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961.
《水文科学杂志》2013,58(4)
Abstract In the first part of this study, a flood wave transformation analysis for the largest historical floods in the Danube River reach Kienstock–Bratislava was carried out. For the simulation of the historical (1899 and 1954) flood propagation, the nonlinear river model NLN-Danube (calibrated on the recent river reach conditions) was used. It was shown that the simulated peak discharges were not changed significantly when compared to their historical counterparts. However, the simulated hydrographs exhibit a significant acceleration of the flood wave movement at discharges of between 5000 and 9000 m3 s-1. In the second part, the travel time-water level relationships between Kienstock and Bratislava were analysed on a dataset of the flood peak water levels for the period 1991–2002. An empirical regression routing scheme for the Danube short-term water level forecast at Bratislava station was derived. This is based on the measured water level at Kienstock gauging station. 相似文献
962.
The potential impact of climate change on fluvial flooding is receiving considerable scientific and political interest thanks to evidence from climate model projections and a widely held belief that flood risk may be increasing at European levels. This review compares published work on historical trends in UK rainfall and river flow records with high‐resolution regional climate change projections, and attempts to reconcile apparent differences between the two. Attention is focused on the techniques used for climate change detection and attribution, as well as the potential confounding effects of land‐use change. International and domestic efforts to build adaptive capacity rest on improved quantification of uncertainty in flood risk at very local, catchment and regional scales. This will involve further research to better integrate climate and land‐management interactions, to understand changes in the dependence between different flood generating mechanisms, and to improve the characterization and communication of uncertainty at all stages of analysis. Resources are also needed to ensure that latest, but still uncertain, science is presented in an appropriate form to underpin policy development and is translated into sensible guidance for practitioners. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
963.
Concerns related to climate change have resulted in an increasing interest in the importance of hydrological events such as droughts in affecting biogeochemical responses of watersheds. The effects of an unusually dry summer in 2002 had a marked impact on the biogeochemistry of three watersheds in the north‐eastern USA. Chemical, isotopic and hydrological responses with particular emphasis on S dynamics were evaluated for Archer Creek (New York), Sleepers River (Vermont) and Cone Pond (New Hampshire) watersheds. From 1 August to 14 September 2002, all three watersheds had very low precipitation (48 to 69 mm) resulting in either very low or no discharge (mean 0·015, 0·15 and 0·000 mm day?1 for Archer Creek, Sleepers River and Cone Pond, respectively). From 15 September to 31 October 2002, there was a substantial increase in precipitation totals (212, 246 and 198 mm, respectively) with increased discharge. Archer Creek was characterized by a large range of SO42? concentrations (152 to 389 µeq L?1, mean = 273 µeq L?1) and also exhibited the greatest range in δ34S values of SO42? (?1·4 to 8·8 ‰ ). Sleepers River's SO42? concentrations ranged from 136 to 243 µeq L?1 (mean = 167 µeq L?1) and δ34S values of SO42? ranged from 4·0 to 9·0 ‰ . Cone Pond's SO42? concentrations (126–187 µeq L?1, mean = 154 µeq L?1) and δ34S values (2·4 to 4·3 ‰ ) had the smallest ranges of the three watersheds. The range and mean of δ18O‐SO42? values for Archer Creek and Cone Pond were similar (3·0 to 8·9 ‰ , mean = 4·5 ‰ ; 3·9 to 6·3 ‰ , mean = 4·9 ‰ ; respectively) while δ18O‐SO42? values for Sleepers River covered a larger range with a lower mean (1·2 to 10·0 ‰ , mean = 2·5). The difference in Sleepers River chemical and isotopic responses was attributed to weathering reactions contributing SO42?. For Archer Creek wetland areas containing previously reduced S compounds that were reoxidized to SO42? probably provided a substantial source of S. Cone Pond had limited internal S sources and less chemical or isotopic response to storms. Differences among the three watersheds in S biogeochemical responses during these storm events were attributed to differences in S mineral weathering contributions, hydrological pathways and landscape features. Further evaluations of differences and similarities in biogeochemical and hydrological responses among watersheds are needed to predict the impacts of climate change. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
964.
This article investigates regional distribution features of rainfall and vapor transport in Northwest China during 1961-2002, achieving that: (1) Three climate zones in this vast region differ in trends of annual precipitation, with rainfall in the westerly belt (denoted as zoneWB) exhibiting an increasing trend from the 1970s, rainfall in the East Asian monsoon belt (denoted as zoneMB) displaying a decreasing trend in the study period and the Qinghai Plateau zone (denoted as zoneQP) precipitation fluctuating roughly around the mean; (2) The net vapor fluxes (NVF) in zoneWB and zoneQP show an increasing trend as opposited to zoneMB, for which the reason may lie behind that the NVF increase in zoneWB and zoneQP is attributed to pronounced decrease in deficit of westerly NVF, whereas the decrease in zoneMB NVF is ascribed to the significant drop in meridional vapor transfer; (3) ZoneWB rainfall and atmospheric vapor transport change abrupt in 1990 and 1985, respectively, without such happening in zoneMB and zoneQP; (4) ZoneWB rainfall increase occurs when atmospheric vapor budget/NVF increases, so that the latter has to occur ahead of the former; zoneMB rainfall decrease relates to the decrease in atmospheric vapor budget after the 1990s,leading to (more and even) successive droughts in the east of Northwest China on a synchronous basis except zoneQP of which the precipitation factors include river evaporation, glaciers, and snow cover in addition to atmospheric vapor. 相似文献
965.
1 INTRODUCTION In southern high latitudes, recent observations have shown a standing mode of ACW (Antarctic Circumpolar Wave) with eastward propagation across the Southern Ocean of the Antarctic in co- varying SST (sea surface temperature) and SLP (sea le… 相似文献
966.
Through a combination of aerobraking (drag deceleration) and ablation, meteoroids which enter planetary atmospheres may be slowed sufficiently to soft-land as meteorites. Results of an earlier study suggest that the current 6 mbar atmosphere of Mars is sufficient to aerobrake significant numbers of small (<10 kg) asteroidal-type meteoroids into survivable, low-velocity (<500 m s−1) impacts with the planet's surface. Since rates of meteorite production depend upon the density of Mars's atmosphere, they must also change as the martian climate changes. However, to date, martian meteorite production has received relatively little attention in the literature Here we expand upon our previous work to study martian meteorite production rates and how they depend upon variations of the martian atmosphere, and to estimate the ranges of mass, velocity and entry-angle that produce meteorites. We find that even the current atmosphere of Mars is sufficient to soft-land significant fractions of incident stony and iron objects, and that these fractions increase dramatically for denser martian atmospheres. Therefore, like impact cratering, meteorite populations may preserve evidence of past martian climates. 相似文献
967.
C. Kasse W. Z. Hoek S. J. P. Bohncke M. Konert J. W. H. Weijers M. L. Cassee R. M. Van Der Zee 《第四纪科学杂志》2005,20(4):377-394
The Niers valley was part of the Rhine system that came into existence during the maximum Saalian glaciation and was abandoned at the end of the Weichselian. The aim of the study was to explain the Late Pleniglacial and Late Glacial fluvial dynamics and to explore the external forcing factors: climate change, tectonics and sea level. The sedimentary units have been investigated by large‐scale coring transects and detailed cross‐sections over abandoned channels. The temporal fluvial development has been reconstructed by means of geomorphological relationships, pollen analysis and 14C dating. The Niers‐Rhine experienced a channel pattern change from braided, via a transformational phase, to meandering in the early Late Glacial. This change in fluvial style is explained by climate amelioration at the Late Pleniglacial to Late Glacial transition (at ca. 12.5 k 14C yr BP) and climate‐related hydrological, lithological and vegetation changes. A delayed fluvial response of ca. 400 14C yr (transitional phase) was established. The channel transformations are not related to tectonic effects and sea‐level changes. Successive river systems have similar gradients of ca. 35–40 cm km?1. A meandering river system dominated the Allerød and Younger Dryas periods. The threshold towards braiding was not crossed during the Younger Dryas, but increased aeolian activity has been observed on the Younger Dryas point bars. The final abandonment of the Niers‐Rhine was dated shortly after the Younger Dryas to Holocene transition. Traces of Laacher See pumice have been found in the Niers valley, indicating that the Niers‐Rhine was still in use during the Younger Dryas. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
968.
Multi-agent Blind Model and Its Application to Regional Eco-environmental Quality Assessment 总被引:3,自引:3,他引:0
LI Ruzhong 《中国地理科学(英文版)》2006,16(3):249-254
1 Introduction Eco-environmental quality assessment is an activity that is affected by man-made factors. As other environmental systems, regional eco-environment is also a complicated and uncertain system (Wu et al., 2005). Owing to these reasons, people may produce a style of subjective un- certainty in mind in evaluating such system (Liu et al. 1999a; Wu et al., 2004). According to unascertained mathematics (Liu et al., 1997; Liu et al., 1999b), we know that this kind of subjective uncerta… 相似文献
969.
Michael R. Rampino 《Icarus》2002,156(2):562-569
The largest explosive volcanic eruptions (supereruptions) produce >1000 km3 of ejected material and ≥1000 Mt (1015 g) of submicron atmospheric aerosols and dust. These eruptions may be capable of creating global climatic disturbances sufficient to cause severe problems for world agriculture and modern civilization. Supereruptions are estimated to occur on average about every 50,000 years, which is about twice the frequency of impacts by comets and asteroids ≥1 km diameter predicted to cause similar climatic effects. Prediction, prevention, and mitigation of global volcanic climatic disasters may be potentially more difficult than planetary protection from the threat of large impacts, so that explosive volcanism might limit the longevity of technological civilizations. 相似文献
970.
枯桩杈断裂南北两侧的构造蚀变岩型金矿 ,在矿体规模、矿化强度、矿物组合等 ,因受后期断裂破坏而存在明显不同。初步研究认为 ,这是矿床沿垂向变化特征的反映 ,是枯桩杈断裂在成矿后的活动造成的。该断裂以南矿体剥蚀程度较浅 ,向深部矿化增强的趋势明显 ,深部找矿有很大潜力 相似文献