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1.
1840年以来长江大洪水演变与气候变化关系初探   总被引：25，自引：3，他引：22  
长江洪水灾害是我国频率高、为患严重的自然灾害之一.本文依据可靠资料,选择1840年至2000年间32次大洪水记录,探讨其演变与气候变化的关系.认知1910s前的19世纪冷期出现大洪水13次(包括1870年的极值大洪水事件)频率为1.9次／10a.1921-2000年间出现了大洪水19次,频率为2.4次／10a.20世纪暖期又分出两个变暖时段,前一变暖时段的峰值期1920s-1940s出现大洪水9次,包含1931年全流域大洪水.后一变暖时段,即1980s与1990s出现大洪水8次.实测记录到的最大洪水1954年位于前一变暖时段结束阶段.1990s是全球,也是我国近百年中最暖年代,受东南季风影响大的中下游地区夏季降水量是近百年最多的,大暴雨频率也是有较多记录的40年来最高的.以此出现了10年5次大洪水高频率现象,包含1998年全流域型大洪水,表明了全球变暖的显著影响.也指示30-40年问周期性振荡中多雨年代.如此可预期21世纪初期降水会有小幅度下降与大洪水频率在短期内降低的可能性.长江上游受西南季风影响较大,19世纪下半期与20世纪上半期为多降水期,大洪水频率较高.20世纪下半期为少降水期,大洪水频率较低.关于气候变化研究有待深入,前景不易预估.  相似文献   

2.
We have measured Ba in Dead Sea samples collected before and after the 1979 overturn, and226Ra in nine samples collected after the overturn. Before this overturn, Ba and the226Ra data measured by Chung and Craig [4] show that a distinct two-layer structure existed, with higher concentrations in the upper layer. After the overturn, both elements were uniformly distributed in the water column. The inventories of Ba and Ra calculated from these data are the same for the periods before and after the overturn. If the inventories were constant during the last meromictic phase then the input rate must be balanced by the removal rate, and a mass balance model can be constructed to estimate physical parameters based on known or deduced sources and sinks. The sources include inputs from the Jordan River, springs around the Dead Sea, and submerged springs or seepages, etc. The sinks include coprecipitation with aragonite, gypsum, precipitation of barite, coprecipitation of Ra with barite, particulate scavenging, and radioactive decay for Ra. Our data include measurements of Ba and226Ra in gypsum, aragonite and halite from the Dead Sea, as well as in some of the inflowing rivers and springs.The inclusion of particulate scavenging as a sink is a major element of the model. We find that, without inclusion of a Ba scavenging term in the deep water, the lake volume at the previous overturn as calculated from the Ba data would be unrealistically high in comparison with historical records. The inclusion of particulate scavenging for Ra in the model reduces the calculated duration of the last meromictic phase significantly.Our model excludes internal mixing between the upper and lower water masses. With this restriction, various sets of model parameters were calculated as a function of theRa/Ba scavenging rate ratio. If the ratio is one, the calculated age of the last meromictic phase is about a hundred years. A substantial increase in the Ra input rate is required to balance the removal rate by particulate scavenging as well as decay. If the ratio is zero, i.e. no particulate scavenging for Ra, the age is about 260 years, as obtained by Stiller and Chung [2].  相似文献   

3.
Rock salt is approximately 1000 times more soluble than limestone and thus displays high rates of geomorphic evolution. Cave stream channel profiles and downcutting rates were studied in the Mount Sedom salt diapir, Dead Sea rift valley, Israel. Although the area is very arid (mean annual rainfall ≈ 50 mm), the diapir contains extensive karst systems of Holocene age. In the standard cave profile a vertical shaft at the upstream end diverts water from a surface channel in anhydrite or clastic cap rocks into the subsurface route in the salt. Mass balance calculations in a sample cave passage yielded downcutting rates of 0–2 mm s?1 during peak flood conditions, or about eight orders of magnitude higher than reported rates in any limestone cave streams. However, in the arid climate of Mount Sedom floods have a low recurrence interval with the consequence that long-term mean downcutting rates are lower: an average rate of 8·8 mm a?1 was measured for the period 1986–1991 in the same sample passage. Quite independently, long-term mean rates of 6·2mm a?1 are deduced from 14C ages of driftwood found in upper levels of 12 cave passages. These are at least three orders of magnitude higher than rates established for limestone caves. Salt cave passages develop in two main stages: (1) an early stage characterized by high downcutting rates into the rock salt bed, and steep passage gradients; (2) a mature stage characterized by lower downcutting rates, with establishment of a subhorizontal stream bed armoured with alluvial detritus. In this mature stage downcutting rates are controlled by the uplift rate of the Mount Sedom diapir and changes of the level of the Dead Sea. Passages may also aggrade. These fast-developing salt stream channels may serve as full-scale models for slower developing systems such as limestone canyons.  相似文献   

4.
The last 2000 years are an important time span both for IGBP-PAGES and CLIVAR of WCRP. One of the main aims of these projects is to obtain high-resolution records of global change, such as that stored in ice cores, tree rings, speleothems, corals, lakes, marine records, etc., and then use these data to make sound estimates for future global change. To accomplish these projects, we first need to obtain high-resolution geological records and proxies for climatic/environ- mental changes. …  相似文献   

5.
In this paper the reaction of the salt‐/freshwater interface due to the changes in the Dead Sea level are elaborated at in details by using the inflows into the Dead Sea, the outflows due to evaporation losses and artificial discharges, and the hydrographic registrations of the Dead Sea level. The analyses show that the interface seaward migration resulted in a groundwater discharge of around 423 Mio m3 per meter drop in the level of the Dead Sea in the period 1994–1998 and of around 525 Mio m3/m in the period 1930–1937. The additional amount of groundwater joining the Dead Sea due to the interface seaward migration was 51 Mio m3 per one square kilometer of shrinkage in the area of the Dead Sea in the period 1930–1937 and 91 Mio m3/km2 in the period 1994–1998. The riparian states of the Dead Sea are nowadays loosing 370 Mio m3/a of freshwater to the Dead Sea through the interface readjustment mechanisms as a result of their over exploitation of waters which formerly fed the Dead Sea.  相似文献   

6.
Water budget analyses are important for the evaluation of the water resources in semiarid and arid regions. The lack of observed data is the major obstacle for hydrological modelling in arid regions. The aim of this study is the analysis and calculation of the natural water resources of the Western Dead Sea subsurface catchment, one which is highly sensitive to rainfall resulting in highly variable temporal and spatial groundwater recharge. We focus on the subsurface catchment and subsequently apply the findings to a large‐scale groundwater flow model to estimate the groundwater discharge to the Dead Sea. We apply a semidistributed hydrological model (J2000g), originally developed for the Mediterranean, to the hyperarid region of the Western Dead Sea catchment, where runoff data and meteorological records are sparsely available. The challenge is to simulate the water budget, where the localized nature of extreme rainstorms together with sparse runoff data results in few observed runoff and recharge events. To overcome the scarcity of climate input data, we enhance the database with mean monthly rainfall data. The rainfall data of 2 satellites are shown to be unsuitable to fill the missing rainfall data due to underrepresentation of the steep hydrological gradient and temporal resolution. Hydrological models need to be calibrated against measured values; hence, the absence of adequate data can be problematic. Therefore, our calibration approach is based on a nested strategy of diverse observations. We calculate a direct surface runoff of the Western Dead Sea surface area (1,801 km2) of 3.4 mm/a and an average recharge (36.7 mm/a) for the 3,816 km2 subsurface drainage basin of the Cretaceous aquifer system.  相似文献   

7.
The high‐density Dead Sea water (1.235 g/cm3) forms a special interface configuration with the fresh groundwater resources of its surrounding aquifers. The fresh groundwater column beneath its surroundings is around one tenth of its length compared to oceanic water. This fact alone indicates the vulnerability of the fresh groundwater resources to the impacts of changes in the Dead Sea level and to saltwater migration. Ghyben‐Herzberg and Glover equations were used to calculate the volumes of water in coastal aquifers which were replaced by freshwater due to the interface seaward migration as a result of the drop in the level of the Dead Sea. For that purpose, the dynamic equation of Glover approach has been integrated to accommodate that type of interface readjustment. The calculated amounts of freshwater which substituted salt Dead Sea water due to the migration of interface are 3.21 · 1011 m3, from a Dead Sea level of –392 m to τ411 m below sea level. The average porosity of coastal aquifers was calculated to range from 2.8 to 2.94%. Geoelectric sounding measurements showed that areas underlying the coastal aquifers formerly occupied by the Dead Sea water are gradually becoming flushed and occupied by freshwater. The latter is becoming salinized due to the residuals of Dead Sea water in the aquifer matrix, the present salinity of which is lower than that of the Dead Sea water. At the same time salt dissolution from the Lisan Marl formation is causing collapses along the shorelines in the form of sinkholes, tens of meters in diameter and depth.  相似文献   

8.
肖洁  李力 《湖泊科学》2003,15(Z1):83-89
本文通过长沙近百年和湖南区域近百站40a来的气象资料统计,分析了在全球气候变暖条件下湖南气候变化事实,揭示了湖南洪水灾害加剧的情况,并提出了应加以重视的问题.  相似文献   

9.
《水文科学杂志》2013,58(6):1121-1136
Abstract

One of the most significant anticipated consequences of global climate change is the change in frequency of hydrological extremes. Predictions of climate change impacts on the regime of hydrological extremes have traditionally been conducted by a top-down approach that involves a high degree of uncertainty associated with the temporal and spatial characteristics of general circulation model (GCM) outputs and the choice of downscaling technique. This study uses the inverse approach to model hydrological risk and vulnerability to changing climate conditions in the Seyhan River basin, Turkey. With close collaboration with the end users, the approach first identifies critical hydrological exposures that may lead to local failures in the Seyhan River basin. The Hydro-BEAM hydrological model is used to inversely transform the main hydrological exposures, such as floods and droughts, into corresponding meteorological conditions. The frequency of critical meteorological conditions is investigated under present and future climate scenarios by means of a weather generator based on the improved K-nearest neighbour algorithm. The weather generator, linked with the output of GCMs in the last step of the proposed methodology, allows for the creation of an ensemble of scenarios and easy updating when improved GCM outputs become available. Two main conclusions were drawn from the application of the inverse approach to the Seyhan River basin. First, floods of 100-, 200- and 300-year return periods under present conditions will have 102-, 293- and 1370-year return periods under the future conditions; that is, critical flood events will occur much less frequently under the changing climate conditions. Second, the drought return period will change from 5.3 years under present conditions to 2.0 years under the future conditions; that is, critical drought events will occur much more frequently under the changing climate conditions.  相似文献   

10.
From stable carbon isotope analysis of tree-rings of Chinese pine (Pinus tabulaeformis) from Mt. Helan, China, we found that high-δ13C values were related to high mean temperatures from June to August (T 68), and Iow-δ13C values corresponded to low T 68. From these data, a transfer function has been used to reconstruct summer temperatures (T 68) for the Mt. Helan region. The explained variance of reconstruction is 34.9% (F=15.01, p<0.001). The time period containing the highest summer temperatures in northern China (late 1920-1930s) was confirmed by our reconstruction. The data indicate that there is a tele-connection between summer temperatures in Mt. Helan area and sea-surface-temperatures in the tropical Pacific. The extreme low temperature periods around the years of 1920 and 1947 for Mt. Helan region correspond well to the cold climate in the tropical Pacific. Along with other analyses, this suggests that climate variations in the Mt. Helan region are driven not only by local events, but also by the global climate. Significant periodicities appearing in the reconstruction are 2.56 and 2.63 years.  相似文献   

11.
The Dead Sea is the lowest spot on Earth. It is a closed saline lake located in the middle of the Jordan Rift Valley between Lake Tiberias and the Red Sea. Its major tributaries are the Jordan River itself and the Dead Sea side wadis. The Dead Sea has a unique ecosystem and its water has curative, industrial and recreational significance. The level of the Dead Sea has been continuously falling since the early 1930s at an average rate of 0·7 m per year. The water level, as of February 1998, is about 410·9 m below mean sea level. In this paper, a water balance model is developed for the Dead Sea by considering different hydrological components of this water balance, including precipitation, runoff, evaporation and groundwater flow. This model is calibrated based on historical levels of the Dead Sea. Different scenarios are investigated, including the proposed Dead Sea–Red Sea Canal. This project is supposed to halt the shrinking of the Dead Sea and restore it to pre‐1950 levels in the next century. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

12.
The projected impacts of climate change and variability on floods in the southern Africa has not been well studied despite the threat they pose to human life and property. In this study, the potential impacts of climate change on floods in the upper Kafue River basin, a major tributary of the Zambezi River in southern Africa, were investigated. Catchment hydrography was delineated using the Hydro1k at a spatial resolution of 1 km. The daily global hydrological model WASMOD-D model was calibrated and validated during 1971–1986 and 1987–2001 with the simple-split sample test and during 1971–1980 and 1981–1990 with the differential split sample test, against observed discharge at Machiya gauging station. Predicted discharge for 2021–2050 and 2071–2100 were obtained by forcing the calibrated WASMOD-D with outputs from three GCMs (ECHAM, CMCC3 and IPSL) under the IPCC’s SRES A2 and B1 scenarios. The three GCMs derived daily discharges were combined by assigning a weight to each of them according to their skills to reproduce the daily discharge. The two calibration and validation tests suggested that model performance based on evaluation criteria including the Nash–Sutcliffe coefficient, Pearson’s correlation coefficient (r), Percent Bias and R 2 was satisfactory. Flood frequency analysis for the reference period (1960–1990) and two future time slices and climate change scenarios was performed using the peak over threshold analysis. The magnitude of flood peaks was shown to follow generalised Pareto distribution. The simulated floods in the scenario periods showed considerable departures from the reference period. In general, flood events increased during both scenario periods with 2021–2050 showing larger change. The approach in our study has a strong potential for similar assessments in other data scarce regions.  相似文献   

13.
Activities of 26Al and 10Be in five chert clasts sampled from two beach ridges of late Pleistocene Lake Lisan, precursor of the Dead Sea in southern Israel, indicate low rates of chert bedrock erosion and complex exposure, burial, and by inference, transport histories. The chert clasts were derived from the Senonian Mishash Formation, a chert‐bearing chalk, which is widely exposed in the Nahal Zin drainage basin, the drainage system that supplied most of the material to the beach ridges. Simple exposure ages, assuming only exposure at the beach ridge sampling sites, range from 35 to 354 ky; using the ratio 26Al/10Be, total clast histories range from 0·46 to 4·3 My, unrelated to the clasts' current position and exposure period on the late Pleistocene beach ridges, 160–177 m below sea level. Optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20·0 ± 1·4 ka and 36·1 ± 3·3 ka. These ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of Lake Lisan, which suggest that the lake reached its highest stand around 27 000 cal. years BP . If the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production, then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50–1300 ky and 390–3130 ky respectively. Alternatively, the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock. Back calculating such rates of rock erosion suggests values between 0·4 and 12 m My?1. The relatively long burial periods indicate extended sediment storage as colluvium on slopes and/or as alluvial deposits in river terraces. Some clasts may have been stored for long periods in abandoned Pliocene and early Pleistocene routes of Nahal Zin to the Mediterranean before being transported again back into the Nahal Zin drainage system and washed on to the shores of Lake Lisan during the late Pleistocene. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

14.
Dead Sea waters are moderately enriched in18O; the degree of enrichment constitutes a balance between the dilution by freshwater influx and the isotope fractionation which accompanies evaporative water loss and vapour exchange with the atmospheric moisture. Modelling of the seasonal cycle and long-term trends of δ18O, in response to the changes in the environmental parameters, shows that the major control is exercised by the salinity of the surface waters, through its effect on the vapour pressure gradient between the lake's surface and the atmosphere; the (steady state) isotopic composition of the more saline brines tends towards less enriched18O values. This fact can explain the relatively high δ18O levels encountered in the Lisan formation, which was deposited from Lake Lisan, —the less saline Pleistocene precursor of the Dead Sea.  相似文献   

15.
The most important source of dissolved manganese, Mn(II), to the Dead Sea is by upward diffusion from bottom sediments. This source contributes about 80 tons of Mn(II) each year. The concentration of dissolved manganese in the Dead Sea is extraordinarily high (7.03 mg 1?1). It appears that the content (some 1.026 × 106 tons) of dissolved manganese in the sea has remained constant during 1977–1979, although oxygen was introduced into deeper layers during the deepening of the pycnocline (1977–1978) and during the overturn of its water masses in the winter of 1978/79. The rate of oxidation of Mn(II) in Dead Sea water is extremely slow hence Mn(II) may practically be considered as the stable form of Mn in Dead Sea waters. Dilution by fresh water causes a pH rise and may facilitate faster oxidation of the dissolved divalent manganese. It is shown here that the shape of the Mn(II) profile, observed in the lake during 1963, may have developed by oxidation of Mn(II) in the more diluted upper layers and subsequent reduction of the oxidation products in the anoxic and more saline deeper layers during 260 years of continuous meromixis.  相似文献   

16.
Sediment cores retrieved from landslide‐dammed Loon Lake recorded events back to the 5th century AD in a forested, mountainous catchment, thereby providing an opportunity to compare the impacts of known recent perturbations, including floods and timber harvesting with those of an early period in the cores, floods, fires, and earthquakes. High‐resolution multi‐parameter (grain size, %TC, %TN, and magnetic susceptibility) data allowed the core stratigraphy to be classified as background sedimentation and events. 137Cs and radiocarbon dating, as well as a varved record in the last 75 years provided age control. Mean mass accumulation rate from 1939 to 1978 AD, the time of peak timber harvest and a cool wet phase of the Pacific Decadal Oscillation, was 0.79 (0.74–0.92, 95% C.L.) g cm‐2 y‐1, significantly higher than mean rates of both the more recent contemporary period (coincident with the passing of the legislation that regulated harvesting practices in the region), 1979–2012 AD, at 0.58 (0.48‐0.70) and the entire early period, 0.44 (0.41–0.46). Several event deposits are coeval with independently estimated ages of eight Cascadia subduction zone earthquakes in the early period, including the 1700 AD Mw 9.0 event. These deposits are predominantly formed by hyperpycnal flows, as are the known event deposits in the contemporary period. The high mass accumulation rate and greater frequency of thick event deposits during the early contemporary period point to the extraordinary role of timber harvesting in priming the landscape for subsequent sedimentary delivery during floods. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

17.
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   

18.
Storm-related sea level variations 1958–2002 along the North Sea coast from a high-resolution numerical hindcast are investigated and compared to the results of earlier studies. Considerable variations were found from year to year and over the entire period. The large-scale pattern of these variations is consistent with that derived from previous studies, while the magnitudes of the long-term trends differ. The latter is attributed to different analysis periods, improvements in the atmospheric forcing, and the enhanced spatial resolution of the numerical simulation. It is shown that the different analysis periods, in particular, represent an issue as the increase in storm-related sea levels was found to be weaker over the last few years that have not been included in earlier studies. These changes are consistent with observed changes of the storm climate over the North Sea. It is also shown that observed and hindcast trends may differ significantly. While the latter are in agreement with observed changes in the storm climate, it may be concluded that observed sea level changes along the North Sea coast comprise a considerable fraction that cannot be attributed to changes in the large-scale atmospheric circulation.
Ralf WeisseEmail:
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19.
Nahal Paran drains 3600 km2 of Egypt's Sinai peninsula and Israel's Negev Desert. Much of the channel is alluvial, but a canyon 10·5 km long has been incised into Late Cretaceous chert and dolomite in the lower portion of the basin. Slackwater deposits and paleostage indicators preserved within the canyon record approximately 10 floods of 200 to 2500 m3 s?1 over a period of at least 350 years. Step-backwater simulations of flood-flow hydraulics indicate extreme variations in stream power per unit area along the length of the canyon, and associated variability in energy expenditure and sediment transport. These variations reflect channel cross-sectional morphology. The greatest values of stream power occur along the lower half of the study reach, in association with three pronounced knickpoints and an inner channel. The locations of these features reflect the exposure of thick, resistant chert layers along the channel. The presence of several similar, but buried and inactive, knickpoints along the upper study reach indicates that the locus of most active channel incision has shifted with time, probably in response to baselevel changes associated with tectonic activity along the Dead Sea Rift. Thus, the rate and manner of channel incision along the canyon of Nahal Paran are controlled by lithologic variability and tectonic uplift as they influence channel morphology and gradient, which in turn influence hydraulics and sediment transport.  相似文献   

20.
The Feshcha springs issue in a 4 km long strip on the Dead Sea shores. They constitute two separate groups: a) T-N waters, similar in their salt composition, temperature and radon content to the many other members of the Rift Valley “Tiberias-Noit water association”. The hydrologic, radon, tritium and carbon-14 indicate they are mixtures of recent meteoric waters with ancient (trapped) T-N waters of an age of at least 18000 years. b) Z-Y waters which, like other members of the Dead Sea basin “Zohar-Yesha water group”, originate by a mixing of T-N waters with Dead Sea waters. This is seen in the chemical compositions and is confirmed by the oxygen-18 and deuterium data.  相似文献   

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