Extreme flood on the Danube River in 2006

Causes and features of an extreme flood on the Danube River in spring and summer 2006 are considered. The water levels at some gauge stations on the Middle Danube and at most gauge stations on the Lower Danube exceeded maxima observed during previous 100–130 years. The flood on the Lower Danube lasted from March to July and led to widespread inundations and damage. The flood was caused by melt of large amounts of snow accumulated in the river basin during winter, very warm spring, and abundant rains. In recent decades, the occurrence frequency of extreme hydrological events on the Danube River (large spring-summer floods and catastrophic rainfall freshets) has increased.     

On the link between extreme floods and excess monsoon epochs in South Asia

This paper provides a synoptic view of extreme monsoon floods on all the nine large rivers of South Asia and their association with the excess (above-normal) monsoon rainfall periods. Annual maximum flood series for 18 gauging stations spread over four countries (India, Pakistan, Bangladesh and Nepal) and long-term monsoon rainfall data were analyzed to ascertain whether the extreme floods were clustered in time and whether they coincided with multi-decade excess monsoon rainfall epochs at the basin level. Simple techniques, such as the Cramer’s t-test, regression and Mann–Kendall (MK) tests and Hurst method were used to evaluate the trends and patterns of the flood and rainfall series. MK test reveals absence of any long-term tendency in all the series. However, the Cramer’s t test and Hurst-Mandelbrot rescaled range statistic provide evidence that both rainfall and flood time series are persistent. Using the Cramer’s t-test the excess monsoon epochs for each basin were identified. The excess monsoon periods for different basins were found to be highly asynchronous with respect to duration as well as the beginning and end. Three main conclusions readily emerge from the analyses. Extreme floods (>90th percentile) in South Asia show a tendency to cluster in time. About three-fourth of the extreme floods have occurred during the excess monsoon periods between ~1840 and 2000 AD, implying a noteworthy link between the two. The frequency of large floods was higher during the post-1940 period in general and during three decades (1940s, 1950s and 1980s) in particular.     

Trends in floods and related climate conditions in Illinois

The climate of Illinois (Midwest U.S.A.) has gradually become cooler and wetter since 1940, raising questions of possible effects on flooding. The frequency and duration of both winter and summer season floods during the 1921–80 period exhibited general up trends, peaking during 1971–80 in basins in the eastern two-thirds of Illinois. Heavy rain (?5.1 cm) events in the summer were found to have similar up trends in the same regions where summer flooding was increased. Summer heavy rain increased 27% from 1921–1980, as compared to 43% increase in flood durations and a 77% increase in flooding events. Winter temperatures have decreased 16% since 1930, whereas winter precipitation has increased in northern and eastern Illinois by 12% where winter flooding increased. The increase in winter precipitation apparently has been more important than the lowering temperatures in producing more winter floods, and particularly longer duration winter floods.     

Development of flood exposure in the Netherlands during the 20th and 21st century

Flood risks of deltaic areas increase because of population growth, economic development, land subsidence and climatic changes such as sea-level rise. In this study, we analyze trends in flood exposure by combining spatially explicit historical, present, and future land-use data with detailed information on the maximum flood inundation in the Netherlands. We show that the total amount of urban area that can potentially become inundated due to floods from the sea or main rivers has increased six-fold during the 20th century, and may double again during the 21st century. Moreover, these developments took, and probably will take, place in areas with progressively higher potential inundation depths. Potential flood damage has increased exponentially over the 20th century (16 times) and is expected to continue to increase exponentially (∼ten-fold by 2100 with respect to 2000) assuming a high economic growth scenario. Flood damages increase more moderately (two- to three-fold by 2100 with respect to 2000) assuming a low growth scenario. The capacity to deal with catastrophic flood losses - expressed as the ratio damage/GDP - will, however, decrease slightly in the low growth scenario (by about 20%). This trend deviates from the historical trend of the 20th century, which shows an increasing capacity to cope with flood damage (almost doubling). Under the high growth scenario the capacity to deal with such losses eventually increases slightly (by about 25%). These findings illustrate that, despite higher projections of potential flood damage, high economic growth scenarios may not necessarily be worse than low growth scenarios in terms of the impact of floods.     

1755年中国东部极端雨涝事件研究

1755年（清乾隆二十年）我国东部大范围、多流域严重雨涝,其后1756、1757年黄河中下游雨涝,连续2年呈现较少见的北涝南旱降水分布格局,这是小冰期中相对温暖时段气候背景下的重大气象灾害和极端气候事件。依据历史文献记载复原多雨的天气实况和气候特征,绘制各年多雨、水灾和伴生的饥荒、虫灾、疫疾的发生地域实况图。结果表明,1755年黄河、长江中下游和淮河流域持续多雨,其中黄淮地区连续雨日超过40 d。有早梅雨,长江下游的梅雨期长达43 d,是18世纪最长的梅雨期,南京的年降水量达1378 mm,是18世纪的最高值。1755年气温偏低,夏寒、秋霜早、冬季寒冷等特征与典型的极端多雨年1823和1954年相同,这3例极端多雨年都是太阳活动周的极小年。     

流域洪涝定量描述及江西省48a流域洪涝分析

分别对单站洪涝强度、流域集中期洪涝强度和流域汛期洪涝强度进行了定量描述。并对1951～1998年江西省5大流域的洪涝分别进行了比较分析,得出了各大流域近半世纪10大洪涝集中期、10大洪涝汛期和南北分片10大洪涝年。     

Extreme value analysis of wet and dry periods in Sicily

Summary For assessing risk of highly unusual events extreme value statistics needs to be applied, which plays an important role in engineering practices for water resources design and management. In hydrology, the typical application of extreme value theory concerns floods in river basins or landslides. The present paper is, instead, focused on the analysis of extreme wet and dry periods in a sample area (Sicily). First, we have studied monthly precipitation extremes both using the annual maximum and partial duration methods, and return times have been estimated by standard statistical techniques. Next, we studied the extremes of the Standardized Precipitation Index (SPI), which has been proposed as an indicator for monitoring wet and dry conditions. We found considerable differences both in the return periods and in the time location of the extremes. From our study it appears that the SPI better describes wet and dry periods than the precipitation does. Maps of return times for extreme conditions in Sicily are also presented, which cluster the territory into areas of different extreme return periods. Finally, the occurrence of extremes in Sicily has been related to large-scale atmospheric circulation.     

Characteristics of anomalous precipitation events over eastern China during the past five centuries

Characteristics of anomalous precipitation events during the past five centuries in North China (NC) and the middle-lower Yangtze River Valley (MLYRV) were investigated using the data network of dryness/wetness index (DWI) over eastern China. The high occurrence frequency of anomalous precipitation events mainly occurred at periods of high solar forcing, active volcanic eruption, and large anthropogenic forcing (the twentieth century). Coherence and dipole were the two dominant modes in spatial patterns of anomalous precipitation events. Coherent floods dominated the eighteenth and nineteenth centuries, whereas coherent droughts occurred frequently in the seventeenth and twentieth centuries. The dipole patterns of anomalous precipitation events were the most frequent in the twentieth century. NC experienced more floods in the cold periods than warm periods. Both NC and the MLYRV experienced far fewer droughts and more floods in the warm eighteenth century when natural climate forcing dominated, and more droughts in the twentieth century when anthropogenic forcing dominated. Coherent drought was the only spatial pattern of precipitation significantly associated with explosive low-latitude volcanic eruptions. The increased coherent droughts and dipole patterns in the twentieth century support the findings of previous modeling studies that the tropospheric aerosols and human-induced land cover changes play important roles in the changes of summer rainfall over eastern China. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. This paper is a contribution to the AMIP-CMIP Diagnostic Sub-project on General Circulation Model Simulation of the East Asian Climate, coordinated by W.-C. Wang.     

东津河流域暴雨洪涝灾害风险区划

本文从暴雨致灾机理出发,以东津河流域为例,开展中小河流域暴雨洪涝灾害风险区划技术研究。根据气象资料、水文资料、地理信息资料、社会经济统计资料以及历史灾情资料等,运用TOPMODEL水文模型并结合统计法确定致洪临界面雨量,利用逐步回归法重建区域站资料序列,基于广义极值分布函数计算出不同重现期的致洪面雨量,根据流域内小时降水雨型分布,将不同重现期致洪面雨量以及叠加堤坝信息的DEM、manning系数等数据代人Flood Area模型进行洪水淹没模拟,得到不同重现期下洪水淹没图,再叠加流域内栅格化的人口、GDP以及土地利用信息,最终得到不同重现期下人口、GDP以及土地利用等风险区划图谱。建立的中小河流域暴雨洪涝灾害风险区划技术方法简便可行,区划结果精度高、实用性强,对于面向实时防灾减灾的动态灾害风险管理具有重要意义。     

Low Frequency Streamflow Regimes over the Central United States: 1939–1998

Intra- to multi-decadal (6–30 year) streamflow regimes over the central United States during the late 20th century are identified and investigated here through a two-stage analysis. The first stage ranks mean annual flow rates during 1939–1998, calculates Mann–Whitney Ustatistics from samples of those rankings over running time windows, and then tests those U statistics for significance. This analysis of the records of 42 Hydro-Climatic Data Network stations over the Great Plains and Midwest reveals consistent patterns of highly ranked annual streamflow during time windows at the end of the century, with most beginning during the late 1960s and early 1970s and ending in either 1997 or 1998. Many of these stations are located in a critical agricultural region known as the Corn Belt. The second stage of analysis compares both the duration of abnormal flow periods and the frequency of hydrological surplus and drought conditions during the high flow years indicated by the first stage, relative to the remaining years of 1939–1998. Among gage stations in the climatologically drier western Corn Belt during the 1980s and 1990s there is a clear tendency toward extended periods of above normal flow, which results in more than a doubling in the average annual frequency of hydrological surplus days relative to previous years. These stations also show more than a 50% reduction in the average annual frequency of hydrological drought days relative to previous years. Similar but less pronounced shifts in hydrological regime are evident in the central and eastern Corn Belt, and in the Mississippi River at Vicksburg during 1973–1998. These results indicate that many areas of the central United States have shifted toward a climate regime of relative hydrological surplus during the closing decades of the 20th century.     

Technogenic influence on the quality of water resources of small river basins (with a special reference to the Protva river)

The underground waters in small river basins in central Russia are recharged as a result of the atmospheric precipitation infiltration on the catchment and river water inflow to the horizons hydraulically connected with the river. In the first case, the atmospheric precipitation on its way of transit is being enriched in elements of water-bearing rocks, in the second case, of the surface runoff and domestic wastes waters. Both fluxes get mixed at the coastal water withdrawals of underground water. Some regularities in the drinking water quality formation connected with climatic conditions and water use regime were established based on geochemical and hydrodynamic studies of underground waters of the Protva River basin deposits.     

Dynamics of occurrence frequency of extreme anomalies of monthly mean air temperature in Georgia in the 20th century and its effect on precipitation and on the river water discharge

The dynamics of the occurrence frequency of extreme anomalies of monthly mean air temperature and its effect on precipitation and river water discharge in the 20th century are studied using weather observations at 40 stations and data on the hydrological regime of 34 rivers in Georgia.     

Dry/Wet Changes and Their Standing Characteristics in China During the Past 531 Years

Time series of the dryness-wetness(DW) index of 531 yr(AD 1470-2000) at 42 stations in regions A(most of North China and the east of Northwest China) and B(the Yangtze-Huaihe River valley) in China are applied to investigating the historical DW characteristics over various periods of the series with a relatively stationary average value using Bernaola-Galvan(BG) algorithm.The results indicate that region A/B underwent three drought-intensive periods(DIP;1471-1560,1571-1640,and 1920-2000/1501-1540,1631-1690,and 1911-1960) in the last 531 years.In the DIP of the last 130 years,the frequency of DW transition has increased in region A,but not obviously changed in region B in comparison with the other two historical DIPs.The dry period started in about 1920 in region A with severe drought events occurring from the late 1970s to the early 1980s.It lasted for about 50-70 yr in this century,and then a DW shift took place.The wet period in region B might maintain for the coming several decades.The variations of DW in region A are positively correlated with changes in temperature,but in region B,the correlation with temperature is weaker.It is found that the number of DW indices of various categories within a running window is an exponential function of the running window length.The dryness scale factor(DSF) is defined as the reciprocal of the characteristic value of the exponential distribution,and it has a band-like fluctuation distribution that is good for the detection of extreme drought(flood) clustering events.The results show that frequencies of the severe large-scale drought events that concurrently occurred in regions A and B were high in the late 12th century,the early 13th century,the early 17th century,and the late 20th century.This provides evidence for the existence of the time-clustering phenomena of droughts(floods).     

Global Analysis of Changes in Water Supply Yields and Costs under Climate Change: A Case Study in China

Using China as a case study, a methodology is presented to estimate the changes in yields and costs of present and future water production systems under climate change scenarios. Yield is important to consider because it measures the actual supply available from a river basin. Costs are incurred in enhancing the natural yield of river basins by the construction and operation of reservoirs and ground water pumping systems. The interaction of ground and surface waters within a river basin and instream flow maintenance are also modeled. The water demands considered are domestic, irrigation, and instream flow needs. We found that under climate change the maximum yields of some basins in China may increase or decrease, depending upon location, and that in some basins it may cost significantly more or it may not be possible to meet the demands. While our results for China could be improved with more hydrologic and economic data, we believe that the cost curves developed have suitable accuracy for initial analysis of water supply costs in Integrated Assessment Models.     

渠江流域汛期强降水时空分布特征

本文从分析研究渠江流域汛期强降水时空分布入手,试图揭示该流域21世纪以来洪水频发的原因。经对渠江流域1970~2012年降水资料分析研究得出:(1)渠江流域汛期降水量、暴雨日数、降水变差系数呈“北大南小”的空间分布;“北区(河流汇水区,下同)”近年来汛期降水量增大、暴雨频率增加、降水趋于极端;(2)短时强降水多发生在04~08时,频发区主要位于“北区”,近年来频次呈上升趋势;(3)小时雨强极值“北区”普遍大于“南区”;近43年渠江流域汛期小时雨强极值总体呈增大趋势,“北区”尤为明显。因此,渠江流域汛期发生的强降水趋势性变化,是导致该流域洪水频发的主要原因之一。      

Long-Term Rainfall Variability in the Eastern Gangetic Plain in Relation to Global Temperature Change

India’s annual weather cycle consists mainly of wet and dry periods with monsoonal rains being one of the significant wet periods that shows strong spatiotemporal variability. This study includes the climatological characteristics, fluctuation features, and periodic cycles of annual, seasonal, and monthly rainfall of seven river basins across the eastern Gangetic Plain (EGP) using the longest possible instrumental area-averaged monthly rainfall series (1829–2012). Understanding the relationships between these parameters and global tropospheric temperature changes and El Niño and La Niña climatic signals is also attempted.

Climatologically, mean annual rainfall in the EGP varies from 1070.5?mm in the Tons River basin to 1508.6?mm in the Subarnarekha River basin. The highest rainfall in the EGP occurs during monsoon (1188?mm). The annual rainfall in all river basins and monsoon rainfall in four river basins is normally distributed. Annual and monsoonal rainfall in the Brahmani and Son River basins show a significant decreasing long-term trend. Over the last 20 years, annual rainfall in all river basins and monsoonal rainfall in five river basins show a decreasing trend. The power spectra for all rainfall series are characterized by consistent significant wavelength peaks at 3–5 years, 10–20 years, 40 years, and more than 80 years. Short-term fluctuations with a period less than 10 years is the major contributor to total variance in annual and/or monsoon rainfall (77.6%), followed by decadal variations with a period of 10–30 years (13.1%) and a long-term trend with a period greater than 30 years (9.3%).Temperature and thickness gradients from the Tibet–Himalaya–Karakoram–Hindu Kush highlands to eight strong highs show a significant correlation with rainfall during the onset and withdrawal phases of summer monsoon in the EGP.     

Recent Progress in Studies of Climate Change in China

An overview of basic research on climate change in recent years in China is presented. In the past 100 years in China, average annual mean surface air temperature (SAT) has increased at a rate ranging from 0.03℃ (10 yr)-1 to 0.12℃ (10 yr)-1 . This warming is more evident in northern China and is more significant in winter and spring. In the past 50 years in China, at least 27% of the average annual warming has been caused by urbanization. Overall, no significant trends have been detected in annual and/or summer precipitation in China on a whole for the past 100 years or 50 years. Both increases and decreases in frequencies of major extreme climate events have been observed for the past 50 years. The frequencies of extreme temperature events have generally displayed a consistent pattern of change across the country, while the frequencies of extreme precipitation events have shown only regionally and seasonally significant trends. The frequency of tropical cyclone landfall decreased slightly, but the frequency of sand/dust storms decreased significantly. Proxy records indicate that the annual mean SAT in the past a few decades is the highest in the past 400-500 years in China, but it may not have exceeded the highest level of the Medieval Warm Period (1000-1300 AD). Proxy records also indicate that droughts and floods in eastern China have been characterized by continuously abnormal rainfall periods, with the frequencies of extreme droughts and floods in the 20th century most likely being near the average levels of the past 2000 years. The attribution studies suggest that increasing greenhouse gas (GHG) concentrations in the atmosphere are likely to be a main factor for the observed surface warming nationwide. The Yangtze River and Huaihe River basins underwent a cooling trend in summer over the past 50 years, which might have been caused by increased aerosol concentrations and cloud cover. However, natural climate variability might have been a main driver for the mean and extreme precipitation variations observed over the past century. Climate models generally perform well in simulating the variations of annual mean SAT in China. They have also been used to project future changes in SAT under varied GHG emission scenarios. Large uncertainties have remained in these model-based projections, however, especially for the projected trends of regional precipitation and extreme climate events.     

The Case of the `Maldá' Anomaly in the Western Mediterranean Basin (AD 1760–1800): An Example of a Strong Climatic Variability

The study of climatic anomalies on the basis of various types of instrumental information and proxy-data allows unusual events to be identified. The objective of this paper is to introduce and explain a hydrometeorological anomaly that occurred between 1760 and 1800 (Maldá Anomaly), characterised by a sequence of both anomalous droughts and floods, and to compare it with the features of the second part of the 20th century. Firstly, some climatic indices obtained from proxy-data (mainly documentary sources) have been generated. Secondly, instrumental observations made in earlier times, in conjunction with data from the bibliography, have been used in order to relate this period to the different circulation patterns and to analyse the geographical extension of the anomaly. The results confirm the presence of considerable variations in the atmospheric action centres, especially between 1780 and 1795, which in the Western Mediterranean gave rise to a simultaneous increase in the frequency of droughts and heavy rainfalls, either having nothing comparable or sharing similarities with periods in the 19th and 20th centuries.     

Changes in Vascular Plant Biodiversity in the Netherlands in the 20th Century Explained by their Climatic and other Environmental Characteristics

In the Netherlands nation-wide databases are available with about 10 million records of occurrences of vascular plant species in the 20th century on a scale of approximately 1 km². These data were analysed with a view to identifying relationships between changes in botanical biodiversity and climatic and other environmental factors. Prior to analysis the data were corrected for several major forms of survey bias. The records were broken down into three periods: 1902–1949, 1975–1984 and 1985–1999. Using multiple regression analysis, differences between successive periods were related to plant functional characteristics as explanatory variables. Between the periods 1902–1949 and 1975–1984 there were small but significant increases in the presence of both thermophilic (‘warm’) and psychrophilic (‘cold’) species. However, in the final decades of the 20th century there was a marked increase in thermophilic species only, coinciding with the marked increase in ambient temperature observed during this period, evidence at least of a rapid response of Dutch flora to climate change. Urbanisation was also examined as an alternative explanation for the increase in thermophilic plant species and was found to explain only 50% of the increased presence of such species in the final decades of the 20th century. Besides temperature-related effects, the most important change during the 20th century was a strong decline in oligotrophic and a marked increase in eutrophic plant species.     

1951-2006年黄河和长江流域雨涝变化分析

 根据1951-2006年黄河和长江流域雨涝灾害灾情统计资料,分析了两个流域雨涝灾害发生频率的时空分布特征,结果表明：近50 a以来,特别是20世纪80年代以来,受气候变化影响,黄河和长江流域雨涝灾害不断增加,农作物受灾、成灾面积呈增加趋势,损失日趋严重,且长江流域受雨涝灾害影响范围较大,灾害发生频率大于黄河流域。受暴雨影响,夏季两个流域雨涝发生频率最高、范围最广。20世纪80年代末以来,黄河流域雨涝灾害增加趋势较为明显,而长江流域80年代初雨涝受灾面积和成灾面积显著增加。两个流域雨涝灾害的受灾率均自上游至下游逐渐增加,其中长江流域中下游地区受雨涝灾害影响较大。