Flood disasters – a global perspective

This paper presents the results of geohazards mapping and evaluation their role in the modifying of the urban landscape in Poznań, Poland. Information on geohazards specific to an urban lowland area (river floods, flash floods, mass movement, wind erosion) because of increasing climate change was compiled into a geomorphological map. The most spatially widespread geohazards in Poznań include: (a) on moraine hills/uplands: mass movement, wind erosion, and flash floods (4.9% of the city area); (b) on outwash plains: mass movement and flash floods (8.6% of the city area); (c) on fluvial landforms: mass movement and river floods (9.8% of the city area); (d) within plains of various origin: flash floods (7.6% of the city area). Mass movement affecting short but numerous (and locally steep) slopes, and flash floods are the most widespread geohazards (16 and 14%, of Poznań’s area, respectively). Extensive urbanisation especially the expansion of impervious surfaces increases the high risk of flash floods.

<p>The poster will present the role of contemporary morphogenetic processes in shaping the morphological landscape of the city of Poznań (530 464 inhabitants). The study is based on geocomputation performed on a digital elevation model, analysis of geomorphological evolution of the city area and analysis of land cover and land use. Particular attention was paid to above-average and extreme processes. The discussed morphogenetic processes included the analysis of floods on the Warta River flowing through the city, flash floods generated in the city streets, mass movements occurring mainly on the slopes of the Warta River valley and on the slopes of moraine hills, and wind erosion occurring in vast areas devoid of vegetation. Most of these processes are related to the progressive climatic changes and sealing of the ground by concreting and asphalting large patches of the city. The analysed processes are visualised on a geomorphological map and a land cover and land use map. Contemporary morphogenetic processes observed in Poznań include: (a) on morainic hills/uplands: mass movements, wind erosion and flash floods; (b) on outwash plains: mass movements and flash floods; (c) on fluvial landforms: mass movements and river floods; (d) within plains of different origin: flash floods. Increasing urbanisation of the city, mainly through the increase in impervious surfaces, increases the risk of flash floods, which have replaced river floods in the list of risks to urban infrastructure.</p>

Flood risk and its reduction in China

Chapter 6: Insurance industry

It is not surprising that, on a hotter planet, the occurrence and impacts of wildfires and floods are becoming magnified. Extra heat enhances the tinder dry conditions required for wildfires to ignite and spread, while a warmer atmosphere holds more water in vapour form, fostering the extreme precipitation that drives flooding. Wildfires have devastated huge areas of North America, Russia, Australia, and southern Europe in recent years, especially where so-called ‘heat domes’ have brought exceptional and persistent temperatures. The greatest wildfires can last for months, becoming self-perpetuating as pyrocumulonimbus clouds build into colossal thunderstorms triggering lightning strikes that cause new burns. As rainfall becomes more extreme and persistent, both river flooding and surface flooding have become more common, and increasingly devastating. Flash floods, which happen with little or no warning, are—in particular—a growing threat to life. Meanwhile, accelerating construction across flood plains means that river flooding is affecting ever more people and having an increasing impact on vulnerable infrastructure. Some of the worst flooding in recent years has been caused by so-called atmospheric rivers—long conveyor belts of moist air that bring torrential rains and can last for days, even weeks. As sea levels continue to rise, the coastal zone is increasingly impacted, not only by flooding but by permanent inundation. This is especially problematical where large cities are constructed on river deltas from which water is being abstracted, and which are sinking rapidly at the same time as the sea rises.

Worldwide, flood is the number one cause of losses from natural events. The insurance of the flood risk has attracted more and more attention in recent years, not only in the fields of science and politics but also within the insurance industry itself Even if the list of great natural disasters is headed by storms and despite the relatively low density of insurance against flooding the large number of local flood events constitutes a major factor for the insurance industry. Flooding comes in very different ways, ranging from storm surges to flash floods and from sometimes country-wide river floods to glacial lake outburst and dam break floods. These different types are important when insurance concepts are regarded, for which adverse selection plays an important role. Various concepts for the difficult field of flood insurance have been investigated and discussed in different countries. In Germany, the insurance industry, in a combined effort, has launched a project to identify zones of similar risk resulting from river floods for the whole country. The identification of possible clients and the calculation of premiums are two uses of the developed model as well as the assessment of probable maximum losses. Only river floods are considered in the model, flash floods and storm surges are excluded; flood control measures are not taken into account either.

Abstract. River floods are among the most damaging natural hazards that frequently occur in Germany. Flooding causes high economic losses and impacts many residents. In 2016, several southern German municipalities were hit by flash floods after unexpectedly severe heavy rainfall, while in 2013 widespread river flooding had occurred. This study investigates and compares the psychological impacts of river floods and flash floods and potential consequences for precautionary behaviour. Data were collected using computer-aided telephone interviews that were conducted among flood-affected households around 9 months after each damaging event. This study applies Bayesian statistics and negative binomial regressions to test the suitability of psychological indicators to predict the precaution motivation of individuals. The results show that it is not the particular flood type but rather the severity and local impacts of the event that are crucial for the different, and potentially negative, impacts on mental health. According to the used data, however, predictions of the individual precaution motivation should not be based on the derived psychological indicators – i.e. coping appraisal, threat appraisal, burden and evasion – since their explanatory power was generally low and results are, for the most part, non-significant. Only burden reveals a significant positive relation to planned precaution regarding weak flash floods. In contrast to weak flash floods and river floods, the perceived threat of strong flash floods is significantly lower although feelings of burden and lower coping appraisals are more pronounced. Further research is needed to better include psychological assessment procedures and to focus on alternative data sources regarding floods and the connected precaution motivation of affected residents.

A study was carried out in 24 Upazillas of 12 districts of Bangladesh with a view to identifying risks, vulnerabilities and impacts of different types of natural disasters commonly occurring in Bangladesh with respect to agricultural production and sustainable agricultural development. Three districts were selected from each category of the disaster viz., drought, saline, river flood and flash flood prone. Two Upazillas were selected randomly from each district by considering the homogeneity (climate, agricultural practices, agricultural production, disaster risks, livelihood system, population, etc.) of the particular disaster affected areas. Of the four disasters, drought prone area covers the highest net cultivable area (NCA) measuring about 121 ha. Flash flood, salinity and river flood prone area covers approximately 115, 60 and 30 ha, respectively. The dominant cropping pattern in drought areas is Fallow-T.Aman-Wheat. In saline areas, it is Fallow-T. Aman- Pulse while in flood areas, it is Fallow-T.Aman- HYV Boro. Trend analysis shows that overall cropped area decreased by 1% in all disaster prone areas from 1984 - 2013. The highest decrease in cropped area was found for pulse in both drought (13%) and river flood (14%) areas. In saline and flash flood areas, it was for spice and potato, respectively. Among 72 farmers, 85% is vulnerable to drought, 90% to salinity, 69% to river flood and 95% to flash flood. Medium high land was found to be the most vulnerable for agricultural production in all disaster prone areas. Due to vulnerability to disasters, medium high land remains fallow in saline (83%), river flood (51%) and flash flood (31%) areas. In case of drought regions, medium low land (37%) remains fallow.Bangladesh J. Sci. Res. 28(2): 91-101, Dec-2015

Climate change is a complex and contentious public issue, but the risk-management options available to us are straightforward and have well-characterized strengths and weaknesses.

In this research, variability of spring (from 1 March to 30 May) and flash (from 1 June to 30 November) floods in rivers of different regions was analysed. The territory of Lithuania is divided into three regions according to hydrological regime of the rivers: Western, Central, and Southeastern. The maximum river discharge data of spring and flash floods [a total of 31 water gauging stations (WGS)] were analysed. Comparison of the data of four periods (1922–2013, 1941–2013, 1961–2013, and 1991–2013) with the data of the reference period (1961–1990) was performed. Analysis included the longest discharge data set of the Nemunas River at Smalininkai WGS (1812–2013) as well. Mixed patterns of flood changes in Lithuanian rivers were detected. The analysis of flood discharges of the Nemunas River indicated that both spring and flash floods in Lithuania were getting smaller.

Geospatial risk assessment of flash floods in Nuweiba area, Egypt

The objective of this research is (1) to raise awareness and prepare for flash flooding among people in the Mekong region which promotes inequality reduction from disasters by using Muang Nong Khai District, Nong Khai Province as a model area, and (2) To develop a policy proposal by designing a joint policy for flash flood preparedness in the Mekong region to promote inequality reduction from disasters. This research is action research in conjunction with policy design focusing on brainstorming. Group discussions with in-depth interviews. The research results were found that: [A] People have a basic understanding of (1) the nature of the disaster, and (2) the experience of the flash flood disaster encountered by the WiangKhuk Sub-district people is about remembering the severity Looking at the floods that have been associated, but in terms of preparation, community leaders see together that they want to develop into a system and plan for a joint rehearsal in the future. [B] Flash flood response weaknesses are (1) Weaknesses for early warning, evacuation, and flash flood drills, (2) Weaknesses of flash flood plans for areas that have not yet been formally planned, And (3) weaknesses in communication. [C] The interesting common policy design guidelines that should be developed are (1) Flash flood knowledge development, (2) direction and coordination for emergency operations, (3) agreements that Formal and informal for flash flood response, (4) resource mobilization focused on the certainty of emergency work. [D] The policy recommendations are: (1) Appropriate policy guidelines for flash flood preparedness in the Mekong River Basin should include precautions, evacuation, flash flood drills, and community-level plans to tackle flash floods. (2) The public sector, civil society, and communities should jointly develop policies to prepare for flash floods, that is, to develop flash flood knowledge to keep up with the changing circumstances of the local context. (3) The key policy to deal with flash floods to help reduce inequality is to develop community capacity or community potential. This is a collaboration of community organizations, the government sector, civil society in the area, which together with driving a community-level response plan. [E] The operation recommendations include (1) the community must be the host to invite government organizations such as the Provincial Disaster Prevention and Mitigation and the Mekong Community Organization Council to drive community-level planning. (2) Organizing a network meeting on flash flood response such as communities, Provincial Disaster Prevention and Mitigation Agency, and Mekong Community Organization Council should hold meetings at least twice a year to understand the situation and implement measures to deal with flash floods in a timely manner. (3) Flash flood drills should be conducted at least once a year in order to build mutual learning among communities and networks in flash flood preparedness, it is also an analysis of the weaknesses each year and can be used to develop the capacity and capacity of the community to handle the flash flood in the future.

Flash floods are the result of climatic and hydrological extremes and are manifested by dynamic and complex processes of movement of water and sediment. They represent the most frequent and widespread natural disaster at the global level, with unwanted ecological and economic consequences. The main causes of flash floods are related to numerous meteorological and physical–geographical factors. In the territory of Serbia, flash floods represent the most common natural risk with serious consequences for people’s lives and activities. Flash flood susceptibility mapping plays a crucial role in flood risk assessment and management. The current study prepared a flood inventory using light detection and ranging (LiDAR) derived digital elevation model, and it used integrated tree machine learning models (random forest [RF], classification and regression trees [CART], and support vector machine [SVM]) to predict flood susceptibility in the Ljuboviđa watershed, municipality Ljubovija, western Serbia. First, 12 independent variables were employed as conditioning factors: lithology, rainfall, land use/cover, elevation, slope angle, aspect, plan curvature, topographic wetness index, stream power index, distance from streams, distance from roads, and normalized vegetation index. Using the well-known scikit-learn (train_test_split) Python module, the flood inventory dataset was split into 70 and 30% for training and validation, respectively. The models’ performance was additionally assessed using the area under the curve (AUC). The results of the accuracy assessment demonstrated that the models for predicting flood susceptibility, RF, CART, and SVM, had AUC values of 0.854, 0.802, and 0.831, respectively; it means that RF had 85.4%, CART 80.2%, and SVM 83.1% chance of correctly ranking a random positive example higher than a random negative example, which represents the predictive power of the used models. When it came to predicting flood susceptibility, the RF model outperformed the other models used. This model estimates that 15.49, 16.04, 15.67, 23.10, and 29.70% of the watershed are very low, low, moderate, high, and extremely highly susceptible to floods, respectively. Thus, our study shows that data produced from LiDAR is potentially helpful in managing flood risk, particularly when assessing flood-related issues in the future. Flash-flood susceptibility maps have become a vital tool for risk prevention and management for government and local authorities (particularly national and local civil protection agencies, urban planning and land management departments, Ministries of Water and Environment), emergency response services (police, fire, and medical services), infrastructure and utilities sectors, insurance companies, and others.

Flash floods induced by heavy rainfall occur frequently in China, which cause severe damages or even casualties every year. Flash floods generally occur in small catchments, and therefore were poorly documented. A Database including 963 flash flood events in China is compiled and studied in this study. Analytical results (a) indicate flash flood condition in China; (b) shed light on the spatial-temporal distribution of flash flood under heavy rainfall and (c) detect the characteristics of the 2016 flash flood. In 2016, the deaths due to flash floods were severe and concentrated, accounting for about half of the elderly and children. Hebei and Fujian provinces were most affected by flash floods. The disasters mainly occurred in July and the major types were river floods. Despite the frequent torrential rains, inadequate monitoring and early warning systems made the flash flooding condition even worse in 2016.

O arquipélago de Cabo Verde encontra-se sujeito a uma grande diversidade de riscos naturais, os quais se devem, fundamentalmente, à posição geográfica do país, que lhe confere condições de acentuada aridez climática com forte irregularidade nas precipitações. Não só os riscos de seca são intrínsecos a esta posição climática mas também outros, como a desertificação, a erosão acelerada dos solos, as cheias e inundações, os movimentos em massa nas vertentes e as tempestades, com um impacte muito nefasto nas vidas das populações. A par desta elevada perigosidade intrínseca, verifica-se um acréscimo significativo das vulnerabilidades particularmente nas áreas urbanas em expansão, o que impulsiona um incremento do risco no território cabo-verdiano.A população das principais cidades, principalmente da capital (Praia), tem sofrido um crescimento muito acelerado nos últimos anos, albergando atualmente cerca de 27% da população nacional. Este crescimento tem sido fomentado tanto pelos fluxos migratórios internos (êxodo rural e migração das restantes ilhas) como externos, provenientes dos países vizinhos da África Ocidental. O ritmo acelerado do crescimento populacional na capital não tem sido acompanhado por políticas e/ou programas habitacionais capazes de dar uma resposta eficaz à procura de habitação. Consequência disso é a proliferação de bairros espontâneos nos subúrbios da capital, bairros em que as construções surgem da noite para o dia, sem obedecer a qualquer tipo de planeamento e sem dotação de infraestruturas básicas. Estes bairros ilegais de ocupação espontânea localizam-se, na sua maioria, em áreas de risco muito elevado (principalmente nos leitos de cheia das ribeiras e em vertentes de elevado declive), sendo ocupados fundamentalmente por uma população de muito baixo rendimento. Neste trabalho, pretendemos apresentar alguns casos concretos, como os dos bairros de Santa Rosa, Jamaica e Achada Grande Frente.