Contributed by France Daupras
Improving flood forecasting has become a technological race. Major advances have been made over the last 20 years in regard to flood detection and forecasts. Moreover, communication technologies improvements have significantly increased the speed of warning dissemination. However, flood warning systems present inherent uncertainties and vulnerabilities. In order to face these deficiencies, it is important to consider that:
- Despite very high level of forecast accuracy, social and behavioural factors remain important sources of uncertainties that can lead to deficiencies or success of flood warning systems;
- People at-risk (mayors, riverside residents, etc.) are not only receivers of institutional warnings. They can be able of analysing different kind of information (formal or informal) and of producing their own interpretation (from scientific and vernacular knowledge);
- These capabilities may be at the source of social adjustments that allow imperfect flood warning systems to achieve their objectives, anticipation and reduction of the harmful effects of flood to people and goods;
- Instead of asking people at risk to adapt their behaviour regards to flood warning system, we need to fit flood warning system to the needs of the people at risk within the local context.
The case of the French Flood Warning System (FFWS)
To illustrate the importance of people at risk being actors of the warning system, we focus on a particular flood event that occurred in the Garonne Marmandaise (GM) territory (south western France) in January 2009. This ordinary flood event portrayed residual or new vulnerabilities of the system, and highlighted how the behaviour of flooded and isolated communities can bring knowledge to the institutional flood warning and favour the reinforcement of the FFWS robustness.
The main features of this event are:
- Between 1855 and 2009, the GM territory experienced 57 floods with water heights greater than 8 meters at the Marmande stream gauge. The return period of the 1875, 1952, 1930 and 2009 floods correspond respectively to 100, 50, 34 and 2 years.
- The January 2009 event appears to be an ordinary flood in regard to water height, but it occurred while the area was concerned by the extra-tropical cyclone Klaus. The Klaus storm provoked electrical power cuts on Saturday morning that made warning transmission more difficult.
- 29 municipalities were flooded, and 5 communities were isolated due to roads being flooded.
- While several communities were already flooded on 23 January in the evening, the local flood forecasting centre (SPC) only set the vigilance level to yellow at 1am on January 24 and the Departmental crisis management service (DCMS) of the Lot-et-Garonne only transmitted the information to the mayors several hours after the yellow threshold (see here for definitions of French alert levels) was produced.
Investigating the robustness of the French Flood Warning System
Our methodology was partly based on documentation reviews and semi-directive interviews. A total of 45 interviews were carried out. They were divided into two sets:
|1st set of interviews||2nd set of interviews|
|Purpose||Determination of decision making vis-à-vis unfolding flood event in the GM section. Different topics were defined:
||A broader comprehension of the functioning of the FFWS: looking for identification of the stakeholders’ perceptions about the warning system’s efficiency:
Vulnerabilities and coping mechanisms put forward by the 2009 event
Conjectural, organisational and structural vulnerabilities are described in detail here. They led to a lack of anticipation and accuracy concerning vigilance thresholds. The main source of vulnerability comes from the difficulty to maintain and to transmit historical and territorial knowledge within the SPC Garonne and the DCMS:
- At the level of the SPC, the reorganisation of the FFWS started in 2002, when the number of local flood warning services in France (Services d’Annonces des Crues – SAC) was reduced. Six offices disappeared in the Adour Garonne Basin, often without forecasters being transferred to the new flood forecast offices. In some cases, it led to a reduction of expertise in hydrological dynamics and territorial knowledge, as it was observed in the GM section.
- At the level of DCMS, the significant staff turnover led to the loss of territorial knowledge in the service and to the reduction of their capacity to interpret technical information. This lack of knowledge participated to the warning delay that was observed.
- At the level of the flooded municipalities, our analysis revealed a general high level of preparedness and coping capacities of the communities. Most of the mayors have a very good vernacular knowledge of the flood behaviour (meteorology, colour and shape of the river, water speed, etc.), and good prevention habits. They could have been able to anticipate and alert the inhabitants. We noticed that the more the communities are used to deal with flood and to be isolated (dark circles in the figure above), the higher is their level of risk evaluation and prevention. The difficulties encountered by some mayors to transmit the warnings at time were overcome thanks to power generators and “rescuers association” involving inhabitants circulating by boat. These associations were indeed actively involved in the information exchange between the mayors and the inhabitants
The sources of improvement of the French Flood Warning system
- The ordinary flood of 2009 in the GM territory disclosed vulnerabilities in the FFWS and led the mayors of the most exposed communities and the DCMS to request improvements. This event can be described as a political crisis because the mayors questioned the French State capacity to manage emergency situations. They pointed out the worsening of the warning process compared to what they have experienced in the past.
- After the 2009 flood event, important interactions between mayors, forecasters and emergency stakeholders took place over the whole year. Such feedback was achieved through the awareness of all stakeholders of the necessity to improve the FFWS by sharing scientific and vernacular knowledge and experience. Mayors were invited by the DCMS and the SPC to complete a questionnaire concerning their respective communities to specify the water heights at which flooding began, the first exposures impacted by floods and the water heights at which the local crisis management becomes fragile. Consequently, the vigilance thresholds were redefined, taking the mayors’ territorial knowledge into account.
- During 2011 and 2012, the DCMS created a working group that required the cooperation of stakeholders to assess material (houses, cut-off roads, retirement homes, schools, livestock farming, electric and gas networks) and human exposures in the case of a 100-year flood of the Garonne river. A series of meetings to better explain the flood warning procedure and to help the mayors to develop their local crisis management plans was launched, and a flood training exercise was organized in December 2012. DCMS have improved their plans and, more importantly, the mayors put forward this kind of event that enabled the development of thrust and the improvement of collective action with all the stakeholders involved.
The example of the 2009 flood event in the GM territory illustrated that:
- Some of the vulnerabilities of the institutional warning can be overcome by the coping capacities and territorial knowledge of the people at risk.
- The improvement of the French flood warning system can be achieved by the combination of vernacular knowledge and scientific knowledge, and an adaptation to local communities’ context: Given the loss of knowledge by the SPC Garonne, their capacity to take vernacular knowledge from local stakeholders into account favoured the re-appropriation and recapitalisation of territorial knowledge within the SPC.
- The reinforcement of the French flood warning system robustness depends on the upholding and the development of collective action, integrating people at-risk, crisis management services and forecasters through regular meetings and flood training exercises outside flooding periods. Such actions allow reinforcing collective action during crisis situations through the development of trustfulness and preparation in crisis management.
For more info:
Daupras F., Antoine J.M., Becerra S., Peltier A. (2014) Analysis of the robustness of the French flood warning system: a study based on the 2009 flood of the Garonne River. Natural Hazards, DOI 10.1007/s11069-014-1318-x.
HEPEX blog posts related to the French flood warning system and events:
- Good practices in forecast uncertainty assessment and communication, by Berthet and Piotte.
- Operational HEPS in France: the country-wide Météo-France system, by Rousset-Regimbeau et al.
- Flash floods in the French western and central Pyrenees (17-19 June 2013), by Ramos.