Coupled modeling of storm surge and coastal inundation: a case study in New York City during Hurricane Sandy

In this paper we describe a new method of modeling coastal inundation arising from storm surge by coupling a widely used storm surge model (ADCIRC) and an urban flood inundation model (FloodMap). This is the first time the coupling of such models is implemented and tested using real events. The method offers a flexible and efficient procedure for applying detailed ADCIRC storm surge modeling results along the coastal boundary (with typical resolution of ∼100 m) to FloodMap for fine resolution inundation modeling ( 70 m). In further testing, we explored the effects of mesh resolution and roughness specification. Results agree with previous studies that fine resolution is essential for capturing intricate flow paths and connectivity in urban topography. While the specification of roughness is more challenging for urban environments, it may be empirically optimized. The successful coupling of ADCIRC and FloodMap models for fine-resolution coastal inundation modeling unlocks the potential for undertaking large numbers of probabilistically-based synthetic surge events for street-level risk analysis

Modelling the impact of land subsidence on urban pluvial flooding: a case study of downtown Shanghai, China.

This paper presents a numerical analysis of pluvial flooding to evaluate the impact of land subsidence on flood risks in urban contexts using a hydraulic model (FloodMap-HydroInundation2D). The pluvial flood event of August 2011 in Shanghai, China is used for model calibration and simulation. Evolving patterns of inundation (area and depth) are assessed over four time periods (1991, 1996, 2001 and 2011) for the downtown area, given local changes in topography and rates of land subsidence of up to 27mm/yr. The results show that land subsidence can lead to non-linear response of flood characteristics. However, the impact on flood depths is generally minor (<5cm) and limited to areas with lowest-lying topographies because of relatively uniform patterns of subsidence and micro-topographic variations at the local scale. Nonetheless, the modelling approach tested here may be applied to other cities where there are more marked rates of subsidence and/or greater heterogeneity in the depressed urban surface. In these cases, any identified hot-spots of subsidence and focusing of pluvial flooding may be targeted for adaptation interventions

Validating city-scale surface water flood modelling using crowd-sourced data

Surface water and surface water related flood modelling at the city-scale is challenging due to a range of factors including the availability of subsurface data and difficulty in deriving runoff inputs and surcharge for individual storm sewer inlets. Most of the research undertaken so far has been focusing on local-scale predictions of sewer surcharge induced surface flooding, using a 1D/1D or 1D/2D coupled storm sewer and surface flow model. In this study, we describe the application of an urban hydro-inundation model (FloodMap-HydroInundation2D) to simulate surface water related flooding arising from extreme precipitation at the city-scale. This approach was applied to model an extreme storm event that occurred on 12 August 2011 in the city of Shanghai, China, and the model predictions were compared with a ‘crowd-sourced’ dataset of flood incidents. The results suggest that the model is able to capture the broad patterns of inundated areas at the city-scale. Temporal evaluation also demonstrates a good level of agreement between the reported and predicted flood timing. Due to the mild terrain of the city, the worst-hit areas are predicted to be topographic lows. The spatio-temporal accuracy of the precipitation and micro-topography are the two critical factors that affect the prediction accuracies. Future studies could be directed towards making more accurate and robust predictions of water depth and velocity using higher quality topographic, precipitation and drainage capacity information

Evaluating the cascading impacts of sea level rise and coastal flooding on emergency response spatial accessibility in Lower Manhattan, New York City

This paper describes a scenario-based approach for evaluating the cascading impacts of sea level rise (SLR) and coastal flooding on emergency responses. The analysis is applied to Lower Manhattan, New York City, considering FEMA’s 100- and 500-year flood scenarios and New York City Panel on Climate Change (NPCC2)’s high-end SLR projections for the 2050s and 2080s, using the current situation as the baseline scenario. Service areas for different response timeframes (3-, 5- and 8-minute) and various traffic conditions are simulated for three major emergency responders (i.e. New York Police Department (NYPD), Fire Department, New York (FDNY) and Emergency Medical Service (EMS)) under normal and flood scenarios. The modelling suggests that coastal flooding together with SLR could result in proportionate but non-linear impacts on emergency services at the city scale, and the performance of operational responses is largely determined by the positioning of emergency facilities and the functioning of traffic networks. Overall, emergency service accessibility to the city is primarily determined by traffic flow speed. However, the situation is expected to be further aggravated during coastal flooding, with is set to increase in frequency and magnitude due to SLR

Evaluating the impact and risk of pluvial flash flood on intra-urban road net- work: A case study in the city center of Shanghai, China

Urban pluvial flood are attracting growing public concern due to rising intense precipitation and increasing consequences. Accurate risk assessment is critical to an efficient urban pluvial flood management, particularly in transportation sector. This paper describes an integrated methodology, which initially makes use of high resolution 2D inundation modeling and flood depth-dependent measure to evaluate the potential impact and risk of pluvial flash flood on road network in the city center of Shanghai, China. Intensity–Duration–Frequency relationships of Shanghai rainstorm and Chicago Design Storm are combined to generate ensemble rainfall scenarios. A hydrodynamic model (FloodMap-HydroInundation2D) is used to simulate overland flow and flood inundation for each scenario. Furthermore, road impact and risk assessment are respectively conducted by a new proposed algorithm and proxy. Results suggest that the flood response is a function of spatio-temporal distribution of precipitation and local characteristics (i.e. drainage and topography), and pluvial flash flood is found to lead to proportionate but nonlinear impact on intra-urban road inundation risk. The approach tested here would provide more detailed flood information for smart management of urban street network and may be applied to other big cities where road flood risk is evolving in the context of climate change and urbanization

Linking a storm water management model to a novel two-dimensional model for urban pluvial flood modeling

This article describes a new method of urban pluvial flood modeling by coupling the 1D storm water management model (SWMM) and the 2D flood inundation model (ECNU Flood-Urban). The SWMM modeling results (the overflow of the manholes) are used as the input boundary condition of the ECNU Flood-Urban model to simulate the rainfall–runoff processes in an urban environment. The analysis is applied to the central business district of East Nanjing Road in downtown Shanghai, considering 5-, 10-, 20-, 50-, and 100-year return period rainfall scenarios. The results show that node overflow, water depth, and inundation area increase proportionately with the growing return periods. Water depths are mostly predicted to be shallow and surface flows generally occur in the urban road network due to its low-lying nature. The simulation result of the coupled model proves to be reliable and suggests that urban surface water flooding could be accurately simulated by using this methodology. Adaptation measures (upgrading of the urban drainage system) can then be targeted at specific locations with significant overflow and flooding

A vulnerability assessment of urban emergency in schools of Shanghai

Schools and students are particularly vulnerable to natural hazards, especially pluvial flooding in cities. This paper presents a scenario-based study that assesses the school vulnerability of emergency services (i.e., Emergency Medical Service and Fire & Rescue Service) to urban pluvial flooding in the city center of Shanghai, China through the combination of flood hazard analysis and GIS-based accessibility mapping. Emergency coverages and response times in various traffic conditions are quantified to generate school vulnerability under normal no-flood and 100-y pluvial flood scenarios. The findings indicate that severe pluvial flooding could lead to proportionate and linear impacts on emergency response provision to schools in the city. Only 11% of all the schools is predicted to be completely unreachable (very high vulnerability) during flood emergency but the majority of the schools would experience significant delay in the travel times of emergency responses. In this case, appropriate adaptations need to be particularly targeted for specific hot-spot areas (e.g., new urbanized zones) and crunch times (e.g., rush hours)

Long-term flood-hazard modeling for coastal areas using InSAR measurements and a hydrodynamic model: The case study of Lingang New City, Shanghai

In this paper, we study long-term coastal flood risk of Lingang New City, Shanghai, considering 100- and 1000-year coastal flood return periods, local seal-level rise projections, and long-term ground subsidence projections. TanDEM-X satellite data acquired in 2012 were used to generate a high-resolution topography map, and multi-sensor InSAR displacement time-series were used to obtain ground deformation rates between 2007 and 2017. Both data sets were then used to project ground deformation rates for the 2030s and 2050s. A 2-D flood inundation model (FloodMap-Inertial) was employed to predict coastal flood inundation for both scenarios. The results suggest that the sea-level rise, along with land subsidence, could result in minor but non-linear impacts on coastal inundation over time. The flood risk will primarily be determined by future exposure and vulnerability of population and property in the floodplain. Although the flood risk estimates show some uncertainties, particularly for long-term predictions, the methodology presented here could be applied to other coastal areas where sea level rise and land subsidence are evolving in the context of climate change and urbanization

A city-scale assessment of emergency response accessibility to vulnerable populations and facilities under normal and pluvial flood conditions for Shanghai, China

This paper describes the development of a scenario-based approach that couples 2D hydrodynamic modeling with Geographic Information System (GIS) network analysis to assess the vulnerability of emergency services to surface water flooding at a large city scale. The method is demonstrated for Emergency Medical Service and Fire & Rescue Service in the city of Shanghai, China. Considering four representative traffic conditions, accessibility in terms of service area, response time, and population coverage within specified timeframes (8-, 12-, and 15-minute for Emergency Medical Service and 5-, 10-, and 15-minute for Fire & Rescue Service) is quantified and mapped under normal as well as pluvial flood scenarios of various magnitudes (5-, 20-, and 100- year return periods). Results show that the performance of operational responses largely depends on the functioning of transportation system, dramatically decreasing from unobstructed to congested traffic. Surface water flooding is found to result in limited (i.e. site-specific) but nonlinear impacts on the city-wide emergency service provisions. The results provide detailed information for optimizing the distribution of emergency stations and developing strategic contingency planning for vulnerable populations and facilities

Self-Wrinkling Patterned Surface of Photocuring Coating Induced by the Fluorinated POSS Containing Thiol Groups (F-POSS-SH) as the Reactive Nanoadditive

We here demonstrate a facile approach of one-step to obtain the complex wrinkling patterned surface of the photocuring coating by using thiol and fluorocarbon chains containing POSS (F₂-POSS-SH₆) as reactive nanoadditive. F₂-POSS-SH₆ can self-assemble into the top layer of the UV-curing liquid resin. As a result, the mismatch of shrinkage caused by the different types of photo-cross-linking reaction between the top layer and bulk layer leads to formation of the wrinkling pattern. The characteristic wavelength (λ) and amplitude (<i>A</i>) are linearly dependent on the concentration of F₂-POSS-SH₆. The resulting surface exhibits superlow surface energy (4.1 mN/m) when the concentration of F₂-POSS-SH₆ is only 1%. The feasibility and generality of this approach for the excellent hydrophobic and oleophobic surface will undoubtedly find practical application in photocuring coating with functions such as self-cleaning