Query: Flood risk

title: Urban flood risk mapping using the GARP and QUEST models: A comparative study of machine learning techniques
abstract: Flood risk mapping and modeling is important to prevent urban flood damage. In this study, a flood risk map was produced with limited hydrological and hydraulic data using two state of the art machine learning models: Genetic Algorithm Rule Set Production (GARP) and Quick Unbiased Efficient Statistical Tree (QUEST) The flood conditioning factors used in modeling were: precipitation, slope, curve number, distance to river, distance to channel, depth to groundwater, land use, and elevation. Based on available reports and field surveys for Sari city (Iran) 113 points were identified as flooded areas (with each flooded zone assigned a value of 1) Different conditioning factors, including urban density, quality of buildings, age of buildings, population density, and socio economic conditions, were taken into account to analyze flood vulnerability. In addition, the weight of these conditioning factors was determined based on expert knowledge and Fuzzy Analytical Network Process (FANP) An urban flood risk map was then produced using flood hazard and flood vulnerability maps. The area under the receiver operator characteristic curve (AUC ROC) and Kappa statistic were applied to evaluate model performance. The results demonstrated that the GARP model (AUC ROC 93.5% Kappa 0.86) had higher performance accuracy than the QUEST model (AUC ROC 89.2% Kappa 0.79) The results also indicated that distance to channel, land use, and elevation played major roles in flood hazard determination, whereas population density, quality of buildings, and urban density were the most important factors in terms of vulnerability. These findings demonstrate that machine learning models can help in flood risk mapping, especially in areas where detailed hydraulic and hydrological data are not available.

title: Perspectives for flood risk assessment and management for mega city metro system
abstract: This paper presents an overview on the risk assessment approaches for inundation of metro systems based on regional flood risk assessment methods. Detailed summarization is conducted based on four types of regional flood risk assessment methods, including (i) statistical methods, (ii) multi criteria analysis, (iii) analysis using geographical information system (GIS) and/or remote sensing (RS) and (iv) scenario based analysis. After reviewing of the existing methods in literatures, a perspective approach of evaluating inundation risk for metro systems is proposed. The proposed approach has the following two characteristics: (i) from regional to local, and (ii) from qualification to quantification. The Guangzhou Metro System is used to demonstrate the application of the perspective methods for flood risk assessment of metro system. The risk prevention procedure uses an iterative cycle that includes risk assessment, precaution, prediction, and technical countermeasures. The integration of GIS, global position system (GPS) and build information modelling (BIM) for development of early warning and risk management systems is recommended to manage the risks of inundation of metro system.

title: Assessing the Co Benefits of green blue grey infrastructure for sustainable urban flood risk management.
abstract: Green blue infrastructures in urban spaces offer several co benefits besides flood risk reduction, such as water savings, energy savings due to less cooling usage, air quality improvement and carbon sequestration. Traditionally, these co benefits were not included in decision making processes for flood risk management. In this work we present a method to include the monetary analysis of these co benefits into a cost benefits analysis of flood risk mitigation measures. This approach was applied to a case study, comparing costs and benefits with and without co benefits. Different intervention strategies were considered, using green, blue and grey measures and combinations of them. The results obtained illustrate the importance of assessing co benefits when identifying best adaptation strategies to improve urban flood risk management. Otherwise green infrastructure is likely to appear less efficient than more conventional grey infrastructure. Moreover, a mix of green, blue and grey infrastructures is likely to result in the best adaptation strategy as these three alternatives tend to complement each other. Grey infrastructure has good performance at reducing the risk of flooding, whilst green infrastructure brings in multiple additional benefits that grey infrastructure cannot offer.

title: Flood risk assessment of metro systems in a subsiding environment using the interval FAHP FCA approach
abstract: Metro systems are vulnerable to flooding during rainstorms and this situation worsens when a subsiding environment prevails. This study adopts the interval fuzzy analytic hierarchy process (FAHP) incorporated with fuzzy clustering analysis (FCA) to assess the flood risk of metro systems in subsiding environments, considering both the regional subsidence of the ground and the longitudinal settlement along metro lines as assessment factors. Shanghai metro system is analysed as an example by using the proposed method (the FAHP FCA approach) together with the geographical information system (GIS) The assessment results show that more than 30% of metro lines in Shanghai are at a high risk of flooding, and the high risk regions of metro lines are located in urban centres. The ratio of high risk regions identified by the FAHP FCA approach exceeds that obtained using the existing FAHP approach, which indicates that the FCA FAHP approach can capture high risk metro systems in Shanghai. Moreover, the comparison also shows that subsiding environments exacerbate the flood risk of metro systems. It is proposed that, to mitigate the risk of flooding, subsidence environments should be considered in more detail.

title: Flood risk and its reduction in China
abstract: Despite massive flood protection efforts in China, undertaken since the ancient times, disastrous floods continue to plague the country. In this paper, we discuss changes in flood hazard and flood risk in China. First, we review published results (including our own works) on change detection in observed records of intense precipitation, high river flow and flood damage in China. We provide information on essential features of extreme floods in last decades floods on large rivers, urban floods, and flash floods. Next, we review available projections for the future (including our own results) related to intense precipitation, high river flow and flood damage in China. We try to interpret the difference in flood hazard projections obtained in various publications. Since the spread of river flood hazard projections is large, projections have to be interpreted with caution, because of the impact on decisions related to climate change adaptation, flood risk reduction, and water resources management. We review flood risk reduction strategies in China, focusing on the present situation and division of responsibilities. China has embarked upon an ambitious and vigorous task to improve flood preparedness, by both structural "hard" defences, such as: dikes, dams and flood control reservoirs, and diversions, as well as non structural "soft" measures: spatial planning and zoning; watershed management (source control) flood forecasting and warning systems; and awareness raising. The strategy of flood mitigation includes flood retention and urban water management to alleviate the burden of flash and urban flooding.

title: Validation of flood risk models: Current practice and possible improvements
abstract: Although often neglected, model validation is a key topic in flood risk analysis, as flood risk estimates are used to underpin large investments and important decisions. In this paper, we discuss the state of the art of flood risk model validation, using as input the discussion among more than 50 experts at two scientific workshop events. The events aimed at identifying policy and research recommendations towards promoting more common practice of validation, and an improvement of flood risk model reliability. We pay specific attention to different components of the risk modelling chain (i.e. flood hazard, defence failure, and flood damage analysis) as well as to their role in risk estimates, to highlight specificities and commonalities with respect to implemented techniques and research needs. The main conclusions from this analysis can be summarised as the need of higher quality data to perform validation and of benchmark solutions to be followed in different contexts, along with a greater involvement of end users in the application on flood risk model validation.

title: Flood risk assessment in metro systems of mega cities using a GIS based modeling approach.
abstract: Metro system is a vital component of mass transportation infrastructure, providing crucial social and economic service in urban area. Flood events may cause functional disruptions to metro systems; therefore, a better understanding of their vulnerability would enhance their resilience. A comparative study of flood risk in metro systems is presented using the analytic hierarchy process (AHP) and the interval AHP (I AHP) methods. The flood risk in the Guangzhou metro system is evaluated according to recorded data. Evaluated results are validated using the flood event occurred in Guangzhou on May 10, 2016 (hereinafter called "May 10th event" which inundated several metro stations. The flood risk is assessed within a range of 500 m around the metro line. The results show that >50% of metro lines are highly exposed to flood risk, indicating that the Guangzhou metro system is vulnerable to flood events. Comparisons between results from AHP and I AHP show that the latter yields a wider range of high flooding risk than the former.

title: Global drivers of future river flood risk
abstract: Global river flood risk is expected to increase substantially over coming decades due to both climate change and socioeconomic development. Model based projections suggest that southeast Asia and Africa are at particular risk, highlighting the need to invest in adaptation measures.

title: Projected increases and shifts in rain on snow flood risk over western North America
abstract: Destructive and costly flooding can occur when warm storm systems deposit substantial rain on extensive snowcover1 6, as observed in February 2017 with the Oroville Dam crisis in California7. However, decision makers lack guidance on how such rain on snow (ROS) flood risk may respond to climate change. Here, daily ROS events with flood generating potential8 are simulated over western North America for a historical (2000 2013) and future (forced under Representative Concentration Pathway 8.59) period with the Weather Research and Forecasting model; 4 km resolution allows the basin scale ROS flood risk to be assessed. In the warmer climate, we show that ROS becomes less frequent at lower elevations due to snowpack declines, particularly in warmer areas (for example, the Pacific maritime region) By contrast, at higher elevations where seasonal snowcover persists, ROS becomes more frequent due to a shift from snowfall to rain. Accordingly, the water available for runoff10 increases for 55% of western North American river basins, with corresponding increases in flood risk of 20 200% the greatest changes of which are projected for the Sierra Nevada, the Colorado River headwaters and the Canadian Rocky Mountains. Thus, flood control and water resource planning must consider ROS to fully quantify changes in flood risk with anthropogenic warming.Rain on snow events pose a significant flood risk. High resolution model simulations reveal that such events will increase in frequency in the higher elevations of western North America, resulting in a 20 200% enhancement of flood risk.

title: Climatic and socioeconomic controls of future coastal flood risk in Europe
abstract: Rising extreme sea levels (ESLs) and continued socioeconomic development in coastal zones will lead to increasing future flood risk along the European coastline. We present a comprehensive analysis of future coastal flood risk (CFR) for Europe that separates the impacts of global warming and socioeconomic development. In the absence of further investments in coastal adaptation, the present expected annual damage (EAD) of EUR1.25 billion is projected to increase by two to three orders of magnitude by the end of the century, ranging between 93 and EUR961 billion. The current expected annual number of people exposed (EAPE) to coastal flooding of 102,000 is projected to reach 1.52 3.65 million by the end of the century. Climate change is the main driver of the future rise in coastal flood losses, with the importance of coastward migration, urbanization and rising asset values rapidly declining with time. To keep future coastal flood losses constant relative to the size of the economy, flood defence structures need to be installed or reinforced to withstand increases in ESLs that range from 0.5 to 2.5 m.Climate change is the main driver for future coastal flood risk in Europe. However, in the absence of increased flood protection, damages may rise by two to three orders of magnitude by the end of the century.