Measuring emergency medical service (EMS) accessibility with the effect of city dynamics in a 100-year pluvial flood scenario
Introduction
As one of the pivotal public health services, emergency medical service (EMS) plays a vital role in reducing the rate of morbidity and mortality, especially in the cases of accidents, sudden illnesses and urgent situations (e.g., life-threatening trauma, cardiac arrest, strokes, and childbirth) (Aringhieri et al., 2017; Liu et al., 2019). However, many uncertain contexts in the urban environment can prolong EMS response time and deteriorate its performance. Overlooking the contextual effects may lead to problematic evaluation of EMS accessibility and misinformed policy interventions (Hawthorne & Kwan, 2012).
Accessibility is an important indicator for evaluating EMS response performance. As widely used in disciplines like transportation, urban planning and geography, accessibility has a variety of definitions (Geurs & van Wee, 2004; Hansen, 1959; Hu & Downs, 2019; Kwan, 1998; Le Vine et al., 2013). Basically, how accessibility is measured depends on how it is conceptualized. According to Penchansky and Thomas (1981), a multi-faceted concept for health care access involves five dimensions (affordability, acceptability, availability, accommodation, and geographic accessibility), which respectively denote the cost, satisfaction, sufficiency, appropriateness, and travel impedance of (using) health care services. Among them, geographic accessibility (also known as spatial or physical accessibility) attracts considerable attention from health- and transport geography studies, where it is given a broader meaning referring to the availability of and proximity to health care services (Luo & Wang, 2003).
In view of this two-dimensional definition, the two-step floating catchment area (2SFCA) method has gained great popularity in relevant studies because it measures availability and proximity simultaneously by considering demand (e.g., population size), supply (e.g., number of EMS facilities), and the spatial interaction between them (Wang, 2017). As the name implies, 2SFCA evaluates accessibility through two steps. The first is assigning a supply-to-demand ratio to each supply node, and the second is calculating the accessibility of each demand node. The catchment area is a constraint of time or space that determines whether a pair of supply and demand nodes can spatially interact. Currently, there are several types of improvements to the original 2SFCA method (Wang, 2012; Tao and Tao & Cheng, 2016), mainly focusing on the distance decay function (e.g., enhanced 2SFCA) (Luo & Qi, 2009), the delimitation of catchment areas (e.g., dynamic 2SFCA) (McGrail & Humphreys, 2014), the competition among demand nodes or supply nodes (e.g., modified 2SFCA) (Delamater, 2013), the travel means of the demand side (e.g., multi-mode 2SFCA) (Mao & Nekorchuk, 2013), and actual human travel behavior (e.g., E2SFCA-ICA) (Pan et al., 2018).
With continuous improvements, the 2SFCA method has been shown to be capable of yielding increasingly reliable and accurate measurement of health care accessibility; but in the context of EMS, new difficulties arise. Unlike non-emergency problems, EMS response is highly time-sensitive. Higher response time may seriously reduce the survivability of victims to be rescued (Amorim et al., 2019). Measuring EMS accessibility, in particular, should incorporate the uncertainties that may cause fluctuations in response times. However, most empirical studies to date conceptualize accessibility in static terms and ignore the variations in demand, supply, and travel impedance over time and space, and thus suffer from the uncertain geographic context problem (UGCoP) (Kwan, 2012, Kwan, 2018). Solutions for this problem should be based on a good understanding of what the uncertainties are or where they stem from. The primary purpose of this study is to answer the following question: How do the typical uncertain contextual factors in urban areas (e.g., the time-varying population and traffic, an extreme pluvial flood which can cause extensive road closures), influence EMS accessibility? Carefully taking these uncertainties into account can help improve the measurement of accessibility in complex spatial and temporal contexts and provide more credible policy and practical recommendations for emergency management to meet greater challenges against a backdrop of the changing climate with more uncertainties.
Section snippets
Literature review
Herein, we reviewed two types of uncertain contexts, which have been discussed in a limited number of studies, encountered by the measurement of EMS accessibility.
The first type of uncertain context is regular uncertain context, namely the daily changes of traffic and demand due to millions of individuals' mobility, which can simply be referred to as city dynamics. Variations in EMS demand have been noted very early (Cusimano et al., 2010; Fransen et al., 2015; Jamtsho et al., 2015), but the
Data and methods
A brief workflow is illustrated in Fig. 1. Slightly different from the chronological order of the workflow, the following subsections first give an introduction to the study area and the EMS system in it, and then successively describe the detailed methods of (1) measuring accessibility using E2SFCA, (2) depicting the daily changes of the population and traffic (the regular context), and (3) defining flood-induced road closures (the irregular context).
Results
Altogether, we evaluated the EMS accessibility under 36 scenarios based on different combinations of the 4 temporal scenarios (2:00, 9:00, 14:00, and 18:00) and 9 flood condition scenarios. The latter refers to 1 normal scenario (NS) without flooding and 8 flood scenarios corresponding to 8 stages of the flooding. Meanwhile, for each flood scenario, we calculated the mean of 8 accessibility values (i.e., FS-mean) as the final assessment to be compared with the normal scenario. Since the
Discussion on the factors that influence accessibility
This section examines whether there are statistically significant associations between EMS accessibility and the factors we are concerned about. In view of the significant spatial heterogeneity in the accessibility patterns (the values of Moran's I range from 0.5411 to 0.7972), geographically weighted regression (GWR) analysis is used. Altogether, six latent factors are selected as independent variables, including 1) population, 2) facility richness, 3) fastest-nearest ratio, 4) real-time
Conclusion
This paper showed that, with a case study in Shanghai, some regular (e.g., dynamic population and traffic) and irregular (e.g., extreme flooding) contextual factors in urban areas can significantly influence the measurement of EMS accessibility. By integrating fine-grained time-varying demand and travel cost in the E2SFCA method, we address the limitations of past studies that assumed static population and traffic and thus ignored the effect of uncertain contexts on EMS accessibility. This
CRediT authorship contribution statement
Mengya Li designed the initial method, performed the data processing and analysis, interpreted the results and wrote the first draft of the manuscript. Mei-Po Kwan performed the reviewing and editing and contributed to the further development of the methods and interpretations. Mengya Li and Mei-Po Kwan together performed the revision according to the comments provided by the editor and the reviewers. Jie Chen performed the estimation of population based on mobile signaling data. Jie Yin and
Declaration of competing interest
The authors declare no competing financial interests.
Acknowledgments
This research is supported by the National Natural Science Foundation of China (41971199, 42001182, 41871164), the Major Program of National Fund of Philosophy and Social Science of China (18ZDA105), the China Postdoctoral Science Foundation (2019M661424). In addition, Mei-Po Kwan was supported by grants from the Hong Kong Research Grants Council (General Research Fund Grant no. 14605920; Collaborative Research Fund Grant no. C4023-20GF) and a grant from the Research Committee on Research
References (51)
- et al.
Duty or safety? Exploring emergency service personnel’s perceptions of risk and decision-making when driving through floodwater
Progress in Disaster Science
(2020) - et al.
An integrated approach for strategic and tactical decisions for the emergency medical service: Exploring optimization and metamodel-based simulation for vehicle location
Computers & Industrial Engineering
(2019) - et al.
Using optimization to provide decision support for strategic emergency medical service planning – Three case studies
International Journal of Medical Informatics
(2020) - et al.
Emergency medical services and beyond: Addressing new challenges through a wide literature review
Computers & Operations Research
(2017) - et al.
Beyond ‘flood hotspots’: Modeling emergency service accessibility during flooding in York, UK
Journal of Hydrology
(2017) Spatial accessibility in suboptimally configured health care systems: A modified two-step floating catchment area (M2SFCA) metric
Health & Place
(2013)- et al.
A commuter-based two-step floating catchment area method for measuring spatial accessibility of daycare centers
Health & Place
(2015) - et al.
Accessibility evaluation of land-use and transport strategies: Review and research directions
Journal of Transport Geography
(2004) - et al.
Time to address the spatiotemporal uncertainties in COVID-19 research: Concerns and challenges
Science of the Total Environment
(2021) - et al.
Measuring and visualizing place-based space-time job accessibility
Journal of Transport Geography
(2019)
A new concept of accessibility to personal activities: Development of theory and application to an empirical study of mobility resource holdings
Journal of Transport Geography
The potential effect of a 100-year pluvial flood event on metro accessibility and ridership: A case study of central Shanghai, China
Applied Geography
Distributionally robust optimization of an emergency medical service station location and sizing problem with joint chance constraints
Transportation Research Part B: Methodological
An enhanced two-step floating catchment area (E2SFCA) method for measuring spatial accessibility to primary care physicians
Health & Place
Measuring spatial accessibility to healthcare for populations with multiple transportation modes
Health & Place
Measuring spatial accessibility to primary health care services: Utilising dynamic catchment sizes
Applied Geography
Low impact development techniques to mitigate the impacts of climate-change-induced urban floods: Current trends, issues and challenges
Sustainable Cities and Society
Allocation of emergency response centres in response to pluvial flooding-prone demand points using integrated multiple layer perceptron and maximum coverage location problem models
International Journal of Disaster Risk Reduction
Measuring spatio-temporal accessibility to emergency medical services through big GPS data
Health & Place
Understanding temporal change of spatial accessibility to healthcare: An analytic framework for location factor impacts
Health & Place
Modeling the impact of land subsidence on urban pluvial flooding: A case study of downtown Shanghai, China
Science of the Total Environment
Modeling the anthropogenic impacts on fluvial flood risks in a coastal mega-city: A scenario-based case study in Shanghai, China
Landscape and Urban Planning
Evaluating the importance of catchment hydrological parameters for urban surface water flood modeling using a simple hydro-inundation model
Journal of Hydrology
Estimating the effect of traffic congestion on accessibility to emergency medical care services: Take Guangzhou as an example
Progress in Geography
Patterns of urban violent injury: A spatio-temporal analysis
PLoS One
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2022, Computers and Industrial EngineeringCitation Excerpt :Cheng et al. (Cheng et al., 2021) evaluated the spatial accessibility pattern using interpolation, and clustering, and outlier and Getis-Ord Gi* analyses. Li et al. (Li et al., 2021) proposed an enhanced two-step floating catchment area (E2SFCA) method to assess emergency medical services (EMS). Among the patient referral models, simulation is widely employed to model a complex medical system.