Quantification of flood hazard for the megacity of Lagos, Nigeria, by hydrodynamic simulation

2020 ◽  
Author(s):  
Tobias Pilz
Keyword(s):  
Flood Risk ◽  
Water Cycle ◽  
Flood Hazard ◽  
Storm Surges ◽  
Heavy Precipitation ◽  
Early Warning Systems ◽  
Data Availability ◽  
Hydrodynamic Simulation ◽  
Local Decision ◽  
The City

<p>Climate change leads to rising temperatures and therefore stimulates the water cycle. As a consequence, extreme events in rainfall and associated flooding are projected to increase in frequency and severity in many regions of the world. Especially in developing countries with high population growth and often unregulated settlement, flood risk may increase due to both increased flood hazard and enhanced exposure. One such example is the megacity of Lagos, Nigeria, belonging to the largest cities in Africa. Floods within the city are recurrent and caused by storm surges from the Atlantic, heavy precipitation, and river floods. Flood risk is an issue and even expected to increase due to enhanced extreme precipitation, sea level rise, enhances storm surges, as well as illegal settlement, poor management, insufficient or blocking of drainage channels, missing early warning systems, and insufficient data.</p><p>The aim of this study is to deliver a first quantification of flood hazard for the city of Lagos based on hydrodynamic simulation with the model TELEMAC-2D. A focus is put on the use of freely available data sources and the design of reproducible workflows in order to enable local decision-makers to individually apply and refine the established workflows. The biggest challenge is the generation of the model mesh as the basis for subsequent hydrodynamic modelling due to limited data availability and the size of the model domain (about 1000 km²).</p>

Rapid Global Exposure Assessment for Extreme River Flood Risk Under Climate Change

2016 ◽  
Vol 11 (6) ◽  
pp. 1128-1136 ◽  
Author(s):  
Youngjoo Kwak ◽  
◽  
Yoichi Iwami ◽  
Keyword(s):  
Climate Change ◽  
Risk Assessment ◽  
Flood Risk ◽  
Large Scale ◽  
Flood Hazard ◽  
Data Availability ◽  
Flood Risk Assessment ◽  
Daily Data ◽  
Extreme Flood ◽  
River Flood

Globally, large-scale floods are one of the most serious disasters, considering increased frequency and intensity of heavy rainfall. This is not only a domestic problem but also an international water issue related to transboundary rivers in terms of global river flood risk assessment. The purpose of this study is to propose a rapid flood hazard model as a methodological possibility to be used on a global scale, which uses flood inundation depth and works reasonably despite low data availability. The method is designed to effectively simplify complexities involving hydrological and topographical variables in a flood risk-prone area when applied in an integrated global flood risk assessment framework. The model was used to evaluate flood hazard and exposure through pixel-based comparison in the case of extreme flood events caused by an annual maximum daily river discharge of 1/50 probability of occurrence under the condition of climate change between two periods, Present (daily data from 1980 to 2004) and Future (daily data from 2075 to 2099). As preliminary results, the maximum potential extent of inundation area and the maximum number of affected people show an upward trend in Present and Future.

scholarly journals Topography- and nightlight-based national flood risk assessment in Canada

2016 ◽  
Author(s):  
Amin Elshorbagy ◽  
Anchit Lakhanpal ◽  
Bharath Raja ◽  
Serena Ceola ◽  
Alberto Montanari ◽  
...  
Keyword(s):  
Flood Risk ◽  
Flood Hazard ◽  
Hazard Mapping ◽  
Hazard Map ◽  
Flood Risk Assessment ◽  
Risk Map ◽  
National Scale ◽  
Digital Elevation ◽  
The City ◽  
Flood Risk Map

Abstract. In Canada, flood analysis and water resource management, in general, are tasks conducted at the provincial level; therefore, unified national-scale approaches to water-related problems are uncommon. In this study, a national-scale flood risk assessment approach is proposed and developed. The study focuses on using global and national datasets available at reasonably fine resolutions to create flood risk maps. First, a flood hazard map of Canada is developed using topography-based parameters derived from digital elevation models namely Elevation Above Nearest Drainage (EAND) and Distance From Nearest Drainage (DFND). This flood hazard mapping method is tested on a smaller area around the city of Calgary, Alberta, against a flood inundation map produced by the City using hydraulic modeling. Second, a flood exposure map of Canada is developed using a land-use map and the satellite-based nightlight luminosity data as two exposure parameters. Third, an economic flood risk map is produced, and subsequently overlaid with population density information to produce a socioeconomic flood risk map for Canada. All three maps of hazard, exposure, and risk are classified into five classes, ranging from very low to severe. A simple way to include flood protection measures in hazard estimation is also demonstrated using the example of the city of Winnipeg, Manitoba. This could be done for the entire country if information on flood protection across Canada were available. The evaluation of the flood hazard map shows that the topography-based method adopted in this study is both practical and reliable for large-scale analysis. Sensitivity analysis regarding the resolution of the digital elevation model is needed to identify the resolution that is fine enough for reliable hazard mapping, but coarse enough for computational tractability. The nightlight data are found to be useful for exposure and risk mapping in Canada; however, uncertainty analysis should be conducted to investigate the effect of the overglow phenomenon on flood risk mapping.

Modelling and analysis of the flood risk at Cavaillon City, Haiti

2018 ◽  
pp. 68-75
Author(s):  
Adermus Joseph ◽  
Nyankona Gonomy ◽  
Yves Zech ◽  
Sandra Soares-Frazão
Keyword(s):  
Flood Risk ◽  
Methodological Approach ◽  
Economic Consequences ◽  
Differential Gps ◽  
Analytic Hierarchy ◽  
Local Decision ◽  
Hierarchy Process ◽  
The City ◽  
The Town ◽  
Local Decision Makers

In Haiti, the vulnerability of urban populations in river flood corridors has disastrous socio-economic consequences on the living conditions of these communities. Mapping of areas prone to this type of risk is not sufficiently developed in Haiti, which complicates the implementation of strategies for the effective management of flood risk. This paper presents a methodological approach allowing to draw up a risk map of the city of Cavaillon, which is confronted to periodic flooding by the Cavaillon river flowing through the city. The reconstruction of the riverbed and floodplain geometry using a differential GPS and a novel drone-based photogrammetry technique made it possible to construct a hydraulic model of the river and to calculate the flow in the river for scenarios corresponding to different periods of return. The vulnerability of the different areas in the city was established using an Analytic Hierarchy Process. Various criteria of vulnerability were identified and their respective weight progressively determined from discussions between local decision-makers. Finally, considering the extent of the inundated area following recent Hurricane Matthew that particularly affected the zone, a vulnerability mapping was drawn for the town of Cavaillon.

scholarly journals Climate Justice Planning in Global South: Applying a Coupled Nature–Human Flood Risk Assessment Framework in a Case for Ho Chi Minh City, Vietnam

Water ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2021
Author(s):  
Chen-Fa Wu ◽  
Szu-Hung Chen ◽  
Ching-Wen Cheng ◽  
Luu Van Thong Trac
Keyword(s):  
Flood Risk ◽  
Flood Hazard ◽  
Climate Justice ◽  
Ho Chi Minh City ◽  
Flood Risk Assessment ◽  
Urban Floods ◽  
Flood Vulnerability ◽  
Urban Flood ◽  
Vulnerability Map ◽  
The City

Developing countries in the global south that contribute less to climate change have suffered greater from its impacts, such as extreme climatic events and disasters compared to developed countries, causing climate justice concerns globally. Ho Chi Minh City has experienced increased intensity and frequency of climate change-induced urban floods, causing socio-economic damage that disturbs their livelihoods while urban populations continue to grow. This study aims to establish a citywide flood risk map to inform risk management in the city and address climate justice locally. This study applied a flood risk assessment framework integrating a coupled nature–human approach and examined the spatial distribution of urban flood hazard and urban flood vulnerability. A flood hazard map was generated using selected morphological and hydro-meteorological indicators. A flood vulnerability map was generated based on a literature review and a social survey weighed by experts’ priorities using the Fuzzy Delphi Method and Analytic Network Process. Vulnerability indicators including demographic characteristics, infrastructure, and land use patterns were used to generate a flood vulnerability map. The results illustrate that almost the entire central and northeastern parts of the city are at high flood risk, whereas the western part is at low flood risk. The findings have implications in urban planning via identifying risk hot spots in order to prioritize resources for mitigating hazards and enhancing community resilience to urban floods.

scholarly journals Geospatial Approach for the Assessment and Analysis of Flood Risk in the region of Nanjangud town, Mysore District, Karnataka, India

2021 ◽  
Vol 1197 (1) ◽  
pp. 012032
Author(s):  
Arunkumar Yadav ◽  
H C Hema ◽  
Pramodkumar Kappadi ◽  
Chandrashekharappa Agasnalli
Keyword(s):  
Rural Areas ◽  
Flood Risk ◽  
Urban Areas ◽  
Water Cycle ◽  
Flood Hazard ◽  
Rainfall Variability ◽  
Meteorological Parameter ◽  
Satellite Image ◽  
Geographical Information ◽  
Topographic Map

Abstract Flooding in urban and rural areas is one of the utmost challenges to human safety. Destruction of the properties is the main issue in urban areas and damage to the agriculture practices in the rural area. Flood risk is rising significantly all over the globe. The regional water cycle and water resource availability are governed by the rainfall event, which is a fundamental meteorological parameter. The objective of the study is to examine the rainfall variability for 25 years from the period from 1995 to 2020 for monthly and annual rainfalls in the part of Nanjangud taluk, Mysore district, Karnataka. During the last three years that is 2017 to 2019 during the southwest monsoon, it is noted that the severity of flood increased in the surrounding of Nanjangud town, due to the heavy rainfall and excess amount of water released has augmented the inflow source of flooding. The assimilation of Remotely Sensing (RS) and Geographical Information System (GIS) is capable to generate a sequence of thematic maps that were helpful to create geospatial data for demarcating flood hazard areas. This study discusses the probable flood risk-prone regions of the Kabini river basin near Nanjangud town based on the multi-ring buffered layer analysis. The buffered layers created for the radius of 250m, 500m 750m, and 1000m were overlaid on the Sentinel-2 satellite image and topographic map to delineate the flood-affected region. To calculate the slope and drainage density, the SRTM DEM data was used. Structural and nonstructural practices are proposed in this study can be implemented to reduce the probability of the effect of floods.

scholarly journals How normative interpretations of climate risk assessment affect local decision-making: an exploratory study at the city scale in Cork, Ireland

2018 ◽  
Vol 376 (2121) ◽  
pp. 20170300 ◽  
Author(s):  
T. K. J. McDermott ◽  
S. Surminski
Keyword(s):  
Climate Change ◽  
Risk Assessment ◽  
Decision Making ◽  
Risk Management ◽  
Flood Risk ◽  
Flood Risk Management ◽  
Climate Risk ◽  
Local Decision ◽  
Local Decision Making ◽  
The City

Urban areas already suffer substantial losses in both economic and human terms from climate-related disasters. These losses are anticipated to grow substantially, in part as a result of the impacts of climate change. In this paper, we investigate the process of translating climate risk data into action for the city level. We apply a commonly used decision-framework as our backdrop and explore where in this process climate risk assessment and normative political judgements intersect. We use the case of flood risk management in Cork city in Ireland to investigate what is needed for translating risk assessment into action at the local city level. Evidence presented is based on focus group discussions at two stakeholder workshops, and a series of individual meetings and phone-discussions with stakeholders involved in local decision-making related to flood risk management and adaptation to climate change, in Ireland. Respondents were chosen on the basis of their expertise or involvement in the decision-making processes locally and nationally. Representatives of groups affected by flood risk and flood risk management and climate adaptation efforts were also included. The Cork example highlights that, despite ever more accurate data and an increasing range of theoretical approaches available to local decision-makers, it is the normative interpretation of this information that determines what action is taken. The use of risk assessments for decision-making is a process that requires normative decisions, such as setting ‘acceptable risk levels' and identifying ‘adequate’ protection levels, which will not succeed without broader buy-in and stakeholder participation. Identifying and embracing those normative views up-front could strengthen the urban adaptation process—this may, in fact, turn out to be the biggest advantage of climate risk assessment: it offers an opportunity to create a shared understanding of the problem and enables an informed evaluation and discussion of remedial action. This article is part of the theme issue ‘Advances in risk assessment for climate change adaptation policy’.

Flood hazard estimation and climate change: impacts and uncertainties for Irish catchments using CMIP6

2020 ◽  
Author(s):  
Hadush Meresa ◽  
Conor Murphy ◽  
Rowan Fealy
Keyword(s):  
Climate Change ◽  
Flood Risk ◽  
Climate Model ◽  
Extreme Event ◽  
Flood Hazard ◽  
Coupled Model ◽  
Climate Change Impacts ◽  
Heavy Precipitation ◽  
Atmospheric Temperature ◽  
Projected Changes

<p>In the coming decades, climate change will likely become a complex issue affecting hydrological regimes and flood hazard conditions. According to the IPCC reports, significant changes in atmospheric temperature, precipitation, humidity, and circulation are expected which may lead to extreme events including flood, droughts, heatwaves, heavy precipitation, and more intense cyclones. Although the effects of climate change on flood hazard indices is subject to large uncertainty, the evaluation of high-flows plays a crucial role in flood risk planning and extreme event management. With the advent of the Coupled Model Intercomparison Project Phase 6 (CMIP6), flood managers are interested to know how changes in catchment flood risk are expected to alter relative to previous assessments. Here we examine catchment based projected changes in flood quantiles and extreme high flow events for Irish catchments, selected to be representative of the range of hydrological conditions on the island. Conceptual hydrological models, together with different downscaling techniques are used to examine changes in flood risk projected from the CMIP6 archive for mid and end of century. Results will inform the range of plausible changes expected for policy relevant flood indices, the sensitivity of findings to use of different climate model ensembles and inform the tailoring of adaptation plans to account for the new generation of climate model outputs.</p>

scholarly journals Topography- and nightlight-based national flood risk assessment in Canada

2017 ◽  
Vol 21 (4) ◽  
pp. 2219-2232 ◽  
Author(s):  
Amin Elshorbagy ◽  
Raja Bharath ◽  
Anchit Lakhanpal ◽  
Serena Ceola ◽  
Alberto Montanari ◽  
...  
Keyword(s):  
Flood Risk ◽  
Flood Hazard ◽  
Hazard Mapping ◽  
Hazard Map ◽  
Flood Risk Assessment ◽  
Risk Map ◽  
National Scale ◽  
Digital Elevation ◽  
The City ◽  
Flood Risk Map

Abstract. In Canada, flood analysis and water resource management, in general, are tasks conducted at the provincial level; therefore, unified national-scale approaches to water-related problems are uncommon. In this study, a national-scale flood risk assessment approach is proposed and developed. The study focuses on using global and national datasets available with various resolutions to create flood risk maps. First, a flood hazard map of Canada is developed using topography-based parameters derived from digital elevation models, namely, elevation above nearest drainage (EAND) and distance from nearest drainage (DFND). This flood hazard mapping method is tested on a smaller area around the city of Calgary, Alberta, against a flood inundation map produced by the city using hydraulic modelling. Second, a flood exposure map of Canada is developed using a land-use map and the satellite-based nightlight luminosity data as two exposure parameters. Third, an economic flood risk map is produced, and subsequently overlaid with population density information to produce a socioeconomic flood risk map for Canada. All three maps of hazard, exposure, and risk are classified into five classes, ranging from very low to severe. A simple way to include flood protection measures in hazard estimation is also demonstrated using the example of the city of Winnipeg, Manitoba. This could be done for the entire country if information on flood protection across Canada were available. The evaluation of the flood hazard map shows that the topography-based method adopted in this study is both practical and reliable for large-scale analysis. Sensitivity analysis regarding the resolution of the digital elevation model is needed to identify the resolution that is fine enough for reliable hazard mapping, but coarse enough for computational tractability. The nightlight data are found to be useful for exposure and risk mapping in Canada; however, uncertainty analysis should be conducted to investigate the effect of the overglow phenomenon on flood risk mapping.

scholarly journals MAPPING INFECTED AREA AFTER A FLASH-FLOODING STORM USING MULTI CRITERIA ANALYSIS AND SPECTRAL INDICES

2017 ◽  
Vol XLII-4/W6 ◽  
pp. 3-7
Author(s):  
S. Al-Akad ◽  
Y. Akensous ◽  
M. Hakdaoui
Keyword(s):  
Flood Risk ◽  
Flood Hazard ◽  
Risk Mapping ◽  
Infected Area ◽  
Multi Criteria Analysis ◽  
Flood Risk Mapping ◽  
Gis Environment ◽  
Mapping Techniques ◽  
Processing Techniques ◽  
The City

This research article is summarize the applications of remote sensing and GIS to study the urban floods risk in Al Mukalla. Satellite acquisition of a flood event on October 2015 in Al Mukalla (Yemen) by using flood risk mapping techniques illustrate the potential risk present in this city. Satellite images (The Landsat and DEM images data were atmospherically corrected, radiometric corrected, and geometric and topographic distortions rectified.) are used for flood risk mapping to afford a hazard (vulnerability) map. This map is provided by applying image-processing techniques and using geographic information system (GIS) environment also the application of NDVI, NDWI index, and a method to estimate the flood-hazard areas. Four factors were considered in order to estimate the spatial distribution of the hazardous areas: flow accumulation, slope, land use, geology and elevation. The multi-criteria analysis, allowing to deal with vulnerability to flooding, as well as mapping areas at the risk of flooding of the city Al Mukalla. The main object of this research is to provide a simple and rapid method to reduce and manage the risks caused by flood in Yemen by take as example the city of Al Mukalla.

scholarly journals Effectiveness of Nature-Based Solutions on Pluvial Flood Hazard Mitigation: The Case Study of the City of Eindhoven (The Netherlands)

Resources ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 24
Author(s):  
Sandra Costa ◽  
Rik Peters ◽  
Ricardo Martins ◽  
Luuk Postmes ◽  
Jan Jacob Keizer ◽  
...  
Keyword(s):  
The Netherlands ◽  
Flood Risk ◽  
Hydrological Cycle ◽  
Risk Mitigation ◽  
Flood Hazard ◽  
Urban Flood ◽  
Storm Intensity ◽  
Impervious Area ◽  
Urban Catchments ◽  
The City

Urbanization leads to changes in the surface cover that alter the hydrological cycle of cities, particularly by increasing the impervious area and, thereby, reducing the interception, storage and infiltration capacity of rainwater. Nature-based solutions (NBS) can contribute to flood risk mitigation in urbanized areas by restoring hydrological functions. However, the effects of NBS on flood risk mitigation are complex and can differ substantially with the type of the NBS. Therefore, the effectiveness of NBS at the urban catchment scale is still subject to much debate, especially at the scale of urban catchments. In this study, the effects of different NBS on urban flood mitigation were evaluated for the city of Eindhoven in The Netherlands, as it has a history of urban flood events. To this end, various NBS scenarios were defined by municipal stakeholders and their impacts modelled with the numerical model Infoworks ICM. This was done for design storms with short, medium and long return periods (5, 10 and 100 years). Overall, the simulated NBS were effective in flood risk mitigation, reducing the flooded area as well as flood depth. The effectiveness of the individual NBS scenarios, however, depended strongly on the location and extension of the NBS, as well as on storm intensity. The effectiveness tended to increase with the increase in NBS surface area, while it tended to decrease with increasing storm intensity and, hence, return period. The NBS solution increasing street water storage was revealed to be more effective than those involving green car parks and green roofs. This study showed that numerical flooding models can be useful tools to assess the effects of NBS to reduce flood extent, water depth and/or velocity, providing insights that can support city planners to design and compare alternative strategies and plans for urban flood risk mitigation.

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