Flood Impacts on Emergency Responders Operating at a City-Scale

Emergency responders often have to operate and respond to emergency situations during dynamic weather conditions, including floods. This paper demonstrates a novel method using existing tools and datasets to evaluate emergency responder accessibility during flood events within the City of Leicester, UK. Accessibility 20 was quantified using the 8and 10-minute legislative targets for emergency provision for the Ambulance and Fire & Rescue services respectively under ‘normal’, no flood conditions, as well as flood scenarios of various magnitudes (namely the 1 in 20 year-, 1 in 100-year and 1 in 1,000-year recurrence intervals), with both surface water and fluvial flood conditions considered. Flood restrictions were processed based on previous hydrodynamic inundation modelling undertaken and inputted into a Network Analysis framework as restrictions 25 for surface water and fluvial flood events. Surface water flooding was shown to cause more disruption to emergency responders operating within the city due to its widespread and spatially distributed footprint when compared to fluvial flood events of comparable magnitude. Fire & Rescue 10-minute accessibility was shown to decrease from 100 %, 66.5 %, 39.8 % and 26.2 % under the no flood, 1 in 20-year, 1 in 100-year and 1 in 1,000year surface water flood scenarios respectively. Furthermore, total inaccessibility was shown to increase with 30 flood magnitude, increasing from 6.0 % to 31.0 % under the 1 in 20-year and 1 in 100-year surface water flooding scenarios respectively. Further, the evolution of emergency service accessibility through a surface water flood event is outlined, demonstrating the rapid onset of impacts on emergency service accessibility within the first 15-minutes of the surface water flood event, with a reduction in service coverage and overlap being witnessed for the Ambulance service under a 1 in 100-year flood event. The study provides evidence to 35 guide strategic planning for decision makers prior to and during emergency response to flood events at the cityscale and provides a readily transferable method to explore the impacts of natural hazards or disruptions on additional cities or regions based on historic, scenario-based events or real-time forecasting if such data is available. 40


Introduction
Floods are one of the most significant natural hazards, affecting 116 million people globally, causing in less than 8 and 10 minutes respectively from when the initial report was logged.These include incidents which may elicit high priority blue light responses such as cardiac arrest, life-threatening/traumatic injury, road traffic collisions and individuals trapped in floodwaters.However, these response targets might be unachievable under certain flood situations that limit the ability of emergency responders to navigate a disrupted road network 85 (Albano et al. 2014).Gil and Steinbach (2008) evaluated the indirect impact of flooding on an urban street network, demonstrating the consequences of localised and larger-scale spatial accessibility during disruptive events demonstrating that, although the effects of a specific flood event may be concentrated or isolated in one location, other areas may still be affected.An urban transport network may be able to cope with small changes of state (i.e.minor flood 90 events where depths are low and spatial extent is limited).However, more severe flooding may result in the transport network reaching a 'tipping point' whereby network routing is considerably impacted (Sakakibaral et al. 2004;Dawson et al. 2011;Albano et al. 2014).According to Gil and Steinbach (2008), locations during floods may become: (i) 'islands', completely cut off with no access; (i) 'peninsulas', with a single critical access route; (iii) 'peripheral areas' that are more difficult to access, or; (iv) 'refugial areas' which are still accessible

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and play an important role for coordinating and managing response efforts.These indirect, cascading impacts may be more detrimental to the functioning of a city than the immediate, directly apparent impacts, and may result in substantial difficulties for road users, including Category One emergency responders, to navigate during flood events.
This paper describes a novel approach to evaluate and forecast the impacts of surface water and fluvial flood 100 events of varying magnitudes on emergency responders operating at the city scale using readily available datasets and functions within a GIS software package (ArcGIS).The City of Leicester was selected as a case study, with a specific focus on emergency response mapping of two Category One responders, namely the Leicestershire Fire & Rescue Service and the East Midlands Ambulance Service.

Case Study Area
Leicestershire, including the City of Leicester, UK (Fig. 1), has experienced a history of localised flooding (Shackley et al. 2001) with council records indicating that annual fluvial flood damages amounted to ~£90k between 2000 and 2010 (Climate East Midlands 2012).In addition, surface water flooding also poses serious 110 problems to the City of Leicester, with Leicester being ranked 16 th out of 4,215 settlements assessed within England in terms of surface water flood risk (Defra 2009)

Network Restrictions
First, flood restrictions were defined using the data detailed in the previous section.A study by the AA (2014) 180 recommended that regular motorists (i.e.small/medium cars) should avoid driving through flood waters ≥15 cm depth as this may be sufficient to stall a car or result in loss of control, while water depths exceeding 30 cm may be sufficient to move vehicles.Additionally, depths ≥15 cm may conceal submerged hazards (e.g.surcharged drains or large debris) which could prevent vehicles from successfully traversing floodwaters.Despite this, emergency vehicles have a greater tolerance to travelling through flood waters than standard vehicles.

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Semi-structured interviews conducted with Leicestershire Fire & Rescue Service found that water depths of approximately 25 cm may be suitable to travel through during an emergency situation.Therefore, a threshold water depth of 25 cm was set for the surface water flood scenarios, with water depths <25cm being removed as restrictions and water depths ≥ 25 cm being treated as restrictions to the flow of traffic along a specific road section.
Surface water flood depths ≥25cm were then processed to remove additional polygons which did not overlap or intercept with the ITN and would not be used for analyses (i.e. in areas which would not affect network routing as their extent did not extend to the road network).Additionally, network restrictions were manually inspected to ensure realistic emergency response zone calculation.Processing included the removal of obstructions due to: (i) isolated pixels of inundation less than 10m 2 in area which would likely be traversable; and (ii) artefact 195 inundated areas over raised transport features such as bridges and bypasses which may not have been correctly represented in the Digital Elevation Model (DEM).Pre-processing of network restrictions used for the surface water flood scenarios improved computational speed and performance significantly, with the 100-year surface water flood event having 201,065 polygons to treat as restrictions prior to inspection but only 10,557 afterwards.
Figure 3 illustrates the no flood restriction transport network, as well as the transport network with overlain 200 surface water flood depths greater than 25cm under the three flood magnitude scenarios; 1 in 20-year, 1 in 100year and 1 in 1,000-year.
To create fluvial inundation restrictions, all fluvial flood hazard categories with the exception of the 'low' flood hazard category were treated barriers and restrictions in all return period scenarios.'Low' flood hazard polygons were removed as restrictions because it was reasonable to assume that emergency vehicles would be able to

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traverse floodwaters in this category based on the description (Section 2.2.2.2).Category One responders suggested that emergency vehicles could have some issues passing through floodwaters in the 'moderate' flood hazard categories and above, especially due to the possibility of submerged obstacles so flood hazard ratings of 'moderate' and above were treated as restrictions within the modelling undertaken.Figure 4 highlights the flood hazard data used to create restrictions for fluvial inundation under the 1 in 20-, 1 in 100-and 1 in 1,000-year 210 flood scenarios.

Network Routing
To quantify accessibility and evaluate service coverage, quickest routing (based on time taken to travel between two points when traversing the Integrated Transport Network), as opposed to shortest path routing (based on the distance between two points), was selected as this algorithm considers road restrictions and impedances.Rescue stations are strategically placed to maximise station coverage and some contingency overlap exists when operating under optimal conditions to ensure resilient operation.
The response zones for East Midlands Ambulance Service (EMAS) under an 8-minute or less (for immediately life-threatening incidents) scenario returned similar findings.Under normal conditions when no flood 275 restrictions were present, it was predicted that 89 % of the City would be reachable within 8 minutes or less (Table 1; Fig. 7).Areas that were predicted to be unreachable within an 8-minute timeframe were mostly situated around the City boundary.However, unlike the Fire & Rescue service which are more dependent on remaining at their stations between incidents (e.g.due to requiring different personal protective equipment [PPE] depending on the incident and because of the size of the emergency vehicle), Ambulance services are 280 more mobile in their operations and have strategic standby points which they are able to occupy between incidents, based on statistical and historic incident records, often only returning to the ambulance depot at the end of a shift.

3.2.2
Impact of Surface Water Flooding 285

Fire & Rescue Service
When restrictions derived from the 20-year surface water flood scenario were incorporated into the model, the Fire & Rescue service was shown to experience a 34 % reduction in service coverage, resulting in 66 % of the road network being accessible in 10-minutes or less (Table 1; Fig. 8a).This reduction in service coverage Furthermore, areas of absolute inaccessibility were also shown to correlate with flood magnitude.Under a no flood scenario, the entire City was accessible by road, while 2.6 %, 12.5 % and 30.9 % of the City was shown to be inaccessible by the Ambulance service under a 1 in 20-, 1 in 100-and 1 in 1,000-year surface water flood scenarios respectively (Table 1). 345

Impact of Fluvial Flooding
When compared to the surface water flood scenarios, incidences of fluvial flooding within Leicester were shown to exert minor impact on emergency response under the 1 in 20-(Fig.12a) and 1 in 100-year (Fig. 12b) fluvial 350 flooding scenarios, with Fire & Rescue and Ambulance service emergency response only becoming significantly impacted under an extreme, 1 in 1,000-year fluvial flood scenario (Fig. 12c).This could be due to the large capacity of the River Soar and associated tributaries passing through the city centre, which have been hard engineered into culverts and linear compound channels to convey floodwaters rapidly and efficiently meaning a large magnitude flood would be required to cause significant disruption.Additionally, it is likely that

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that Leicester Royal Infirmary would be inundated by floodwaters, rendering the hospital's ambulance station inoperable and large areas in the north, north-east, south and south-east of the City becoming inaccessible within an 8-minute response time (Fig. 13).Furthermore, the 1 in 1,000-year fluvial flood scenarios show a partitioning of the City into two separately functioning entities divided into east and west along the River Soar, where emergency resources would be unable to be exchanged by road because of key access roads crossing the River 370 Soar (e.g. the A-roads surrounding Frog Island; A47, A50, A6) becoming blocked with floodwaters.

Temporal Evolution of Accessibility through a Surface Water Flood Event
The above sections show a static representation of emergency response under maximum flood depths.However, it is also likely that the accessibility of emergency responders using a City's road network during flood 375 conditions may evolve through the duration of the flood event, from 0 hours where no disruptions are present (i.e.no flood conditions), to the end of the rainfall event where the maximum flood depths, as outlined in the surface water flood scenarios above, are experienced and emergency response is compromised.
To further understand the temporal evolution of accessibility through a surface water flood event, the 380 Ambulance service 8-minute response under a 1 in 100-year flood event was examined.Surface water flood depths were extracted at multiple points in time through the flood event (namely 0hrs, 0.25hrs, 1hrs, 2hrs, 3hrs, 4hrs, 5hrs, 6hrs and the maximum flood depths recorded during the design rainfall event; Fig. 2).Next, surface water flood depths were processed into flood restrictions and inputted into the Ambulance service response model.Figure 14 shows the temporal evolution of Ambulance 8-minute response zones through a 1 in 100-year 385 surface water flood event.
Results from the temporal inundation modelling demonstrate that the influence of flooding on emergency response is dynamic through a surface water flood event.Rapid onset impacts are witnessed within the first 15 minutes of the event, with service coverage overlap within the City centre being shown to be reduced.

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Goodwood, Leicester Royal Infirmary, Gorse Hill and Leicester General Hospital stations are all shown to experience a reduction in their service areas, and overlap between station coverage, very early on during the flood event.Notably, the model predicts that inundation extent increases dramatically between 1 and 2 hours, affecting many of the primary access routes around the City and causing Ambulance accessibility and service coverage overlap to decrease considerably.Because surface water flood events are often unpredictable and have

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short lead times, this highlights the requirement for emergency responders to be aware and prepared for rapid onset flood events.

Conclusion
Under normal operating conditions, both emergency services considered were shown to reach the majority of 400 the City (100 % and 89 % for Fire & Rescue and Ambulance services respectively) within the legislated response times for 'Red 1' incidents (8-or 10-minutes), suggesting that the stations are strategically situated to provide efficient response during an emergency.In addition, there is sufficient overlap in the polygonal response zones of each emergency responder station, indicating a degree of resilience if one station was unable to respond due to being occupied with another emergency situation.However, when surface water and fluvial Findings suggest that it is important to ensure that primary access locations within the City's road network,

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predominantly the higher hierarchy roads (e.g.A-roads identified in the above analyses) are kept restriction free and specific effort should be focused on ensuring that these locations do not become blocked.Furthermore, the Ambulance service could ensure that they are situated in strategic stand-by points during flood conditions to minimise the impact of a blocked road network on delaying emergency response to vulnerable locations.

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Although findings indicate that the City of Leicester's emergency service could be under pressure during certain flood scenarios when responding to high-priority incidents, the modelled response times are considered to be conservative as congestion and behavioural factors were not incorporated in the analysis.As such, travel times during flood events of the presented magnitudes may be greater and emergency responders may encounter forms of disruption that the model is unable to represent.Further work could seek to incorporate traffic 435 modelling and consider human behaviour although this may prove difficult to assess without congestion data available during observed flood events.Additionally, the analysis conducted does not consider future climatic changes in precipitation regimes which may result in the occurrence of more frequent and severe flood events resulting in a more impacted emergency response (Wilby et al. 2008;Whitfield 2012;Kendon et al. 2014;Watts et al. 2015).Moreover, although the use of Environment Agency and local council flood hazard return period 440 based mapping of accessibility can be useful, particularly for planning purposes, their utility in flood emergencies can be limited due the spatial and temporal heterogeneity of rainfall distribution which may differ between flood events.Further study may be directed at coupling nowcast meteorological data with city-scale hydrodynamic inundation models to assist operational response and decision making during actual flood events in real time.Additionally, further study could also focus on analysing the impact of flood events (or other 445 natural hazards, i.e. tsunami, landslide, wildfire etc.) on vulnerable infrastructural nodes (i.e.emergency centres or nursing homes) to develop contingency plans and analyse site vulnerability to flooding (Liu et al. 2016).
Although vulnerability analyses were conducted as part of this study using care homes as indicators of high densities of vulnerable persons, the data could only be communicated internally to project partners due to confidentially of data.Thus, vulnerability analyses have been excluded from this paper but offer an effective 450 method of communicating indirect flood risk to vulnerable people and locations.
Leicester City Council, Leicester Fire & Rescue Service, Environment Agency and East Midlands Ambulance Service prior to and during the project, without which this project would have not been possible.In particular,

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we gratefully acknowledge the support from Martin Fletcher, Nira Sumaria and Chryse Tinsley from Leicester City Council and Garry Mawby from East Midlands Ambulance Service for their contribution to the research undertaken and to AECOM and the Environment Agency for producing the flood data used as inputs for the analyses conducted.Nat.Hazards Earth Syst.Sci. Discuss., doi:10.5194/nhess-2016-309, 2016 Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 28 September 2016 c Author(s) 2016.CC-BY 3.0 License.

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Quickest routing between facility and destination was based onDijkstra's (1959)  shortest path algorithm with network routing weighted by travel time rather than distance, allowing the inclusion of travel impedances and restrictions.Quickest routing was applied because the shortest route by distance may not necessarily be the quickest traversable route because a shorter path may be more weighted due to a restriction (e.g. a length of arterial road with a lower speed restriction of 20 mph) than a longer route (e.g. a motorway with a speed 220 restriction of 70 mph).All network analyses took into account ITN road restriction and impedances specifically for emergency vehicles, as defined by the UKGovernment's Traffic Signs Regulations and General Directions Act (2002).Vehicle qualifier information, metadata imbedded within the ITN dataset which indicates whether a restriction or impedance applied to a specific vehicle depending on its use, load and type (e.g.taxi, bus, wide-load HGV,225emergency vehicles, hazardous/dangerous loads etc.) was set to 'emergency vehicles' to reflect the motoring regulations which emergency vehicles are exempt from during blue light response.Nat.Hazards Earth Syst.Sci.Discuss., doi:10.5194/nhess-2016-309,2016 Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 28 September 2016 c Author(s) 2016.CC-BY 3.0 License.Basic origin to destination 'A to B' routing between two points and response zone calculation was undertaken for key Fire & Rescue and Ambulance nodes identified using the National Receptors Database.To calculate A to B routing, an origin node (A) was identified (i.e.Fire & Rescue Station) and a destination node (B) was 230 highlighted where an emergency vehicle may have to attend, i.e. an evacuation centre where affected persons would be gathered in the event of an emergency.Quickest routing between both points was then calculated to give a journey duration under normal, no flood conditions.Flood restrictions were then overlain over these routes and routing was re-calculated to understand the specific impact of flooding upon an origin to destination routing.Next, to calculate polygon response zones of emergency responders, relevant nodes (i.e.Fire & Rescue 235 stations, ambulance stations and hospitals) identified from the National Receptors Dataset were treated as 'facilities' within an ArcGIS Network Analysis framework.Using these facilities as starting points for vehicle routing, polygon response zones highlighting all road network locations lying within a 10-minute (Fire & Rescue) or 8-minute (Ambulance) radius were calculated for each individual station, based on legislated response timeframes for 'Red 1', high priority incidents.Individual station service polygon areas were then 240 combined and overlain to visualise and evaluate the zonal emergency service coverage for the whole City under unimpeded, no flood conditions.Flood restriction data for surface water and fluvial flood scenarios could then be inputted into Network Analysis and the response polygons could be re-calculated for different magnitude surface water and fluvial flood scenarios to understand the impact of flooding on emergency response.origin to destination routing, a route between Western Fire & Rescue station and St. Andrew'sMethodist Church, an evacuation centre within a close proximity to Western Fire & Rescue station was calculated.Figure5ahighlights the modelled quickest route under normal conditions when no flood restrictions were present, demonstrating that Fire & Rescue services responding from Western station would be able to 250 reach the destination within a 5-minute timeframe, travelling a distance of 4.6 km (2.86 miles).However, when flood restrictions derived from a 1 in 100-year fluvial flood event were integrated into the model, journey travel times were shown to increase to 8 minutes (+60 %; Fig.5b) under a 'flood informed' scenario, where responders are prepared and informed of network restrictions before responding and are able to plan an alternative route before leaving the station, and 15 minutes (+200 %; Fig.5c) under a uniformed scenario, where 255 impassable floodwaters are encountered by responders en-route.This demonstrates the potential impacts which flood events may have upon origin to destination routing for emergency responders, as legislated response times may be unachievable under potential flood situations which may limit the efficiency of emergency responders traversing across a disrupted road network, resulting in affected individuals being at greater risk(Arkell and Darch 2006).Furthermore, the importance of preparedness is shown to be of critical importance, as emergency 260 responders may be able to respond more rapidly if up-to-date information on the extent of flood-related network restrictions is available.Nat.Hazards Earth Syst.Sci.Discuss., doi:10.5194/nhess-2016-309,2016 Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 28 September 2016 c Author(s) 2016.CC-BY 3.0 License.undertaken suggests that Leicestershire Fire & Rescue Service (LFRS) would be able to reach 100 % of the City road network within 10-minutes when operating under normal conditions (i.e.no flooding or disruptions present), meeting the 10-minute legislative timeframe (Fig. 6).Furthermore, significant areas of the City are shown to be within a 10-minute response zone from one or more Fire & Rescue stations as there are numerous areas across the City where overlaps in station coverage exist.This indicates that the Fire & 270

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appears to be due to difficulties in access due to a decrease in the road network connectivity along primary, high hierarchy road linkages (i.e.A-roads) which are intended to provide large-scale transport links within or between areas as opposed to lower hierarchy arterial roads which are intended for local traffic to smaller housing estates (Department of Transport 2012).Large parts of the southwest of the City appear to be inaccessible within a legislated 10-minute timeframe due to key access roads (e.g.A5460, A563 and M1 295 motorway) surrounding Southern Fire & Rescue station experiencing floodwaters overlaying the ITN resulting in a reduction in service coverage (Fig. 8a).Additionally, ITN blockages along primary access roads, including New Parks Way (A563) by Hinkley Road Roundabout and the A47 result in Western and Central Fire & Rescue stations becoming unable to access areas located within the southwest of the City.Moreover, 6 % of the City area was predicted to be completely inaccessible or 'islanded', either due to flood water occupying the road 300 network directly or due to zones of the City being isolated and surrounded entirely by floodwaters.Nat.Hazards Earth Syst.Sci.Discuss., doi:10.5194/nhess-2016-309,2016 Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 28 September 2016 c Author(s) 2016.CC-BY 3.0 License.Nat.Hazards Earth Syst.Sci.Discuss., doi:10.5194/nhess-2016-309,2016 Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 28 September 2016 c Author(s) 2016.CC-BY 3.0 License.

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the impacts of fluvial flooding on emergency response are limited at lower magnitudes when compared to surface water flood events of similar magnitude due to the spatially concentrated footprint of fluvial flooding surrounding watercourses, meaning disruptions are more confined and less widespread.The assessment suggests that emergency responders operating within the City of Leicester are resilient to fluvial flood events of low to medium magnitude, with such events having limited impact on emergency response times and 360 accessibility across the City.However, the 1 in 1000-year (Fig.12c) fluvial flood scenario was shown to significantly impact emergency response and accessibility, with some stations becoming compromised by floodwaters.The Fire & Rescue service scenario suggested that Eastern Fire & Rescue station would be severely impacted by fluvial flooding from Willow Brook resulting in the station only being able to respond to localised incidents, similar to the situation depicted in Fig.8, while the Ambulance service scenario suggested

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flood situations of different magnitudes are introduced into the model, wider ramifications of localised flooding on city-scale emergency response times become apparent.Specifically, surface water flood mechanisms are shown to exert significant disruption to emergency response due to floodwaters: (i) being spatially distributed and widespread across the City; (ii) having areal extents and depths which are sufficient to cause restrictions to road users, even at lower magnitudes, and; (iii) occupying many of the key access routes (i.e.primary A-roads) 410 and critical areas needed to traverse the City road network.In contrast, the impacts of fluvial flooding on emergency response are limited, especially for lower magnitude events.This is principally due to the spatially concentrated nature of the fluvial inundation footprint in the City, and the large channel capacity of the River Soar and associated tributaries.The River Soar running through the 415 City Centre has been hard-engineered into a linear compound channel with a large channel capacity meaning that high flood flows are conveyed rapidly and efficiently downstream and beyond the City boundaries.Bridges and overpasses built over watercourses in the City are generally higher than the bank full channel capacity, thus allowing the transport network surrounding the River Soar to continue to be operational under small to medium Nat.Hazards Earth Syst.Sci.Discuss., doi:10.5194/nhess-2016-309,2016 Manuscript under review for journal Nat.Hazards Earth Syst.Sci.Published: 28 September 2016 c Author(s) 2016.CC-BY 3.0 License.flood events.Under fluvial flood conditions, the key risk to emergency responders is the direct flooding of 420 emergency responder locations resulting in the stations becoming inoperable, which is apparent in the 1,000year flood scenario when Goodwood Ambulance station and Eastern Fire & Rescue station become compromised by floodwaters (Fig. 12c & 13c).

Figure 1 :
Figure 1: Location of the City of Leicester, United Kingdom.

Figure
Figure 2: Design rainfall scenarios for the 1 in 20-, 1 in 100-and 1 in 1,000-year surface water flood modelling conducted by Leicester City Council.575

Figure 3 :
Figure 3: ITN network under: (a) 'normal', no flood conditions, and overlain with restrictions under a: (b) 1 in 20-year, (c) 1 in 100-year, and; (d) 1 in 1,000-year surface water flood scenarios showing the extent of flooding above a 25 cm threshold which intersects the ITN network.580

Figure 5 :
Figure 5: Quickest routing between Western Fire & Rescue Station and St. Andrew's Methodist Church [Evacuation centre; 300 people capacity] under: (a) normal conditions, and; high (>100 year) fluvial flood risk scenarios.(b) shows a prepared and 'informed' scenario whereby fire appliances are aware of network restrictions before responding, whereas (c) shows an 'uniformed' scenario where impassable flood waters are encountered by responders en-route.

Figure 8 :
Figure 8: Eastern Fire & Rescue station under a 1 in 100-year flood event shows the surrounding roads experiencing inundation, predominantly surrounding Willow Brook (centre).The green line indicates the accessible road network without mitigation measures.Floodwaters surrounding Willow Brook were removed at the Humberstone Road intercept because a large bridge passed over the Brook.Floodwaters blocking access to the A6030 were also removed as these would likely be pumped.

Figure 9 :
Figure 9: Southern Fire & Rescue station under a 1 in 100-year flood event shows that the station is directly at risk of flooding and if sufficient mitigation measures are not taken during a flood of similar or greater magnitude, functioning of the station could be compromised

Figure 11 :
Figure 11: Accessibility of the City (within an 8-minute timeframe) for Ambulance service stations under: (i) 1 in 20-year; (ii) 1 in 100-year, and; (iii) 1 in 1,000-year surface water flooding scenarios.The key access roads referred to in the text are highlighted in the rectangle in Figure 11a.

2.2 Flooding Scenarios 155
Nat. Hazards Earth Syst.Sci.Discuss., doi:10.5194/nhess-2016-309,2016Manuscriptunder review for journal Nat.Hazards Earth Syst.Sci.The impact of surface water and fluvial flooding on the City of Leicester's emergency response times for Ambulance and Fire & Rescue were both considered.Existing surface water and fluvial inundation datasets associated with flooding of various magnitudes were obtained directly from the Leicester City Council and (Winn 2014;Cho and Yoon 2015)lable on historic flood events within Leicester although details on specific flood 115 mechanisms, severity and areal extent are largely absent.Based on the total number of historic incidents collated by Leicester City Council, the flood events which occurred in July 1968 and June 1993 appear to be the most severe historical events, with reports indicating that the July 1968 flood event affected up to 1,800 propertiesNat.Hazards Earth Syst.Sci.Discuss., doi:10.5194/nhess-2016-309,2016ManuscriptunderreviewforjournalNat.Hazards Earth Syst.Sci.Published: 28 September 2016 c Author(s) 2016.CC-BY 3.0 License.and28factorieswithin the City (Leicester City Council 2011).More recently (June 2012), Leicester experienced severe surface water flooding following a short, intense period of precipitation where ~30 mm of 120 rainfall fell in 20 minutes, overwhelming the City's drainage and resulting in widespread flooding across the including the main hospital, Leicester Royal Infirmary, as well as a number of densely populated, low income areas of the City.These have been important in informing flood planning and instigating flood management efforts within the City but have focused largely on the direct impacts of flooding in the City and have not studied the indirect impacts of flooding, for example, on the emergency response and accessibility.The City of Leicester's transport network was represented using Ordnance Survey Integrated Transport Network (ITN) data, which, in addition to including the road network geometry and routing, included metadata which outlined standard road restrictions which may inhibit or delay the traversing of a vehicle across a specific section of road.Restrictions contained within the ITN included height and weight limits, speed restrictions 135 based on national speed limits, mandatory turn restrictions (i.e.no right turns) and one-way roads.Although it is likely that congestion and human behavioural changes may affect the routing of emergency vehicles during flood events, the network analysis undertaken did not consider congestion or the impact of traffic.Although congestion data could be implemented into the modelling framework based on historic traffic data(Winn 2014;Cho and Yoon 2015)which was available for the City of Leicester from Leicestershire County Council, 140 congestion data was not used due to uncertainties associated with how human behaviour and patterns of congestion may differ under flood conditions when compared to normal conditions in which the traffic data was based on.Furthermore, emergency vehicles are able to bypass the majority of congestion when responding to incidents which elicit a blue light response.Still, because congestion data was not implemented into the modelling conducted, the results presented demonstrate a 'best-case' scenario, ignoring potential delays 145 associated with other road users.2.