Accessibility Of Urban Emergency Service With The Influence Of Pluvial Flooding

In the context of climate change and rapid urbanization,extreme precipitation events and the resulting pluvial flood disasters have been quite usual in urban areas,which comes to a great threat to local people’s life and property.When residents’ life and property safety are under threat,urban emergency service(UES),e.g.,medical,fire and police service,can provide corresponding emergency rescue to reduce the loss.In the process of disaster relief,uninterrupted and efficient UES is the key to disaster response.However,the UES is dramatically limited with the influence of pluvial flood,which could further aggravate the loss.Therefore,how to accurately evaluate and improve the UES ability with the influence of pluvial flood has become one of the issues in the fields of disaster research.City carries on high-intensity economic activity,so urban population,traffic and economic are changing constantly.Therefore,the dynamic activity is an important factor that cannot be ignored in the fine assessment of the impact of pluvial flood in urban areas.Based on dynamic population and traffic simulation,this study dynamically evaluated the capacity of UESs(120 emergency medical service and 119 fire service)during pluvial flood from the perspective of accessibility,and then focused on analyzing the exposure of population and critical areas.A case study was conducted for the central Shanghai on workday.The main contents and conclusions are as follows.(1)Propose a novel method for estimating dynamic population distribution in central Shanghai,in order to provide basic data for measuring accessibility.The method took “activity zones(ACZs)” as a medium unit,and then built a relationship model among ACZs,Amap Index(a real time value to indicate the population heat at a given address),time,and population to estimate the population distribution each 2 hours in a workday.The results show that the average population density of central Shanghai is about 18800 people/ km2 at day,and 17500 people/ km2 at night.The Huangpu river and Inner Ring of Shanghai form the boundary between low population density and high population density.(2)Simulate the traffic during pluvial flood,in order to estimate the UES response time.A road network risk model and OD Matrixes were built respectively based on numerical simulation data of pluvial flood and taxi trajectory data.Then,a traffic simulation model was used to simulate the traffic process under compound scenarios by incorporating pluvial flood and various OD Matrixes.The results show that,under normal weather conditions,the average speed of central Shanghai’s road network is 26.9 km/h,26.3 km/h and 30.8km/h in the morning peak,evening peak and non-rush hours respectively.Under 100-year pluvial flood scenarios,more than 73% vehicles will be blocked because of road water-logging.The travel distance and travel time increase by more than 3% and 75 min respectively,compared with the normal weather.(3)Based on dynamic population distribution and cost matrix between supply point and demand point,1000 m grid was token as study unit,and enhanced two-step floating catchment area(E2SFCA)method was used to calculate the accessibility of emergency medical service(EMS)and fire service(FS).Under normal weather conditions,the accessibility in evening peak hours is the worst.The accessibility generally decreases as a function of distance from UES stations,and worse traffic and lower UES station density further reduce its value.Affected by changes of road status during 100-year pluvial flood,the UES accessibility decreases significantly,and the spatial accessibility is extremely uneven.Less than 16% grids,2.2 million population could receive an EMS response within the golden response time(8 min).Less than 4% grids,0.6 million population could receive a FS response within 5 min.Besides,more than 14 EMS and FS stations stop offering service due to pluvial flood.(4)According to the vulnerability,risk and harmfulness,the critical prevention areas(CPAs)of EMS and FS were classified respectively to evaluate their accessibility.The CPAs of EMS were classified into three types,namely vulnerable population area,crowded area and hazardous area,while the CPAs of FS includes vulnerable population area,crowded area,flammable and combustible area,and key protection area.For different kinds of CPA,more than 60% were inaccessible under 100-year pluvial flood scenarios.The comprehensive risks of EMS/FS were calculated by incorporating CPAs and general prevention areas.Based on the accessibility and comprehensive risk of EMS/FS,the study area was divided into 6 areas,including low risk and inaccessible area,low risk and low accessibility area,low risk and high accessibility area,high risk and inaccessible area,high risk and low accessibility area,high risk and high accessibility area,which provides scientific support for the disaster response.