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1.
1 INTRODUCTION In the watershed of the Jiangjia Ravine, the frequency of occurrence of rainstorms which can mobilize debris flows is high, and there are abundant unconsolidated materials deposited in the upstream area, these resulted in frequent eruption …  相似文献   

2.
The determination of the critical particle size between solid and fluid phases, i.e., the suspension competence, is fundamental for debris flow. A method for determining suspension competence based on particle size analysis is presented in this paper. Suspension competence of static experimental water-debris mixtures prepared with the sediment of Jiangjia Gully is -0.025 mm if the bulk density is less than 1,800 kg m-3 and it increases with bulk density of more concentrated mixtures. Suspension competence of natural debris flows in Jiangjia Gully increases exponentially with the bulk density. These two data sets are compared in order to understand the suspension mechanism. It is concluded that turbulence may play a leading role in particle suspension in non-viscous and sub-viscous debris flows, while in viscous debris flows both matrix strength and excess pore water pressure play important roles.  相似文献   

3.
A five year Environmental Monitoring Programme (EMP) was set up in east-Australian coastal waters to determine the environmental effects of diverting most of Sydney's primary treated sewage from cliff face outfalls to diffuser outfall systems some 3 km offshore in 60–80 m of water. Many component EMP studies adopted Before and After Control Impact (BACI and ‘beyond BACI’) designs, to isolate outfall impacts on the marine ecosystem from background variability. Although seasonal patterns dominated ambient conditions in coastal waters, long-term climatic signals, such as the El Nino Southern Oscillation (ENSO), were apparent during the EMP. The Southern Oscillation Index (SOI) indicated the two year post-commissioning study period of 1991–1993 was dominated by an El Nino episode, while the 1989–1990 pre-commissioning period experienced a La Nina episode. Anomalous rainfall conditions and ocean temperature structure were associated with these episodes with respect to long-term records. Rainfall patterns suggested that the pre-commissioning period experienced high rainfall causing an increased incidence of stormwater pollution in coastal waters. Effects of the lower rain levels during post-commissioning phase were, however, outweighed by the dramatic improvements due to the commissioning of the deepwater outfalls. Decreased thermal stratification was experienced during the winter months of the 1992–1993 El Nino episode, and promoted increased dilutions associated with a greater frequency in sewage plume surfacing. There was, however, no apparent short-term effect of this change in plume behaviour on the marine environment as measured by EMP indicators.  相似文献   

4.
RIIEOLOGICAL PROPERTmS OF V1SCOUS DEBmS FLOWS1N THE JIANGat RAVIN'E, YUNNAN, CmNA*fYuy WANG', Chyandeg JAN', Changzhi LI3 and WeIiliang HAN4Abstract:The rheological ProPethes of natural debris flow are studied using exPerimental data obtained froma formeter bullt by the aUthOrS. The Present study is aimed to addrss the rheological Propenies ofviscous debris flow at lOw shear od. It is found that oversboss effeet and shearbo-thinninPhenomenon chM the viscous …  相似文献   

5.
Rivers display temporal dependence in suspended sediment–water discharge relationships. Although most work has focused on multi‐decadal trends, river sediment behavior often displays sub‐decadal scale fluctuations that have received little attention. The objectives of this study were to identify inter‐annual to decadal scale fluctuations in the suspended sediment–discharge relationship of a dry‐summer subtropical river, infer the mechanisms behind these fluctuations, and examine the role of El Niño Southern Oscillation climate cycles. The Salinas River (California) is a moderate sized (11 000 km2), coastal dry‐summer subtropical catchment with a mean discharge (Qmean) of 11.6 m3 s?1. This watershed is located at the northern most extent of the Pacific coastal North America region that experiences increased storm frequency during El Niño years. Event to inter‐annual scale suspended sediment behavior in this system was known to be influenced by antecedent hydrologic conditions, whereby previous hydrologic activity regulates the suspended sediment concentration–water discharge relationship. Fine and sand suspended sediment in the lower Salinas River exhibited persistent, decadal scale periods of positive and negative discharge corrected concentrations. The decadal scale variability in suspended sediment behavior was influenced by inter‐annual to decadal scale fluctuations in hydrologic characteristics, including: elapsed time since small (~0.1 × Qmean), and moderate (~10 × Qmean) threshold discharge values, the number of preceding days that low/no flow occurred, and annual water yield. El Niño climatic activity was found to have little effect on decadal‐scale fluctuations in the fine suspended sediment–discharge relationship due to low or no effect on the frequency of moderate to low discharge magnitudes, annual precipitation, and water yield. However, sand concentrations generally increased in El Niño years due to the increased frequency of moderate to high magnitude discharge events, which generally increase sand supply. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

6.
Some previous global and regional studies have indicated teleconnection between the extreme phases of the Southern Oscillation (SO) and Turkish climate and hydrologic variables; however, they failed to suggest a strong correlation structure. In this study, categorised Southern Oscillation index (SOI) and Multivariate ENSO (El Nino Southern Oscillation) index (MEI) series were used to examine the far‐reaching effects of the SO on temperature, precipitation and streamflow patterns in Turkey. These SO indicators were categorised into five subgroups according to their empirical distributions. Correlations between the categorised SO indicators and three analysis variables were computed using the Spearman's rho from lag‐0 to lag‐4. Significance of calculated correlations was tested at the 0·01 level for station‐based analysis and at the 0·05 level for regional analysis. Temperature records demonstrated significant correlations with the categorised SOI and MEI in nearly half of the entire stations. For some categories, precipitation and streamflow were found to be correlated with the SO indicators in some stations mainly in western Turkey. Regional analyses of temperature and precipitation revealed a clear and strong correlation structure with the categorised SO indicators on a large portion of Turkey. This was not concluded by the earlier pertinent studies. Besides, this study showed that significant correlations were obtained not only for the SO extreme phases (namely, El Nino and La Nina) but also for neutral and moderate phases of the SO. Plausible explanations for the observed teleconnection are presented. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

7.
We use conditional nonlinear optimal perturbation(CNOP)to investigate the optimal precursory disturbances in the ZebiakCane El Nino-Southern Oscillation(ENSO)model.The conditions of the CNOP-type precursors are highly likely to evolve into El Nino events in the Zebiak-Cane model.By exploring the dynamic behaviors of these nonlinear El Nino events caused by the CNOP-type precursors,we find that they,as expected,tend to phase-lock to the annual cycles in the Zebiak-Cane model,with the SSTA peak at the end of a calendar year.However,El Nino events with CNOPs as initial anomalies in the linearized Zebiak-Cane model are inclined to phase-lock earlier than nonlinear El Nino events despite the existence of annual cycles in the model.It is clear that nonlinearities play an important role in El Nino’s phase-locking.In particular,nonlinear temperature advection increases anomalous zonal SST differences and anomalous westerlies,which weakens anomalous upwelling and acts on the increasing anomalous vertical temperature difference and,as a result,enhances El Nino and then delays the peak SSTA.Finally,we demonstrate that nonlinear temperature advection,together with the effect of the annual cycle,causes El Nino events to peak at the end of the calendar year.  相似文献   

8.
白莹莹  管兆勇  张焱 《地球物理学报》2009,52(11):2689-2697
利用NCEP/NCAR月平均再分析资料,研究了南半球夏季（12~2月）纬向平均环流的垂直结构异常及其与南极涛动（AAO）和ENSO的联系.结果表明,南半球夏季纬向平均［u］的异常分布的主要模态（EOF1）显示出极区、50°S~70°S、以及50°S以北的区间内“三极”型振荡.EOF1 既反映了AAO的特征又与ENSO有着显著的关系.由于AAO指数与Nino3区指数之间存在着统计相关,为进一步弄清AAO和ENSO在南半球纬向平均气流变动的相关分量及其结构,利用Nino3区指数使用一元回归方法滤除ENSO影响,再对剩下的部分作EOF分解,得到了独立于ENSO的纬向平均［u］的第一模态AEOF1.相关分析表明AEOF1为与AAO相对应的纬向平均［u］异常的分布.用南半球纬向平均［u］去掉其与AAO相联系的模态AEOF1,进行EOF分解得到的第一模SEOF1,其与Nino3 区指数的相关高达0.9.由此给出了纬向平均气流的变动与ENSO无关的模态和与ENSO有关的模态.时间变化分析表明,近30年中,除了年代际变化和3~7年的年际变化外,纬向平均的纬向基本气流尚有极地西风减弱、副极地西风加强、副热带西风减弱、热带东风加强的长期趋势.  相似文献   

9.
River flow constitutes an important element of the terrestrial branch of the hydrological cycle, yet knowledge regarding the extent to which its variability, at a range of timescales, is linked to a number of modes of atmospheric circulation is meagre. This is especially so in the Southern Hemisphere where strong candidates, such as El Niño Southern Oscillation and the Southern Annular Mode (SAM), for influencing climate and thus river flow variability can be found. This paper presents the results of an analysis of the impact of the SAM on winter and summer river flow variability across New Zealand, purposefully controlling for the influence of El Niño Southern Oscillation and the tendency for the SAM to adopt a positive phase over the last 10–20 years. Study results, based on identifying hydrological regions and applying circulation‐to‐environment and environment‐to‐circulation approaches commonly used in synoptic climatology, reveal a seasonal asymmetry of the response of river flow variability to the SAM; winter flows demonstrate a higher degree of statistical association with the SAM compared to summer flows. Further, because of the complex orography of New Zealand and its general disposition normal to zonal flows of moisture bearing winds, there are intraseasonal spatial variations in river flow SAM associations with clear rain shadow effects playing out in resultant river flow volumes. The complexity of SAM river flow associations found in this study warns against using indices of large scale modes of atmospheric circulation as blunt tools for hydroclimatological prediction at scales beyond hydroclimatological regions or areas with internal hydrological consistency.  相似文献   

10.
Impact forces associated with major debris flows (Jiangjia Ravine, China, August 25, 2004) were recorded in real time by a system consisting of three strain sensors installed at different flow depths. This provides the first real‐time and long‐duration record of impact forces associated with debris flows. A comprehensive approach including low‐pass filtering and moving average methods were used to preprocess the recorded signals. The upper limit of impact frequency in the debris flows was estimated at 188?66 Hz under the assumption that only coarse grains cause effective impact loadings. Thus, a low‐pass filter with a 200 Hz cut‐off frequency was needed to denoise the original data in order to extract the impact force. Then the moving average method was applied to separate long‐term and random components of the filtered data. These were interpreted as, respectively, the fluid pressure and grain impact loading. It was found that the peak grain impacts at different depths were non‐synchronous within the debris flows. The impact loadings were far greater than, and not proportional to the fluid pressures. Analysis of the impact force of 38 debris flow surges gives an empirical value for the ratio of the hydrodynamic pressure to the momentum flow density, i.e. the product of debris‐flow density and mean velocity square, which provides a very valuable basis for understanding debris flow dynamics and designing debris flow management systems. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

11.
Empirical studies have shown that warm El Nino/Southern Oscillation (ENSO) episodes are associated during northern summer with, first, a southward location of the intertropical convergence zone (ITCZ) over the tropical Atlantic, and, second, a weakened convection over West Africa where the ITCZ is near its mean latitude. A modelling experiment presented here is used to help explain this apparent contradiction. In simulated ENSO conditions, the ITCZ is located southwards over the tropical Atlantic. Over West Africa the intertropical front is also displaced southwards, but more slightly; the ITCZ is located at its climatological latitude and the vertical development of convective clouds over West and Central Africa is reduced due to dynamical subsidence in the upper levels.  相似文献   

12.
The Whangaehu fan is the youngest sedimentary component on the eastern ring plain surrounding Ruapehu volcano. Fan history comprises constructional (830–200 years bp) and dissectional (<200 years bp) phases. The constructional phase includes four aggradational periods associated with both syneruptive and inter-eruptive behavior. All four aggradational periods began when deposition by large lahars changed flow conditions on the fan from channelized to unchannelized. Subsequent behavior was a function of the rate of sediment influx to the fan. The rate of sediment influx, in turn, was controlled by frequency and magnitude of volcanic eruptions, short-term climate change, and the amount of sediment stored on the volcano flanks. Fanwide aggradation occurred when rates of sediment influx and deposition on the fan were high enough to maintaìn unchannelized flow conditions on the fan surface. Maintenance of an undissected surface required sedimentation from frequent and large lahars that prevented major dissection between events. These conditions were best met during major eruptive episodes when high frequency and magnitude eruptions blanketed the volcano flanks with tephra and rates of lahar initiation were high. During major eruptive episodes, volcanism is the primary control on sedimentation. Climatic variations do not influence sediment accumulation. Local aggradation occurred when lahars were too small to maintain unchannelized flow across the entire fan. In this case, only the major channel system received much sediment following the deposition from the initial lahar. This localized aggradation occurred if (1) the sediment reservoir on the flank was large enough for floods to bulk into debris flows and (2) sedimentation events were frequent enough to maintain sediment supply to only some parts of the fan. These conditions were met during both minor eruptive and inter-eruptive episodes. In both cases, a large sediment reservoir remained on the volcano flanks from previous major eruptive intervals. Periods of increased storm activity produced floods that bulked to relatively small debris flows. When the sediment reservoir was depleted, the fan entered the present dissectional phase. Syneruptive and noneruptive lahars are mostly channelized and sediment bypasses the fan. Fan deposits are rapidly reworked. This is the present case at Ruapehu, even though the volcano is in a minor eruptive episode and the climate favors generation of intense storm floods.  相似文献   

13.
Book Review     
The objective of the work discussed in this paper was to seek possible links between surface hydrology in Southwestern (SW) Poland and El Ni?o/Southern Oscillation (ENSO). Although the impact of ENSO on hydrology in Europe has been investigated by many researchers, no clear picture demonstrating spatial variability of such a teleconnection has yet been unequivocally reported. In particular, there is no comprehensive study on ENSO–streamflow links for Polish rivers. Herein, discharge time series from 15 sites located at lowland and mountain rivers in SW Poland and different ENSO indices are examined. They include atmospheric time series (axial component of atmospheric angular momentum, Southern Oscillation Index), oceanic indices (Ni?o 3.4 Index, Global SST Index), geodetic data (length-of-day), and the combined index (Multivariate ENSO Index). The data span the period from November 1971 to October 2006. On the basis of cross-correlation and wavelet analyses it was found that there is a weak but significant link between ENSO and surface hydrology in SW Poland. It is inferred that ENSO episodes may be among a few factors affecting winter and early spring discharges of rivers in SW Poland and may have a (probably limited) impact on snow-melt flood generation.  相似文献   

14.
There is increasing interest in the magnitude of the flow of freshwater to the Arctic Ocean due to its impacts on the biogeophysical and socio‐economic systems in the north and its influence on global climate. This study examines freshwater flow based on a dataset of 72 rivers that either directly or indirectly contribute flow to the Arctic Ocean or reflect the hydrologic regime of areas contributing flow to the Arctic Ocean. Annual streamflow for the 72 rivers is categorized as to the nature and location of the contribution to the Arctic Ocean, and composite series of annual flows are determined for each category for the period 1975 to 2015. A trend analysis is then conducted for the annual discharge series assembled for each category. The results reveal a general increase in freshwater flow to the Arctic Ocean with this increase being more prominent from the Eurasian rivers than from the North American rivers. A comparison with trends obtained from an earlier study ending in 2000 indicates similar trend response from the Eurasian rivers, but dramatic differences from some of the North American rivers. A total annual discharge increase of 8.7 km3/y/y is found, with an annual discharge increase of 5.8 km3/y/y observed for the rivers directly flowing to the Arctic Ocean. The influence of annual or seasonal climate oscillation indices on annual discharge series is also assessed. Several river categories are found to have significant correlations with the Arctic Oscillation, the North Atlantic Oscillation, or the Pacific Decadal Oscillation. However, no significant association with climate indices is found for the river categories leading to the largest freshwater contribution to the Arctic Ocean.  相似文献   

15.
The objective of the work discussed in this paper was to seek possible links between surface hydrology in Southwestern (SW) Poland and El Niño/Southern Oscillation (ENSO). Although the impact of ENSO on hydrology in Europe has been investigated by many researchers, no clear picture demonstrating spatial variability of such a teleconnection has yet been unequivocally reported. In particular, there is no comprehensive study on ENSO–streamflow links for Polish rivers. Herein, discharge time series from 15 sites located at lowland and mountain rivers in SW Poland and different ENSO indices are examined. They include atmospheric time series (axial component of atmospheric angular momentum, Southern Oscillation Index), oceanic indices (Niño 3.4 Index, Global SST Index), geodetic data (length-of-day), and the combined index (Multivariate ENSO Index). The data span the period from November 1971 to October 2006. On the basis of cross-correlation and wavelet analyses it was found that there is a weak but significant link between ENSO and surface hydrology in SW Poland. It is inferred that ENSO episodes may be among a few factors affecting winter and early spring discharges of rivers in SW Poland and may have a (probably limited) impact on snow-melt flood generation.  相似文献   

16.
Deciphering the mechanisms through which the El Niño/Southern Oscillation (ENSO) affects hydrometeorological parameters in the tropics and extratropics is of great interest. We investigate climatic teleconnections between warm or cold phases of ENSO and streamflow patterns over South Korea using an empirical methodology designed to detect regions showing a strong and consistent hydroclimatic signal associated with ENSO. We calculate not only spatial coherence values by monthly streamflow composite formed over 2‐year ENSO cycle and the first harmonic fit to detect candidate regions but also temporal consistency rates by aggregate composite and index time series to determine core regions. As a result, the core regions, namely, the Han river basin and the Nakdong river basin, are detected with a high level of response of ENSO phenomena to streamflow patterns. The ENSO composites for both core regions indicate drier (wetter) conditions in early autumn of the warm (cold) episode years and wetter (drier) conditions from winter to spring of the following year. For both regions, the spatial coherences are over 92% (82%) and the temporal consistencies are 71% (75%) during the El Niño (La Niña) events. In addition, for the core regions identified by composite‐harmonic analysis for both extreme episodes, the results of comparative analyses by using correlation, annual cycle, and Wilcoxon rank sum test indicate that 2 opposite phases‐streamflow relationships have a tendency of sign reversal of the streamflow anomaly. Also, the positive departures during the El Niño years show more coherent and strong responses than the negative anomalies in the La Niña events. In conclusion, South Korea experiences climatic teleconnection between ENSO forcing and midlatitude streamflow patterns.  相似文献   

17.
The El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) are two important climate oscillations that affect hydrological processes at global and regional scales. However, few studies have attempted to identify their single and combined influences on water discharge variability at multiple timescales. In this study, we examine temporal variation in water discharge from the Yangtze River into the sea and explore the influence of the ENSO and the PDO on multiscale variations in water discharge over the last century. The results of the wavelet transform analysis of the water discharge series show significant periodic variations at the interannual timescale of 2 to 8 years and the decadal timescale of 15 to 17 years. Water discharge tended to be higher during the La Niña–PDO cold phase and lower during the El Niño–PDO warm phase. The results of the cross wavelet spectrum and wavelet coherence analyses confirm the relationship between the interannual (i.e., 2 to 8 years) and decadal (i.e., 15 to 17 years) periodicities in water discharge with the ENSO and the PDO, respectively. As an important large‐scale climate background, the PDO can modulate the influence of the ENSO on water discharge variability. In general, the warm PDO enhances the influence of El Niño events, and the cold PDO enhances the influence of La Niña events. Our study is helpful in understanding the influencing mechanism of climate change on hydrological processes and provides an important scientific guideline for water resource prediction and management.  相似文献   

18.
The purpose of this paper is twofold. First, we demonstrate that the asymmetry between El Niño and La Niña events recorded in sea level variation occurs only during extreme episodes of El Niño/Southern Oscillation. Second, we explain that the asymmetry is controlled by certain regular cycles which have time-variable amplitudes. Gridded maps of sea level anomaly that form a spatial-temporal time series (spatial resolution: 1° × 1°, sampling interval: 1 week) spanning the time interval from 14/10/1993 to 18/04/2012 were used. We examined those time series and found that certain regular harmonic signals (periods: 365, 182, 120, 90 and 62 days) are dominant terms of their temporal variability. By subtracting those oscillations from sea level anomaly data, residuals were determined. Using skewness and kurtosis as measures of asymmetry and nonlinearity — after adopting 10-year moving window — we found that the extreme El Niño 1997/1998 has been a dominant driving force of the asymmetry and nonlinearity of El Niño/Southern Oscillation since the end of 1993. In order to detect residual signals that are responsible for the asymmetry, we applied the Fourier Transform Band Pass Filter and found that there are two important oscillations remaining in the residual sea level anomaly data, i.e. the annual and semiannual ones with time-varying amplitudes. We hypothesize that temporarily uneven amplitudes have meaningful impact on the aforementioned asymmetry.  相似文献   

19.
Small, steep watersheds are prolific sediment sources from which sediment flux is highly sensitive to climatic changes. Storm intensity and frequency are widely expected to increase during the 21st century, and so assessing the response of small, steep watersheds to extreme rainfall is essential to understanding landscape response to climate change. During record winter rainfall in 2016–2017, the San Lorenzo River, coastal California, had nine flow peaks representing 2–10‐year flood magnitudes. By the third flood, fluvial suspended sediment showed a regime shift to greater and coarser sediment supply, coincident with numerous landslides in the watershed. Even with no singular catastrophic flood, these flows exported more than half as much sediment as had a 100‐year flood 35 years earlier, substantially enlarging the nearshore delta. Annual sediment load in 2017 was an order of magnitude greater than during an average‐rainfall year, and 500‐fold greater than in a recent drought. These anomalous sediment inputs are critical to the coastal littoral system, delivering enough sediment, sometimes over only a few days, to maintain beaches for several years. Future projections of megadroughts punctuated by major atmospheric‐river storm activity suggest that interannual sediment‐yield variations will become more extreme than today in the western USA, with potential consequences for coastal management, ecosystems, and water‐storage capacity. The occurrence of two years with major sediment export over the past 35 years that were not associated with extremes of the El Niño Southern Oscillation or Pacific Decadal Oscillation suggests caution in interpreting climatic signals from marine sedimentary deposits derived from small, steep, coastal watersheds, to avoid misinterpreting the frequencies of those cycles. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

20.
Lareef Zubair 《水文研究》2003,17(12):2439-2448
As part of an effort to demonstrate the use of climate predictions for water resources management, the El Niño/Southern Oscillation (ENSO) influences on stream flow in the Kelani River in Sri Lanka were investigated using correlation analysis, composite analysis and contingency tables. El Niño (warm phase of ENSO) was associated with decreased annual stream flow and La Niña (cold phase of ENSO) with increased annual flows. The annual stream flow had a negative correlation with the simultaneous ENSO index of NINO3·4 that was significant at the 95% level. This negative correlation is enhanced to a 99% level if the aggregate January to September or the April to September stream flow alone were considered. Although, there is little correlation between ENSO indices and stream flow during the October to December period, there is a high correlation between rainfall and NINO3·4 (r = 0·51, significant at the 99% level). Therefore ENSO based rainfall predictions can be used along with a hydrological model to predict the October to December stream flow. This study demonstrates the viability of using ENSO based predictors for January to September or April to September stream flow predictions in the Kelani River. The October to December stream flow may be predicted by exploiting the strong relationship between ENSO and rainfall during that period. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

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