Evaluating the cascading impacts of flooding on emergency service response and spatial accessibility in Carlisle, UK

Abstract

First responders, such as ambulance and fire & rescue services often have to respond and operate to urgent cases throughout a dynamic flood event. This paper adopts a novel method that utilises flood modelling with GIS-based network analysis to evaluate the spatio-temporal impacts of the 2015 flood event on emergency response and accessibility in the City of Carlisle, UK, as well as to assess the vulnerability of care homes, community centres and sheltered accommodation. The practicality of emergency services in gaining access to these facilities is determined by the 7- and 8-minute legislative targets, for life-threatening cases and critical incidents. To demonstrate this method, we use a hydrodynamic flood inundation model (FloodMap) to simulate the 2015 fluvial and pluvial flood events. Inundation predictions were used as flood impedances (applying a depth value of >25 cm) on the road network to identify critical areas in the city where access is potentially restricted. We quantify and map the evolution of road network inaccessibility to emergency responders using; (i) the service coverage from individual responder stations within the legislated timeframes, and; (ii) quickest routing between responder stations to vulnerable group facilities throughout the flooded event. Results indicate that, during the 2015 event, fluvial flooding had severely disrupted emergency access within the city districts. The areas that were serviceable by two of the three Ambulance stations reduced significantly after 1 hour of flooding, with 41% and 42% respectively. Whereas the remaining station experienced a marginal increase in coverage of 8%, while also gaining 14% in coverage, post 5 hours of flooding. Similarly, service areas had were reduced by 40% and 82% for two out of three Fire & Rescue station respectively. Emergency response times had increased for 3 out of 21 (14%) care homes and 2 out of 15 (13%) community centres, beyond the 7-and 8- min threshold. The disruption to emergency service areas and response times depend on the timing and spread of flooding. Despite this, emergency response times were greater when surface water flooding was considered, with 24% of care homes and 20% community centres being affected.

Overall, the methods demonstrated in this study could be applied in other cities, to guide future emergency planning and evacuation operations during a flood event of this magnitude and extent.