新疆天山北坡中段河流冰凌洪水特征分析

冰凌洪水(冰洪)是新疆天山北坡中段河流冬季的一种特殊洪水,其暴发主要受气温、逆温带范围、冬季河流来水量、冰情冰厚、地势.河道弯曲率和河床条件等多种因素影响."冰洪"具有随机性、规律性和不重复性三种特性,冰凌洪水的峰型类似于暴雨洪水具有陡涨陡落的特点,峰前陡峭而落峰则相对缓一些.以四棵树河为典型流域,对冰凌洪水的成因、发展和运动规律进行研究,并发现冰凌洪水具有"水鼓冰开"现象.对四棵树河1967-2006年冰洪流量的年内、年际分布情况看,20世纪70-80年代由于冬季气候寒冷,是"冰洪"发生最多的时期;自进入20世纪90年代以来由于受全球气候变暖等因素影响,冰凌洪水呈现衰退趋势,气候变暖对冰洪影响非常大.     

Analysis of flood causes and associated socio-economic damages in the Hindukush region

Pakistan is exposed to numerous hazards, but the problem of recurrent floods has been causing massive losses to lives and other properties. Swat valley is no exception to it. In this paper, an attempt has been made to analyse the causes and associated socio-economic impacts of floods on the Swat valley, Pakistan. Swat valley falls in the Hindukush region, North-west-Pakistan. The valley has been studied with special reference to its physical and socio-economic environment. Similarly, three-sample villages were also randomly selected from the active floodplain for micro-level analysis. The sample villages include Ningolai, Delay and Ghureijo. All the three-sample communities are located on the right bank of river Swat. This area is located in the active flood zone of Swat valley. The analysis revealed that in the study area, floods occur during summer season, which is mainly caused by heavy rainfall as well as rapid melting of snow and glacier. Besides these, there are some floods intensifying factors, which accelerate intensity of floods and enhance resultant damages in the valley. It was found that during flood season, water overflows the natural levees and trigger tremendous loses to housing, agricultural land, standing crops and other properties. The flood-related Government Departments have only implemented limited structural mitigation measures. However, in addition to structural measure, land-use zoning and flood abatement strategies would largely help in reducing the adverse consequences of this recurrent phenomenon.     

Hydrological impact of forest fires and climate change in a Mediterranean basin

Forest fire can modify and accelerate the hydrological response of Mediterranean basins submitted to intense rainfall: during the years following a fire, the effects on the hydrological response may be similar to those produced by the growth of impervious areas. Moreover, climate change and global warming in Mediterranean areas can imply consequences on both flash flood and fire hazards, by amplifying these phenomena. Based on historical events and post-fire experience, a methodology to interpret the impacts of forest fire in terms of rainfall-runoff model parameters has been proposed. It allows to estimate the consequences of forest fire at the watershed scale depending on the considered burned area. In a second stage, the combined effect of forest fire and climate change has been analysed to map the future risk of forest fire and their consequence on flood occurrence. This study has been conducted on the Llobregat river basin (Spain), a catchment of approximately 5,000 km² frequently affected by flash floods and forest fires. The results show that forest fire can modify the hydrological response at the watershed scale when the burned area is significant. Moreover, it has been shown that climate change may increase the occurrence of both hazards, and hence, more frequent severe flash floods may appear.     

Glacial Lake Outburst Floods in the Nepal Himalaya: A Manageable Hazard?

Within the past fifteen years, glacial lake outburst floods have become an activetopic of discussion within the development community focused on Nepal. Suchfloods endanger thousands of people, hundreds of villages, and basic infrastructuresuch as trails and bridges. The flood risk is also a major impediment to hydroelectricdevelopment in several river basins. Unlike most other mountain hazards in Nepal,reducing the possibility of outburst floods is technically feasible. The first attemptwithin Nepal to reduce the hazard of one lake by artificially lowering its water levelwas partially completed in June 2000. Completing this task and beginning work onother hazardous lakes will require difficult decisions about risk by downstream residentsand substantial investment from the international aid community.     

Participatory modelling of vulnerability and adaptive capacity in flood risk management

Being part of the EU-project NeWater on adaptive water resources management, the Ukrainian Tisa river basin is presented as an example for a participatory study dealing with flood risk, vulnerability and adaptive capacity. The Tisa valley is regularly and increasingly faced with hazardous floods at very limited local budgets and high poverty rates. In order to make flood risk management more resilient and better adapted to climate change, scientists and stakeholders applied a set of qualitative and quantitative modelling approaches to characterise prevailing flood risk management, to discover respective vulnerabilities and to identify barriers and options of adaptive capacity. The former were found in the defensive mentality paradigm and the inert and hierarchical structure of present institutions, the latter in, firstly, an enormous potential to link the knowledge of different stakeholders in the region, secondly, a better integration of the individual flood preparedness of households and thirdly, the active involvement of the Church as institution in local flood risk management.     

A reconstruction of the palaeohydrological conditions of a flood‐plain: a multi‐proxy study from the Grabia River valley mire,central Poland

This study investigated the Grabia River valley mire in central Poland to reconstruct its palaeoenvironmental conditions from the Younger Dryas to the present. We analysed sedimentological, biological and geochemical data from the palaeo‐oxbow lake and valley mire to identify the principal hydrological trends, especially episodes of high water level. During the Lateglacial and Holocene, the Grabia River had a meandering channel, and its hydraulic parameters and the channel dimensions changed in response to climatic oscillations and vegetation development. We identified phases of high flood intensity and high groundwater level that correlate with regional and supraregional climatic events. The frequency and timing of palaeohydroclimatic oscillations show strong similarities to records from other sites in Poland and the rest of Europe. We show that various analytical methods, namely, pollen, plant macrofossils, Cladocera, Chironomidae, sedimentological, geochemical and radiocarbon data, can be effective tools for reconstructing past hydroclimatic changes in palaeo‐oxbow lakes and investigating the effects of past climate changes on river environments. The high sensitivity of the biota, especially Cladocera, to changes in water level permits the reconstruction of palaeoecological changes, especially flood episodes that occurred in the river valley. In particular, the increase in the proportion of sediment‐associated Cladocera and pelagic taxa was closely correlated with floods. Through comparisons with the palaeobiological data, geochemical data allowed the identification of humid phases within the fen associated with a rising groundwater table, direct fluvial activity (floods) and alluvial deposition. We also discuss the limitations of palaeohydrological reconstructions based on these proxies, especially on fossil aquatic invertebrates.     

Characteristics of glacier outburst flood in the Yarkant river,Karakorum mountains

Conclusions 1. The drainage of the Kyagar glacier dammed lake and the Tram Kangri glacier dammed lake at the upper Shaksgam is the main reason for glacier outburst floods in the Yarkant river. The Kyagar glacier dammed lake is characterized by subglacial drainage, while the Tram Kangri glacier dammed lake by mainly lateral drainage and, secondly, by subglacial drainage. 2. The drainage mechanism of the Tram Kangri ice dam determines the main characteristics of flood hydrography of the Kagun station, while the Kyagar glacier dammed lake plays an important role in the formation of floods. 3. Glacier outburst floods in the Yarkant river are characterized mainly by high peak discharge, big rising rate, small total volume and short duration. The floods happen mostly from late summer to early autumn. A period of 6 to 10 years in occurrence of large scale glacier outburst floods exist. The periodicity depends mainly on large scale drainage in the Kyagar ice-dammed lake. 4. Formation and dimensions of glacier dams at the upper Shaksgam were determined by long-term variations of the regional climate, whereas the changes of storage capacity in the lake reflect cold and warm changes of alpine region. Therefore, frequent glacier outburst floods indicate glacier advance and climatic variations.     

Hydrological hazards in Russia: origin,classification, changes and risk assessment

Hydrological extreme events pose an imminent risk to society and economics. In this paper, various aspects of hydrological hazards in Russia are analysed at different scales of risk assessment. It is shown that the number of hydrological and meteorological hazards in Russia has been growing every year. The frequency of economic losses associated with extreme low flow in this century has increased by factor five compared to the last decade of the previous century. With regard to floods, an interesting spatial patter can be observed. On the one hand, the number of floods in the Asian part of the country has increased, whereas on the other hand, the number and intensity of floods in estuarine areas in the European part of Russia have significantly reduced since the middle of the twentieth century, especially in the 2000s. This decrease can be attributed to runoff flooding in the mouths of regulated rivers, with an effective system of flood and ice jam protection. The analysis shows that there is an 8–12-year periodicity in the number of flood occurrences and that flood surges have intensified over the last 110 years, especially on the European territory of Russia. An integrated index that accounts for flood hazards and socio-economic vulnerability was calculated for each region of Russia. A classification of flood risk was also developed, taking into account more than 20 hydrological and social–economic characteristics. Based on these characteristics, hazard and vulnerability maps for entire Russia were generated which can be used for water management and the development of future water resources plans.

     

From flood control to flood adaptation: a case study on the Lower Green River Valley and the City of Kent in King County,Washington

Despite massive investment in flood control infrastructure (FCI), neither cities nor rivers have been well served—flooding continues to challenge cities around the world, while riverine ecosystems are degraded by FCI. Although new flood hazard management concepts have shifted the focus away from FCI, many cities continue to count on FCI to prevent flood damage. It is assumed that existing built-up areas can only count on FCI, as large-scale retreat is often impossible. However, flood adaptation—retrofitting the built environment to prevent damage during flooding—as an option is often ignored. This paper argues against the continual use of FCI to prevent flood damage by reviewing FCI’s established problems. The paper examines human–river interactions associated with FCI, focusing on the feedback mechanisms in the interactions, with a case study on the Lower Green River (LGR) valley in King County, Washington, USA. An urban ecology research model is employed to organize the case study, where interactions between floodplain urbanization, FCI, flow and sediment changes, flood risk, and riverine ecosystem are explored and two feedback mechanisms—river adjustment and flood risk perception—are explicitly addressed. The resulting complex dynamics, in terms of cross–scale interactions, emergence, nonlinearity, and surprises, are synthesized and limitations of FCI outlined. Flood adaptation is explored as a plausible alternative to flood control to nurture flood resilience. A management scenario of flood adaptation for the City of Kent—the largest municipality in the LGR valley—is developed to discuss the implications of flood adaptation on flood risk and river restoration.     

Repeated glacial-lake outburst floods in Patagonia: an increasing hazard?

Five similar glacial-lake outburst floods (GLOFs) occurred in April, October, December 2008, March and September 2009 in the Northern Patagonia Icefield. On each occasion, Cachet 2 Lake, dammed by the Colonia Glacier, released circa 200-million m³ water into the Colonia River. Refilling has occurred rapidly, such that further outbreak floods can be expected. Pipeflow calculations of the subglacial tunnel drainage and 1D hydraulic models of the river flood give consistent results, with an estimated peak discharge surpassing 3,000 m³ s^?1. These floods were larger in magnitude than any flood on record, according to gauged data since 1963. However, geomorphological analysis of the Colonia valley shows physical evidence of former catastrophic outburst floods from a larger glacial-lake, with flood discharges possibly as high as 16,000 m³ s^?1. Due to potential impacts of climate change on glacier dynamics in the area, jökulhlaups may increase future flood risks for infrastructure and population. This is particularly relevant in view of the current development of hydropower projects in Chilean Patagonia.     

A risk analysis for floods and lahars: case study in the Cordillera Central of Colombia

The glacier-covered Nevado del Tolima in the Colombian Cordillera Central is an active volcano with potential lahars that might be more hazardous than those on Nevado del Ruiz. Furthermore, rainfall-triggered floods and landslides notoriously and severely affect the region. For effective disaster prevention, a risk analysis is of primary importance. We present here a risk analysis methodology that is based on the assessment of lahar and rainfall-related flood hazard scenarios and different aspects of vulnerability. The methodology is applied for populated centres in the Combeima valley and the regional capital Ibagué (~500,000 inhabitants). Lahar scenarios of 0.5, 1, 5, and 15?million m³ volume are based on melting of 1, 2, 10, and 25?% of ice, firn and snow, respectively, due to volcanic activity and subsequent lahar formation. For flood modelling, design floods with a return period of 10 and 100?years were calculated. Vulnerability is assessed considering physical vulnerability, operationalized by market values of dwelling parcels and population density, whereas social vulnerability is expressed by the age structure of the population and poverty. Standardization of hazard and vulnerability allows for the integration into a risk equation, resulting in five-level risk maps, with additional quantitative estimate of damage. The probability of occurrence of lahars is low, but impacts would be disastrous, with about 20,000 people and more directly exposed to it. Floods are much more recurrent, but affected areas are generally smaller. High-risk zones in Ibagué are found in urban areas close to the main river with high social vulnerability. The methodology has proven to be a suitable tool to provide a first overview of spatial distribution of risk which is considered by local and regional authorities for disaster risk reduction. The harmonization of technical-engineering risk analysis and approaches from social sciences into common reference concepts should be further developed.     

Assessing flood disaster impacts in agriculture under climate change in the river basins of Southeast Asia

Natural Hazards - This study focused on flood damage assessment for future floods under the impact of climate change. Four river basins of Southeast Asia were selected for the study. They included...     

Hazard and risk from large landslides from Mount Meager volcano,British Columbia,Canada

During the past 8000 years, large volcanic debris flows from Mount Meager, a Quaternary volcano in southwest British Columbia, have reached several tens of kilometres downstream in Lillooet River valley, with flow velocities of many metres per second and flow depths of several metres. These debris flows inundated areas that have become settled in the past 100 years and are now experiencing rapid urban growth. Notably, Pemberton, 65 km from Mount Meager, has doubled in size in the past five years. Approval of subdivision and building permits in Pemberton and adjacent areas requires assessment and mitigation of flood hazards, but large, rare debris flows from Mount Meager are not considered in the permitting process. Unlike floods, some volcanic debris flows occur without warning. We quantify the risk to residents in Lillooet River valley from non-eruption triggered volcanic debris flows based on Holocene landslide activity at Mount Meager. The calculated risk exceeds, by orders of magnitude, risk tolerance thresholds developed in Hong Kong, Australia, England, and in one jurisdiction in Canada. This finding poses a challenge for local governments responsible for public safety.     

A review of multiple natural hazards and risks in Germany

Although Germany is not among the most hazard-prone regions of the world, it does experience various natural hazards that have caused considerable economic and human losses in the past. Moreover, risk due to natural hazards is expected to increase in several regions of Germany if efficient risk management is not able to accommodate global changes. The most important natural hazards, in terms of past human and economic damage they caused, are storms, floods, extreme temperatures and earthquakes. They all show a pronounced spatial and temporal variability. In the present article, a review of these natural hazards, associated risks and their management in Germany is provided. This review reveals that event and risk analyses, as well as risk management, predominantly focus on one single hazard, generally not considering the cascading and conjoint effects in a full multi-hazard and risks approach. However, risk management would need integrated multi-risk analyses to identify, understand, quantify and compare different natural hazards and their impacts, as well as their interactions.     

Spatially distributed rainfall information and its potential for regional landslide early warning systems

Hydrological extreme events pose an imminent risk to society and economics. In this paper, various aspects of hydrological hazards in Russia are analysed at different scales of risk assessment. It is shown that the number of hydrological and meteorological hazards in Russia has been growing every year. The frequency of economic losses associated with extreme low flow in this century has increased by factor five compared to the last decade of the previous century. With regard to floods, an interesting spatial patter can be observed. On the one hand, the number of floods in the Asian part of the country has increased, whereas on the other hand, the number and intensity of floods in estuarine areas in the European part of Russia have significantly reduced since the middle of the twentieth century, especially in the 2000s. This decrease can be attributed to runoff flooding in the mouths of regulated rivers, with an effective system of flood and ice jam protection. The analysis shows that there is an 8–12-year periodicity in the number of flood occurrences and that flood surges have intensified over the last 110 years, especially on the European territory of Russia. An integrated index that accounts for flood hazards and socio-economic vulnerability was calculated for each region of Russia. A classification of flood risk was also developed, taking into account more than 20 hydrological and social–economic characteristics. Based on these characteristics, hazard and vulnerability maps for entire Russia were generated which can be used for water management and the development of future water resources plans.     

基于星载雷达特征参数的黄河冰厚反演及冰储量估算

冰厚是冰凌成因分析及预报的重要基础信息,可为防凌减灾提供重要依据。以黄河内蒙古段包头至头道拐水文站为例,利用Sentinel-1雷达影像结合Sentinel-2光学影像对研究区河冰厚度进行估算,首先对Sentinel-2光学影像进行处理,提取凌汛期前黄河主河道边界;然后对Sentinel-1雷达影像进行处理,提取2个强度信息和4个极化分解参数,分析6个雷达特征参数与河冰厚度的相关性;选择相关性最高的参数,采用统计回归方法建立冰厚反演线性回归模型,模型的调整R²为0.657,验证RMSE为9.82 cm,MRE为13.46%,MAE为8.26 cm;对凌汛期黄河冰厚进行反演,分析冰厚时空变化特征,并估算冰储量,同时讨论了河冰的散射机制。研究证明了主动微波遥感数据在黄河冰厚反演中的可行性,可为黄河内蒙古段防凌减灾提供科学参考。     

长江流域历史洪水的周期地理学研究

从周期地理学的角度,探讨长江历史洪水的频发特点和周期规律,认为影响长江历史洪水的基本周期因子,与近日点日月交食年周期、太阳黑子活动周期和历史气候周期等因素有较大的关联性。而近几个世纪以来长江洪水频率的不断加快,表明人类活动扰乱和改变了历史洪水原有的周期值,使长江历史洪水周期打上了人类活动的深刻烙印。     

Use of documentary sources on past flood events for flood risk management and land planning

The knowledge of past catastrophic events can improve flood risk mitigation policy, with a better awareness against risk. As such historical information is usually available in Europe for the past five centuries, historians are able to understand how past society dealt with flood risk, and hydrologists can include information on past floods into an adapted probabilistic framework. In France, Flood Risk Mitigation Maps are based either on the largest historical known flood event or on the 100-year flood event if it is greater. Two actions can be suggested in terms of promoting the use of historical information for flood risk management: (1) the development of a regional flood data base, with both historical and current data, in order to get a good feedback on recent events and to improve the flood risk education and awareness; (2) the commitment to keep a persistent/perennial management of a reference network of hydrometeorological observations for climate change studies.     

Fashion and phases of late Pleistocene aggradation and incision in the Alaknanda River Valley, western Himalaya, India

We study the aggradation and incision of the Alaknanda River Valley during the late Pleistocene and Holocene. The morphostratigraphy in the river valley at Deoprayag shows the active riverbed, a cut terrace, and a fill terrace. The sedimentary fabric of the fill terrace comprises four lithofacies representing 1) riverbed accretion, 2) locally derived debris fan, 3) the deposits of waning floods and 4) palaeoflood records. The sedimentation style, coupled with geochemical analysis and Optically Stimulated Luminescence (OSL) dating, indicate that this terrace formed in a drier climate and the river valley aggraded in two phases during 21–18 ka and 13–9 ka. During these periods, sediment supply was relatively higher. Incision began after 10 ka in response to a strengthened monsoon and aided by increase of the tectonic gradient. The cut terrace formed at ~ 5 ka during a phase of stable climate and tectonic quiescence. The palaeoflood records suggest wetter climate 200–300 yr ago when the floods originated in the upper catchment of the Higher Himalaya and in the relatively drier climate ~ 1.2 ka when locally derived sediments from the Lesser Himalaya dominated flood deposits. Maximum and minimum limits of bedrock incision rate at Deoprayag are 2.3 mm/a and 1.4 mm/a.