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排序方式: 共有163条查询结果,搜索用时 31 毫秒
81.
Development of a 3D groundwater model based on scarce data: the Wadi Kafrein catchment/Jordan 总被引:2,自引:2,他引:0
Yajie Wu Wenqing Wang Mathias Toll William Alkhoury Martin Sauter Olaf Kolditz 《Environmental Earth Sciences》2011,64(3):771-785
In this work, a 3D groundwater flow model integrating all important geological features of the hydrogeological system is developed
to investigate hydrological processes in the Wadi Kafrein area of Jordan. A large amount of available geological and hydrological
data is integrated to construct a 3D groundwater flow model for the Wadi Kafrein area. Using the newly developed mapping approach,
the translation of the highly detailed geological formations to an unstructured finite element grids, can be accomplished
with high precision. The existing data set for model calibration is scarce, which is a typical situation for many hydrogeological
case studies. At first, the steady state calibration of the groundwater model is carried out based on the observation wells.
Then, the time and space-dependent recharge from precipitation are applied at the top surface of the finite element model.
The transient simulation is conducted during the period of 1996–2008 considering the abstraction rates of the production wells
and discharge of the springs. The calculated water levels are close to the observed values. The difference is partly caused
by return flows from irrigation and the groundwater inflow from the adjacent aquifers which are not taken into consideration
so far. Since the Wadi Kafrein area is an important agricultural area in the semiarid region of the Lower Jordan Valley, the
model developed in this study can be regarded as a useful tool for analyzing the hydrological processes and improving groundwater
management practices elsewhere affected by similar geological and hydrogeological conditions. 相似文献
82.
Saleh A.S. Yahya Martin Gullström Marcus C. ÖhmanNarriman S. Jiddawi Mathias H. AnderssonYunus D. Mgaya Ulf Lindahl 《Estuarine, Coastal and Shelf Science》2011,94(1):16-23
Degradation and mortality of corals is increasing worldwide and is expected to have significant effects on coral reef fish; hence studies on these effects are essential. In the present study, a field experiment was set up within Mafia Island Marine Park in Tanzania (East Africa) to examine the effects of bleaching and habitat structure on colonisation of coral reef fish assemblages. Live and bleached staghorn coral Acropora formosa was transplanted onto plots in a site dominated by sand and rubble, and the experimental design comprised of three treatments: live coral, bleached coral and eroded coral rubble. There was an immediate increase (within 24 h) in fish abundance and diversity in the two treatments with standing corals. Overall, live and bleached coral plots showed similar effects, but differed from the eroded coral plots which had a much lower abundance and diversity of fish. In general, fish species diversity changed with time over the study period while fish abundance did not. Multivariate analyses showed that while there were differences in fish assemblage structure between standing corals and the eroded coral treatment, there was neither a difference between live and bleached coral treatments nor any temporal effects on fish assemblage structure. Our findings suggest that physical structure and complexity of habitat have stronger effects on colonisation of reef fish assemblages than changes in coral health (such as bleaching) which do not affect coral structure. This may have important implications for appropriate coral reef management. 相似文献
83.
Annual floods in New England (USA) and Atlantic Canada: synoptic climatology and generating mechanisms 总被引:1,自引:1,他引:0
Mathias J. Collins Johnathan P. Kirk Joshua Pettit Arthur T. DeGaetano M. Sam McCown Thomas C. Peterson 《自然地理学》2014,35(3):195-219
New England and Atlantic Canada are characterized by mixed flood regimes that reflect different storm types, antecedent land surface conditions, and flood seasonality. Mixed flood regimes are known to complicate flood risk analyses, yet the synoptic climatology and precipitation mechanisms that generate annual floods in this region have not been described in detail. We analyzed a set of long-term annual flood records at climate-sensitive stream gauges across the region and classified the synoptic climatology of each annual flood, quantitatively describing the precipitation mechanisms, and characterize flood seasonality. We find that annual floods here are dominantly generated by Great Lakes-sourced storms and Coastal lows, known locally as ‘nor’easters.’ Great Lakes storms tend to be associated with lower magnitude annual floods (<75th percentile) and Coastal lows are more clearly associated with higher magnitude events (>75th percentile). Tropical cyclones account for few of all annual floods, including extreme events, despite causing some of the region’s largest and most destructive floods. Late winter/early spring is when the greatest number of annual floods occur region wide, and rainfall is the dominant flood-producing mechanism. Rainfall in combination with snowmelt is also important. Both mechanisms are expected to be impacted by projected regional climate change. We find little evidence for associations between flood-producing synoptic storm types or precipitation mechanisms and large-scale atmospheric circulation indices or time periods, despite upward trends in New England annual flood magnitudes. To more completely investigate such associations, partial duration flood series that include more floods than just the largest of each year, and their associated synoptic climatologies and precipitation mechanisms, should be analyzed. 相似文献
84.
AbstractWe evaluate flood magnitude and frequency trends across the Mid-Atlantic USA at stream gauges selected for long record lengths and climate sensitivity, and find field significant increases. Fifty-three of 75 study gauges show upward trends in annual flood magnitude, with 12 showing increases at p < 0.05. We investigate trends in flood frequency using partial duration series data and document upward trends at 75% of gauges, with 27% increasing at p < 0.05. Many study gauges show evidence for step increases in flood magnitude and/or frequency around 1970. Expanding our study area to include New England, we find evidence for lagged positive relationships between the winter North Atlantic Oscillation phase and flood magnitude and frequency. Our results suggest hydroclimatic changes in regional flood response that are related to a combination of factors, including cyclic atmospheric variability and secular trends related to climate warming affecting both antecedent conditions and event-scale processes.Editor Z.W. Kundzewicz; Associate editor H. Lins 相似文献
85.
Carlo Donadio Fernando Magdaleno Adriano Mazzarella G. Mathias Kondolf 《Pure and Applied Geophysics》2015,172(7):1975-1984
86.
Rüdiger Glaser Dirk Riemann Johannes Schönbein Mariano Barriendos Rudolf Brázdil Chiara Bertolin Dario Camuffo Mathias Deutsch Petr Dobrovolný Aryan van Engelen Silvia Enzi Monika Halíčková Sebastian J. Koenig Oldřich Kotyza Danuta Limanówka Jarmila Macková Mirca Sghedoni Brice Martin Iso Himmelsbach 《Climatic change》2010,101(1-2):235-256
The paper presents a qualitative and quantitative analysis of flood variability and forcing of major European rivers since AD 1500. We compile and investigate flood reconstructions which are based on documentary evidence for twelve Central European rivers and for eight Mediterranean rivers. Flood variability and underlying climatological causes are reconstructed by using hermeneutic approaches including critical source analysis and by applying a semi-quantitative classification scheme. The paper describes the driving climatic causes, seasonality and variability of observed flood events within the different river catchments covering the European mainland. Historical flood data are presented and recent research in the field of historical flood reconstructions is highlighted. Additionally, the character of the different flood series is discussed. A comparison of the historical flood seasonality in relation to modern distribution is given and aspects of the spatial coherence are presented. The comparative analysis points to the fact that the number of flood events is predominately triggered by regional climatic forcing, with at most only minor influence on neighbouring catchments. The only exceptions are extreme, supra-regional climatic events and conditions such as anomalous cold winters, similar to that of 1784, which affected large parts of Europe and triggered flood events in several catchments as a result of ice-break at the beginning of the annual thaw. Four periods of increased occurrence of flooding, mostly affecting Central European Rivers, have been identified; 1540–1600, 1640–1700, 1730–1790, 1790–1840. The reconstruction, compilation and analysis of European-wide flood data over the last five centuries reveal the complexity of the underlying climatological causes and the high variability of flood events in temporal and spatial dimension. 相似文献
87.
Mathias Versichele Tijs Neutens Matthias Delafontaine Nico Van de Weghe 《Applied geography (Sevenoaks, England)》2012,32(2):208-220
In this paper, proximity-based Bluetooth tracking is postulated as an efficient and effective methodology for analysing the complex spatiotemporal dynamics of visitor movements at mass events. A case study of the Ghent Festivities event (1.5 million visitors over 10 days) is described in detail and preliminary results are shown to give an indication of the added value of the methodology for stakeholders of the event. By covering 22 locations in the study area with Bluetooth scanners, we were able to extract 152,487 trajectories generated by 80,828 detected visitors. Apart from generating clear statistics such as visitor counts, the share of returning visitors, and visitor flow maps, the analyses also reveal the complex nature of this event by hinting at the existence of several mutually different visitor profiles. We conclude by arguing why Bluetooth tracking offers significant advantages for tracking mass event visitors with respect to other and more prominent technologies, and outline some of its remaining deficiencies. 相似文献
88.
A. P. Butler S. A. Mathias A. J. Gallagher D. W. Peach A. T. Williams 《Hydrogeology Journal》2009,17(8):1849-1858
An integrated set of different measurements has been used to study the behavior of groundwater in an observation well in a fractured rock formation, the UK Chalk, under pumped and ambient conditions. Under pumped conditions, the response of the open borehole was relatively straightforward with flow mainly concentrated along four discrete flow horizons. Furthermore, excellent correspondence was observed between the three methods of borehole flow velocity measurement: impeller flowmeter, heat-pulse flowmeter and dilution testing. Under ambient conditions, the system appeared more complicated. Specifically, in the upper half of the borehole, the impeller flowmeter exhibited substantial downward flow and the heat-pulse flowmeter exhibited almost negligible upward flow, whilst dilution testing indicated significant dilution. It was concluded that this was due to cross-flow occurring over the upper 29 m. Analysis of drawdown data, recovery data and a Drost analysis of the ambient cross-flow data yielded aquifer transmissivity estimates of 2,049, 2,928 and > 4,388 m2/day respectively. The discrepancy between the drawdown and recovery estimates was attributed to non-linear head-losses associated with turbulence and inertial effects. The difference between the pumping test and Drost results was explained by the flow during the pumping test bypassing this aforementioned 29 m region of rock. 相似文献
89.
K. Raschke 《Theoretical and Applied Climatology》1956,7(2):240-268
Zusammenfassung Die Energieumsätze eines Alocasiablattes setzen sich im wesentlichen aus dem sichtbaren und dem infraroten Strahlungsaustausch, den Konvektionsumsätzen und den Transpirationsverlusten zusammen. Sie wurden, getrennt in die Werte von Ober- und Unterseite des Blattes, unter verschiedenen Bedingungen in natürlichen Verhältnissen gemessen. Die Ergebnisse werden sowohl in der Form von Tagesläufen der Einzelkomponenten als auch in Bilanzen dargeboten.Die Ermittlungen wurden nach zwei Grundmethoden durchgeführt. Beide basierten einmal auf direkten Strahlungsmessungen, zum anderen entweder auf Bestimmungen der Wärmeübergangszahlen und der relativen Wasserbedeckungsfaktoren der Blattseiten oder auf Messungen der Temperatur- und Feuchtegradienten in Blattnähe. Beide Verfahren setzen die Kenntnis des Verhältnisses der Konvektionsverluste der beiden Blattseiten (das für das waagrechte Blatt meistens den Wert 1,0 annimmt) voraus, das zweitgenannte Verfahren dazu noch die des Verhältnisses der Austauschkoeffizienten für Wasserdampf und Wärme (das zu 1,00±0,05 gefunden wurde).Aus den Ergebnissen lassen sich Aussagen über die Eigenschaften des Alocasiablattes als Strahlungspartner im Sichtbaren und im Infraroten und über das Verhältnis der Transpirations- und der Konvektionsverluste eines besonnten Blattes und dessen Auswirkung auf die Blattemperatur herleiten. Die transpirationsbeeinflussende Wirkung der Strahlung erweist sich als groß, die des Windes als sehr gering, während die unabhängig voneinander reagierenden Stomata zu eigenartigen Schwankungen des Verhältnisses zwischen Ober- und Unterseitentranspiration Anlaß geben. Schließlich werden Wechselwirkungen zwischen Mikroklima und Wärmehaushalt besprochen.
Mit 8 Textabbildungen
Diese Arbeit wurde durch ein Stipendium der indischen Regierung im Rahmen des Indo-German Industrial Cooperation Scheme ermöglicht. 相似文献
Summary The energy-balance of an Alocasia leaf is made up primarily of the radiation exchange in the visible and infra-red, of the convective transfer, and of the losses by transpiration. Each of these items has been split up into the values for the upper and for the lower surfaces of the leaf and was measured under different conditions in situ. Results are presented in the form of graphs showing the diurnal variations of the different energy components as well as in the form of balance sheets.Two methods were applied, both of which required direct radiation measurements. The first method further utilised determinations of the heat transfer coefficients and the relative wetness factors of the leaf surfaces, whereas the other method was based on measurements of the gradients of temperature and humidity close to the leaf. For both cases the ratio of the convective losses from both the surfaces of the leaf must be known (which for a horizontal leaf almost always is equal to unity). In addition to this, the second method requires information about the ratio of the Austausch coefficients for water vapour and heat (experimentally it was found to be 1,00±0.05).The results give some insight regarding the radiative properties of an Alocasia leaf in the visible and infra-red and regarding the ratio of the losses by transpiration and by convection and its effects on leaf temperature in sunshine. The effect of radiation on transpiration proves to be strong; wind, however, has only little effect. The stomata of both the leaf surfaces were functioning independently of each other, which resulted in peculiar variations in the ratio of the water lost by the upper and lower surfaces. Finally mutual relationships between energy exchange and microclimate are discussed.
Résumé Le bilan énergétique d'une feuille d'Alocasia se compose principalement des échanges radiatifs de la lumière visible et infra-rouge ainsi que des échanges convectifs et des pertes de transpiration. Les composantes furent mesurées, séparément sur les surfaces supérieure et inférieure de la feuille, dans des conditions différentes en milieu naturel. Les résultats sont représentés par des bilans et, sous forme de graphiques, par les variations diurnes des différentes composantes d'énergie.A cet effet on a utilisé deux méthodes différentes qui se basent d'une part chacune sur des mesures directes du rayonnement, d'autre part, ou bien sur la détermination des échanges convectifs et des facteurs relatifs du recouvrement d'eau des surfaces de la feuille, ou bien sur des mesures des gradients de température et d'humidité a proximité de la feuille. Dans les deux méthodes on est sensé connaître le rapport des pertes de convection des deux surfaces de la feuille qui, en position horizontale est généralement de 1,0. Dans la seconde il faut encore connaître le rapport des coéfficients d'échange pour la vapeur d'eau et pour la chaleur qui fut trouvé être de 1,00±0,05.Les résultats obtenus permettent de nous renseigner au sujet des propriétés de la feuille d'Alocasia en ce qui concerne la radiation dans le domaine visible et infra-rouge, et le rapport des pertes de transpiration et de convection d'une feuille exposée au soleil et d'en déduire les effets sur la température de celle-ci. La radiation se révèle comme ayant une forte influence sur la transpiration, tandis que celle du vent est très faible. Les stomas des surfaces supérieure et inférieure réagissant séparément, provoquent de curieuses fluctuations du rapport de la transpiration de celles-ci. Finalement l'auteur discute encore les relations réciproques entre le microclimat et l'économie thermique.
Mit 8 Textabbildungen
Diese Arbeit wurde durch ein Stipendium der indischen Regierung im Rahmen des Indo-German Industrial Cooperation Scheme ermöglicht. 相似文献
90.