Going against the flow Travel patterns in Southern France: A Vulnerability to flash floods

Going against the flow

Travel patterns in Southern France: A Vulnerability to flash floods

Isabelle RUIN ASP Post-Doc NCAR - [email protected]

1- Statement of research problem

2- Objectives, study area and

methods

3- Main results

4- Conclusion and looking ahead

2

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1- Statement of research problem

Why people decide to travel in crisis situation?

Two assumptions:

➀ People’s unwillingness to change their daily routines

➁ Discrepancy between individual space-time representations and actual flash flood phenomenon characteristics

2- Objectives of flash flood vulnerability assessment

2

1

3

Study area and methods

Cognitive mapping sampling Questionnaires surveys

✓ 960 residents (quotas)✓ 260 tourists

Cognitive mapping

✓ 200 residents: spatially stratified sampling

So

urc

e :

IGN

- G

EO

FL

A D

épar

tem

ents

Réa

lisa

tio

n :

L.

Avv

enen

go

Du

cca,

200

6

Study area

Post-flood investigations (2002, 2005)

✓30 in-depth interviews✓Analysis of loss of life circumstances ✓Observations during the crisis period

3- Main results:

External factors

1. Spatio-temporal scales of Flash Floods

2. Road network exposure

3. Human exposure

Spatio-temporal scales of Flash Floods

Source : Creutin, 2001

1 hour

1 day

Scale of hydrological responses

Scale of atmospheric objects (Orlanski, 1975)

Wate

rsh

ed

s t

ime

resp

on

ses (

mn

)

Flash Flood domain

2- Meso-scale convective system

Several hours

100 Km

2

1

1- Convective cell

10 Km

One hour

Large road network exposure

Administrative area boundaryMain streamsTributariesToll motorwaysHighwaysSecondary roadsRoad’s sections regularly flooded

ALESALES

NIMESNIMES

✓ 11 young individuals died in 9 watersheds smaller than 20 km2

✓ 11 old individuals died in 5 watersheds bigger than 1000 km2

Human exposure during the 2002 Flash flood event (1)Loss of life: hydrometeorological circumstances

Extreme speed of watershed responses

Extremely short lead-time for

warnings

Human exposure during the 2002 Flash flood event (2) Loss of life: Warning efficiency

3- Main results:

Internal factors

1. Motorists’ danger perceptions on daily itineraries

2. Perceptions of vulnerability

3. At-risk travel patterns in the Gard region

Road network

✓ 29% of the road sections used by our sample are prone to flooding

The 2/3 are not considered as dangerous

Source : DDE30, Cognitive mapping survey, 2006. N = 200Ruin, 2007

Comparison between often flooded road sections and

risk perceptions

ALÈSALÈS

NIMESNIMESNIMESNIMES

Main streamsEast rural zoneSouth urban zoneWest rural zoneNorth urban zone

76 to 100% of users51 to 75% of users26 to 50% of users1 to 25% of users

Road sections prone to flooding

Road sections used and peceived as non dangerous

Road sections used and peceived as dangerous by:

Motorists’

danger

perception on

daily itineraries

Perceptions of vulnerability

✓ Rapidity of watershed time response is mostly underestimated, specially for small catchments

✓ More than 60% ignore that 2 feet of moving water may sweep a car away while critical water depth for a person (to be knocked off their feet) is better evaluated

✓ Only 35% of the residents think Météo-France Orange alert is to a warning for fatal danger, but 55% associate it with danger on their own daily itinerary

Traveling during a flash flood event is known to be dangerous, but thresholds of dangerousness are hardly perceived

East rural zoneSouth urban zoneWest rural zoneNorth urban zone

Main itineraries taken by the 200 interviewees

High rate usageMidle rate usageLow rate usageVery low rate usage

Source : DDE30, Cognitive mapping survey, 2006. N = 200

Ruin, 2007

NIMESNIMES

ALÈSALÈS➁

➁

➁ At-risk mobility of rural retired- 20% of the sample

- frequent but little hazardous travels - weak perception of risk on roads

Three kinds of at-risk mobility in the Gard area

➀ Commuting is highly risky- 30% of the sample

- frequent and highly hazardous

travels- weak perception of risk on roads

➀

➂ Inter-state mobility fairly risky- 10% of the sample

- unfrequent and fairly hazardous travels- weak perception of risk on roads

➂

3- Main results:

Contextual factors

1. Influence of spatial and settings

2. Main constraints to evacuation

3. Main constraints to travel’s flexibility

Influence of spatial and temporal settings

✓ Stakes located at the confluence of watersheds of different sizes

✓ Succession or simultaneity of flood peaks due to differences in catchment sizes

✓ Vulnerability variations within the time of the day, week, season...

16

Catchment

Hydographic network Catchment outletRelief

1000 km2

20 km2

Main constraints to evacuation

✓ Afraid of spreading the family:

37% tourists

✓ Feeling of safety: 27% residents

✓ Afraid of leaving pets: 18%

residents

Afraid of spreading the family

Reasons for non-instant evacuation

No reason

Others

Handicap (me or relative’s)

Feeling of safety

Afraid to leave

pets

Afraid of spreading the family

Afraid of loosing goods

Don’t know

Residents (N=908)

Tourists (N=258)

Don’t know

Evacuation refusal

Wait and see

Look for information

Instant evacuation

Response to evacuation order

Residents (N=922)

Tourists (N=258)

Réaction alors qu'une alerte est déclenchée pendant que les enfants sont à

l'école

46%

44%

4% 6%

Va immédiatement chercher ses enfantsrien, vous savez qu'ils sont pris en charge par l'étab.Demande à un parent ou ami d'aller les chercherAutres

Parental reaction to warnings when children are in schools

Immediatly pick up their childrenNothing, you know they are safe in school You ask a relative to pick them upOthers

Workers would

hardly cancel their

travels

Main constraints to travel’s flexibility

In reaction to warnings, 50% of

the parents would pick up their

children from school.

Responses to Météo-France watches (orange) and warnings (red) for heavy precipitations

Cancel Travels

Search information

Unchanged activities and/or travel patterns

WorkersResponse to orange alert

Non-workersResponse to red alert

Workers Non-workers

Mean deviation

4- Conclusion and looking

ahead

1. Complementarity of qualitative and quantitive

methods in behavioral studies 2. Synthesis of vulnerability factors in crisis period

3. Research perspectives

Complementarity of qualitative and quantitive methods in behavioral

studies

1- The cautious58 % (sample 2004)

2- Workers constrained by professional activities13 % (sample 2004)

Those avoiding evacuation

3 % (Sample. 2004)

Synthesis of vulnerability factors in crisis period

• Age (< 25 / > 65 years

old)

• Gender

• Type of mobility

• New residents

• Language barrier

(tourists)

• Area of living (ZUsud)

• very small

catchments (< 20km2)

• Confluence of

watersheds of

differents sizes

• Time of impact: rush-

hours / night...

• Parental duty

• Professional activity

1. Observe behaviors in both normal daily life and

extreme weather conditions

2. Organize extreme events post investigations

Research perspectives (1)

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Need for Behavioral

verification surveys to

assess adaptative capacities

of drivers in different

weather conditions:

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Research perspectives (2) :

Behavioral survey project: NCAR ASP proposal

(2008-2009)

1. Observe driver’s behavior at low water

crossings in Texas (Austin)

Quantitative survey:

• Use of video, car counting

Qualitative survey:

• Use Youtube video, travels

log and in-depth interviews

Research perspectives (3) : DELUGE

network E. Gruntfest submitted NSF proposal (2008-2013)2. Disasters: Evolving Lessons Using Global

Experience

Focus on post-event field studies for floods to maximize interactions between social scientists, hydrologists and meteorologists

New guidelines on post-event investigations for use by integrated teams of physical scientists, social scientists, and practitioners.

Thank youThank you