Sub‐grid scale parameterization of hillslope runoff and erosion processes for catchment‐scale models of semi‐arid landscapes          下载免费PDF全文

Christopher Hutton  Andrew Nicholas  Richard Brazier 《水文研究》2014,28(4):1713-1721

The processes of hillslope runoff and erosion are typically represented at coarse spatial resolution in catchment‐scale models due to computational limitations. Such representation typically fails to incorporate the important effects of topographic heterogeneity on runoff generation, overland flow, and soil erosion. These limitations currently undermine the application of distributed catchment models to understand the importance of thresholds and connectivity on hillslope and catchment‐scale runoff and erosion, particularly in semi‐arid environments. This paper presents a method for incorporating high‐resolution topographic data to improve sub‐grid scale parameterization of hillslope overland flow and erosion models. Results derived from simulations conducted using a kinematic wave overland flow model at 0.5 m spatial resolution are used to parameterize the depth–discharge relationship in the overland flow model when applied at 16 m resolution. The high‐resolution simulations are also used to derive a more realistic parameterization of excess flow shear stress for use in the 16 m resolution erosion model. Incorporating the sub‐grid scale parameterization in the coarse‐resolution model (16 m) leads to improved predictions of overland flow and erosion when evaluated using results derived from high‐resolution (0.5 m) model simulations. The improvement in performance is observed for a range of event magnitudes and is most notable for erosion estimates due to the non‐linear dependency between the rates of erosion and overland flow. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The link between abrupt climate change and basin stratigraphy: a numerical approach     

Mark D. Morehead  James P. Syvitski  Eric W. H. Hutton 《Global and Planetary Change》2001,28(1-4)

To use basin stratigraphy for studying past climate change, it is important to understand the influence of evolving boundary conditions (river discharge and sediment flux, initial bathymetry, sea level, subsidence) and the complex interplay of the redistribution processes (plumes, turbidity currents, debris flows). To provide understanding of this complexity, we have employed source to sink numerical models to evaluate which process dominates the observed variability in a sedimentary record of two coastal Pacific basins, Knight Inlet in British Columbia and the Eel Margin of northern California.During the last glacial period, the Eel River supplied comparatively more sediment with a less variable flux to the ocean, while today the river is dominated by episodic events. Model results show this change in the variability of sediment flux to be as important to the deposit character as is the change in the volume of sediment supply. Due to the complex interaction of flooding events and ocean storm events, the more episodic flood deposits of recent times are less well preserved than the flood deposits associated with an ice-age climate.In Knight Inlet, the evolving boundary conditions (rapidly prograding coastline, secondary transport by gravity flows from sediment failures) are a strong influence on the sedimentary record. The delta and gravity flow deposits punctuate the sedimentary record formed by hemipelagic sedimentation from river plumes. Missing time intervals due to sediment failures can take away the advantage of the otherwise amplified lithologic record of discharge events, given the enclosed nature of the fjord basin.  相似文献   

Dependence on agriculture and ecosystem services for livelihood in Northeast India and Bhutan: vulnerability to climate change in the Tropical River Basins of the Upper Brahmaputra   总被引：1，自引：0，他引：1  

Fiifi Amoako Johnson  Craig William Hutton 《Climatic change》2014,127(1):107-121

The Upper Brahmaputra River Basin is prone to natural disasters and environmental stresses (floods, droughts and bank erosion, delayed rainfall, among others) creating an environment of uncertainty and setting the basin back in terms of socio-economic development. The climate change literature shows that agriculture and ecosystems and their services are highly climate sensitive, yet they are the main sources of livelihood that supports a large proportion of residents of the tributaries of the Brahmaputra River Basin. The continuous depletion of ecosystems and loss of agricultural outputs resulting from environmental stressors has a substantial impact on the socio-economic wellbeing of the basins residents, particularly the vulnerable rural poor. This paper uses spatially explicit data from Census, Household Surveys and Earth Observation to develop a transferable methodological approach which investigates the extent of dependence on agriculture and ecosystems as a source of livelihood in the contrasting sub-basins of the Brahmaputra River in the State of Assam, India and Bhutan, and the risk to these livelihood dependencies in these sub-basins due to potential environmental impacts of climate change. The results from this study constitute a case study in the development of a systematic and spatially explicit set of tools that inform and assist policy makers in the appropriate interventions to secure the livelihood benefits of sustainably managed agriculture in the face of environmental change.  相似文献   

Ethnic Capital and Assimilation to the Great Australian (Homeownership) Dream: the early housing experience of Australia's skilled immigrants   总被引：1，自引：0，他引：1  

James Forrest  Ron Johnston  Michael Poulsen 《The Australian geographer》2014,45(2):109-129

We use the Longitudinal Survey of Immigrants to Australia, 2005–2006, to examine the housing tenure experience of skilled immigrants to Australia 6 and 18 months after arrival for relationships with ethnic capital (cultural background), visa category streams, aspects of human capital, demographics, social capital and discrimination. Homeownership experience is used to indicate integration into Australia's dominantly middle-class society. Multinomial regression analysis identifies visa entry category as the most important independent group of variables accounting for immigrants' short-term dwelling tenure, followed by aspects of human capital, family status, and the importance of ethnic capital for immigrants of both English-speaking and non-English-speaking backgrounds, and discrimination.  相似文献   

ROBERT E. DICKINSON AND THE GROWTH OF URBAN GEOGRAPHY: AN EVALUATION     

Ron Johnston 《Urban geography》2013,34(8):702-736

Although an innovative researcher on urban geography during the 1930s, and a prolific textbook writer thereafter, Robert Dickinson is not now recognized as one of the influential pioneers of that subfield. This paper explores why that was the case by examining his career, writings and influence, and by setting him in the context of a model of scholarly impact. [Key words: Robert Dickinson, pioneers, influence, history of urban geography.]  相似文献   

The role of metropolitan opportunity structures for understanding variation in the rate of Black household affluence     

Ron Malega 《Urban geography》2013,34(4):530-549

This study explores Black household affluence at the metropolitan scale and suggests that metropolitan-level opportunity structures shaped rates of Black affluence for the 100 largest American metropolitan areas in 2000. I hypothesize that affluent black households favored metropolitan areas of opportunity, those places characterized by having (1) economic opportunities, (2) favorable Black–White relational standing, (3) metropolitan diversity and residential opportunities, and (4) their location in the South, which serves as a Black homeplace. Results fail to suggest evidence regarding the role of the ‘new South’ for understanding metropolitan-level rates of Black affluence. More generally, findings from this study challenge our understanding of socioeconomic stratification by investigating diversity within America’s Black community.  相似文献   

Development of daily spatial heat unit mapping from monthly climatic surfaces for the Australian continent     

Nicholas Coops  Andrew Loughhead  Philip Ryan  Ron Hutton 《International journal of geographical information science》2013,27(4):345-361

In absence of other limitations, the growth rate of a plant is dependent upon the amount of heat it receives. Each species, whether a crop, weed or disease organism, is adapted to grow at its optimum rate within a specific temperature range. Within this range, the growing degree days (GDD) is the heat accumulation above a given base temperature for a specific time period, such as a crop's growing season or phenological stage. In this paper we detail a methodology to predict GDD for synthetically generated average growing seasons derived from long term average climate data over the Australian continent. An application of these techniques has been made using the GEODATA 9 second DEM, with temperature threshold values estimated to characterize optimum growth in citrus (Citrus sinensis (L.) Osbeck). Three major determinants of the annual growth cycle of Citrus sp. were established and predicted on a spatial basis including the starting day of the growing season, the GDD for a growing season, and the time required to accumulate an arbitrarily selected 2000 GDD from the estimated starting day. When these critical environmental factors are expressed on a spatial basis, covering the Australian continent, the combination can be used to identify locations where new crop varieties can most effectively be grown to maximize fruit quality and productivity, or to extend the harvest season. Likewise, new germplasm introduced to Australia from overseas can be horticulturally assessed at sites climatically matched to the source location.  相似文献   

Knowing our own history? Geography department archives in the UK   总被引：1，自引：0，他引：1  

Ron Johnston  Charles W J Withers 《Area》2008,40(1):3-11

The paper presents an analysis of the returns to a questionnaire survey on the state of department archives within UK departments of geography. The results of the survey are discussed in relation to recent work in geography which has examined the archive as a site for knowledge's making but seldom in its own terms as a resource for the history of geography, and studies within the archival sciences which have considered the archive as something more than a 'storehouse' for collective memory. The paper reveals that the archival record for the history of British geography is at best uneven, and in many departments non-existent, although information on departmental history is held, often as memory, by individual geographers. The paper considers the survey's implications for the future histories of British geography and addresses the nature of the UK geography department archive as resource and responsibility.  相似文献   

The climatic and physiographic controls of the eastern Mediterranean over the late Pleistocene climates in the southern Levant and its neighboring deserts   总被引：1，自引：0，他引：1  

Yehouda Enzel  Rivka Amit  Uri Dayan  Onn Crouvi  Ron Kahana  Baruch Ziv  David Sharon   《Global and Planetary Change》2008,60(3-4):165-192

Modern-day synoptic-scale eastern Mediterranean climatology provides a useful context to synthesize the diverse late Pleistocene (60–12 ka) paleohydrologic and paleoenvironmental indicators of past climatic conditions in the Levant and the deserts to its south and east. We first critically evaluate, extract, and summarize paleoenvironmental and paleohydrologic records. Then, we propose a framework of eastern Mediterranean atmospheric circulation features interacting with the morphology and location of the southeast Mediterranean coast. Together they strongly control the spatial distribution of rainfall and wind pattern. This cyclone–physiography interaction enforces the observed rainfall patterns by hampering rainfall generation south and southeast of the latitude of the north Sinai coast, currently at 31°15′.The proposed framework explains the much-increased rains in Lebanon and northern Israel and Jordan as deduced from pollen, rise and maintenance of Lake Lisan, and speleothem formation in areas currently arid and semiarid. The proposed framework also accounts for the southward and eastward transition into semiarid, arid, and hyperarid deserts as expressed in thick loess accumulation at the deserts' margins, dune migration from west to east in the Sinai and the western Negev, and the formation of hyperarid (< 80 mm yr^− 1) gypsic–salic soils in the southern Negev and Sinai. Our climatic synthesis explains the hyperarid condition in the southern Negev, located only 200–250 km south of the much-increased rains in the north, probably reflecting a steeper rainfall gradient than the present-day gradient from the wetter Levant into its bordering southern and eastern deserts.At present, the rainiest winter seasons in Lebanon and northern and central Israel are associated with more frequent (+ 20%), deeper Cyprus Lows traversing the eastern Mediterranean at approximately the latitude of southern Turkey. Even these wettest years in northern Israel do not yield above average annual rainfall amounts in the hyperarid southern Negev. This region is mainly influenced by the Active Red Sea Troughs that produce only localized rains. The eastern Mediterranean Cyprus Lows also produce more dust storms and transport higher amounts of suspended dust to the loess area than any other atmospheric pattern. Concurrent rainfall and dust are essential to the late Pleistocene formation of the elongated thick loess zone along the desert northern margin. Even with existing dust storms, the lack of rain and very sparse vegetation account for the absence of late Pleistocene loess sequences from the southern Negev and the formation of hyperarid soils.When the north Sinai coast shifted 30–70 km northwest due to last glacial global sea level lowering, the newly exposed coastal areas supplied the sand and dust to these active eastern Mediterranean cyclones. This enforced the latitude of the northern boundary of the loess zone to be directly due east of the LGM shoreline. This shift of coast to the northwest inhibited rainfall in the southern Levant deserts and maintained their hyperaridity. Concurrently, frequent deep eastern Mediterranean Cyprus Lows were funneled along the northern Mediterranean increasing (probably doubling) the rains in central and northern Israel, Lebanon, southwestern Syria and northern Jordan. These storms and rains formed lakes, forests, and speleothems only a short distance north of the deserts in the southern Levant.  相似文献   

Sediment remobilisation from decomposing cordgrass (Spartina anglica) patches on a wave‐exposed intertidal flat     

Andrew Swales  Ron Ovenden  Iain T. MacDonald  Andrew M. Lohrer  Karen L. Burt 《新西兰海洋与淡水研究杂志》2013,47(6):1305-1319

Abstract

Concerns about the potential adverse effects of Spartina invasion on New Zealand estuaries, such as habitat loss and degradation, have led to herbicide use to control its spread. An experiment was conducted in the Manukau Harbour (New Zealand) to determine sediment remobilisation rates (?E) from herbicide‐treated S. anglica patches. Paired treatment and control patches (≤25 m diam.) were monitored at two sites 500 m apart with different wave exposures. Above‐ (AGB) and below‐ground (BGB) biomass decomposition and AE were determined from repeat surveys over c. 2.5 years. Work done by waves (W), which integrates wave‐energy dissipation at the bed over time, was used as a surrogate measure of sediment transport potential. Complete AGB loss occurred in both treated patches within 3 months of initial herbicide application, whereas BGB (a matrix of roots and rhizomes) persisted much longer. An exponential decay model (r ² = 0.6) fitted to the site‐two treatment data predicted an c. 85% reduction in BGB after 5 years, whereas the BGB changes for the larger and more heterogeneous site‐one treatment were more complex. BGB was a better predictor of average bed elevation than AGB in multiple regression models and, although bed elevation decreased through time and with waves, BGB was positively related to bed elevation at both sites. AE was similar for both treatment patches (c. 0.05 and c. 0.06 m yr^‐1, P < 0.001, r² ≥ 0.97) and complete sediment loss was predicted to occur within 6–10 years. The site‐one control patch accumulated sediment (0.01 m yr^‐1 , P < 0.001, r ² = 0.81) whereas the more wave‐exposed site‐two control eroded (0.01 m yr^‐1, P = 0.0017, r ² = 0.61). The potential for adverse sediment effects resulting from Spartina control at wave‐exposed sites will be minimal if the treated areas are small relative to the size of the estuary.  相似文献