumm and Lichty produced if not quite the impact of Chapman’s Homer on John Keats a sense of both relief and excitement. But and this is true it
TL;DR: The classic monograph is usually seen as a methodological and conceptual break with the past, a work which introduces a new discourse and is ahead of its time as mentioned in this paper. But the excellence of a classic can also lie in the fact that it is typical of its times and represents the best that was possible with the available knowledge and insights.
Abstract: The classic monograph is usually seen as a methodological and conceptual break with the past, a work which introduces a new discourse and is ahead of its time. Yet the excellence of a classic can also lie in the fact that it is typical of its time and represents the best that was possible with the available knowledge and insights. Such a work was Wellington's Southern Africa, Part 1.
TL;DR: A review of reconstructions of the last Barents ice mass, and compares these models with geological and palaeoceanographic information from the area in order to provide a summary of what is presently known, and to indicate explicitly what is not known.
Abstract: Reconstructions of the Late Weichselian ice sheet within the Barents Sea have varied from complete coverage of a large (3 km thick) grounded ice mass, to a situation in which glacier extent was restricted to the Svalbard coast. Recently obtained geological data indicate that 1) glaciation of the Barents Sea occurred after 25 000 years ago; 2) the ice sheet was at its maximum extent at around 20 000 years ago; 3) the maximum-sized ice sheet covered the entire Barents Shelf; and 4) ice-sheet decay began at about 16 500 years ago. The ice sheet was, consequently, one of the last to grow and first to decay during the last glacial. However, this recently derived chronology of glacial events has reintroduced problems concerning the thickness distribution of the maximum-sized ice sheet, and the glaciological processes by which rapid glaciation and ice decay happened. In particular, the situation in which regional glaciation of Bjornoya occurred at the same time as grounded ice (and ice-stream activity) within the relatively deep Bjornoyrenna is yet to be understood fully. This article provides a review of reconstructions of the last Barents ice mass, and compares these models with geological and palaeoceanographic information from the area in order to provide a summary of what is presently known, and to indicate explicitly what is not known, about the Late Weichselian Barents Sea ice sheet.
TL;DR: Biogeochemical modelling has been used to provide new insight into the geographical distribution and underlying mechanisms of palatable (sweetveld) and unpalatable (sour veld) grasslands and high-herbivory and low- herbivory savannas as discussed by the authors.
Abstract: Biogeochemical modelling is largely concerned with the cycling of carbon, nitrogen, phosphorus and sulphur in the biosphere. It offers a robust approach to modelling many aspects of ecosystem function at the regional scale, since it is not highly dependent on a detailed know ledge of species or organism-level processes. In southern Africa biogeochemical modelling has been used to provide new insight into the geographical distribution and underlying mechanisms of palatable (sweetveld) and unpalatable (sourveld) grasslands and high-herbivory and low- herbivory savannas. It has also been applied to the problem of estimating the emissions of trace gases and smoke particles from vegetation fires in the region, and suggests that the emissions are much lower than previously believed. Work in progress relates to the modelling of tropospheric ozone precursors produced by the soil and plants. Biogeochemical modelling has the potential to be an integrating tool, drawing together data collected at widely different sc...
TL;DR: In this article, the importance of tropical geomorphology against the current background of increasing environmental urgency is reasserted, in which the massive environmental changes now affecting tropical and savannah ecosystems.
Abstract: Tropical geomorphology has formed a ’corestone’ of geomorphological thinking for the best part of a century, and has provided the inspiration and testing ground for many major theories of geomorphological evolution. Some of these have not weathered well in the face of new insight and analytical data, while others have become refined into a durable residuum of established ideas and thought. Nevertheless, it is true to say that study of tropical landforms, and the processes governing their formation, have remained a central part of modern geomorphological science, though in recent decades interest has perhaps enjoyed a higher profile within the Australian literature compared with that of the European and American schools. This book reasserts the importance of tropical geomorphology against the current background of increasing environmental urgency; namely, the massive environmental changes now affecting tropical and savannah ecosystems. Written by one of the leading experts in the subject, it is a timely addition to existing texts because it re-evaluates the concepts of tropical geomorphology amidst the modern concerns of environmental change and its associated implications. From the outset this book makes clear its aim to emphasize the wider importance of understanding of landscape evolution, soil-forming processes and climate change within tropical regions. An entire section considers the effects of Quaternary environmental change with regard to tropical geomorphology, and effectively summarizes much of the current thinking on this subject. Nevertheless, while due consideration is given to what may, arguably, turn out to be fashionable themes in research and literature, the text resists the urge to follow these unquestioningly and, as a result, the overall concept and thematic structure are not sacrificed to current geomorphological vogues. Whether or not this has been a conscious decision on behalf of the author, it should ensure a place for this book
TL;DR: The practice of river channel restoration is evolving rapidly as appreciation grows of how geomorphological, hydrological and ecological processes together determine the character of aquatic ecosystems as mentioned in this paper, and this realization coincides with a growing pressure for improvement of river systems that have been impacted globally by attempts to control their natural functioning whether for navigation, power, land drainage or flood control.
Abstract: The practice of river channel restoration is evolving rapidly as appreciation grows of how geomorphological, hydrological and ecological processes together determine the character of aquatic ecosystems. This realization is timely, as it coincides with a growing pressure for improvement of river systems that have been impacted globally by attempts to control their natural functioning whether for navigation, power, land drainage or flood control. These processes affect the preservation of biodiversity, and maintenance of the range of habitats required to sustain the diverse flora and fauna that characterize river channels and their associated landforms. Conservation of the beneficial attributes of
TL;DR: At moderate Reynolds numbers, the restraining effects of viscosity are too weak to prevent small, random disturbances in a shear flow from amplifying as discussed by the authors, and the disturbances grow, become nonlinear and interact with neighbouring disturbances.
Abstract: At moderate Reynolds numbers the restraining effects of viscosity are too weak to prevent small, random disturbances in a shear flow from amplifying. The disturbances grow, become nonlinear and interact with neighbouring disturbances. This mutual interaction leads to a tangling of vorticity filaments. Eventually the flow reaches a chaotic, nonrepeating form that is describable only in statistical terms. This is turbulent flow. Turbulent flow initially was treated as a stochastic entity, where randomized fluctuations occurred about the mean flow. However, it