Flood Evacuation Research Articles

Characterizing recurrent flood hazards in the Himalayan foothill region through data-driven modelling

Floods are frequently occurring hazards in the Himalayan foothills that primarily affect the physical environment and socio-economic profile of the local people. To this end, we used some data-driven models and techniques such as multi-criteria decision analysis, bivariate statistical method, machine learning, and sub-watershed prioritization by morphometric analysis (SWPMA) in the Kaljani River basin for the flood susceptibility mapping (FSM). The study used 200 non-flood points and 200 historical flood points for developing the testing (30%) and training (70%) datasets. Multicollinearity diagnostic test (VIF) and information gain ratio (IGR) were used to measure the consistency of the selected twelve influencing factors. Rainfall, drainage density, clay content, distance from the river and elevation were the most important drivers of the selected influencing parameters. We found that the high and very high FSM areas of the basin were around 32.24% for random forest (RF), 47.46% for frequency ratio (FR), 46.41% for analytical hierarchic process (AHP), and 40.5% for SWPMA. Most of these areas lie in Alipurduar town surrounding areas and the lower part of the basin. The ROC (receiver operating characteristic), MAE (mean absolute error), RMSE (root mean square error), Kappa index and Pearson’s correlation coefficients were employed for the performance efficiency of four data-driven models. Achieved ROC values of the RF model, FR model, AHP model and SWPMA model were at 92.4%, 86.6%, 83.1% and 79.4% respectively. Compared to all four methods the machine learning approach, the RF method performed most accurately. This study can help researchers for choosing the right approaches to the FSM. The present FSM may be instrumental before the various stakeholders while designing the flood evacuation plan, preparation of future flood shelters, and planning for future development for the local community.

Investigating pedestrian behavioral patterns under different floodwater conditions: A video analysis on real flood evacuations

Understanding how people behave during emergencies is fundamental to improve their safety. In the case of flood evacuation, people have to deal with built environments extremely modified by the floodwaters and that hence influences human-environment interactions both from a qualitative and quantitative standpoint. In this sense, the observation of real events is fundamental to define behavioral patterns and their relation to floodwater conditions. To this end, in this work, we analyzed 139 videotapes of recent real-world flood evacuations in outdoor Built Environments involving about 1000 people all over the World (the largest set analyzed so far). The frequencies of behavioral patterns are associated with water depth (measured with respect to ankles, knees, and waist), flow (i.e., still or flowing), and evacuation phase in which they are observed (that is before, during, and after the evacuation). Specific factors like voluntariness, human response, and presence of reference elements in the flooded built environment are also considered. Frequent by-literature behaviors have been considered, and new-noticed ones have been assessed. Results unveil that the most frequent floodwater conditions and thresholds to trigger each behavior concern waters between the ankles and the waist, thus excluding slight and extreme interactions with floodwater. The retrieved behavioral patterns could be employed to develop and validate behavioral models for flood evacuation simulators, and to create critical scenarios for people’s training. Furthermore, they trace quick insights to help safety planners in the design of risk-reduction measures also considering local and/or temporary risks due to the floodwater conditions.

Protection or Peril of Following the Crowd in a Pandemic-Concurrent Flood Evacuation

The decisions of whether and how to evacuate during a climate disaster are influenced by a wide range of factors, including emergency messaging, social influences, and sociodemographics. Further complexity is introduced when multiple hazards occur simultaneously, such as a flood evacuation taking place amid a viral pandemic that requires physical distancing. Such multihazard events can necessitate a nuanced navigation of competing decision-making strategies wherein a desire to follow peers is weighed against contagion risks. To better understand these trade-offs, we distributed an online survey during a COVID-19 pandemic surge in July 2020 to 600 individuals in three midwestern and three southern states in the United States with high risk of flooding. In this paper, we estimate a random parameter discrete choice model in both preference space and willingness-to-pay space. The results of our model show that the directionality and magnitude of the influence of peers’ choices of whether and how to evacuate vary widely across respondents. Overall, the decision of whether to evacuate is positively impacted by peer behavior, while the decision of how to evacuate (i.e., ride-type selection) is negatively impacted by peer influence. Furthermore, an increase in flood threat level lessens the magnitude of peer impacts. In terms of the COVID-19 pandemic impacts, respondents who perceive it to be a major health risk are more reluctant to evacuate, but this effect is mitigated by increased flood threat level. These findings have important implications for the design of tailored emergency messaging strategies and the role of shared rides in multihazard evacuations. Specifically, emphasizing or deemphasizing the severity of each threat in a multihazard scenario may assist in: (1) encouraging a reprioritization of competing risk perceptions; and (2) magnifying or neutralizing the impacts of social influence, thereby (3) nudging evacuation decision-making toward a desired outcome.

Fundamental diagrams for straight movement of pedestrians in water

Flood is one of the most destructive disasters in the world with high frequency, which normally results in considerable casualties and economic losses. Understanding the basic laws of crowd movement in water is helpful for establishing effective evacuation guidelines under floods. However, there is a lack of empirical data and research on crowd movement in floods. In this study, a series of experiments were carried out in an 8 m long corridor in a swimming pool with the depth of 0.60 m. It is found that the free speed of pedestrians in water is 51.61% lower than that on land, and the male is +25% faster than the female. The speed-density relation shows two phases under the observed density range [0.30,2.20]ped/m2. The speed firstly decreases with the increasing density and then stays at 0.81 m/s when the density exceeds 1.50 ped/m2, whereas the flow increases monotonically with the increase of density. The influence of water on speed and flow is emphasized by comparison with the fundamental diagrams on land. In water, the lateral swaying amplitude of crowds decreases with increasing density, but the swaying frequency remains around 1 Hz. The swaying amplitude (the mean amplitude is 0.10 m) is 100% larger than walking on land (the mean amplitude is 0.05 m) under the speed range [0.50,1.10]m/s, and the crowd step frequency in water was 33.07% less than that on land. Our findings can be useful for the improvement of flood evacuation modeling and establishing evacuation guidelines.

Human-centered flood mapping and intelligent routing through augmenting flood gauge data with crowdsourced street photos

The number and intensity of flood events have been on the rise in many regions of the world. In some parts of the U.S., for example, almost all residential properties, transportation networks, and major infrastructure (e.g., hospitals, airports, power stations) are at risk of failure caused by floods. The vulnerability to flooding, particularly in coastal areas and among marginalized populations is expected to increase as the climate continues to change, thus necessitating more effective flood management practices that consider various data modalities and innovative approaches to monitor and communicate flood risk. Research points to the importance of reliable information about the movement of floodwater as a critical decision-making parameter in flood evacuation and emergency response. Existing flood mapping systems, however, rely on sparsely installed flood gauges that lack sufficient spatial granularity for precise characterization of flood risk in populated urban areas. In this paper, we introduce a floodwater depth estimation methodology that augments flood gauge data with user-contributed photos of flooded streets to reliably estimate the depth of floodwater and provide ad-hoc, risk-informed route optimization. The performance of the developed technique is evaluated in Houston, Texas, that experienced urban floods during the 2017 Hurricane Harvey. A subset of 20 user-contributed flood photos in combination with gauge readings taken at the same time is used to create a flood inundation map of the experiment area. Results show that augmenting flood gauge data with crowdsourced photos of flooded streets leads to shorter travel time and distance while avoiding flood-inundated areas.

Flood disaster evacuation route choice in Indonesian urban riverbank kampong: Exploring the role of individual characteristics, path risk elements, and path network configuration

Emergency evacuation is regarded as the most important disaster response action for protecting human life from potentially lethal threats. Despite growing research aimed at evaluating and modelling evacuation for strategic flood disaster preparedness, remarkably little is known about how informal settlement dwellers realized and negotiated surrounding environment for evacuation path route choice. The purpose of this paper is to analyze the dynamic interaction between human characteristics, path risk elements, and path network configuration in constructing flood evacuation route choices based on two cases study of urban riverbank kampongs in Yogyakarta, Indonesia. To understand these interactions, we applied a mixed method based on a qualitative research approach, which included (1) walking evacuation simulation with video analysis to understand the informality practices and kampong's space setting, (2) an analysis of dweller's narrative experience collected from walking interviews, (3) computational path network configuration analysis using space syntax. Our findings suggest that kampong dwellers selected evacuation routes differently based on their individual capacity, the safety performance of path design, and path network characteristics in accommodating the safest travel. When juxtaposing space syntax results with walking evacuation simulation, the individual evacuation route choice is highly related to space syntax measures (normalized angular choice at local radii), implying that the majority of residents still prefer to walk on the straightest route (the route with the least angular deviation) to reach the assembly/exit points. Furthermore, this research demonstrates that not all residents have the same capabilities to walk on the straightest evacuation route due to physical capacity and limitation that relates to gender and ages differences in negotiating path risk elements. The use of mixed method approaches provided a practical insight into emphasizing the human-centered perspective in planning an effective flood emergency evacuation for informal riverbank settlements through spatial design, planning, that respect vulnerable groups.

An Assessment to Determine the Typology of Spaces for a Flood Evacuation Centre in Malaysia

Flooding is a yearly tragedy in Malaysia, hence the need for evacuation centres is paramount. However, the majority of Malaysia's evacuation centres in flood-prone areas have been criticized for having problems, particularly with space management. As a result, the study aims to develop a recommended typology of spaces model for a flood evacuation centre in Malaysia based on local agreement and perception. Likert scale questionnaires are used as a quantitative strategy in this paper to fulfil the research purpose. Overall, the study suggests nine typologies of space that must be provided for flood evacuation centres in Malaysia. Keywords: Flood disaster, evacuation centre, typology of space. eISSN: 2398-4287 © 2022. The Authors. Published for AMER ABRA cE-Bs by e-International Publishing House, Ltd., UK. This is an open access article under the CC BYNC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer–review under responsibility of AMER (Association of Malaysian Environment-Behaviour Researchers), ABRA (Association of Behavioural Researchers on Asians/Africans/Arabians) and cE-Bs (Centre for Environment-Behaviour Studies), Faculty of Architecture, Planning & Surveying, Universiti Teknologi MARA, Malaysia. DOI: https://doi.org/10.21834/ebpj.v7i20.3435

Proposed flood evacuation routes for heritage areas based on spatial configuration analysis: a case study of Penang, Malaysia

PurposeBecause of the global increase of climate change effects, floods are becoming more frequent and severer, especially in urban areas of coastal cities and islands where floodplains have turned into buildings because of rapid urbanisation, leading to a higher risk of damages. Urban heritage areas should be highly considered in the time of evacuation because of the vulnerability of streets and buildings and limitations on taking counteractions. Given these limitations, this study aims to propose a network of potential evacuation routes based on spatial configuration analysis of the heritage areas.Design/methodology/approachPenang Island's heritage site, namely, George Town, located on the northwest coast of Malaysia, is chosen as the case study. By using an approach of spatial configuration analysis using space syntax techniques in addition to considering the potential starting points for evacuation and flood risk map of the area, this study analysed the area's street network values for evacuation function during flood crisis time.FindingsPotential evacuation routes were identified for flood disasters in the George Town heritage area. Furthermore, the proposed evacuation routes were evaluated in terms of time for evacuation by metric step-depth analysis of space syntax.Originality/valueA few studies have focused on practical guidelines for evacuation routes based on spatial configuration analysis, an important yet neglected approach in this regard, especially concerning urban island areas. This study can contribute to providing strategies to reduce vulnerability and casualties in urban heritage areas.

Simplified flood evacuation simulation in outdoor built environments. Preliminary comparison between setup-based generic software and custom simulator

• We investigate evacuation simulation in flooded outdoor built environments. • We compare a generic and a custom simulation model based on a microscopic approach. • We set a generic simulator up to reproduce flood-related behaviors. • Simulators are applied to an idealized literature-based case study, including comparisons with real-world data. • Results seem to encourage the proposed generic simulator setup. Floods are among the most destructive sudden-onset disasters affecting worldwide communities and society. Pedestrians can be forced to evacuate affected areas thus being exposed to multiple risks. Outdoor built environment flood risks analyses should be performed through rapid, easy, and sustainable tools to speed up and support risk assessment and mitigations. Custom evacuation simulators have been developed, but are generally used in research, are not user-friendly, and need high-level training. On the contrary, generic (e.g. commercial) software tools seem to be more suitable for low-trained technicians but should be modified to include human behaviors effects, especially considering the evacuation, when people's peculiar choices depend on interactions with floodwaters and built environment layout/composing elements. This work provides preliminary setups of a generic software tool to perform quick and sustainable assessments of pedestrians’ flood safety in outdoor spaces, using an easy-to-apply no-code modification approach to include flood peculiar behaviors. Simulation outputs of the setup-based generic software are compared with a custom simulator relying on the same modelling approach, and with real-world observations, using an idealized literature-based outdoor scenario. Results provide the best setup of the generic software to reliably represent evacuation phenomena, thus encouraging its future application also by local authorities.

Short-notice flood evacuation plan under dynamic demand in high populated areas

Driven primarily by climate change, natural disasters are expected to continue increasing throughout the years. A multitude of approaches for modelling disaster evacuation have been proposed for over decades and most of them focus on minimizing the travelling times or costs after a disaster strikes. However, evacuating all vulnerable people to safer places with sufficient vehicles before a disaster strikes is a better option. Owing to this operation's importance at such a crucial time, we have developed a short-notice flood evacuation model by utilising public transportation to evacuate an uncertain number of people, particularly in areas with a high population. The proposed model aims to find the minimum number of vehicles required and its sequence trips to save all evacuees before the water reaches the predicted areas. A closing time window at each evacuation point and evacuees-dependant service times are taken into account to tackle the flood propagation. Due to the limitation of available vehicles at the early stage of the disaster, the model considers splitting the demands and reusing the vehicles, i.e. multi-trips, to cover all the necessary routes within a time horizon. We apply the new model to some synthetic and real-world instances. In addition, we study the trade-off between the minimization of the number of vehicles and total travelling times. The results show that the proposed model has effectively saved more resources when split deliveries and multi-trips are imposed.

A systematic review of agent-based model for flood risk management and assessment using the ODD protocol

Recently, applications of agent-based model (ABM) have been used to understand the interaction between social and hydrological systems. These systems are dynamic and co-evolving, which can be captured through different decision-making entities in an ABM simulation. Therefore, this review aims to better understand the use of ABM for flood risk management and assessment (FRMA). The review comprises a systematic selection of literature using the PRISMA method, which is then assessed using an adapted version of the overview, design, and detail (ODD) protocol to better understand the ABM model development process for FRMA. The review finds that the use of the ODD protocol was only seen in 25% of the studies. The studies which did not explicitly use the ODD had a comprehensive description of the models, albeit done in a non-standardised way. Modellers continue to face the dilemma between parsimony and the breadth of the model as identified from the design component of the ODD. The hydrological component is mainly captured in the sub-model process of the ODD, however, improvements in the definition of the sub-model component may warrant a more comprehensive description of the processes and facilitate comparison across studies. The applications of ABM have shown promise to understand long term flood risks, test the efficacy of policies and better understand the factors that affect warning response during the flood evacuation process. ODD adopted for this review may consequently allow for the adoption and more coherent use of the protocol to document models in FRMA.

The development of Firefly algorithm with fuzzy logic integration for priority search simulation of flood evacuation routes

Heavy rain in a particular area can cause flooding in both the primary area and the surrounding area. A flood is an event where water is inundated in an area due to increased water volume. Due to high level of water and other hazards arising from flooding, flood victims need to move to a location prepared for evacuation. To get to that location prepared, the victims must get through a safe route. Searching for safe evacuation routes is important to save flood victims and bring them to the evacuation centre safely. Search for evacuation routes related to obstacles on the road to get through. Slippery roads, high puddles of water on the roads, rivers that are located close to the roads that flood victims will have to get through, drainage of waterways and the vulnerability of victims are taken into consideration in choosing a route to get to the evacuation location. There are several problems in choosing a safe route: (1) how to take into account the obstacles on the road to be passed (2) how to choose the priority of the route to be passed with the obstacles encountered. The proposed solution to deal with the problems encountered are (1) to take into account road obstacles by giving the obstacle weights. Fuzzy logic is used to calculate the value of obstacle weights (2) the problem of selecting route priorities will be solved using the firefly algorithm. The firefly algorithm is an algorithm inspired by the social life of fireflies. The priority route for evacuation of flood victims is sought using the method proposed in this study which is the optimal route. The optimal route referred to in this study is the route that has the smallest obstacle weight value. The simulation results show that the fuzzy logic integrated into the firefly algorithm (FuFA) provides a safe route priority, indicated by the smallest obstacle weight value.

Priority search simulation for flood evacuation routes using fuzzy AHP approach

A flood is an event of an increase in water volume above the standard limit due to increased rainfall, rising sea levels, storms, and others that result in submerging an area. Floods are disasters that can cause damage and loss of property, disrupt community activities and even cause loss of life. The central defiance to rescue flood victims is choosing a safe route for flood victims to reach the evacuation site. To be able to choose a safe route for flood victims, a flood evacuation simulation is made. Flood evacuation simulation is part of the game that has been created and aims to provide education about the weight of the obstacle that needs to be considered in selecting routes for flood victims. In this flood evacuation simulation, each road has obstacles. The method proposed for choosing safe routes for flood victims is the Fuzzy-based Analytical Hierarchy Process (Fuzzy AHP). The calculation of road route weight using the Fuzzy AHP method will produce the weight for each route. The smallest weight route shows the priority route and the safe route for flood victims to pass. In this case, the Fuzzy AHP method's calculation produces the lowest weight of 0.02347, which is achieved by route 5, the route passing through S-a-b-d-D. This route is a priority route that is safe for flood victims to pass through.

Flood–pedestrian simulator for modelling human response dynamics during flood-induced evacuation: Hillsborough stadium case study

Abstract. The flood–pedestrian simulator uses a parallel approach to couple a hydrodynamic model to a pedestrian model in a single agent-based modelling (ABM) framework on graphics processing units (GPU), allowing dynamic exchange and processing of multiple-agent information across the two models. The simulator is enhanced with more realistic human body characteristics and in-model behavioural rules. The new features are implemented in the pedestrian model to factor in age- and gender-related walking speeds for the pedestrians in dry zones around the floodwater and to include a maximum excitement condition. It is also adapted to use age-related moving speeds for pedestrians inside the floodwater, with either a walking condition or a running condition. The walking and running conditions are applicable without and with an existing two-way interaction condition that considers the effects of pedestrian congestion on the floodwater spreading. A new autonomous change of direction condition is proposed to make pedestrian agents autonomous in wayfinding decisions driven by their individual perceptions of the flood risk or the dominant choice made by the others. The relevance of the newly added characteristics and rules is demonstrated by applying the augmented simulator to reproduce a synthetic test case of a flood evacuation in a shopping centre, to then contrast its outcomes against the version of the simulator that does not consider age and gender in the agent characteristics. The enhanced simulator is demonstrated for a real-world case study of a mass evacuation from the Hillsborough football stadium, showing usefulness for flood emergency evacuation planning in outdoor spaces where destination choice and individual risk perception have great influence on the simulation outcomes.

Factors of Influence on Evacuation Behaviour: Survey Results from the Riverine Floodplain Communities in Bangladesh

Abstract River floods are distinct because not all of them are destructive and typically affect the people who are living in riverine areas. Therefore, people often refuse to evacuate even when they face imminent danger. River floods are a recurrent phenomenon in Bangladesh. This research aims to analyse the flood evacuation behaviour of riverine people in Bangladesh. A total of 377 households were selected for the questionnaire survey and were interviewed from April 2019 to May 2019. Bivariate and multivariate statistics were employed to analyse riverine people's evacuation behaviour based on their socio-demographic and economic characteristics. This study found that although 82% of the households had received flood warning messages, only 40% had evacuated. Results from multivariate analysis suggested that the age of household heads, their education, whether they are disabled/chronically ill members, their income, the height of floodwater inside the house, and the type of warning messages they receive appear to be key determinants that influenced their decisions regarding evacuation. Elderly household heads had a lower likelihood to evacuate. The results showed a negative association between early warning messages and evacuation. Household with disabled/chronically ill member(s) was associated with a higher likelihood of evacuation. Similarly, higher water depth in the home was associated with evacuation. These findings will be helpful for policymakers to enhance awareness of riverine households.

Assessing the flood risk to evacuees in outdoor built environments and relative risk reduction strategies

Climate-change induced disasters, like floods, are expected to increase in the future. In outdoor built environments, flood risk to evacuees depends on interactions between floodwater spreading, built environment features, flood-induced modifications, and individuals’ reaction in emergency phases. Disaster risk reduction strategies should mitigate the immediate flood impacts and improve the community resilience, while being easy-to-implement and effectively supporting evacuees during the initial phases of the emergency. Simulation-based methodologies could support safety planners in evaluating the effectiveness of such strategies, especially if basing on a micro-scale-oriented approach that represents emergency interactions between each individual and the surrounding outdoor built environment. This study adopts an existing micro-scale simulator (FlooPEDS) reproducing experimental-based flood evacuation behaviours. According to a behavioural design-based approach, simulation results focus on individual responses in the outdoor built environment through Key Performance Indicators (KPIs) aimed at providing evidence of critical interactions between evacuees, floodwaters and the outdoor built environment. A case study is selected by considering different flood scenarios to test such KPIs. Risk reduction solutions are then provided, and their effectiveness is checked by simulations. Results show the micro-scale and behavioural design-based approach capabilities in proposing multi-scenarios solutions (e.g.: architectural elements to support evacuees; emergency planning).

How effective are evacuation orders? An analysis of decision making among vulnerable populations in Florida during hurricane Irma

Natural disasters preparedness measures are of paramount importance in reducing fatalities, economic tolls, and health concerns for vulnerable populations. One such preparedness measure that policymakers can take is issuing an evacuation order. Our study focuses on vulnerable populations including people in low lying areas, flood evacuation zones, low income communities, sparsely populated areas, and in manufactured or mobile homes. We analyze the evacuation decision and distance of over 170,000 individuals using passively collected location-based service (LBS) data in Florida before, during and after Hurricane Irma. We control for evacuation order, evacuation order date, and storm path. The results of the analysis are in line with hurricane evacuation studies using survey data, which provides validation that using big data can be a reliable and efficient method to analyze hurricane evacuation decision making. Our major findings are that (1) individuals issued a mandatory order are far more likely to evacuate than if given a voluntary order, (2) manufactured and mobile home residents are more likely to evacuate short distances than site-built home residents but less likely to evacuate longer distances, (3) people living in low income census tracts were less likely to evacuate longer distances than those in higher income census tracts and (4) population, employment and road density were positively associated with decision to evacuate. The authors recommend that policies and hurricane preparation measures pay particular attention to less densely populated and low-income regions as these were identified as vulnerable areas that were less likely to evacuate.

Efficiency-fairness trade-offs in evacuation management of urban floods: The effects of the shelter capacity and zone prioritization.

With increasing flood risk, evacuation has become an important research topic in urban flood management. Urban flood evacuation is a complex problem due to i) the complex interactions among several components within a city and ii) the need to consider multiple, often competing, dimensions/objectives in evacuation analysis. In this study, we focused on the interplay between two such objectives: efficiency and fairness. We captured the evacuation process in a conceptual agent-based model (ABM), which was analyzed under different hard infrastructure and institutional arrangement conditions, namely, various shelter capacity distributions as a hard infrastructure property and simultaneous/staged evacuation as an institutional arrangement. Efficiency was measured as the time it takes for a person to evacuate to safety. Fairness was defined by how equally residents suffered from floods, and the level of suffering depended on the perceived risk and evacuation time. Our findings suggested that efficiency is more sensitive to the shelter capacity distribution, while fairness changes more notably according to the evacuation priority assigned to the divided zones in staged evacuation. Simultaneous evacuation generally tended to be more efficient but unfairer than staged evacuation. The efficiency-fairness trade-off was captured by Pareto-optimal strategies, among which uniform capacity cases led to a higher efficiency while prioritizing high-risk residents increases fairness. Strategies balancing efficiency and fairness featured a uniform capacity and prioritized high-risk residents at an intermediate time delay. These findings more clearly exposed the interactions between different factors and could be adopted as benchmarks to inform more complicated evacuation ABMs.

Dueling emergencies: Flood evacuation ridesharing during the COVID-19 pandemic

Volunteered sharing of resources is often observed in response to disaster events. During evacuations the sharing of resources and vehicles is a crucial mechanism for expanding critical capacity and enabling inclusive disaster response. This paper examines the complexity of rideshare decision-making in the wake of simultaneous emergencies. Specifically, the need for physical distancing measures during the coronavirus (COVID-19) pandemic complicates face-to-face resource sharing between strangers. The ability of on-demand ridesharing to provide emergency transportation to individuals without access to alternatives calls for an understanding of how evacuees weigh risks of contagion against benefits of spontaneous resource sharing. In this research, we examine both sociodemographic and situational factors that contribute to a willingness to share flood evacuation rides with strangers during the COVID-19 pandemic. We hypothesize that the willingness to share is significantly correlated with traditional emergency resource sharing motivations and current COVID-19 risk factors. To test these hypotheses, we distributed an online survey during the pandemic surge in July 2020 to 600 individuals in three midwestern and three southern states in the United States with high risk of flooding. We estimate a random parameter multinomial logit model to determine the willingness to share a ride as a driver or passenger. Our findings show that willingness to share evacuation rides is associated with individual sociodemographics (such as being female, under 36 years old, Black, or republican-identifying) and the social environment (such as households with children, social network proximity, and neighborly sharing attitudes). Moreover, our findings suggest higher levels of income, COVID-19 threat perception, evacuation fear, and household preparedness all correspond with a lower willingness to share rides. We discuss the broader implications of emergency on-demand mobility during concurrent disasters to formulate strategies for transportation agencies and on-demand ridehailing providers.

An efficient dynamic route optimization for urban flooding evacuation based on Cellular Automata

Flooding has been one of the major issues that have seriously hampered the developments of the urban systems, as well as threatened the urban water environments. To mitigate the impacts of floods, it is highly important to identify effective evacuation plans with the aid of computer-based methods. However, effectively identifying the dynamic evacuation route based on the evolution of flooding status is difficult and challenging. To this end, this study develops a Cellular Automata-based Dynamic Route Optimization (CADRO) algorithm to identify the dynamic flood evacuation route (FER), where the hydrodynamics, topography and human response time are incorporated. The proposed CADRO is applied in a suburb of Yangzhou City, China, and results demonstrate the people trapped rate, the mean and maximum length of FERs are shortened by nearly 32.70%, 34.04% and 7.90%, respectively compared with the traditional A* algorithm used for evacuation route optimization. One important feature of the proposed CADRO is that it can identify the dynamical variation of terrain connectivity within the flooding process, thereby offering the optimal FERs. In addition, the impacts of the human response time to the FERs are investigated in this study. It is anticipated that the proposed CADRO can be greatly beneficial to the urban flooding risk management.