Flood Risk Assessment in the Lower Valley of Ouémé, Benin

In response to the increased frequency of flood events in recent years, it has become crucial to enhance preparedness and anticipation through precise flood risk assessments. To this end, this study aims to produce updated and precise flood risk maps for the Lower Valley of Ouémé River Basin, located in the South of Benin. The methodology used consisted of a combination of geographical information systems (GIS) and multi-criteria analysis, including Analytical Hierarchy Process (AHP) methods to define and quantify criteria for flood risk assessment. Seven hydro-geomorphological indicators (elevation, rainfall, slope, distance from rivers, flow accumulation, soil type, and drainage density), four socio-economic vulnerability indicators (female population density, literacy rate, poverty index, and road network density), and two exposure indicators (population density and land use) were integrated to generate risk maps. The results indicate that approximately 21.5% of the Lower Valley is under high and very high flood risk, mainly in the south between Dangbo, So-Ava, and Aguégués. The study findings align with the historical flood pattern in the region, which confirms the suitability of the used method. The novelty of this work lies in its comprehensive approach, the incorporation of AHP for weighting factors, and the use of remote sensing data, GIS technology, and spatial analysis techniques which adds precision to the mapping process. This work advances the scientific understanding of flood risk assessment and offers practical insights and solutions for flood-prone regions. The detailed flood risk indicator maps obtained stand out from previous studies and provide valuable information for effective flood risk management and mitigation efforts in the Lower Valley of Ouémé.

Urban flood risk assessment under rapid urbanization in Zhengzhou City,China

With accelerated urbanization and climate change,urban flooding is becoming more and more serious.Flood risk assessment is an important task for flood management,so it is crucial to map the spatial and temporal distribution of flood risk.This paper proposed an urban flood risk assessment method that takes into account the influences of hazard,vulnerability,and exposure,by constructing a multi-index urban flood risk assessment framework based on Geographic Information System(GIS).To determine the weight values of urban flood risk index factors,we used the analytic hierarchy process(AHP).Also,we plotted the temporal and spatial distribution maps of flood risk in Zhengzhou City in 2000,2005,2010,2015,and 2020.The analysis results showed that,the proportion of very high and high flood risk zone in Zhengzhou City was 1.362%,5.270%,4.936%,12.151%,and 24.236%in 2000,2005,2010,2015,and 2020,respectively.It is observed that the area of high flood risk zones in Zhengzhou City showed a trend of increasing and expanding,of which Dengfeng City,Xinzheng City,Xinmi City,and Zhongmu County had the fastest growth rate and the most obvious increase.The flood risk of Zhengzhou City has been expanding with the development of urbanization.The method is adapted to Zhengzhou City and will have good adaptability in other research areas,and its risk assessment results can provide a scientific reference for urban flood management personnel.In the future,the accuracy of flood risk assessment can be further improved by promoting the accuracy of basic data and reasonably determining the weight values of index factors.The risk zoning map can better reflect the risk distribution and provide a scientific basis for early warning of flood prevention and drainage.

Flood risk assessment of check dams in the Wangmaogou watershed on the Loess Plateau of China

Check dams have been widely used in China’s Loess Plateau region due to their effectiveness in erosion and flood control.However,the safety and stability of the check dam decrease with the operation process,which increases the probability of dam failure during flood events and threatens local residents’ life and property.Thus,this study simulated flood process of the check dam failure in the Wangmaogou watershed in Yulin City,Shaanxi Province,China,calculated different types of inundation losses based on the flood inundation area within the watershed,and determined the number of key flood protection check dams by classifying the flood risk levels of the check dams.The results showed that 5 dams in the watershed were subject to overtopping during different rainfall return periods,which was related to their flood discharge capacity.Dam failure flood process showed a rapid growth trend followed by slow decrease,and the time of flood peak advanced with increase in the return period.After harmonization of evaluation scales,the magnitude of flood inundation losses can be ranked as:economic losses(212.409 million yuan) > life losses(10.368 million yuan) > ecological losses(6.433 million yuan).The risk value for both individual dams and the whole dam system decreases as the return period increases.The number of key flood protection check dams in the Wangmaogou watershed was 2,3,3,3,4,and 5 for floods with return periods of 10,20,30,50,100,and 200 years,respectively.The results provided a theoretical basis for the safe operation and risk evaluation of check dams in the Loess Plateau Hills watershed.

Farmers＇ vulnerability to flood risk： A case study in the Poyang Lake Region

This paper quantitatively explores farmers＇ vulnerability to flood in the Poyang Lake Region （PLR） with the supports of GIS spatial functions. The analysis consists of three major steps, which is based on the spatial unit of township. Firstly, the spatial extent and characteristics of flood risk areas were determined using a digital elevation model （DEM） derived from the 1：50,000 topographic map. Secondly, for each of the township, six indices indicating the economic activities of local farmers were calculated. These indices are： rural population proportion, cultivated land proportion, GDP per unit area, employment proportion of primary industry, net rural income per capita and agricultural income proportion. These six indices were then normalized and used for later vulnerability assessment. Thirdly, the normalized indices （as GIS data layers） were overlaid with the flood risk areas to produce the risk coefficient for each township and to calculate the overall vulnerability for each township. The analysis results show that in the PLR there are high flood risk areas where the farmers＇ livings are seriously influenced or threatened. About 55.56% of the total 180 townships in the flood risk areas have a high degree of flood vulnerability. The townships under flood risk are mainly distributed in the areas around the Poyang Lake and the areas along the ＂five rivers＂.

From China’s Heavy Precipitation in 2020 to a “Glocal” Hydrometeorological Solution for Flood Risk Prediction

The prolonged mei-yu/baiu system with anomalous precipitation in the year 2020 has swollen many rivers and lakes,caused flash flooding,urban flooding and landslides,and consistently wreaked havoc across large swathes of China,particularly in the Yangtze River basin.Significant precipitation and flooding anomalies have already been seen in magnitude and extension so far this year,which have been exerting much higher pressure on emergency responses in flood control and mitigation than in other years,even though a rainy season with multiple ongoing serious flood events in different provinces is not that uncommon in China.Instead of delving into the causes of the uniqueness of this year’s extreme precipitation-flooding situation,which certainly warrants in-depth exploration,in this article we provide a short view toward a more general hydrometeorological solution to this annual nationwide problem.A“glocal”(global to local)hydrometeorological solution for floods(GHS-F)is considered to be critical for better preparedness,mitigation,and management of different types of significant precipitation-caused flooding,which happen extensively almost every year in many countries such as China,India and the United States.Such a GHS-F model is necessary from both scientific and operational perspectives,with the strength in providing spatially consistent flood definitions and spatially distributed flood risk classification considering the heterogeneity in vulnerability and resilience across the entire domain.Priorities in the development of such a GHS-F are suggested,emphasizing the user’s requirements and needs according to practical experiences with various flood response agencies.

Modeling and Mapping Flood Hazard with a Flood Risk Assessment Tool: A Case Study of Austin, Texas

As a hazard, flood is an extremely important indicator of how a city is resilient to waterborne diseases and epidemics. Over many decades, flood as a hazard has been a major factor in inducing displacement of marginalized section of the people. Austin city within Central Texas has been identified as one of the major hotspots for flooding in recent decades. Thus, the objectives of the paper are two folded: 1) Empirically, we analyzed and mapped out the susceptibility levels from the factors of physical environments to assess the risk of urban flooding (rainfall data, surface water bodies and topography);in Austin, Texas and 2) Methodologically, we created a re-useable ArcGIS scripting tool that can be used by researchers to automate the process of flood risk modelling with certain criteria. The paper showcases a novel time sensitive building of a tool which will enable better visibility of flood within the city of Austin.

Community Based Flood Risk Management: Local Knowledge and Actor’s Involvement Approach from Lower Karnali River Basin of Nepal

Connecting to the disaster risk reduction (DRR) studies, community-based initiatives are found to be more effective in both developed and developing countries, with a specific focus on the empowerment of local communities to build resilience. Building on social capital theory, the paper investigates on local knowledge (LK) practices experienced by the actors in an emerging economy using the community-based flood risk management (CB-FRM) approach. The qualitative research method was used by collecting data from focused group discussions, and interviews with the key informants including actors from local governments and non-government organizations. Additionally, informal discussions, field visits, and desk studies were undertaken to support the findings. The findings reveal that the local communities carry out various local knowledge experiences to respond during disaster management phases. They own a creative set of approaches based on the LK and that empowers them to live in the flood-prone areas, accepting the paradigm shift from fighting with floods to living with that. The local actor’s involvement is recognized as an essential component for CB-FRM activities. Yet, their program’s implementation is more oriented towards humanitarian assistance in emergency responses. Even, they often overlook the role of LK. Additionally, the results show a high level of presence of local communities during the preparedness and recovery phases, while NGOs and local governments have a medium role in preparedness and low in recovery phase. The lack of local ownership has also emerged as the major challenge. The research provides valuable insights for integrated CB-FRM policies by adopting to LK practices.

Preface for special section on coastal flood risk

Global concerns about changes in the world＇s climate have been well documented. The consequent impacts on coastal cities, agriculture, and coastal mariculture are difficult to quantify, but it is clear that there is a need for both better estimates of future climate and improved forecasting of storms and their impacts.

Projected Flood Risks in China Based on CMIP5

Based on the simulations of 22 CMIP5 models in combination with socio-economic data and terrain elevation data,the spatial distribution of risk levels of flood disaster and the vulnerability to flood hazards in China are projected under the RCP8.5 for the near term period(2016–2035), medium term period(2046–2065) and long term period(2080–2099),respectively. The results show that regions with high flood hazard levels are mainly located in Southeast China, while the vulnerability to flood hazards is high in eastern China. Under the RCP8.5 greenhouse gas emissions scenario, future high flood risk levels will mainly appear in the eastern part of Sichuan, in major part of East China, and in the provinces of Hebei, Beijing, and Tianjin. The major cities in Northeast China, some areas in Shaanxi and Shanxi, as well as the coastal areas in southeastern China will also encounter high flood risks. Compared with the baseline period, the regional flood risk levels will increase towards the end of the 21 st century, although the occurrences of floods change little. Due to the coarse resolution of the climate models and the indistinct methodology for determining the weight coefficients,large uncertainty still exists in the projection of flood risks.

Flood risk control of dams and dykes in middle reach of Huaihe River

Three stochastic mathematical models for calculation of the reservoir flood regulation process, river course flood release, and flood risk rate under flood control were established based on the theory of stochastic differential equations and features of flood control systems in the middle reach of the Huaihe River from Xixian to the Bengbu floodgate, comprehensively considering uncertain factors of hydrology, hydraulics, and engineering control. They were used to calculate the flood risk rate with flood regulation of five key reservoirs, including the Meishan, Xianghongdian, Nianyushan, Mozitan, and Foziling reservoirs in the middle reach of the Huaihe River under different flood frequencies, the flood risk rate with river course flood release under design and check floods for the trunk of the Huaihe River in conjunction with relevant flood storage areas, and the flood risk rate with operation of the Linhuaigang Project under design and check floods. The calculated results show that （l） the five reservoirs can withstand design floods, but the Xianghongdian and Foziling reservoirs will suffer overtopping accidents under check floods; （2） considering the service of flood storage areas under the design flood conditions of the Huaihe River, the mean flood risk rate with flood regulation of dykes and dams from Xixian to the Bengbu floodgate is about 0.2, and the trunk of the Huaihe River can generally withstand design floods; and （3） under a check flood with the flood return period of 1 000 years, the risk rate of overtopping accidents of the Linhuaigang Project is not larger than 0.15, indicating that it has a high flood regulation capacity. Through regulation and application of the flood control system of the Linhuigang Project, the Huaihe River Basin can withstand large floods, and the safety of the protected area can be ensured.

Flood Risk Analysis and Flood Potential Losses Assessment

The heavy floods in the Taihu Basin showed increasing trend in recent years. In this work, a typical area in the northern Taihu Basin was selected for flood risk analysis and potential flood losses assessment. Human activities have strong impact on the study area’s flood situation (as affected by the polders built, deforestation, population increase, urbanization, etc.), and have made water level higher, flood duration shorter, and flood peaks sharper. Five years of different flood return periods [(1970), 5 (1962), 10 (1987), 20 (1954), 50 (1991)] were used to calculate the potential flood risk area and its losses. The potential flood risk map, economic losses, and flood-impacted population were also calculated. The study’s main conclusions are: 1) Human activities have strongly changed the natural flood situation in the study area, increasing runoff and flooding; 2) The flood risk area is closely related with the precipitation center; 3) Polder construction has successfully protected land from flood, shortened the flood duration, and elevated water level in rivers outside the polders; 4) Economic and social development have caused flood losses to increase in recent years.

Hydrological Modeling Using GIS for Mapping Flood Zones and Degree Flood Risk in Zeuss-Koutine Basin (South of Tunisia)

This study lies within the scope of a strategy of prevention from inundations by the contribution of new technology in stage of the hydrological and geomorphological modeling for protection against the floods in a medium of weak at the average risk in South-eastern Tunisia, starting from the catchment area of Zeuss-Koutine. Considering the lack of studies we were brought to extract the area catchment in question, and to deduce its geomorphological and hydrometric characteristics, starting from the digital terrain model. We could obtain, by overlaying maps of slopes, indices and flows, the hydrological zonation of the catchment area of Zeuss-Koutine. The hydrological study of the basin’s slopes of Zeuss-Koutine is not lying out that very little physical information rests primarily on cartographic processes. The use of the latter can be regarded as an allowing indicator, by the crossing of the explanatory factors of the surface flow (slopes and direction of flow), to define a set of homogeneous hydrological zones in the level of the hydrological characteristics (average slopes, altitudes, roughness, etc). It is mainly a question of better taking account of the physical properties of the basins slopes.

Government and Community Involvement in Environmental Protection and Flood Risk Management: Lessons from Keko Machungwa, Dar es Salaam, Tanzania

Since the 1960s, most cities in developing countries have faced a high rate of urbanization, which in turn has caused more harm to low-income earners, in urban areas. A majority of low-income earners most often face difficulties in accessing land in planned areas, as a result they are forced to build houses in unplanned settlements that are vulnerable to natural hazards. The situation is worse to the extent that people encroach the most vulnerable areas (hazard lands). As concentration of people increases, these unplanned areas become more unsafe to live in. This is partly due to the risks associated with natural hazards particularly flooding. Further, vulnerability of unplanned settlements in developing countries is aggravated by hosts of problems caused by many factors, including inadequate Government involvement in: environmental protection especially managing hazard lands and helping the community to minimize risks associated with hazards. This paper addresses this issue. It argues that community and Government initiatives are vital to any strategy for flood risk reduction and environmental protection in general. The study employed both the primary and the secondary data sources. Data collection tools and techniques involved in this study included: Checklist to various leaders, interview using questionnaires, focus group discussion, analysis of aerial photographs and non participant observation. A total of 70 households from within Keko Machungwa were interviewed. The study revealed that flooding is largely contributed by construction done by a large scale developer on a water course;and when affected community initiated a strategy to solve the problem they partially succeed due to inadequate support from the Government and other stakeholders. These findings could be useful to strengthen policy and legislation in environmental protection, management and flood control as well as in intervening land use conflicts between local community and developers.

Flood Risk Code Mapping Using Multi Criteria Assessment

Flash flood is a dangers natural disaster causes lots of structure damage, traffic collapse, economic defects and human life loss. An efficient way to reduce its effects is preparing flash flood mapping to identify zones at risk due to flood. Flash flood mapping is a powerful tool for urban planners, traffic and infrastructure engineers, emergency and rescue services. This article proposes an approach utilizes remote sensing (RS) and geographic information system (GIS) to prepare flood risk code (FRC) map for Jeddah city, Saudi Arabia. The proposed approach applied the Curve Number (CN) method of flood modelling and uses runoff depth, land use, soil hydrological parameters, surface slope, and longest flow path to generate FRC. SPOT satellite image of the study area was classified to generate land use map, Digital Elevation Model (DEM) was used for generating slope map and for hydrology analysis using HEC-GeoHMS tool, and soil properties were generated from scanned soil maps. All data were integrated in ArcGIS 10.4.1 to prepare the final flood risk map. The results show that a precipitation of 106.3 mm will generate 136.5 million m3 of flood water. The results according to the developed flood risk code show that due to this amount of precipitation, about 1 million people live in Jeddah are prone to extreme flood risk and about 2 million of population are at major risk, the rest of population (about 0.5 million) are vulnerable to moderate to minor fold risk. The approach was verified using ground truth data and proofed precision.

Repercussions of Improved Municipal Solid Waste Management on Flood Risk Reduction: The Case of Dar es Salaam, Tanzania

Indisputably, flooding is one of the predicaments that have plagued many countries throughout the world. Consequently, Improvement of Municipal Solid Waste Management-(MSWM) has recently become one of the ways that is believed to help in reducing the impact of flooding. Following the fact that Dar es Salaam, the commercial capital, has nearly 5 million inhabitants and several of the wards are in flood-prone areas, the City authorities introduced new models of MSWM by incorporating public-private partnership as a deliberate action envisioned to improve MSWM. Nevertheless, the extent to which the strategy is effective in minimizing flood risks had not been adequately researched, which prompted a need to conduct a study. Specifically, the study sought to: assess the current practice of SWM in the settlement;examine the extent to which flood risk had been reduced given the application of the new models of SWM. This is primarily a case study which used Keko Machungwa in Dar es Salaam as the study area. Different forms of data collections tools were used for instance interviews of households and officials, photographs, spatial data etc. The findings indicated that Jukwaa la Wanawake in Keko Machungwa, a newly emerged community-driven organization was doing a fairly good job in handling SWM. This social entity was capable of collecting 40 tons of solid wastes per week and arranged for transportation. Overall, there was a marked decrease in haphazard dumping within the settlement. Despite the improvement, however, flooding was still persistent and was an alarming challenge. To that effect, this study recommends that improving solid waste collection could help overcome the problem of flooding particularly if integrated with other initiatives which include 1) Investment in robust flood control structures;2) Adherence to Urban planning and disaster management policies which prohibit development in hazardous areas, an instance of which being demolishing the existing building structures located in the water way in Keko Machungwa and;3) Initiate large scale flood risk reduction settlement schemes.

Global Aspects of Flood Risk Management

Various flood disasters in the last decade have confirmed that the risk from flooding has been increasing significantly worldwide. The driving factors for the risk are the unabated increase in global population, the concentration of people in high-risk areas such as coasts and flood plains, the rise in vulnerability of assets, infrastructure and social systems, and the consequences of climate change. Risk reduction is based on comprehensive risk management from identification of the hazard and assessing the risk to building defenses. To achieve this, general awareness at all levels in a society is key. It is not sufficient merely to be aware of the situation-findings must be acted upon with no significant delay. Flood-related computations have progressed considerably in recent years, but model results can only be as good as their input data. Modeling floods and flood losses is very complex, as model parameters are subject to change during an event and conditions sometimes greatly depend on small-scale factors.

Assessment of Flood Risk in Cotonou Areas Surrounding NokouéLake Due to the Effect of Climate Change

Cotonou, like West African cities, experiences recurrent flooding. This work aimed to study the effect of climate change on the risk of flooding in Cotonou’s zoos on the periphery Nokoué Lake. We analysed climate data (rainfall and temperature) in Cotonou over the period 1953 to 2013, the flow of the Ouémé River at Bonou, and the variation in the height (elevation) of Lake Nokoué. The results of the analysis of temperatures over the period 1953-2013 show an upward break from 1987 onwards (+0.7°C between 1987 and 2013), while for rainfall, no break was observed over the same period. None of the 13 rainfall indices calculated is statistically significant, but they show a relatively stable or declining trend except for the average daily rainfall, the maximum number of consecutive dry days and the 95th percentile, which all show a slightly upward trend. We have shown that the rainfall recorded in Cotonou does not reveal any abnormal or exceptional character over the last ten years, on the one hand, and the flooding of Ouémé River influences that of Nokoué Lake, on the other hand. This study shows that the floods observed in this area are more related to the effect of climate change.